Ryan J. Heitmann, DO
Understanding human and pelvic anatomy is essential to the fundamental knowledge of an obstetrician/gynecologist. The basic facts and anatomic structures do not change, but our knowledge and understanding of relationships and function continues to increase. Advances in surgical techniques continue to place more importance on a physician’s understanding of surgical landmarks. There can be significant variation in surgical anatomy, so the practitioner should be well versed in “normal” anatomy and prepared for the “nontextbook” cases.
ABDOMINAL WALL
Topographic Anatomy
The anterior abdominal wall is divided into sections for descriptive purposes and to allow the physician to outline relationships of the viscera in the abdominal cavity. The center point of reference is the sternoxiphoid process, which is in the same plane as the 10th thoracic vertebra. The upper 2 sections are formed by the subcostal angle; the lower extends from the lower ribs to the crest of the ilium and forward to the anterior superior iliac spines. The base is formed by the inguinal ligaments and the symphysis pubica.
The viscera are located by dividing the anterolateral abdominal wall into regions. One line is placed from the level of each ninth costal cartilage to the iliac crests. Two other lines are drawn from the middle of the inguinal ligaments to the cartilage of the eighth rib. The 9 regions formed (Fig. 1–1) are the epigastric, umbilical, hypogastric, and right and left hypochondriac, lumbar, and ilioinguinal.
Figure 1–1. Regions of the abdomen.
Within the right hypochondriac zone are the right lobe of the liver, the gallbladder at the anterior inferior angle, part of the right kidney deep within the region, and, occasionally, the right colic flexure.
The epigastric zone contains the left lobe of the liver and part of the right lobe, the stomach, the proximal duodenum, the pancreas, the suprarenal glands, and the upper poles of both kidneys (Fig. 1–2).
Figure 1–2. Abdominal viscera in situ. Inset shows projection of fetus in situ.
The left hypochondriac region marks the situation of the spleen, the fundus of the stomach, the apex of the liver, and the left colic flexure.
Within the right lumbar region are the ascending colon, coils of intestine, and, frequently, the inferior border of the lateral portion of the right kidney.
The central umbilical region contains the transverse colon, the stomach, the greater omentum, the small intestine, the second and third portions of the duodenum, the head of the pancreas, and parts of the medial aspects of the kidneys.
Located in the left lumbar region are the descending colon, the left kidney, and the small intestine. Within the limits of the right ilioinguinal region are the cecum and appendix, part of the ascending colon, the small intestine, and, occasionally, the right border of the greater omentum.
The hypogastric region includes the greater omentum, loops of small intestine, the pelvic colon, and often part of the transverse colon.
The left ilioinguinal region encloses the sigmoid colon, part of the descending colon, loops of small intestine, and the left border of the greater omentum.
There is considerable variation in the position and size of individual organs due to differences in body size, conformation, and disease processes. Throughout life, variations in the positions of organs are dependent not only on gravity but also on the movements of the hollow viscera, which induce further changes in shape when filling and emptying. The need to recognize the relationships of the viscera to the abdominal regions becomes most apparent when taking into account the distortion that occurs during pregnancy. For example, the appendix lies in the right ilioinguinal region (right lower quadrant) until the 12th week of gestation. At 16 weeks, it is at the level of the right iliac crest. At 20 weeks, it is at the level of the umbilicus, where it will remain until after delivery. Because of this displacement, the symptoms of appendicitis will be different during the 3 trimesters. Similarly, displacement will also affect problems involving the bowel.
Skin, Subcutaneous Tissue, & Fascia
The abdominal skin is smooth, fine, and very elastic. It is loosely attached to underlying structures except at the umbilicus, where it is firmly adherent. Langer’s lines are lines of tension based on the orientation of dermal fibers in the skin. On the anterior abdominal wall, these lines are arranged mostly in a transverse fashion. As a consequence, vertical incisions heal under more tension and therefore have a propensity to develop into wider scars. This is more noticeable in those patients who tend to form keloids. Conversely, transverse incisions, like a Pfannenstiel, heal with a much better cosmetic appearance.
Beneath the skin is the superficial fascia (tela subcutanea). This fatty protective fascia covers the entire abdomen. Below the navel, it consists principally of 2 layers: Camper’s fascia, the more superficial layer containing most of the fat; and Scarpa’s fascia (deep fascia), the fibroelastic membrane firmly attached to midline aponeuroses and to the fascia lata.
Arteries
Arteries of the Upper Abdomen
The lower 5 intercostal arteries (Fig. 1–3) and the subcostal artery accompany the thoracic nerves. Their finer, terminal branches enter the rectus sheath to anastomose with the superior and inferior epigastric arteries. The superior epigastric artery is the direct downward prolongation of the internal mammary artery. This artery descends between the posterior surface of the rectus muscle and its sheath to form an anastomosis with the inferior epigastric artery upon the muscle.
Figure 1–3. Superficial veins and arteries of abdomen.
The inferior epigastric artery, a branch of the external iliac artery, usually arises just above the inguinal ligament and passes on the medial side of the round ligament to the abdominal inguinal ring. From there, it ascends in a slightly medial direction, passing above and lateral to the subcutaneous inguinal ring, which lies between the fascia transversalis and the peritoneum. Piercing the fascia transversalis, it passes in front of the linea semicircularis, turns upward between the rectus and its sheath, enters the substance of the rectus muscle, and meets the superior epigastric artery. The superior epigastric supplies the upper central abdominal wall, the inferior supplies the lower central part of the anterior abdominal wall, and the deep circumflex supplies the lower lateral part of the abdominal wall.
Arteries of the Lower Abdomen
The deep circumflex iliac artery is also a branch of the external iliac artery, arising from its side either opposite the epigastric artery or slightly below the origin of that vessel. It courses laterally behind the inguinal ligament lying between the fascia transversalis and the peritoneum. The deep circumflex artery perforates the transversus near the anterior superior spine of the ilium and continues between the transversus and internal oblique along and slightly above the crest of the ilium, finally running posteriorly to anastomose with the iliolumbar artery. A branch of the deep circumflex iliac artery is important to the surgeon because it forms anastomoses with branches of the inferior epigastric.
The various incisions on the abdomen encounter some muscle planes and vasculature of clinical significance. The McBurney incision requires separation of the external and internal oblique muscles and splitting of the transversus. The deep circumflex artery may be frequently encountered. The paramedian incision is made in the right or left rectus. Below the arcuate line, the fascia of the external and internal oblique, as well as the transversus muscles when present, goes over the rectus abdominis; above the arcuate line, the transversus and part of the internal oblique go under the rectus. The vasculature is primarily perforators and frequently the thoracoabdominal vein. Inferiorly, the superficial epigastric may be encountered.
In the Pfannenstiel or low transverse incision, the fascia of the external and internal oblique goes over the rectus muscle as well as the transversus muscle when present. After the fascia over the rectus is incised, the muscles can be separated. The superficial epigastric artery and vein are encountered in Camper’s fascia. Laterally, the superficial and deep circumflex iliac arteries may be at the margin of the incision. Lying under the transversus muscle and entering the rectus approximately halfway to the umbilicus is the inferior epigastric artery.
In the Cherney incision, care should be taken to avoid the inferior epigastric artery, which is the primary blood supply to the rectus abdominis. Abdominal incisions are shown in Figure 1–4. The position of the muscles influences the type of incision to be made. The aim is to adequately expose the operative field, avoiding damage to parietal structures, blood vessels, and nerves. Low transverse incisions ideally do not extend past the lateral edges of the rectus muscles to avoid damage to the inferior epigastric vessels.
Figure 1–4. Abdominal incisions. Transverse incisions are those in which rectus muscles are cut. A Cherney incision is one in which the rectus is taken off the pubic bone and then sewed back; the pyramidalis muscle is left on pubic tubercles.
Veins
The superficial veins are more numerous than the arteries and form more extensive vascular networks. Above the level of the umbilicus, blood returns through the anterior cutaneous and the paired thoracoepigastric veins, the superficial epigastric veins, and the superficial circumflex iliac veins in the tela subcutanea. A cruciate anastomosis exists, therefore, between the femoral and axillary veins.
The deep veins correspond in name with the arteries they accompany. Below the umbilicus, these veins run caudally and medially to the external iliac vein; above that level, they run cephalad and laterally into the intercostal veins. Lymphatic drainage in the deeper regions of the abdominal wall follows the deep veins directly to the superficial inguinal nodes.
Lymphatics
The lymphatic drainage of the lower abdominal wall (Fig. 1–5) is primarily to the superficial inguinal nodes, 10–20 in number, which lie in the area of the inguinal ligament. These nodes may be identified by dividing the area into quadrants by intersecting horizontal and vertical lines that meet at the saphenofemoral junction. The lateral abdominal wall drainage follows the superficial circumflex iliac vein and drains to the lymph nodes in the upper lateral quadrant of the superficial inguinal nodes. The drainage of the medial aspect follows the superficial epigastric vein primarily to the lymph nodes in the upper medial quadrant of the superficial inguinal nodes. Of major clinical importance are the frequent anastomoses between the lymph vessels of the right and left sides of the abdomen.
Figure 1–5. Lymphatics of abdominal wall. Only one side is shown, but contralateral drainage occurs (ie, crosses midline to the opposite side).
Abdominal Nerves
The lower 6 thoracic nerves align with the ribs and give off lateral cutaneous branches (Fig. 1–6). The intercostal nerves pass deep to the upturned rib cartilages and enter the abdominal wall. The main trunks of these nerves run forward between the internal oblique and the transversus. The nerves then enter the rectus sheaths and the rectus muscles, and the terminating branches emerge as anterior cutaneous nerves.
Figure 1–6. Cutaneous innervation of the abdominal wall.
The iliohypogastric nerve springs from the first lumbar nerve after the latter has been joined by the communicating branch from the last (12th) thoracic nerve. It pierces the lateral border of the psoas and crosses anterior to the quadratus lumborum muscle but posterior to the kidney and colon. At the lateral border of the quadratus lumborum, it pierces the aponeurosis of origin of the transversus abdominis and enters the areolar tissue between the transversus and the internal oblique muscle. Here, it frequently communicates with the last thoracic nerve and with the ilioinguinal nerve, which also originates from the first lumbar and last thoracic nerves.
The iliohypogastric divides into 2 branches. The iliac branch pierces the internal and external oblique muscles, emerging through the latter above the iliac crest and supplying the integument of the upper and lateral part of the thigh. The hypogastric branch, as it passes forward and downward, gives branches to both the transversus abdominis and internal oblique. It communicates with the ilioinguinal nerve and pierces the internal oblique muscle near the anterior superior spine. The hypogastric branch proceeds medially beneath the external oblique aponeurosis and pierces it just above the subcutaneous inguinal ring to supply the skin and symphysis pubica.
Similarly as with arteries and veins, care should be taken to avoid any nerve damage when performing surgery. With a low transverse incision, the iliohypogastric and ilioinguinal nerves are commonly encountered. Risk of damage or entrapment increases the more lateral an incision is made. When repairing the fascial layers, to help avoid entrapment of the iliohypogastric or ilioinguinal nerve, one should be careful not to place stitches lateral to the angle/apex of fascial incisions.
Abdominal Muscles & Fascia
The muscular wall that supports the abdominal viscera (Fig. 1–7) is composed of 4 pairs of muscles and their aponeuroses. The 3 paired lateral muscles are the external oblique, the internal oblique, and the transversus. Their aponeuroses interdigitate at the midline to connect opposing lateral muscles, forming a thickened band at this juncture, the linea alba, which extends from the xiphoid process to the pubic symphysis. Anteriorly, a pair of muscles—the rectus abdominis, with the paired pyramidalis muscles at its inferior border with its sheath—constitutes the abdominal wall.
Figure 1–7. Musculature of abdominal wall.
Function of Abdominal Muscles
In general, the functions of the abdominal muscles are 3-fold: (1) support and compression of the abdominal viscera by the external oblique, internal oblique, and transversus muscles; (2) depression of the thorax in conjunction with the diaphragm by the rectus abdominis, external oblique, internal oblique, and transversus muscles, as evident in respiration, coughing, vomiting, defecation, and parturition; and (3) assistance in bending movements of the trunk through flexion of the vertebral column by the rectus abdominis, external oblique, and internal oblique muscles. There is partial assistance in rotation of the thorax and upper abdomen to the same side when the pelvis is fixed by the internal oblique and by the external oblique to the opposite side. In addition, the upper external oblique serves as a fixation muscle in abduction of the upper limb of the same side and adduction of the upper limb of the opposite side. The pyramidalis muscle secures the linea alba in the median line.
External Oblique Muscle
The external oblique muscle consists of 8 pointed digitations attached to the lower 8 ribs. The lowest fibers insert into the anterior half of the iliac crest and the inguinal ligament. At the linea alba, the muscle aponeurosis interdigitates with that of the opposite side and fuses with the underlying internal oblique.
Internal Oblique Muscle
The internal oblique muscle arises from thoracolumbar fascia, the crest of the ilium, and the inguinal ligament. Going in the opposite oblique direction, the muscle inserts into the lower 3 costal cartilages and into the linea alba on either side of the rectus abdominis. The aponeurosis helps to form the rectus sheath both anteriorly and posteriorly. The posterior layer extends from the rectus muscle rib insertions to below the umbilicus.
Transversus Muscle
The transversus muscle, the fibers of which run transversely and arise from the inner surfaces of the lower 6 costal cartilages, the thoracolumbar fascia, the iliac crest, and the inguinal ligament, lies beneath the internal oblique. By inserting into the linea alba, the aponeurosis of the transversus fuses to form the posterior layer of the posterior rectus sheath. The termination of this layer is called the arcuate line, and below it lies the transversalis fascia, preperitoneal fat, and peritoneum. Inferiorly, the thin aponeurosis of the transversus abdominis becomes part of the anterior rectus sheath.
Rectus Muscles
The rectus muscles are straplike and extend from the thorax to the pubis. They are divided by the linea alba and outlined laterally by the linea semilunaris. Three tendinous intersections cross the upper part of each rectus muscle, and a fourth may also be present below the umbilicus. The pyramidalis muscle, a vestigial muscle, is situated anterior to the lowermost part of the rectus muscle. It arises from and inserts into the pubic periosteum. Beneath the superficial fascia and overlying the muscles is the thin, semitransparent deep fascia. Its extensions enter and divide the lateral muscles into coarse bundles.
Special Structures
There are several special anatomic structures in the abdominal wall, including the umbilicus, linea alba, linea semilunaris, and rectus sheath.
Umbilicus
The umbilicus is positioned opposite the disk space between the third and fourth lumbar vertebrae, approximately 2 cm below the midpoint of a line drawn from the sternoxiphoid process to the top of the pubic symphysis. The umbilicus is a dense, wrinkled mass of fibrous tissue enclosed by and fused with a ring of circular aponeurotic fibers in the linea alba. Normally, it is the strongest part of the abdominal wall. It also represents the shortest distance between the skin and the abdominal cavity, and it is the most common place to enter the abdomen with the primary trochar when performing laparoscopic surgery.
Linea Alba
The linea alba, a fibrous band formed by the fusion of the aponeuroses of the muscles of the anterior abdominal wall, marks the medial side of the rectus abdominis; the linea semilunaris forms the lateral border, which courses from the tip of the ninth costal cartilage to the pubic tubercle. The linea alba extends from the xiphoid process to the pubic symphysis, represented above the umbilicus as a shallow median groove on the surface.
Rectus Sheath & Aponeurosis of the External Oblique
The rectus sheath serves to support and control the rectus muscles. It contains the rectus and pyramidalis muscles, the terminal branches of the lower 6 thoracic nerves and vessels, and the inferior and superior epigastric vessels. Cranially, where the sheath is widest, its anterior wall extends upward onto the thorax to the level of the fifth costal cartilage and is attached to the sternum. The deeper wall is attached to the xiphoid process and the lower borders of the seventh to ninth costal cartilages and does not extend upward onto the anterior thorax. Caudally, where the sheath narrows considerably, the anterior wall is attached to the crest and the symphysis pubica. Above the costal margin on the anterior chest wall, there is no complete rectus sheath (Fig. 1–8). Instead, the rectus muscle is covered only by the aponeurosis of the external oblique. In the region of the abdomen, the upper two-thirds of the internal oblique aponeurosis split at the lateral border of the rectus muscle into anterior and posterior lamellas. The anterior lamella passes in front of the external oblique and blends with the external oblique aponeurosis.
Figure 1–8. Formation of rectus sheath.
The posterior wall of the sheath is formed by the posterior lamella and the aponeurosis of the transversus muscle. The anterior and posterior sheaths join at the midline. The lower third of the internal oblique aponeurosis is undivided. Together with the aponeuroses of the external oblique and transversus muscles, it forms the anterior wall of the sheath. The posterior wall is occupied by transversalis fascia, which is spread over the interior surfaces of both the rectus and the transversus muscles, separating them from peritoneum and extending to the inguinal and lacunar ligaments. The transition from aponeurosis to fascia usually is fairly sharp, marked by a curved line called the arcuate line.
Variations of Abdominal Muscles
Variations have been noted in all of the abdominal muscles.
Rectus Muscle
The rectus abdominis muscle may differ in the number of its tendinous inscriptions and the extent of its thoracic attachment. Aponeurotic slips or slips of muscle on the upper part of the thorax are remnants of a more primitive state in which the muscle extended to the neck. Absence of part or all of the muscle has been noted. The pyramidalis muscle may be missing, only slightly developed, double, or extend upward to the umbilicus.
External Oblique Muscle
The external oblique muscle varies in the extent of its origin from the ribs. Broad fascicles may be separated by loose tissue from the main belly of the muscle, either on its deep or on its superficial surface. The supracostalis anterior is a rare fascicle occasionally found on the upper portion of the thoracic wall. Transverse tendinous inscriptions may also be found.
Internal Oblique Muscle
The internal oblique deviates at times, both in its attachments and in the extent of development of the fleshy part of the muscle. Occasionally, tendinous inscriptions are present, or the posterior division forms an extra muscle 7–7.5 cm wide and separated from the internal oblique by a branch of the iliohypogastric nerve and a branch of the deep circumflex iliac artery.
Transversus Muscle
The transversus muscle fluctuates widely in the extent of its development but is rarely absent. Rarely, it extends as far inferiorly as the ligamentum teres uteri (round ligament), and infrequently, it is situated superior to the anterior superior spine. However, it generally occupies an intermediate position.
BONY PELVIS
The pelvis (Fig. 1–9) is a basin-shaped ring of bones that marks the distal margin of the trunk. The pelvis rests on the lower extremities and supports the spinal column. It is composed of 2 innominate bones, one on each side, joined anteriorly and articulated with the sacrum posteriorly. The 2 major pelvic divisions are the pelvis major (upper or false pelvis) and the pelvis minor (lower or true pelvis). The pelvis major consists primarily of the space superior to the iliopectineal line, including the 2 iliac fossae and the region between them. The pelvis minor, located below the iliopectineal line, is bounded anteriorly by the pubic bones, posteriorly by the sacrum and coccyx, and laterally by the ischium and a small segment of the ilium.
Figure 1–9. The bony pelvis. (Reproduced, with permission, from Benson RC. Handbook of Obstetrics & Gynecology. 8th ed. Los Altos, CA: Lange; 1983.)
Innominate Bone
The innominate bone is composed of 3 parts: ilium, ischium, and pubis.
Ilium
The ilium consists of a bladelike upper part or ala (wing) and a thicker, lower part called the body. The body forms the upper portion of the acetabulum and unites with the bodies of the ischium and pubis. The medial surface of the ilium presents as a large concave area: The anterior portion is the iliac fossa; the smaller posterior portion is composed of a rough upper part, the iliac tuberosity; and the lower part contains a large surface for articulation with the sacrum. At the inferior medial margin of the iliac fossa, a rounded ridge, the arcuate line, ends anteriorly in the iliopectineal eminence. Posteriorly, the arcuate line is continuous with the anterior margin of the ala of the sacrum across the anterior aspect of the sacroiliac joint. Anteriorly, it is continuous with the ridge or pecten on the superior ramus of the pubis.
The lateral surface or dorsum of the ilium is traversed by 3 ridges: the posterior, anterior, and inferior gluteal lines. The superior border is called the crest, and at its 2 extremities are the anterior and posterior superior iliac spines. The principal feature of the anterior border of the ilium is the heavy anterior inferior iliac spine. Important aspects of the posterior border are the posterior superior and the inferior iliac spines and, below the latter, the greater sciatic notch, the inferior part of which is bounded by the ischium. The inferior border of the ilium participates in the formation of the acetabulum.
The main vasculature (Fig. 1–10) of the innominate bone appears where the bone is thickest. Blood is supplied to the inner surface of the ilium through twigs of the iliolumbar, deep circumflex iliac, and obturator arteries by foramens on the crest, in the iliac fossa, and below the terminal line near the greater sciatic notch. The outer surface of the ilium is supplied mainly below the inferior gluteal line through nutrient vessels derived from the gluteal arteries. The inferior branch of the deep part of the superior gluteal artery forms the external nutrient artery of the ilium and continues in its course to anastomose with the lateral circumflex artery. Upon leaving the pelvis below the piriformis muscle, it divides into a number of branches, a group of which passes to the hip joint.
Figure 1–10. Blood supply to pelvis.
Ischium
The ischium is composed of a body, superior and inferior rami, and a tuberosity. The body is the heaviest part of the bone and is joined with the bodies of the ilium and pubis to form the acetabulum. It presents 3 surfaces. (1) The smooth internal surface is continuous above with the body of the ilium and below with the inner surface of the superior ramus of the ischium. Together, these parts form the posterior portion of the lateral wall of the pelvis minor. (2) The external surface of the ischium is the portion that enters into the formation of the acetabulum. (3) The posterior surface is the area between the acetabular rim and the posterior border. It is convex and is separated from the ischial tuberosity by a wide groove. The posterior border, with the ilium, forms the bony margin of the greater sciatic notch. The superior ramus of the ischium descends from the body of the bone to join the inferior ramus at an angle of approximately 90 degrees.
The large ischial tuberosity and its inferior portion are situated on the convexity of this angle. The inferior portion of the tuberosity forms the point of support in the sitting position. The posterior surface is divided into 2 areas by an oblique line. The lesser sciatic notch occupies the posterior border of the superior ramus between the spine and the tuberosity. The inferior ramus, as it is traced forward, joins the inferior ramus of the pubis to form the arcus pubis (ischiopubic arch).
The ischium is supplied with blood from the obturator medial and lateral circumflex arteries. The largest vessels are situated between the acetabulum and the sciatic tubercle.
Pubis
The pubis is composed of a body and 2 rami, superior and inferior. The body contributes to the formation of the acetabulum, joining with the body of the ilium at the iliopectineal eminence and with the body of the ischium in the region of the acetabular notch. The superior ramus passes medially and forward from the body to meet the corresponding ramus of the opposite side at the symphysis pubica. The medial or fore portion of the superior ramus is broad and flattened anteroposteriorly. Formerly called “the body,” it presents an outer and an inner surface, the symphyseal area, and an upper border or “crest.”
Approximately 2 cm from the medial edge of the ramus and in line with the upper border is the prominent pubic tubercle, an important landmark. Below the crest are the anterior surface and the posterior or deep surface. The medial portion of the superior ramus is continuous below with the inferior ramus, and the lateral part presents a wide, smooth area anterosuperiorly, behind which is an irregular ridge, the pecten ossis pubis. The pecten pubis forms the anterior part of the linea terminalis. In front of and below the pectineal area is the obturator crest, passing from the tubercle to the acetabular notch. On the inferior aspect of the superior ramus is the obturator sulcus. The inferior ramus is continuous with the superior ramus and passes downward and backward to join the inferior ramus of the ischium, forming the “ischiopubic arch.” The pubis receives blood from the pubic branches of the obturator artery and from branches of the medial and lateral circumflex arteries.
Pubic Symphysis
The pubic symphysis is a synarthrodial joint of the symphyseal surfaces of the pubic bones. The ligaments associated with it are (1) the interpubic fibrocartilage, (2) the superior pubic ligament, (3) the anterior pubic ligament, and (4) the arcuate ligament. The interpubic fibrocartilage is thicker in front than behind and projects beyond the edges of the bones, especially on the posterior aspect, blending intimately with the ligaments at its margins. Sometimes it is woven throughout, but often the interpubic fibrocartilage presents an elongated, narrow fissure with fluid in the interspace, partially dividing the cartilage into 2 plates.
The interpubic cartilage is intimately adherent to the layer of hyaline cartilage that covers the symphyseal surface of each pubic bone. The superior pubic ligament extends laterally along the crest of the pubis on each side to the pubic tubercle, blending in the middle line with the interpubic cartilage. The thick and strong anterior pubic ligament is closely connected with the fascial covering of the muscles arising from the conjoined rami of the pubis. It consists of several strata of thick, decussating fibers of different degrees of obliquity, the superficial being the most oblique and extending lowest over the joint. The arcuate ligament is a thick band of closely connected fibers that fills the angle between the pubic rami to form a smooth, rounded top to the pubic arch. Both on the anterior and posterior aspects of the joint, the ligament gives off decussating fibers that, interlacing with one another, strengthen the joint.
Sacrum
The sacrum is formed in the adult by the union of 5 or 6 sacral vertebrae; occasionally, the fifth lumbar vertebra is partly fused with it. The process of union is known as “sacralization” in the vertebral column. The sacrum constitutes the base of the vertebral column. As a single bone, it is considered to have a base, an apex, 2 surfaces (pelvic and dorsal), and 2 lateral portions. The base faces upward and is composed principally of a central part, formed by the upper surface of the body of the first sacral vertebra, and 2 lateral areas of alae. The body articulates by means of a fibrocartilage disk with the body of the fifth lumbar vertebra. The alae represent the heavy transverse processes of the first sacral vertebra that articulate with the 2 iliac bones. The anterior margin of the body is called the promontory and forms the sacrovertebral angle with the fifth lumbar vertebra. The rounded anterior margin of each ala constitutes the posterior part (pars sacralis) of the linea terminalis.
The pelvic surface of the sacrum is rough and convex. In the midline is the median sacral crest (fused spinal processes), and on either side is a flattened area formed by the fused laminae of the sacral vertebrae. The laminae of the fifth vertebra and, in many cases, those of the fourth and occasionally of the third are incomplete (the spines also are absent), thus leaving a wide opening to the dorsal wall of the sacral canal known as the sacral hiatus. Lateral to the laminae are the articular crests (right and left), which are in line with the paired superior articular processes above. The lateral processes articulate with the inferior articular processes of the fifth lumbar vertebra. The inferior extensions of the articular crests form the sacral cornua that bind the sacral hiatus laterally and are attached to the cornua of the coccyx. The cornua can be palpated in life and are important landmarks indicating the inferior opening of the sacral canal (for sacral-caudal anesthesia).
The lateral portions of the sacrum are formed by the fusion of the transverse processes of the sacral vertebrae. They form dorsally a line of elevations called the lateral sacral crests. The parts corresponding to the first 3 vertebrae are particularly massive and present a large area facing laterally called the articular surface, which articulates with the sacrum. Posterior to the articular area, the rough bone is called the sacral tuberosity. It faces the tuberosity of the ilium. The apex is the small area formed by the lower surface of the body of the fifth part of the sacrum. The coccyx is formed by 4 (occasionally 3 or 5) caudal or coccygeal vertebrae. The second, third, and fourth parts are frequently fused into a single bone that articulates with the first by means of a fibrocartilage. The entire coccyx may become ossified and fused with the sacrum (the sacrococcygeal joint).
The sacrum receives its blood supply from the middle sacral artery, which extends from the bifurcation of the aorta to the tip of the coccyx, and from the lateral sacral arteries that branch either as a single artery that immediately divides or as 2 distinct vessels from the hypogastric artery. The lowest lumbar branch of the middle sacral artery ramifies over the lateral parts of the sacrum, passing back between the last vertebra and the sacrum to anastomose with the lumbar arteries above and the superior gluteal artery below. The lateral sacral branches (usually 4) anastomose anteriorly to the coccyx with branches of the inferior lateral sacral artery that branch from the hypogastric artery. They give off small spinal branches that pass through the sacral foramens and supply the sacral canal and posterior portion of the sacrum.
Sacroiliac Joint
The sacroiliac joint is a diarthrodial joint with irregular surfaces. The articular surfaces are covered with a layer of cartilage, and the cavity of the joint is a narrow cleft. The cartilage on the sacrum is hyaline in its deeper parts but much thicker than that on the ilium. A joint capsule is attached to the margins of the articular surfaces, and the bones are held together by the anterior sacroiliac, long and short posterior sacroiliac, and interosseous ligaments. In addition, there are 3 ligaments (Fig. 1–11), classed as belonging to the pelvic girdle itself, which also serve as accessory ligaments to the sacroiliac joint: the iliolumbar, sacrotuberous, and sacrospinous ligaments.
Figure 1–11. Ligaments of the pelvis.
The anterior sacroiliac ligaments unite the base and the lateral part of the sacrum to the ilium, blending with the periosteum of the pelvic surface and, on the ilium, reaching the arcuate line to attach in the paraglenoid grooves. The posterior sacroiliac ligament is extremely strong and consists essentially of 2 sets of fibers, deep and superficial, forming the short and long posterior sacroiliac ligaments, respectively. The short posterior sacroiliac ligament passes inferiorly and medially from the tuberosity of the ilium, behind the articular surface and posterior interior iliac spine, to the back of the lateral portion of the sacrum and to the upper sacral articular process, including the area between it and the first sacral foramen.
The long posterior sacroiliac ligament passes inferiorly from the posterior superior iliac spine to the second, third, and fourth articular tubercles on the back of the sacrum. It partly covers the short ligament and is continuous below with the sacrotuberous ligament. The interosseous ligaments are the strongest of all and consist of fibers of different lengths passing in various directions between the 2 bones. They extend from the rough surface of the sacral tuberosity to the corresponding surface on the lateral aspect of the sacrum, above and behind the articular surface.
Ligaments
The sacrotuberous ligament, in common with the long posterior sacroiliac ligament, is attached above to the crest of the ilium and posterior iliac spine and to the posterior aspect of the lower 3 sacral vertebrae. Below, it is attached chiefly to the medial border of the ischial tuberosity. Some of the fibers at the other end extend forward along the inner surface of the ischial ramus, forming the falciform process. Other posterior fibers continue into the tendons of the hamstrings.
The sacrospinous ligament is triangular and thin, extending from the lateral border of the sacrum and coccyx to the spine of the ischium. It passes medially (deep) to the sacrotuberous ligament and is partly blended with it along the lateral border of the sacrum.
The iliolumbar ligament connects the fourth and fifth lumbar vertebrae with the iliac crest. It originates from the transverse process of the fifth lumbar vertebra, where it is closely woven with the sacrolumbar ligament. Some of its fibers spread downward onto the body of the fifth vertebra, and others ascend to the disk above. It is attached to the inner lip of the crest of the ilium for approximately 5 cm. The sacrolumbar ligament is generally inseparable from the iliolumbar ligament and is regarded as part of it.
Foramens
Several foramens are present in the bony pelvis. The sacrospinous ligament separates the greater from the lesser sciatic foramen. These foramens are subdivisions of a large space intervening between the sacrotuberous ligament and the femur. The piriformis muscle passes out of the pelvis into the thigh by way of the greater sciatic foramen, accompanied by the gluteal vessels and nerves. The internal pudendal vessels, the pudendal nerve, and the nerve to the obturator internus muscle also leave the pelvis by this foramen, after which they enter the perineal region through the lesser sciatic foramen. The obturator internus muscle passes out of the pelvis by way of the lesser sciatic foramen.
The obturator foramen is situated between the ischium and the pubis. The obturator membrane occupies the obturator foramen and is attached continuously to the inner surface of the bony margin except above, where it bridges the obturator sulcus, converting the latter into the obturator canal, which provides passage for the obturator nerve and vessels.
On either side of the central part of the pelvic surface of the sacrum are 4 anterior sacral foramens that transmit the first 4 sacral nerves. Corresponding to these on the dorsal surface are the 4 posterior sacral foramens for transmission of the small posterior rami of the first 4 sacral nerves.
TYPES OF PELVES
Evaluation of the pelvis is best achieved by using the criteria set by Caldwell and Moloy, which are predicated upon 4 basic types of pelves: (1) the gynecoid type (from Greek gyne meaning woman); (2) the android type (from Greek aner meaning man); (3) the anthropoid type (from Greek anthropos meaning human); and (4) the platypelloid type (from Greek platys meaning broad and pella meaning bowl) (Fig. 1–12).
Figure 1–12. Types of pelves. White lines in the diagrams at right (after Steele) show the greatest diameters of the pelves at left. (Reproduced, with permission, from Benson RC. Handbook of Obstetrics & Gynecology. 8th ed. Los Altos, CA: Lange; 1983.)
Gynecoid
In pure form, the gynecoid pelvis provides a rounded, slightly ovoid, or elliptical inlet with a well-rounded forepelvis (anterior segment). This type of pelvis has a well-rounded, spacious posterior segment, an adequate sacrosciatic notch, a hollow sacrum with a somewhat backward sacral inclination, and a Norman-type arch of the pubic rami. The gynecoid pelvis has straight side walls and wide interspinous and intertuberous diameters. The bones are primarily of medium weight and structure.
Android
The android pelvis has a wedge-shaped inlet, a narrow fore-pelvis, a flat posterior segment, and a narrow sacrosciatic notch, with the sacrum inclining forward. The side walls converge, and the bones are medium to heavy in structure.
Anthropoid
The anthropoid pelvis is characterized by a long, narrow, oval inlet; an extended and narrow anterior and posterior segment; a wide sacrosciatic notch; and a long, narrow sacrum, often with 6 sacral segments. The subpubic arch may be an angled Gothic type or rounded Norman type. Straight side walls are characteristic of the anthropoid pelvis, whose interspinous and intertuberous diameters are less than those of the average gynecoid pelvis. A medium bone structure is usual.
Platypelloid
The platypelloid pelvis has a distinct oval inlet with a very wide, rounded retropubic angle and a wider, flat posterior segment. The sacrosciatic notch is narrow and has a normal sacral inclination, although it is often short. The subpubic arch is very wide, and the side walls are straight, with wide interspinous and intertuberous diameters.
The pelvis in any individual case may be one of the 4 “pure” types or a combination of mixed types. When one discusses the intermediate pelvic forms, the posterior segment with its characteristics generally is described first and the anterior segment with its characteristics next (eg, anthropoid-gynecoid, android-anthropoid, or platypelloid-gynecoid). It is impossible to have a platypelloid-anthropoid pelvis or a platypelloid-android pelvis.
Pelvic Relationships
Several important relationships should be remembered, beginning with those at the inlet of the pelvis. The transverse diameter of the inlet is the widest diameter, where bone is present for a circumference of 360 degrees. This diameter stretches from pectineal line to pectineal line and denotes the separation of the posterior and anterior segments of the pelvis. In classic pelves (gynecoid), a vertical plane dropped from the transverse diameter of the inlet passes through the level of the interspinous diameter at the ischial spine.
These relationships may not hold true, however, in combination or intermediate (mixed type) pelves. The anterior transverse diameter of the inlet reaches from pectineal prominence to pectineal prominence; a vertical plane dropped from the anterior transverse passes through the ischial tuberosities. For good function of the pelvis, the anterior transverse diameter should never be more than 2 cm longer than the transverse diameter (Fig. 1–13).
Figure 1–13. Urogenital and anal triangles.
Obstetric Conjugate
The obstetric conjugate differs from both the diagonal conjugate and the true conjugate. It is represented by a line drawn from the posterior superior portion of the pubic symphysis (where bone exists for a circumference of 360 degrees) toward intersection with the sacrum. This point need not be at the promontory of the sacrum. The obstetric conjugate is divided into 2 segments: (1) the anterior sagittal, originating at the intersection of the obstetric conjugate with the transverse diameter of the inlet and terminating at the symphysis pubica; and (2) the posterior sagittal, originating at the transverse diameter of the inlet to the point of intersection with the sacrum.
Interspinous Diameter
A most significant diameter in the midpelvis is the interspinous diameter. It is represented by a plane passing from ischial spine to ischial spine. The posterior sagittal diameter of the midpelvis is a bisecting line drawn at a right angle from the middle of the interspinous diameter, in the same plane, to a point of intersection with the sacrum. This is the point of greatest importance in the midpelvis. It is sometimes said that the posterior sagittal diameter should be drawn from the posterior segment of the intersecting line of the interspinous diameter, in a plane from the inferior surface of the symphysis, through the interspinous diameter to the sacrum. However, this configuration often places the posterior sagittal diameter lower in the pelvis than the interspinous diameter. It is the interspinous diameter, together with the posterior sagittal diameter of the midpelvis, that determines whether or not there is adequate room for descent and extension of the head during labor.
Intertuberous Diameter
The intertuberous diameter of the outlet will reflect the length of the anterior transverse diameter of the inlet (ie, the former cannot be larger than the latter if convergent or straight side walls are present). Therefore, the intertuberous diameter determines the space available in the anterior segment of the pelvis at the inlet, and, similarly, the degree of convergence influences the length of the biparietal diameter at the outlet.
Posterior Sagittal Diameter
The posterior sagittal diameter of the outlet is an intersecting line drawn from the middle of the intertuberous diameter to the sacrococcygeal junction and reflects the inclination of the sacrum toward the outlet for accommodation of the head at delivery. It should be noted that intricate measurements of the pelvis are significant only at minimal levels. Evaluation of the pelvis for a given pregnancy, size of the fetus for a given pelvis, and conduct of labor engagement are far more important.
Outlets of the True Pelvis
The true pelvis is said to have an upper “inlet” and a lower “outlet.” The pelvic inlet to the pelvis minor is bounded, beginning posteriorly, by (1) the promontory of the sacrum; (2) the linea terminalis, composed of the anterior margin of the ala sacralis, the arcuate line of the ilium, and the pecten ossis pubis; and (3) the upper border or crest of the pubis, ending medially at the symphysis. The conjugate or the anteroposterior diameter is drawn from the center of the promontory to the symphysis pubica, with 2 conjugates recognized: (1) the true conjugate, measured from the promontory to the top of the symphysis; and (2) the diagonal conjugate, measured from the promontory to the bottom of the symphysis.
The transverse diameter is measured through the greatest width of the pelvic inlet. The oblique diameter runs from the sacroiliac joint of one side to the iliopectineal eminence of the other. The pelvic outlet, which faces downward and slightly backward, is very irregular. Beginning anteriorly, it is bounded by (1) the arcuate ligament of the pubis (in the midline), (2) the ischiopubic arch, (3) the ischial tuberosity, (4) the sacrotuberous ligament, and (5) the coccyx (in mid-line). Its anteroposterior diameter is drawn from the lower border of the symphysis pubica to the tip of the coccyx. The transverse diameter passes between the medial surfaces of the ischial tuberosities.
INGUINAL REGION
The inguinal region of the abdominal wall is bounded by the rectus abdominis muscle medially, the line connecting the anterior superior iliac spines superiorly, and the inguinal ligament inferiorly. The region contains 8 layers of abdominal wall. These layers, from the most superficial inward, are (1) the skin, (2) the tela subcutanea (subcutaneous tissue), (3) the aponeurosis of the external oblique muscle, (4) the internal oblique muscle, (5) the transversus abdominis muscle (below the free border, the layer is incomplete), (6) the transversalis fascia, (7) the subperitoneal fat and connective tissue, and (8) the peritoneum. The tela subcutanea consists of the superficial fatty Camper’s fascia, which is continuous with the tela subcutanea of the whole body, and the deeper membranous Scarpa’s fascia, which covers the lower third of the abdominal wall and the medial side of the groin, both joining below the inguinal ligament to form the fascia lata of the thigh.
Subcutaneous (External) Inguinal Ring
A triangular evagination of the external oblique aponeurosis, the subcutaneous inguinal ring (external abdominal ring), is bounded by an aponeurosis at its edges and by the inguinal ligament inferiorly. The superior or medial crus is smaller and attaches to the symphysis pubica. The inferior or lateral crus is stronger and blends with the inguinal ligament as it passes to the pubic tubercle. The sharp margins of the ring are attributed to a sudden thinning of the aponeurosis. In the female, the ligamentum teres uteri (round ligament) pass through this ring. The subcutaneous inguinal ring is much smaller in the female than in the male, and the abdominal wall is relatively stronger in this region.
Abdominal (Internal) Inguinal Ring
The abdominal inguinal ring (internal abdominal ring) is the rounded mouth of a funnel-shaped expansion of transversalis fascia that lies approximately 2 cm above the inguinal ligament and midway between the anterior superior iliac spine and the symphysis pubica. Medially, it is bounded by the inferior epigastric vessels; the external iliac artery is situated below. The abdominal inguinal ring represents the area where the round ligament emerges from the abdomen. The triangular area medial to the inferior epigastric artery, bounded by the inguinal ligament below and the lateral border of the rectus sheath, is known as the trigonum inguinale (Hesselbach’s triangle), the site of congenital direct hernias.
Inguinal Canal
The inguinal canal in the female is not well demarcated, but it normally gives passage to the round ligament of the uterus, a vein, an artery from the uterus that forms a cruciate anastomosis with the labial arteries, and extraperitoneal fat. The fetal ovary, like the testis, is an abdominal organ and possesses a gubernaculum that extends from its lower pole downward and forward to a point corresponding to the abdominal inguinal ring, through which it continues into the labia majora.
The processus vaginalis is an evagination of peritoneum at the level of the abdominal inguinal ring occurring during the third fetal month. In the male, the processus vaginalis descends with the testis. The processus vaginalis of the female is rudimentary, but occasionally a small diverticulum of peritoneum is found passing partway through the inguinal region; this diverticulum is termed the processus vaginalis peritonei (canal of Nuck). Instead of descending, as does the testis, the ovary moves medially, where it becomes adjacent to the uterus.
The intraabdominal portion of the gubernaculum ovarii becomes attached to the lateral border of the developing uterus, evolving as the ligament of the ovary and the round ligament of the uterus. The extra-abdominal portion of the round ligament of the uterus becomes attenuated in the adult and may appear as a small fibrous band. The inguinal canal is an intermuscular passageway that extends from the abdominal ring downward, medially, and somewhat forward to the subcutaneous inguinal ring (about 3–4 cm). The canal is roughly triangular in shape, and its boundaries are largely artificial. The lacunar and inguinal ligaments form the base of the canal. The anterior or superficial wall is formed by the external oblique aponeurosis, and the lowermost fibers of the internal oblique muscle add additional strength in its lateral part. The posterior or deep wall of the canal is formed by transversalis fascia throughout and is strengthened medially by the falx inguinalis.
Abdominal Fossae
The abdominal fossae in the inguinal region consist of the foveae inguinalis lateralis and medialis. The fovea inguinalis lateralis lies lateral to a slight fold, the plica epigastrica, formed by the inferior epigastric vessels, and just medial to the abdominal inguinal ring, which slants medially and upward toward the rectus muscle. From the lateral margin of the tendinous insertion of the rectus muscle, upward toward the umbilicus, and over the obliterated artery extends a more accentuated fold, the plica umbilicalis lateralis. The fovea inguinalis medialis lies between the plica epigastrica and the plica umbilicalis lateralis, with the bottom of the fossa facing the trigonum inguinale (Hesselbach’s triangle). This region is strengthened by the interfoveolar ligament at the medial side of the abdominal inguinal ring and the conjoined tendon lateral to the rectus muscle; however, these bands vary in width and thus are supportive.
Ligaments & Spaces
The falx inguinalis or conjoined tendon is formed by the aponeurosis of the transversus abdominis and internal oblique muscles. These fibers arise from the inguinal ligament and arch downward and forward to insert on the pubic crest and pecten ossis pubis, behind the inguinal and lacunar ligaments. The interfoveolar ligament is composed partly of fibrous bands from the aponeurosis of the transversalis muscle of the same and opposite sides. Curving medial to and below the internal abdominal ring, they attach to the lacunar ligament and pectineal fascia.
The inguinal ligament itself forms the inferior thickened border of the external oblique aponeurosis, extending from the anterior superior iliac spine to the pubic tubercle. Along its inferior border, it becomes continuous with the fascia lata of the thigh. From the medial portion of the inguinal ligament, a triangular band of fibers attaches separately to the pecten ossis pubis. This band is known as the lacunar (Gimbernat’s) ligament. The reflex inguinal ligament (ligament of Colles or triangular fascia) is represented by a small band of fibers, often poorly developed, and derived from the superior crus of the subcutaneous inguinal ring and the lower part of the linea alba. These fibers cross to the opposite side to attach to the pecten ossis pubis. The inguinal ligament forms the roof of a large osseoligamentous space leading from the iliac fossa to the thigh. The floor of this space is formed by the superior ramus of the pubis medially and by the body of the ilium laterally.
The iliopectineal ligament extends from the inguinal ligament to the iliopectineal eminence, dividing this area into 2 parts. The lateral, larger division is called the muscular lacuna and is almost completely filled by the iliopsoas muscle, along with the femoral nerve medially and the lateral femoral cutaneous nerves laterally. The medial, smaller division is known as the vascular lacuna and is traversed by the external iliac (femoral) artery, vein, and lymphatic vessels, which do not completely fill the space. The anterior border of the vascular lacuna is formed by the inguinal ligament and the transversalis fascia. The posterior boundary is formed by the ligamentum pubicum superius (Cooper’s ligament), a thickening of fascia along the public pecten where the pectineal fascia and iliopectineal ligament meet.
The transversalis fascia and iliac fascia are extended with the vessels, forming a funnel-shaped fibrous investment, the femoral sheath. The sheath is divided into 3 compartments: (1) the lateral compartment, containing the femoral artery; (2) the intermediate compartment, containing the femoral vein; and (3) the medial compartment or canal, containing a lymph node (nodi lymphatici inguinales profundi [node of Rosenmüller or Cloquet]) and the lymphatic vessels that drain most of the leg, groin, and perineum.
The femoral canal also contains areolar tissue, which frequently condenses to form the “femoral septum.” Because of the greater spread of the pelvis in the female, the muscular and vascular lacunae are relatively large spaces. The upper or abdominal opening of the femoral canal is known as the femoral ring and is covered by the parietal peritoneum.
Arteries
In front of the femoral ring, the arterial branches of the external iliac artery are the inferior epigastric and the deep circumflex iliac. The inferior epigastric artery arises from the anterior surface of the external iliac, passing forward and upward on the anterior abdominal wall between peritoneum and transversalis fascia. It pierces the fascia just below the arcuate line, entering the rectus abdominis muscle or coursing along its inferior surface to anastomose with the superior epigastric from the internal thoracic. The inferior epigastric artery forms the lateral boundary of the trigonum inguinale (Hesselbach’s triangle). At its origin, it frequently gives off a branch to the inguinal canal, as well as a branch to the pubis (pubic artery), which anastomoses with twigs of the obturator artery. The pubic branch of the inferior epigastric often becomes the obturator artery.
The deep circumflex iliac artery arises laterally and traverses the iliopsoas to the anterior superior iliac spine, where it pierces the transversus muscle to course between the transversus and the internal oblique, sending perforators to the surface. It often has anastomoses with penetrating branches of the inferior epigastric via its perforators through the rectus abdominis. The veins follow a similar course.
As the external iliac artery passes through the femoral canal, which underlies the inguinal ligament, it courses medial to the femoral vein and nerve, resting in what is termed the femoral triangle (Scarpa’s triangle). The femoral sheath is a downward continuation of the inguinal ligament anterior to the femoral vessel and nerve.
The branches of the femoral artery supplying the groin are (1) the superficial epigastric, (2) the superficial circumflex iliac, (3) the superficial external pudendal, and (4) the deep external pudendal. The superficial epigastric artery passes upward through the femoral sheath over the inguinal ligament, to rest in Camper’s fascia on the lower abdomen. The superficial circumflex iliac artery arises adjacent to the superior epigastric, piercing the fascia lata and running parallel to the inguinal ligament as far as the iliac crest. It then divides into branches that supply the integument of the groin, the superficial fascia, and the lymph glands, anastomosing with the deep circumflex iliac, the superior gluteal, and the lateral femoral circumflex arteries.
The superficial external pudendal artery arises from the medial side of the femoral artery, close to the preceding vessels. It pierces the femoral sheath and fascia cribrosa, coursing medially across the round ligament to the integument on the lower part of the abdomen and the labium majus, anastomosing with the internal pudendal. The deep external pudendal artery passes medially across the pectineus and adductor longus muscles, supplying the integument of the labium majus and forming, together with the external pudendal artery, a rete with the labial arteries.
Hernias
A hernia (Fig. 1–14) is a protrusion of any viscus from its normal enclosure, which may occur with any of the abdominal viscera, especially the jejunum, ileum, and greater omentum. A hernia may be due to increased pressure, such as that resulting from strenuous exercise, lifting heavy weights, tenesmus, or increased expiratory efforts, or it may result from decreased resistance of the abdominal wall (congenital or acquired), such as occurs with debilitating illness or old age, prolonged distention from ascites, tumors, pregnancy, corpulence, emaciation, injuries (including surgical incisions), congenital absence, or poor development. Hernias are likely to occur where the abdominal wall is structurally weakened by the passage of large vessels or nerves and developmental peculiarities. Ventral hernias occur through the linea semilunaris or the linea alba.
Figure 1–14. Hernia sites.
During early fetal development, portions of the mesentery and a loop of the intestine pass through the opening to occupy a part of the body cavity (the umbilical coelom) situated in the umbilical cord. Normally, the mesentery and intestine later return to the abdominal cavity. If they fail to do so, a congenital umbilical hernia results. Infantile umbilical hernias occur if the component parts fail to fuse completely in early postnatal stages. The unyielding nature of the fibrous tissue forming the margin of the ring predisposes to strangulation.
NERVES OF THE PELVIS
The pelvic autonomic system can be divided into the superior hypogastric plexus (the presacral plexus and the uterinus magnus), the middle hypogastric plexus, and the inferior hypogastric plexus. The superior hypogastric plexus begins just below the inferior mesenteric artery. It is composed of 1–3 intercommunicating nerve bundles connected with the inferior mesenteric ganglia, but no ganglia are an integral part of the plexus. The intermesenteric nerves receive branches from the lumbar sympathetic ganglia.
Superior Hypogastric Plexus
The superior hypogastric plexus continues into the mid-hypogastric plexus. The presacral nerves spread out into a latticework at the level of the first sacral vertebra, with connecting rami to the last of the lumbar ganglia. The greater part of the superior mid-hypogastric plexus may be found to the left of the midline.
Inferior Hypogastric Plexus
At the first sacral vertebra, this plexus divides into several branches that go to the right and left sides of the pelvis. These branches form the beginning of the right and left inferior hypogastric plexus. The inferior hypogastric plexus, which is the divided continuation of the mid-hypogastric plexus, the superior hypogastric plexus, the presacral nerve, and the uterinus magnus, is composed of several parallel nerves on each side. This group of nerves descends within the pelvis in a position posterior to the common iliac artery and anterior to the sacral plexus, curves laterally, and finally enters the sacrouterine fold or ligaments. The medial section of the primary division of the sacral nerves sends fibers (nervi erigentes) that enter the pelvic plexus in the sacrouterine folds. The plexus now appears to contain both sympathetic (inferior hypogastric plexus) and parasympathetic (nervi erigentes) components.
Nervi Erigentes
The sensory components, which are mostly visceral, are found in the nervi erigentes; however, if one takes into account the amount of spinal anesthetic necessary to eliminate uterine sensation, one must assume that there are a number of sensory fibers in the sympathetic component.
Common Iliac Nerves
The common iliac nerves originate separately from the superior hypogastric plexus and descend on the surface of the artery and vein, one part going through the femoral ring and the remainder following the internal iliac, finally rejoining the pelvic plexus.
Hypogastric Ganglion
On either side of the uterus, in the base of the broad ligament, is the large plexus described by Lee and Frankenhäuser, the so-called hypogastric ganglion. The plexus actually consists of ganglia and nerve ramifications of various sizes, as well as branches of the combined inferior hypogastric plexus and the nervi erigentes. It lies parallel to the lateral pelvic wall, its lateral surface superficial to the internal iliac and its branches; the ureter occupies a position superficial to the plexus. The middle vesical artery perforates and supplies the plexus, its medial branches supplying the rectal stalk. The greater part of the plexus terminates in large branches that enter the uterus in the region of the internal os, while another smaller component of the plexus supplies the vagina and the bladder. The branches of the plexus that supply the uterus enter the isthmus primarily through the sacrouterine fold or ligament. In the isthmus, just outside the entrance to the uterus, ascending rami pass out into the broad ligament to enter the body of the uterus at higher levels—besides supplying the uterine tubes. A part of the inferior hypogastric plexus may pass directly to the uterus without involvement in the pelvic plexus.
Ganglia are in close proximity to the uterine arteries and the ureters, in the adventitia of the bladder and vagina, and in the vesicovaginal septum. The nerve bundles entering the ganglia contain both myelinated and unmyelinated elements. Corpuscula lamellosa (Vater-Pacini corpuscles) may be found within the tissues and are often observed within nerve bundles, especially within those in the lower divisions of the plexus. Both myelinated and unmyelinated nerves are present within the uterus. The nerves enter along the blood vessels, the richest supply lying in the isthmic portion of the uterus. The fibers following the blood vessels gradually diminish in number in the direction of the fundus, where the sparsest distribution occurs. The fibers run parallel to the muscle bundles, and the nerves frequently branch to form a syncytium before terminating on the sarcoplasm as small free nerve endings.
Sensory Corpuscles
Vater-Pacini corpuscles (corpuscula lamellosa) are present outside the uterus. Dogiel and Krause corpuscles (corpuscula bulboidea) appear in the region of the endocervix. They may also be found in the broad ligament along with Vater-Pacini corpuscles and at the juncture of the uterine arteries with the uterus. These corpuscles may act to modulate the stretch response that reflexively stimulates uterine contractions during labor.
The innervation of the cervix shows occasional free endings entering papillae of the stratified squamous epithelium of the pars vaginalis. The endocervix contains a rich plexus of free endings that is most pronounced in the region of the internal os. The endocervix and the isthmic portion of the uterus in the nonpregnant state both contain the highest number of nerves and blood vessels of any part of the uterus. The presence here of a lamellar type of corpuscle has already been noted.
Nerves pass through the myometrium and enter the endometrium. A plexus with penetrating fibers involving the submucosal region is present in the basal third of the endometrium, with branches terminating in the stroma, in the basilar arterioles, and at the origin of the spiral arterioles. The outer two-thirds of the endometrium are devoid of nerves.
STRUCTURES LINING THE PELVIS
The walls of the pelvis minor are made up of the following layers: (1) the peritoneum, (2) the subperitoneal or extraperitoneal fibroareolar layer, (3) the fascial layer, and (4) the muscular layer. The anatomy of the floor of the pelvis is comparable to that of the walls except for the absence of an osseoligamentous layer.
Peritoneum
The peritoneum presents several distinct transverse folds that form corresponding fossae on each side. The most anterior is a variable fold, the transverse vesical, extending from the bladder laterally to the pelvic wall. It is not the superficial covering of any definitive structure. Behind it lies the broad ligament, which partially covers and aids in the support of the uterus and adnexa.
Ligaments
The broad ligament extends from the lateral border on either side of the uterus to the floor and side walls of the pelvis. It is composed of 2 layers, anterior and posterior, the anterior facing downward and the posterior facing upward, conforming to the position of the uterus. The inferior or “attached” border of the broad ligament is continuous with the parietal peritoneum on the floor and on the side walls of the pelvis. Along this border, the posterior layer continues laterally and posteriorly in an arc to the region of the sacrum, forming the uterosacral fold. Another fold—the rectouterine fold—frequently passes from the posterior surface of the cervix to the rectum in the midline.
The anterior layer of the broad ligament is continuous laterally along the inferior border with the peritoneum of the paravesical fossae and continuous medially with peritoneum on the upper surface of the bladder. Both layers of the attached border continue up the side walls of the pelvis to join with a triangular fold of peritoneum, reaching to the brim of the pelvis to form the suspensory ligament of the ovary or infundibular ligament. This ligament contains the ovarian vessels and nerves. The medial border of the broad ligament on either side is continuous with the peritoneal covering on both uterine surfaces. The 2 layers of the ligament separate to partially contain the uterus, and the superior or “free” border, which is laterally continuous with the suspensory ligament of the ovary, envelops the uterine tube.
The broad ligament can be divided into regions as follows: (1) a larger portion, the mesometrium, which is associated especially with the lateral border of the uterus; (2) the mesovarium, the fold that springs from the posterior layer of the ovary; and (3) the thin portion, the mesosalpinx, which is associated with the fallopian tube in the region of the free border. The superior lateral corner of the broad ligament has been referred to as the suspensory ligament of the ovary, or infundibulopelvic ligament, because it suspends the infundibulum as well as the ovary.
Fossae & Spaces
Corresponding to the peritoneal folds are the peritoneal fossae. The prevesical or retropubic space is a potential space that is crossed by the transverse vesical fold. It is situated in front of the bladder and behind the pubis. When the bladder is displaced posteriorly, it becomes an actual space, anteriorly continuous from side to side and posteriorly limited by a condensation of fatty areolar tissue extending from the base of the bladder to the side wall of the pelvis.
The vesicouterine pouch is a narrow cul-de-sac between the anterior surface of the body of the uterus and the upper surface of the bladder when the uterus is in normal ante-flexed position. In the bottom of this pouch, the peritoneum is reflected from the bladder onto the uterus at the junction of the cervix and corpus. Therefore, the anterior surface of the cervix is below the level of the peritoneum and is connected with the base of the bladder by condensed areolar tissue.
The peritoneum on the posterior surface of the body of the uterus extends downward onto the cervix and onto the posterior fornix of the vagina. It is then reflected onto the anterior surface of the rectum to form a narrow cul-de-sac continuous with the pararectal fossa of either side. The entire space, bounded anteriorly by the cervix and by the fornix in the midline, the uterosacral folds laterally, and the rectum posteriorly, is the rectouterine pouch or cul-de-sac (pouch of Douglas).
Subperitoneal & Fascial Layers
The subperitoneal layer consists of loose, fatty areolar tissue underlying the peritoneum. External to the subperitoneal layer, a layer of fascia lines the wall of the pelvis, covering the muscles and, where these are lacking, blending with the periosteum of the pelvic bones. This layer is known as the parietal pelvic fascia and is subdivided into the obturator fascia, the fascia of the urogenital diaphragm, and the fascia of the piriformis.
The obturator fascia is of considerable thickness and covers the obturator internus muscle. Traced forward, it partially blends with the periosteum of the pubic bone and assists in the formation of the obturator canal. Traced upward, it is continuous at the arcuate line with the iliac fascia. Inferiorly, it extends nearly to the margin of the ischiopubic arch, where it is attached to the bone. In this lower region, it also becomes continuous with a double-layered triangular sheet of fascia, the fasciae of the urogenital diaphragm, passing across the anterior part of the pelvic outlet. A much thinner portion of the parietal pelvic fascia covers the piriformis and coccygeus muscles in the posterior pelvic wall. Medially, the piriformis fascia blends with the periosteum of the sacrum around the margins of the anterior sacral foramens and covers the roots and first branches of the sacral plexus.
Visceral pelvic fascia denotes the fascia in the bottom of the pelvic bowl, which invests the pelvic organs and forms a number of supports that suspend the organs from the pelvic walls. These supports arise in common from the obturator part of the parietal fascia, along or near the arcus tendineus. This arc or line extends from a point near the lower part of the symphysis pubica to the root of the spine of the ischium. From this common origin, the fascia spreads inward and backward, dividing into a number of parts classified as either investing (endopelvic) fascia or suspensory and diaphragmatic fascia.
Muscular Layer
The muscles of the greater pelvis are the psoas major and iliacus. Those of the lesser pelvis are the piriformis, obturator internus, coccygeus, and levator ani; they do not form a continuous layer.
Greater Pelvis
Psoas Major
The fusiform psoas major muscle originates from the 12th thoracic to the fifth lumbar vertebrae. Parallel fiber bundles descend nearly vertically along the side of the vertebral bodies and extend along the border of the minor pelvis, beneath the inguinal ligament, and on toward insertion in the thigh. The medial border inserts into the lesser trochanter, whereas the lateral border shares its tendon with the iliacus muscle. Together with the iliacus, it is the most powerful flexor of the thigh, acting as a lateral rotator of the femur when the foot is off the ground and free and as a medial rotator when the foot is on the ground and the tibia is fixed. The psoas component flexes the spine and the pelvis and abducts the lumbar region of the spine. The psoas, having longer fibers than the iliacus, gives a quicker but weaker pull.
Iliacus
The fan-shaped iliacus muscle originates from the iliac crest, the iliolumbar ligament, the greater part of the iliac fossa, the anterior sacroiliac ligaments, and frequently the ala of the sacrum. It also originates from the ventral border of the ilium between the 2 anterior spines. It is inserted in an oblique manner on the lateral surface of the tendon that emerges from the psoas above the inguinal ligament and directly on the femur immediately distal to the lesser trochanter. The lateral portion of the muscle arising from the ventral border of the ilium is adherent to the direct tendon of the rectus femoris and the capsule of the hip joint.
Lesser Pelvis
Piriformis
The piriformis has its origin from the lateral part of the ventral surface of the second, third, and fourth sacral vertebrae, from the posterior border of the greater sciatic notch, and from the deep surface of the sacrotuberous ligament near the sacrum. The fiber bundles pass through the greater sciatic foramen to insert upon the anterior and inner portion of the upper border of the greater trochanter. The piriformis acts as an abductor, lateral rotator, and weak extensor of the thigh.
Obturator Internus
The obturator internus arises from the pelvic surface of the pubic rami near the obturator foramen, the pelvic surface of the ischium between the foramen and the greater sciatic notch, the deep surface of the obturator internus fascia, the fibrous arch that bounds the canal for the obturator vessels and nerves, and the pelvic surface of the obturator membrane. The fiber bundles converge toward the lesser sciatic notch, where they curve laterally to insert into the trochanteric fossa of the femur. The obturator internus is a powerful lateral rotator of the thigh. When the thigh is bent at a right angle, the muscle serves as an abductor and extensor.
Coccygeus
The coccygeus muscle runs from the ischial spine and the neighboring margin of the greater sciatic notch to the fourth and fifth sacral vertebrae and the coccyx. A large part of the muscle is aponeurotic. It supports the pelvic and abdominal viscera and possibly flexes and abducts the coccyx.
Levator Ani
The levator ani muscle forms the floor of the pelvis and the roof of the perineum. It is divisible into 3 portions: (1) the iliococcygeus, (2) the pubococcygeus, and (3) the puborectalis.
1. Iliococcygeus—The iliococcygeus arises from the arcus tendineus, which extends from the ischial spine to the superior ramus of the pubis near the obturator canal and for a variable distance downward below the obturator canal. Its insertion is into the lateral aspect of the coccyx and the raphe that extends from the tip of the coccyx to the rectum. Many fiber bundles cross the median line.
2. Pubococcygeus—The pubococcygeus arises from the inner surface of the os pubis, the lower margin of the symphysis pubica to the obturator canal, and the arcus tendineus as far backward as the origin of the iliococcygeus. It passes backward, downward, and medially past the urogenital organs and the rectum, inserting into the anterior sacrococcygeal ligament, the deep part of the anococcygeal raphe, and each side of the rectum. The pubococcygeus lies to some extent on the pelvic surface of the insertion of the iliococcygeus.
3. Puborectalis—The puborectalis arises from the body and descending ramus of the pubis beneath the origin of the pubococcygeus, the neighboring part of the obturator fascia, and the fascia covering the pelvic surface of the urogenital diaphragm. Many of the fiber bundles interdigitate with those of the opposite side, and they form a thick band on each side of the rectum behind which those of each side are inserted into the anococcygeal raphe.
The levator ani serves to slightly flex the coccyx, raise the anus, and constrict the rectum and vagina. It resists the downward pressure that the thoracoabdominal diaphragm exerts on the viscera during inspiration.
Pelvic Diaphragm
The pelvic diaphragm (Fig. 1–15) extends from the upper part of the pelvic surface of the pubis and ischium to the rectum, which passes through it. The pelvic diaphragm is formed by the levator ani and coccygeus muscles and covering fasciae. The diaphragmatic fasciae cloaking the levator ani arise from the parietal pelvic fascia (obturator fascia), the muscular layer lying between the fasciae. As viewed from above, the superior fascia is the best developed and is reflected onto the rectum, forming the “rectal sheath.” The coccygeus muscle forms the deeper portion of the posterolateral wall of the ischiorectal fossa, helping to bind the pelvic outlet. The diaphragm presents a hiatus anteriorly, occupied by the vagina and urethra. The pelvic diaphragm is the main support of the pelvic floor; it suspends the rectum and indirectly supports the uterus.
Figure 1–15. Pelvic diaphragm from above.
Arteries & Veins
The blood supply to the muscles lining the pelvis is primarily from branches of the hypogastric artery, accompanied by contributions from the external iliac artery. The iliolumbar branch of the hypogastric artery runs upward and laterally beneath the common iliac artery, then beneath the psoas muscle to the superior aperture of the pelvis minor, where it divides into iliac and lumbar branches. The iliac supplies both the iliacus and psoas muscles. It passes laterally beneath the psoas and the femoral nerve and, perforating the iliacus, ramifies in the iliac fossa between the muscle and the bone. It supplies a nutrient artery to the bone and then divides into several branches that can be traced as follows: (1) upward toward the sacroiliac synchondrosis to anastomose with the last lumbar artery, (2) laterally toward the crest of the ilium to anastomose with the lateral circumflex and gluteal arteries, and (3) medially toward the pelvis minor to anastomose with the deep circumflex iliac from the external iliac. The lumbar branch ascends beneath the psoas and supplies that muscle along with the quadratus lumborum. It then anastomoses with the last lumbar artery.
Another branch of the hypogastric artery, the lateral sacral artery, may be represented as 2 distinct vessels. It passes medially in front of the sacrum and turns downward to run parallel with the sympathetic trunk. Crossing the slips of origin of the piriformis muscle, it sends branches to that muscle. On reaching the coccyx, it anastomoses in front of the bone with the middle sacral artery and with the inferior lateral sacral artery of the opposite side. The obturator artery usually arises from the hypogastric, but occasionally it may stem from the inferior epigastric or directly from the external iliac artery. It runs forward and downward slightly below the brim of the pelvis, lying between the peritoneum and endopelvic fascia. Passing through the obturator canal, it emerges and divides into anterior and posterior branches that curve around the margin of the obturator foramen beneath the obturator externus muscle.
When the obturator artery arises from the inferior epigastric or external iliac artery, its proximal relationships are profoundly altered, the vessel coursing near the femoral ring where it may be endangered during operative procedures. The anterior branch of the obturator artery runs around the medial margin of the obturator foramen and anastomoses with both of its posterior branch and the medial circumflex artery. It supplies branches to the obturator muscles. The internal pudendal artery is a terminal branch of the hypogastric artery that arises opposite the piriformis muscle and accompanies the inferior gluteal artery downward to the lower border of the greater sciatic foramen. It leaves the pelvis between the piriformis and coccygeus muscles, passing over the ischial spine to enter the ischiorectal fossa through the small sciatic foramen. Then, running forward through the canalis pudendalis (Alcock’s canal) in the obturator fascia, it terminates by dividing into the perineal artery and the artery of the clitoris.
Within the pelvis, the artery lies anterior to the piriformis muscle and the sacral plexus of nerves, lateral to the inferior gluteal artery. Among the small branches that it sends to the gluteal region are those that accompany the nerve to the obturator internus. Another of its branches, the inferior hemorrhoidal artery, arises at the posterior part of the ischiorectal fossa. Upon perforating the obturator fascia, it immediately breaks up into several branches. Some of them run medially toward the rectum to supply the levator ani muscle. The superior gluteal artery originates as a short trunk from the lateral and back part of the hypogastric artery, associated in origin with the iliolumbar and lateral sacral and sometimes with the inferior gluteal or with the inferior gluteal and the internal pudendal. It leaves the pelvis through the greater sciatic foramen above the piriformis muscle, beneath its vein and in front of the superior gluteal nerve. Under cover of the gluteus maximus muscle, it breaks into a superficial and a deep division.
The deep portion further divides into superior and inferior branches. The inferior branch passes forward between the gluteus medius and minimus toward the greater trochanter, where it anastomoses with the ascending branch of the lateral circumflex. It supplies branches to the obturator internus, the piriformis, the levator ani, and the coccygeus muscles and to the hip joint. The deep circumflex iliac artery arises from the side of the external iliac artery either opposite the epigastric or a little below the origin of that vessel. It courses laterally behind the inguinal ligament, lying between the fascia transversalis and the peritoneum or in a fibrous canal formed by the union of the fascia transversalis with the iliac fascia. It sends off branches that supply the psoas and iliacus muscles, as well as a cutaneous branch that anastomoses with the superior gluteal artery.
VULVA
The vulva consists of the mons pubis, the labia majora, the labia minora, the clitoris, and the glandular structures that open into the vestibulum vaginae (Fig. 1–16). The size, shape, and coloration of the various structures, as well as the hair distribution, vary among individuals and racial groups. Normal pubic hair in the female is distributed in an inverted triangle, with the base centered over the mons pubis. Nevertheless, in approximately 25% of normal women, hair may extend upward along the linea alba. The type of hair is dependent, in part, on the pigmentation of the individual. It varies from heavy, coarse, crinkly hair in black women to sparse, fairly fine, lanugo-type hair in Asian women. The length and size of the various structures of the vulva are influenced by the pelvic architecture, as is the position of the external genitalia in the perineal area. The external genitalia of the female have their exact counterparts in the male.
Figure 1–16. External genitalia of adult female (parous).
Labia Majora
Superficial Anatomy
The labia majora are comprised of 2 rounded mounds of tissue, originating in the mons pubis and terminating in the perineum. They form the lateral boundaries of the vulva and are approximately 7–9 cm long and 2–4 cm wide, varying in size with height, weight, race, age, parity, and pelvic architecture. Embryologically, these permanent folds of skin are homologous to the scrotum of the male. Hair is distributed over their surfaces, extending superiorly in the area of the mons pubis from one side to the other. The lateral surfaces are adjacent to the medial surface of the thigh, forming a deep groove when the legs are together. The medial surfaces of the labia majora may oppose each other directly or may be separated by protrusion of the labia minora. The cleft that is formed by this opposition anteriorly is termed the anterior commissure. Posteriorly, the cleft is less clearly defined and termed the posterior commissure. The middle portion of the cleft between the 2 labia is the rima pudendi.
Deep Structures
Underlying the skin is a thin, poorly developed muscle layer called the tunica dartos labialis, the fibers of which course, for the most part, at right angles to the wrinkles of the surface, forming a crisscross pattern. Deep to the dartos layer is a thin layer of fascia, most readily recognizable in the old or the young because of the large amount of adipose and areolar tissue. Numerous sweat glands are found in the labia majora, with the greater number on the medial aspect. In the deeper substance of the labia majora are longitudinal bands of muscle that are continuous with the ligamentum teres uteri (round ligament) as it emerges from the inguinal canal. Occasionally, a persistent processus vaginalis peritonei (canal of Nuck) may be seen in the upper region of the labia. This can occasionally fill with fluid causing a cyst in the canal of Nuck to be present in the labia majora. Complete surgical obliteration of this persistent tract will solve this problem.
Arteries
The arterial supply into the labia majora comes from the internal and external pudendals, with extensive anastomoses. Within the labia majora is a circular arterial pattern originating inferiorly from a branch of the perineal artery, from the external pudendal artery in the anterior lateral aspect, and from a small artery of the ligamentum teres uteri superiorly. The inferior branch from the perineal artery, which originates from the internal pudendal as it emerges from the canalis pudendalis (Alcock’s canal), forms the base of the rete with the external pudendal arteries. These arise from the medial side of the femoral and, occasionally, from the deep arteries just beneath the femoral ring, coursing medially over the pectineus and adductor muscles, to which they supply branches. They terminate in a circular rete within the labium majus, penetrating the fascia lata adjacent to the fossa ovalis and passing over the round ligament to send a branch to the clitoris.
Veins
The venous drainage is extensive and forms a plexus with numerous anastomoses. In addition, the veins communicate with the dorsal vein of the clitoris, the veins of the labia minora, and the perineal veins, as well as with the inferior hemorrhoidal plexus. On each side, the posterior labial veins connect with the external pudendal vein, terminating in the great saphenous vein (saphena magna) just prior to its entrance (saphenous opening) in the fossa ovalis. This large plexus is frequently manifested by the presence of large varicosities during pregnancy.
Lymphatics
The lymphatics of the labia majora are extensive and utilize 2 systems, one lying superficially (under the skin) and the other deeper, within the subcutaneous tissues. From the upper two-thirds of the left and right labia majora, superficial lymphatics pass toward the symphysis and turn laterally to join the medial superficial inguinal nodes. These nodes drain into the superficial inguinal nodes overlying the saphenous fossa. The drainage flows into and through the femoral ring (fossa ovalis) to the nodi lymphatici inguinales profundi (nodes of Rosenmüller or Cloquet; deep subinguinal nodes), connecting with the external iliac chain.
The superficial subinguinal nodes, situated over the femoral trigone, also accept superficial drainage from the lower extremity and the gluteal region. This drainage may include afferent lymphatics from the perineum. In the region of the symphysis pubica, the lymphatics anastomose in a plexus between the right and left nodes. Therefore, any lesion involving the labia majora allows direct involvement of the lymphatic structures of the contralateral inguinal area. The lower part of the labium majus has superficial and deep drainage that is shared with the perineal area. The drainage passes, in part, through afferent lymphatics to superficial subinguinal nodes; from the posterior medial aspects of the labia majora, it frequently enters the lymphatic plexus surrounding the rectum.
Nerves
The innervation of the external genitalia has been studied by many investigators. The iliohypogastric nerve originates from T12 and L1 and traverses laterally to the iliac crest between the transversus and internal oblique muscles, at which point it divides into 2 branches: (1) the anterior hypogastric nerve, which descends anteriorly through the skin over the symphysis, supplying the superior portion of the labia majora and the mons pubis; and (2) the posterior iliac, which passes to the gluteal area.
The ilioinguinal nerve originates from L1 and follows a course slightly inferior to the iliohypogastric nerve, with which it may frequently anastomose, branching into many small fibers that terminate in the upper medial aspect of the labium majus.
The genitofemoral nerve (L1–L2) emerges from the anterior surface of the psoas muscle to run obliquely downward over its surface, branching in the deeper substance of the labium majus to supply the dartos muscle and that vestige of the cremaster present within the labium majus. Its lumboinguinal branch continues downward onto the upper part of the thigh.
From the sacral plexus, the posterior femoral cutaneous nerve, originating from the posterior divisions of S1 and S2 and the anterior divisions of S2 and S3, divides into several rami that, in part, are called the perineal branches. They supply the medial aspect of the thigh and the labia majora. These branches of the posterior femoral cutaneous nerve are derived from the sacral plexus. The pudendal nerve, composed primarily of S2, S3, and S4, often with a fascicle of S1, sends a small number of fibers to the medial aspect of the labia majora. The pattern of nerve endings is illustrated in Table 1–1.
Table 1–1. Quantitative distribution of nerve endings in selected regions of the female genitalia.
Labia Minora
Superficial Anatomy
The labia minora are 2 folds of skin that lie within the rima pudendi and measure approximately 5 cm in length and 0.5–1 cm in thickness. The width varies according to age and parity, measuring 2–3 cm at its narrowest diameter to 5–6 cm at its widest, with multiple corrugations over the surface. The labia minora begin at the base of the clitoris, where fusion of the labia is continuous with the prepuce, extending posteriorly and medially to the labia majora at the posterior commissure. On their medial aspects superiorly beneath the clitoris, they unite to form the frenulum adjacent to the urethra and vagina, terminating along the hymen on the right and left sides of the fossa navicularis and ending posteriorly in the frenulum of the labia pudendi, just superior to the posterior commissure. A deep cleft is formed on the lateral surface between the labium majus and the labium minus.
The skin on the labia minora is smooth, pigmented, and hairless. The color and distention vary, depending on the level of sexual excitement and the pigmentation of the individual. The glands of the labia are homologous to the glandulae preputiales (glands of Littre) of the penile portion of the male urethra.
Arteries
The main source of arterial supply (Fig. 1–17) occurs through anastomoses from the superficial perineal artery, branching from the dorsal artery of the clitoris, and from the medial aspect of the rete of the labia majora. Similarly, the venous pattern and plexus are extensive.
Figure 1–17. Arteries and nerves of perineum.
Veins
The venous drainage is to the medial vessels of the perineal and vaginal veins, directly to the veins of the labia majora, to the inferior hemorrhoidals posteriorly, and to the clitoral veins superiorly.
Lymphatics
The lymphatics medially may join those of the lower third of the vagina superiorly and the labia majora laterally, passing to the superficial subinguinal nodes and to the deep subinguinal nodes. In the midline, the lymphatic drainage coincides with that of the clitoris, communicating with that of the labia majora to drain to the opposite side.
Nerves
The innervation of the labia minora originates, in part, from fibers that supply the labia majora and from branches of the pudendal nerve as it emerges from the canalis pudendalis (Alcock’s canal) (Fig. 1–17). These branches originate from the perineal nerve. The labia minora and the vestibule area are homologous to the skin of the male urethra and penis. The short membranous portion, approximately 0.5 cm of the male urethra, is homologous to the midportion of the vestibule of the female.
Clitoris
Superficial Anatomy
The clitoris is about 2 cm in length and is a homologue to the dorsal part of the penis. It consists of 2 small erectile cavernous bodies, terminating in a rudimentary glans clitoridis. The erectile body, the corpus clitoridis, consists of the 2 crura clitoridis and the glans clitoridis, with overlying skin and prepuce, a miniature homologue of the glans penis. The crura extend outward bilaterally to their position in the anterior portion of the vulva. The cavernous tissue, homologous to the corpus spongiosum penis of the male, appears in the vascular pattern of the labia minora in the female.
At the lower border of the pubic arch, a small triangular fibrous band extends onto the clitoris (suspensory ligament) to separate the 2 crura, which turn inward, downward, and laterally at this point, close to the inferior rami of the pubic symphysis. The crura lie inferior to the ischiocavernosus muscles and bodies. The glans is situated superiorly at the fused termination of the crura. It is composed of erectile tissue and contains an integument, hoodlike in shape, termed the prepuce. On its ventral surface, there is a frenulum clitoridis, the fused junction of the labia minora.
Arteries
The blood supply to the clitoris is from its dorsal artery, a terminal branch of the internal pudendal artery, which is the terminal division of the posterior portion of the internal iliac (hypogastric) artery. As it enters the clitoris, it divides into 2 branches, the deep and dorsal arteries. Just before entering the clitoris itself, a small branch passes posteriorly to supply the area of the external urethral meatus.
Veins
The venous drainage of the clitoris begins in a rich plexus around the corona of the glans, running along the anterior surface to join the deep vein and continuing downward to join the pudendal plexus from the labia minora, labia majora, and perineum, forming the pudendal vein.
Lymphatics
The lymphatic drainage of the clitoris coincides primarily with that of the labia minora, the right and left sides having access to contralateral nodes in the superficial inguinal chain. In addition, its extensive network provides further access downward and posteriorly to the external urethral meatus toward the anterior portion of the vestibule.
Nerves
The innervation of the clitoris is through the terminal branch of the pudendal nerve, which originates from the sacral plexus as previously discussed. It lies on the lateral side of the dorsal artery and terminates in branches within the glans, corona, and prepuce. The nerve endings in the clitoris vary from a total absence within the glans to a rich supply primarily located within the prepuce (Table 1–1). A total absence of endings within the clitoris itself takes on clinical significance when one considers the emphasis placed on the clitoris in discussing problems of sexual gratification in women.
Vestibule
Superficial Anatomy
The area of the vestibule is bordered by the labia minora laterally, by the frenulum labiorum pudendi (or posterior commissure) posteriorly, and by the urethra and clitoris anteriorly. Inferiorly, it is bordered by the hymenal ring. The opening of the vagina or junction of the vagina with the vestibule is limited by a membrane stretching from the posterior and lateral sides to the inferior surface of the external urethral orifice. This membrane is termed the hymen. Its shape and openings vary and depend on age, parity, and sexual experience. The form of the opening may be infantile, annular, semilunar, cribriform, septate, or vertical; the hymen may even be imperforate. In parous women and in the postcoital state, the tags of the hymenal integument are termed carunculae myrtiformes.
The external urethral orifice, which is approximately 2–3 cm posterior to the clitoris, on a slightly elevated and irregular surface with depressed areas on the sides, may appear to be stellate or crescentic in shape. It is characterized by many small mucosal folds around its opening. Bilaterally and on the surface are the orifices of the paraurethral and periurethral glands (ductus paraurethrales [ducts of Skene and Astruc]).
At approximately the 5 and 7 o’clock positions, just external to the hymenal rings, are 2 small papular elevations that represent the orifices of the ducts of the glandulae vestibulares majores or larger vestibular glands (Bartholin) of the female (bulbourethral gland of the male). The fossa navicularis lies between the frenulum labiorum pudendi and the hymenal ring. The skin surrounding the vestibule is stratified squamous in type, with a paucity of rete pegs and papillae.
Arteries
The blood supply to the vestibule is an extensive capillary plexus that has anastomoses with the superficial transverse perineal artery. A branch comes directly from the pudendal anastomosis with the inferior hemorrhoidal artery in the region of the fossa navicularis. The blood supply of the urethra anteriorly, a branch of the dorsal artery of the clitoris and the azygos artery of the anterior vaginal wall, also contributes.
Veins
Venous drainage is extensive, involving the same areas described for the arterial network.
Lymphatics
The lymphatic drainage has a distinct pattern. The anterior portion, including that of the external urethral meatus, drains upward and outward with that of the labia minora and the clitoris. The portion next to the urethral meatus may join that of the anterior urethra, which empties into the vestibular plexus to terminate in the superficial inguinal nodes, the superficial subinguinal nodes, the deep subinguinal nodes, and the external iliac chain. The lymphatics of the fossa navicularis and the hymen may join those of the posterior vaginal wall, intertwining with the intercalated lymph nodes along the rectum, which follow the inferior hemorrhoidal arteries. This pattern becomes significant with cancer. Drainage occurs through the pudendal and the hemorrhoidal chain and through the vestibular plexus onto the inguinal region.
Nerves
The innervation of the vestibular area is primarily from the sacral plexus through the perineal nerve. The absence of the usual modalities of touch is noteworthy. The vestibular portion of the hymenal ring contains an abundance of free nerve endings (pain).
Vestibular Glands
The glandulae vestibulares majores (larger vestibular glands or Bartholin glands) have a duct measuring approximately 5 mm in diameter. The gland itself lies just inferior and lateral to the bulbocavernosus muscle. The gland is tubular and alveolar in character, with a thin capsule and connective tissue septa dividing it into lobules in which occasional smooth muscle fibers are found. The epithelium is cuboid to columnar and pale in color, with the cytoplasm containing mucigen droplets and colloid spherules with acidophilic inclusions. The epithelium of the duct is simple in type, and its orifice is stratified squamous like the vestibule. The secretion is a clear, viscid, and stringy mucoid substance with an alkaline pH. Secretion is active during sexual activity.
The greater vestibular gland is homologous to the bulbourethral gland (also known as Cowper’s glands, Duverney’s glands, Tiedemann’s glands, or the Bartholin glands of the male). If the opening to the gland becomes clogged, then a painful Bartholin’s cyst can develop.
The arterial supply to the greater vestibular gland comes from a small branch of the artery on the bulbocavernosus muscle, penetrating deep into its substance. Venous drainage coincides with the drainage of the bulbocavernosus body. The lymphatics drain directly into the lymphatics of the vestibular plexus, having access to the posterior vaginal wall along the inferior hemorrhoidal channels. They also drain via the perineum into the inguinal area. Most of this minor drainage is along the pudendal vessels in the canalis pudendalis and explains, in part, the difficulty in dealing with cancer involving the gland. The innervation of the greater vestibular gland is from a small branch of the perineal nerve, which penetrates directly into its substance.
Muscles of External Genitalia
The muscles (Fig. 1–18) of the external genitalia and cavernous bodies in the female are homologous to those of the male, although they are less well developed.
Figure 1–18. Pelvic musculature (inferior view).
Bulbocavernosus Muscle
The bulbocavernosus muscle and deeper bulbus vestibuli or cavernous tissues arise in the midline from the posterior part of the central tendon of the perineum, where each opposes the fibers from the opposite side. Each ascends around the vagina, enveloping the bulbus vestibuli (the corpus cavernosum bodies of the male) to terminate in 3 heads: (1) the fibrous tissue dorsal to the clitoris, (2) the tunica fibrosa of the corpus cavernosa overlying the crura of the clitoris, and (3) decussating fibers that join those of the ischiocavernosus to form the striated sphincter of the urethra at the junction of its middle and lower thirds.
The blood supply is derived from the perineal branch of the internal pudendal artery as it arises in the anterior part of the ischiorectal fossa. Deep to the fascia diaphragmatis urogenitalis inferior (Colles’ fascia) and crossing between the ischiocavernosus and bulbocavernosus muscles, the pudendal artery sends 1–2 branches directly into the bulbocavernosus muscle and vestibular body, continuing anteriorly to terminate in the dorsal artery of the clitoris.
The venous drainage accompanies the pudendal plexus. In addition, it passes posteriorly with the inferior hemorrhoidal veins and laterally with the perineal vein, a branch of the internal pudendal vein. The lymphatics run primarily with those of the vestibular plexus, with drainage inferiorly toward the intercalated nodes of the rectum and anteriorly and laterally with the labia minora and majora to the superficial inguinal nodes. Contralateral drainage in the upper portion of the muscle and body is evident.
Ischiocavernosus Muscle
The ischiocavernosus muscle and its attendant cavernous tissue arise from the ischial tuberosity and inferior ramus to the ischium. It envelops the crus of its cavernous tissue in a thin layer of muscle ascending toward and over the medial and inferior surfaces of the symphysis pubica to terminate in the anterior surface of the symphysis at the base of the clitoris. It then sends decussating fibers to the region of the upper and middle thirds of the urethra, forming the greater part of the organ’s voluntary sphincter. The blood supply is through perforating branches from the perineal artery as it ascends between the bulbocavernosus and ischiocavernosus muscles to terminate as the dorsal artery of the clitoris. The innervation stems from an ischiocavernosus branch of the perineal division of the pudendal nerve.
Transversus Muscle
The transversus perinei superficialis muscle arises from the inferior ramus of the ischium and from the ischial tuberosity. The fibers of the muscle extend across the perineum and are inserted into its central tendon, meeting those from the opposite side. Frequently, the muscle fibers from the bulbocavernosus, the puborectalis, the superficial transverse perinei, and occasionally the external anal sphincter will interdigitate. The blood supply is from a perforating branch of the perineal division of the internal pudendal artery, and the nerve supply is from the perineal division of the pudendal nerve.
Inferior Layer of Urogenital Diaphragm
The inferior layer of urogenital diaphragm is a potential space depending upon the size and development of the musculature, the parity of the female, and the pelvic architecture. It contains loose areolar connective tissue interspersed with fat. The bulbocavernosus muscles, with the support of the superficial transverse perinei muscles and the puborectalis muscles, act as a point of fixation on each side for support of the vulva, the external genitalia, and the vagina.
Surgical Considerations
A midline episiotomy is most effective to minimize trauma to vital supports of the vulva, bulbocavernosus, and superficial transverse perinei muscles. Overdistention of the vagina caused by the presenting part and body of the infant forms a temporary sacculation. If distention occurs too rapidly or if dilatation is beyond the resilient capacity of the vagina, rupture of the vaginal musculature may occur, often demonstrated by a cuneiform groove on the anterior wall and a tonguelike protrusion on the posterior wall of the vagina. Therefore, return of the vagina and vulva to the nonpregnant state is dependent upon the tonus of the muscle and the degree of distention of the vagina during parturition.
Special and deliberate consideration should be paid to the repair of the perineal body, the external anal sphincter, and the rectal mucosa. Whether created spontaneously or iatrogenically with episiotomy, lack of proper repair and attention to return of proper anatomic function will result in long-term morbidity with dyspareunia or anal incontinence.
CONTENTS OF THE PELVIC CAVITY
The organs that occupy the female pelvis (Figs. 1–19 to 1–21) are the bladder, the ureters, the urethra, the uterus, the uterine (fallopian) tubes or oviducts, the ovaries, the vagina, and the rectum.* With the exception of the inferior portion of the rectum and most of the vagina, all lie immediately beneath the peritoneum. The uterus, uterine tubes, and ovaries are almost completely covered with peritoneum and are suspended in peritoneal ligaments. The remainder are partially covered. These organs do not completely fill the cavity; the remaining space is occupied by ileum and sigmoid colon.
Figure 1–19. Female pelvic contents from above.
Figure 1–20. Pelvic viscera (sagittal view).
Figure 1–21. Pelvic organs (midsagittal view). (Reproduced, with permission, from Benson RC. Handbook of Obstetrics & Gynecology. 8th ed. Los Altos, CA: Lange; 1983.)
Bladder
Anatomy
The urinary bladder is a muscular, hollow organ that stores urine and lies posterior to the pubic bones and anterior to the uterus and broad ligament. Its form, size, and position vary with the amount of urine it contains. When empty, it takes the form of a somewhat rounded pyramid, having a base, a vertex (or apex), a superior surface, and a convex inferior surface that may be divided by a median ridge into 2 inferolateral surfaces.
Relationships
The superior surface of the bladder is covered with peritoneum that is continuous with the medial umbilical fold, forming the paravesical fossae laterally. Posteriorly, the peritoneum passes onto the uterus at the junction of the cervix and corpus, continuing upward on the anterior surface to form the vesicouterine pouch. When the bladder is empty, the normal uterus rests upon its superior surface. When the bladder is distended, coils of intestine may lie upon its superior surface. The base of the bladder rests below the peritoneum and is adjacent to the cervix and the anterior fornix of the vagina. It is separated from these structures by areolar tissue containing plexiform veins. The area over the vagina is extended as the bladder fills. The inferolateral surfaces are separated from the wall of the pelvis by the potential prevesical space, containing a small amount of areolar tissue but no large vessels. This surface is nonperitoneal and thus suitable for operative procedures. Posterolateral to the region facing the symphysis, each of the inferolateral surfaces is in relation to the fascia of the obturator internus, the obturator vessels and nerve, the obliterated umbilical artery above, and the fascia of the levator ani below. Posteriorly and medially, the inferior surface is separated from the base by an area called the urethrovesical junction, the most stationary portion of the bladder.
Fascia, Ligaments, & Muscle
The bladder is enclosed by a thin layer of fascia, the vesical sheath. Two thickenings of the endopelvic fascia, the medial and lateral pubovesical or puboprostatic ligaments, extend at the vesicourethral junction abutting the levator ani muscle from the lower part of the anterior aspect of the bladder to the pubic bones. Similar fascial thickenings, the lateral true ligaments, extend from the sides of the lower part of the bladder to the lateral walls of the pelvis. Posteriorly, the vesicourethral junction of the bladder lies directly against the anterior wall of the vagina.
A fibrous band, the urachus or medial umbilical ligament, extends from the apex of the bladder to the umbilicus. This band represents the remains of the embryonic allantois. The lateral umbilical ligaments are formed by the obliterated umbilical arteries and are represented by fibrous cords passing along the sides of the bladder and ascending toward the umbilicus. Frequently, the vessels will be patent, thus forming the superior vesical arteries. The peritoneal covering of the bladder is limited to the upper surface. The reflections of the peritoneum to the anterior abdominal wall and the corresponding walls of the pelvis are sometimes described as the superior, lateral, and posterior false ligaments. The muscle (smooth) of the bladder is represented by an interdigitated pattern continuous with and contiguous to the inner longitudinal and anterior circumferential muscles of the urethra. No distinct muscle layers are apparent.
Mucous Membrane
The mucous membrane is rose-colored and lies in irregular folds that become effaced by distention. The 3 angles of the vesical trigone are represented by the orifices of the 2 ureters and the internal urethral orifice. This area is redder in color and free from plication. It is bordered posteriorly by the plica interureterica, a curved transverse ridge extending between the orifices of the ureters. A median longitudinal elevation, the uvula vesicae, extends toward the urethral orifice. The internal urethral orifice is normally situated at the lowest point of the bladder, at the junction of the inferolateral and posterior surfaces. It is surrounded by a circular elevation, the urethral annulus, approximately level with the center of the symphysis pubica. The epithelial lining of the bladder is transitional in type. The mucous membrane rests on the submucous coat, composed of areolar tissue superficial to the muscular coat. There is no evidence of a specific smooth muscle sphincter in the vesical neck.
Arteries, Veins, & Lymphatics
The blood supply to the bladder comes from branches of the hypogastric artery. The umbilical artery, a terminal branch of the hypogastric artery, gives off the superior vesical artery prior to its obliterated portion. It approaches the bladder (along with the middle and inferior vesical arteries) through a condensation of fatty areolar tissue, limiting the prevesical “space” posterosuperiorly, to branch out over the upper surface of the bladder. It anastomoses with the arteries of the opposite side and the middle and inferior vesical arteries below. The middle vesical artery may arise from one of the superior vessels, or it may come from the umbilical artery, supplying the sides and base of the bladder. The inferior vesical artery usually arises directly from the hypogastric artery—in common with or as a branch of the uterine artery—and passes downward and medially, where it divides into branches that supply the lower part of the bladder. The fundus may also receive small branches from the middle hemorrhoidal, uterine, and vaginal arteries. The veins form an extensive plexus at the sides and base of the bladder from which stems pass to the hypogastric trunk.
The lymphatics, in part, accompany the veins and communicate with the hypogastric nodes. They also communicate laterally with the external iliac glands, and some of those from the fundus pass to nodes situated at the promontory of the sacrum. The lymphatics of the bladder dome are separate on the right and left sides and rarely cross, but extensive anastomoses are present among the lymphatics of the base, which also involve those of the cervix.
Nerves
The nerve supply to the bladder is derived partly from the hypogastric sympathetic plexus and partly from the second and third sacral nerves (the nervi erigentes).
Ureters
Anatomy & Relationships
The ureter is a slightly flattened tube that extends from the termination of the renal pelvis to the lower outer corner of the base of the bladder, a distance of 26–28 cm. It is partly abdominal and partly pelvic and lies entirely behind the peritoneum. Its diameter varies from 4–6 mm, depending on distention, and its size is uniform except for 3 slightly constricted portions.
The first of 3 constrictions is found at the junction of the ureter with the renal pelvis and is known as the upper isthmus. The second constriction—the lower isthmus—is at the point where the ureter crosses the brim of the pelvis minor. The third (intramural) constriction is at the terminal part of the ureter as it passes through the bladder wall.
The pelvic portion of the ureter begins as the ureter crosses the pelvic brim beneath the ovarian vessels and near the bifurcation of the common iliac artery. It conforms to the curvature of the lateral pelvic wall, inclining slightly laterally and posteriorly until it reaches the pelvic floor. The ureter then bends anteriorly and medially at about the level of the ischial spine to reach the bladder. In its upper portion, it is related posteriorly to the sacroiliac articulation; then, lying upon the obturator internus muscle and fascia, it crosses the root of the umbilical artery, the obturator vessels, and the obturator nerve.
In its anterior relationship, the ureter emerges from behind the ovary and under its vessels to pass behind the uterine and superior and middle vesical arteries. Coursing anteriorly, it comes into close relation with the lateral fornix of the vagina, passing 8–12 mm from the cervix and vaginal wall before reaching the bladder. When the ureters reach the bladder, they are about 5 cm apart. The ureters open into the bladder by 2 slitlike apertures, the urethral orifices, about 2.5 cm apart when the bladder is empty.
Wall of Ureter
The wall of the ureter is approximately 3 mm thick and is composed of 3 coats: connective tissue, muscle, and mucous membrane. The muscular coat has an external circular and an internal longitudinal layer throughout its course and an external longitudinal layer in its lower third. The mucous membrane is longitudinally plicated and covered by transitional epithelium. The intermittent peristaltic action of the ureteral musculature propels urine into the bladder in jets. The oblique passage of the ureter through the bladder wall tends to constitute a valvular arrangement, but no true valve is present. The circular fibers of the intramural portion of the ureter possess a sphincter like action. Still, under some conditions of overdistention of the bladder, urine may be forced back into the ureter.
Arteries, Veins, & Lymphatics
The pelvic portion of the ureter receives its blood supply from a direct branch of the hypogastric artery, anastomosing superiorly in its adventitia with branches from the iliolumbar and inferiorly with branches from the inferior vesical and middle hemorrhoidal arteries. Lymphatic drainage passes along the hypogastric vessels to the hypogastric and external iliac nodes, continuing up the ureters to their middle portion where drainage is directed to the periaortic and interaorticocaval nodes.
Nerves
The nerve supply is provided by the renal, ovarian, and hypogastric plexuses. The spinal level of the afferents is approximately the same as the kidney (T12, L1, L2). The lower third of the ureter receives sensory fibers and postganglionic parasympathetic fibers from the Frankenhäuser plexus and sympathetic fibers through this plexus as it supplies the base of the bladder. These fibers ascend the lower third of the ureter, accompanying the arterial supply. The middle segment appears to receive postganglions of sympathetic and parasympathetic fibers through and from the middle hypogastric plexus. The upper third is supplied by the same innervation as the kidney.
Urethra
Anatomy & Relationships
The female urethra is a canal 2.5–4 cm long. It extends downward and forward in a curve from the neck of the bladder (internal urethral orifice), which lies nearly opposite the symphysis pubica. Its termination, the external urethral orifice, is situated inferiorly and posteriorly from the lower border of the symphysis. Posteriorly, it is closely applied to the anterior wall of the vagina, especially in the lower two-thirds, where it actually is integrated with the wall, forming the urethral carina. Anteriorly, the upper end is separated from the prevesical “space” by the pubovesical (puboprostatic) ligaments, abutting against the levator ani and vagina and extending upward onto the pubic rami.
Anatomy of Walls
The walls of the urethra are very distensible, composed of spongy fibromuscular tissue containing cavernous veins and lined by submucous and mucous coats. The mucosa contains numerous longitudinal lines when undistended, the most prominent of which is located on the posterior wall and termed the crista urethralis. Also, there are numerous small glands (the homologue of the male prostate, paraurethral and periurethral glands of Astruc, ducts of Skene) that open into the urethra. The largest of these, the paraurethral glands of Skene, may open via a pair of ducts beside the external urethral orifice in the vestibule. The epithelium begins as transitional at the upper end and becomes squamous in the lower part.
External to the urethral lumen is a smooth muscle coat composed of an outer circular layer and an inner longitudinal layer in the lower two-thirds. In the upper third, the muscle bundles of the layers interdigitate in a basketlike weave to become continuous with and contiguous to those of the bladder. The entire urethral circular smooth muscle acts as the involuntary sphincter. In the region of the juncture of the middle and lower thirds of the urethra, decussating fibers (striated in type) form the middle heads of the bulbocavernosus and ischiocavernosus muscles and encircle the urethra to form the sphincter urethrae (voluntary sphincter).
Arteries & Veins
The arterial supply is intimately involved with that of the anterior vaginal wall, with cruciate anastomoses to the bladder. On each side of the vagina are the vaginal arteries, originating in part from the coronary artery of the cervix, the inferior vesical artery, or a direct branch of the uterine artery. In the midline of the anterior vaginal wall is the azygos artery, originating from the coronary or circular artery of the cervix. Approximately 5 branches traverse the anterior vaginal wall from the lateral vaginal arteries to the azygos in the midline, with small sprigs supplying the urethra. A rich anastomosis with the introitus involves the clitoral artery (urethral branches) as the artery divides into the dorsal and superficial arteries of the clitoris, a terminal branch of the internal pudendal artery. The venous drainage follows the arterial pattern, although it is less well defined. In the upper portion of the vagina, it forms an extensive network called the plexus of Santorini.
Nerves
The nerve supply is parasympathetic, sympathetic, and spinal. The parasympathetic and sympathetic nerves are derived from the hypogastric plexus; the spinal supply is via the pudendal nerve.
Uterus
Anatomy
The uterus is a pear-shaped, thick-walled, muscular organ, situated between the base of the bladder and the rectum. Covered on each side by the 2 layers of the broad ligament, it communicates above with the uterine tubes and below with the vagina. It is divided into 2 main portions, the larger portion or body above and the smaller cervix below, connected by a transverse constriction, the isthmus. The body is flattened so that the side-to-side dimension is greater than the anteroposterior dimension and larger in women who have borne children. The anterior or vesical surface is almost flat; the posterior surface is convex. The fallopian tubes join the uterus at the superior (lateral) angles. The round portion that extends above the plane passing through the points of attachment of the 2 tubes is termed the fundus. This portion is the region of greatest breadth.
The cavity of the body, when viewed from the front or back, is roughly triangular with the base up. The communication of the cavity below with the cavity of the cervix corresponds in position to the isthmus and forms the internal orifice (internal os uteri). The cervix, also called the portio vaginalis, is somewhat barrel-shaped and is 2–4 cm in length, its lower end joining the vagina at an angle varying from 45–90 degrees. It projects into the vagina and is divided into a supravaginal and a vaginal portion by the line of attachment. About one fourth of the anterior surface and half of the posterior surface of the cervix belong to the vaginal portion. At the extremity of the vaginal portion is the opening leading to the vagina, the external orifice (external os uteri), which is round or oval before parturition but takes the form of a transverse slit in women who have borne children. The cavity of the cervix is fusiform in shape, with longitudinal folds or furrows, and extends from the internal to the external orifice. The endocervical canal is composed of columnar, mucus-secreting cells, whereas the external cervix is lined by nonkeratinizing squamous epithelium. The junction between these 2 areas is called the squamocolumnar junction or transitional zone.
The size of the uterus varies, under normal conditions, at different ages and in different physiologic states. In the adult woman who has never borne children, it is approximately 7–8 cm long, 4–5 cm at its widest point, and 30–40 g in weight. In the prepubertal period, it is considerably smaller. In women who have borne children, it is larger. Its shape, size, and characteristics in the pregnant state become considerably modified depending on the stage of gestation.
Layers of Uterine Wall
The wall of the uterus is very thick and consists of 3 layers: serous, muscular, and mucous. The serous layer (perimetrium) is simply the peritoneal covering. It is thin and firmly adherent over the fundus and most of the body, and then thickens posteriorly and becomes separated from the muscle by the parametrium. The muscular layer (myometrium) is extremely thick at about 1.5–2.5 cm and continuous with that of the tubes and vagina. It also extends into the ovarian and round ligaments, into the cardinal ligaments at the cervix, and minimally into the uterosacral ligaments. Two principal layers of the muscular coat can be distinguished: (1) the outer layer, which is weaker and composed of longitudinal fibers; and (2) a stronger inner layer, the fibers of which are interlaced and run in various directions, having intermingled within them large venous plexuses. The muscle layer hypertrophies with the internal os to form a sphincter.
The cervix, from the internal os distally, progressively loses its smooth muscle, finally to be entirely devoid of smooth muscle and elastic in its distal half. It is, in fact, the “dead-end tendon” of the uterus, at which point, during the active component of labor, both the uterus and the vagina direct their efforts. The mucous layer (endometrium) is soft and spongy, composed of tissue resembling embryonic connective tissue. The surface consists of a single layer of ciliated columnar epithelium. The tissue is rather delicate and friable and contains many tubular glands that open into the cavity of the uterus.
Position & Axis Direction
The direction of the axis of the uterus varies greatly. Normally, the uterus forms a sharp angle with the vagina so that its anterior surface lies on the upper surface of the bladder and the body is in a horizontal plane when the woman is standing erect. There is a bend in the area of the isthmus, at which the cervix then faces downward. This position is the normal anteversion or angulation of the uterus, although it may be placed backward (retroversion), without angulation (military position), or to one side (lateral version). The forward flexion at the isthmus is referred to as anteflexion, or there may be a corresponding retroflexion or lateral flexion. There is no sharp line between the normal and pathologic state of anterior angulation.
Relationships
Anteriorly, the body of the uterus rests upon the upper and posterior surfaces of the bladder, separated by the uterovesical pouch of the peritoneum. The whole of the anterior wall of the cervix is below the floor of this pouch, and it is separated from the base of the bladder only by connective tissue. Posteriorly, the peritoneal covering extends down as far as the uppermost portion of the vagina; therefore, the entire posterior surface of the uterus is covered by peritoneum, and the convex posterior wall is separated from the rectum by the rectouterine pouch (cul-de-sac or pouch of Douglas). Coils of intestine may rest upon the posterior surface of the body of the uterus and may be present in the rectouterine pouch.
Laterally, the uterus is related to the various structures contained within the broad ligament: the uterine tubes, the round ligament and the ligament of the ovary, the uterine artery and veins, and the ureter. The relationships of the ureters and the uterine arteries are very important surgically. The ureters, as they pass to the bladder, run parallel with the cervix for a distance of 8–12 mm. The uterine artery crosses the ureter anterosuperiorly near the cervix, about 1.5 cm from the lateral fornix of the vagina. In effect, the ureter passes under the uterine artery “as water flows under a bridge.”
Ligaments
Although the cervix of the uterus is fixed, the body is free to rise and fall with the filling and emptying of the bladder. The so-called ligaments supporting the uterus consist of the uterosacral ligaments, the transverse ligaments of the cervix (cardinal ligaments, cardinal supports, ligamentum transversum colli, ligaments of Mackenrodt), the round ligaments, and the broad ligaments. The cervix is embedded in tissue called the parametrium, containing various amounts of smooth muscle. There are 2 pairs of structures continuous with the parametrium and with the wall of the cervix: the uterosacral ligaments and the transverse (cardinal) ligament of the neck, the latter of which is the chief means of support and suspends the uterus from the lateral walls of the pelvis minor. The uterosacral ligaments are, in fact, the inferior posterior folds of peritoneum from the broad ligament. They consist primarily of nerve bundles from the inferior hypogastric plexus and contain preganglionic and postganglionic fibers and C fibers of the sympathetic lumbar segments, parasympathetic in part from sacral components and in part from sensory or C fibers of the spinal segments.
The cardinal ligaments are composed of longitudinal smooth muscle fibers originating superiorly from the uterus and inferiorly from the vagina, fanning out toward the fascia visceralis to form, with the internal os of the cervix, the primary support of the uterus. There is a natural defect in the muscle at its sides (hilum of the uterus) and at the cervical isthmus (internal os), where the vasculature and nerve supply enter the uterus.
The round ligaments of the uterus, although forming no real support, may assist in maintaining the body of the uterus in its typical position over the bladder. They consist of fibrous cords containing smooth muscle (longitudinal) from the outer layer of the corpus. From a point of attachment to the uterus immediately below that of the ovarian ligament, each round ligament extends downward, laterally, and forward between the 2 layers of the mesometrium, toward the abdominal inguinal ring that it traverses and the inguinal canal, to terminate in a fanlike manner in the labia majora and become continuous with connective tissue. The round ligament is the gubernaculum (ligamentum teres uteri), vestigial in the female. It is accompanied by a funicular branch of the ovarian artery, by a branch from the ovarian venous plexus, and, in the lower part of its course, by a branch from the inferior epigastric artery (Sampson’s artery), over which it passes as it enters the inguinal ring. Through the inguinal canal, it is accompanied by the ilioinguinal nerve and the external spermatic branch of the genitofemoral nerve.
The broad ligament, consisting of a transverse fold of peritoneum that arises from the floor of the pelvis between the rectum and the bladder, provides minimal support. In addition to the static support of these ligaments, the pelvic diaphragm (levator ani) provides an indirect and dynamic support. These muscles do not actually come in contact with the uterus, but they aid in supporting the vagina and maintain the entire pelvic floor in resisting downward pressure. The effectiveness of these muscles depends on an intact perineum (perineal body, bulbocavernosus muscle and body), for if it is lacerated or weakened the ligaments will gradually stretch and the uterus will descend. The uterus and its components and the vagina are, in fact, one continuous unit.
Arteries
The blood supply to the uterus is from the uterine and ovarian arteries. As a terminal branch of the hypogastric artery, the uterine artery runs downward and medially to cross the ureter near the cervix. It then ascends along the lateral border of the uterus in a tortuous course through the parametrium, giving off lateral branches to both uterine surfaces. Above, it anastomoses to join with the ovarian artery in the mesometrium, which creates the main accessory source of blood. The uterine arteries within the uterus form a series of arches over the fundus, creating cruciate anastomoses with the opposite side.
Branches of the arcuate arteries (radial) penetrate the myometrium at right angles to terminate in the basilar arterioles for the basilar portion of the endometrium and in the spinal arteries of the endometrium. The spinal arteries are tortuous in structure, not because of endometrial growth but because, ontogenically, an organ carries its arterial supply with it as it changes size and position. Therefore, the spiral arteries are able to maintain adequate arterial flow to the placenta while it is attached within the uterus.
On the other hand, the veins of the endometrium are a series of small sinusoids that connect to the larger sinusoids of the myometrium, the latter coalescing into the larger veins of the uterine complex. It is useful here to note the significance of the muscular role of the uterus in helping to control venous bleeding during parturition.
The arterial supply to the cervix is primarily through the cervical branches of the right and left uterine arteries, which form a rete around the cervix (coronary artery), creating the azygos artery in the midline anteriorly and posteriorly. Anastomoses between this artery and the vaginal artery on both sides afford cruciate flow on the anterior wall, whereas on the posterior wall of the vagina, anastomoses occur with the right and left middle hemorrhoidal arteries as they supply the wall and the rectum.
Veins
The veins form a plexus and drain through the uterine vein to the hypogastric vein. There are connections with the ovarian veins and the inferior epigastric by way of the vein accompanying the round ligament.
Lymphatics
Lymphatic drainage involves several chains of lymph nodes. From the subperitoneal plexus, the collecting trunks of the lower uterine segment may drain by way of the cervix to the external iliac chain or by way of the isthmus to the lateral sacral nodes. Drainage along the round ligament progresses to the superficial inguinal nodes, then to the femoral, and finally to the external iliac chain. Drainage laterally to the suspensory ligament of the ovary involves the lumbar pedicle and progresses in a retroperitoneal manner across and anteriorly to the ureter, to the lumbar nodes (interaorticocaval) that lie along the aorta, and inferiorly to the kidney.
Fallopian Tubes (Uterine Oviducts)
Anatomy
The fallopian tubes serve to convey the ova (eggs) to the uterus. They extend from the superior angles of the uterus to the region of the ovaries, running in the superior border of the broad ligament (mesosalpinx). The fallopian tubes and ovaries are collectively referred to as the adnexa. The course of each tube is nearly horizontal at first and slightly backward. Upon reaching the lower (uterine) pole of the ovary, the tube turns upward, parallel with the anterior (mesovarian) border, then arches backward over the upper pole and descends posteriorly to terminate in contact with the medial surface. Each tube is 7–12 cm long and may be divided into 4 parts: isthmus, ampulla, infundibulum, and interstitial.
The isthmus is the narrow and nearly straight portion immediately adjoining the uterus. It has a rather long intramural course, and its opening into the uterus, the uterine ostium, is approximately 1 mm in diameter. Following the isthmus is the wider, more tortuous ampulla. It terminates in a funnel-like dilatation, the infundibulum. The margins of the infundibulum are fringed by numerous diverging processes, the fimbriae, the longest of which, the fimbria ovarica, is attached to the ovary. The funnel-shaped mouth of the infundibulum, the abdominal ostium, is about 3 mm in diameter and actually leads into the peritoneal cavity, although it probably is closely applied to the surface of the ovary during ovulation. The interstitial is the portion of the tube that lies within the uterine wall. The innermost portion is seen from the uterine cavity as the tubal ostea.
Layers of Wall
The wall of the tube has 4 coats: serous (peritoneal), subserous or adventitial (fibrous and vascular), muscular, and mucous. Each tube is enclosed within a peritoneal covering except along a small strip on its lower surface, where the mesosalpinx is attached. At the margins of the infundibulum and the fimbriae, this peritoneal covering becomes directly continuous with the mucous membrane lining the interior of the tube. The subserous tissue is lax in the immediate vicinity of the tube. The blood and nerve supply is found within this layer. The muscular coat has an outer longitudinal and an inner circular layer of smooth muscle fibers, more prominent and continuous with that of the uterus at the uterine end of the tube. The mucous coat is ciliated columnar epithelium with coarse longitudinal folds, simple in the region of the isthmus but becoming higher and more complex in the ampulla. The epithelial lining extends outward into the fimbriae. The ciliary motion is directed toward the uterus.
Arteries & Veins
The blood supply to the tubes is derived from the ovarian and uterine arteries. The tubal branch of the uterine artery courses along the lower surface of the uterine tube as far as the fimbriated extremity and may also send a branch to the ligamentum teres. The ovarian branch of the uterine artery runs along the attached border of the ovary and gives off a tubal branch. Both branches form cruciate anastomoses in the mesosalpinx. The veins accompany the arteries.
Lymphatics
The lymphatic drainage occurs through trunks running retroperitoneally across and anterior to the ureter, into the lumbar nodes along the aorta, and inferior to the kidney.
Ovaries
Anatomy
The ovaries are paired organs situated close to the wall on either side of the pelvis minor, a little below the brim. Each measures 2.5–5 cm in length, 1.5–3 cm in breadth, and 0.7–1.5 cm in width, weighing about 4–8 g. The ovary has 2 surfaces, medial and lateral; 2 borders, anterior or mesovarian and posterior or free; and 2 poles, upper or tubal and lower or uterine. When the uterus and adnexa are in the normal position, the long axis of the ovary is nearly vertical, but it bends somewhat medially and forward at the lower end so that the lower pole tends to point toward the uterus. The medial surface is rounded and, posteriorly, may have numerous scars or elevations that mark the position of developing follicles and sites of ruptured ones.
Structure of Ovary
The ovary is covered by cuboid or low columnar epithelium and consists of a cortex and a medulla. The medulla is made up of connective tissue fibers, smooth muscle cells, and numerous blood vessels, nerves, lymphatic vessels, and supporting tissue. The cortex is composed of a fine areolar stroma, with many vessels and scattered follicles of epithelial cells within which are the definitive ova (oocytes) in various stages of maturity. The more mature follicles enlarge and project onto the free surface of the ovary, where they are visible to the naked eye. These are called graafian follicles. When fully mature, the follicle bursts, releasing the ovum and becoming transformed into a corpus luteum. The corpus luteum, in turn, is later replaced by scar tissue, forming a corpus albicans if pregnancy is not achieved that particular menstrual cycle.
Relationships
The upper portion of this surface is overhung by the fimbriated end of the uterine tube, and the remainder lies in relation to coils of intestine. The lateral surface is similar in shape and faces the pelvic wall, where it forms a distinct depression, the fossa ovarica. This fossa is lined by peritoneum and is bounded above by the external iliac vessels and below by the obturator vessels and nerve; its posterior boundary is formed by the ureter and uterine artery and vein, and the pelvic attachment of the broad ligament is located anteriorly.
The mesovarian or anterior border is fairly straight and provides attachment for the mesovarium, a peritoneal fold by which the ovary is attached to the posterosuperior layer of the broad ligament. Because the vessels, nerves, and lymphatics enter the ovary through this border, it is referred to as the hilum of the ovary.
Mesovarium
The ovary is suspended by means of the mesovarium, the suspensory ligament of the ovary (infundibulopelvic [IP] ligament), and the ovarian ligament. The mesovarium consists of 2 layers of peritoneum, continuous with both the epithelial coat of the ovary and the posterosuperior layer of the broad ligament. It is short and wide and contains branches of the ovarian and uterine arteries, with plexuses of nerves, the pampiniform plexus of veins, and the lateral end of the ovarian ligament. The suspensory ligament of the ovary is a triangular fold of peritoneum and is actually the upper lateral corner of the broad ligament, which becomes confluent with the parietal peritoneum at the pelvic brim. It attaches to the mesovarium as well as to the peritoneal coat of the infundibulum medially, thus suspending both the ovary and the tube. It contains the ovarian artery, veins, and nerves after they pass over the pelvic brim and before they enter the mesovarium.
The ovarian ligament is a band of connective tissue, with numerous small muscle fibers, that lies between the 2 layers of the broad ligament on the boundary line between the mesosalpinx and the mesometrium, connecting the lower (uterine) pole of the ovary with the lateral wall of the uterus. It is attached just below the uterine tube and above the attachment of the round ligament of the uterus and is continuous with the latter.
Arteries
The ovarian artery is the chief source of blood for the ovary. Though both arteries may originate as branches of the abdominal aorta, the left frequently originates from the left renal artery; the right, less frequently. The vessels diverge from each other as they descend. Upon reaching the level of the common iliac artery, they turn medially over that vessel and ureter to descend tortuously into the pelvis on each side between the folds of the suspensory ligament of the ovary into the mesovarium. An additional blood supply is formed from anastomosis with the ovarian branch of the uterine artery, which courses along the attached border of the ovary. Blood vessels that enter the hilum send out capillary branches centrifugally.
The veins follow the course of the arteries and, as they emerge from the hilum, form a well-developed plexus (the pampiniform plexus) between the layers of the mesovarium. Smooth muscle fibers occur in the meshes of the plexus, giving the whole structure the appearance of erectile tissue.
Lymphatics
Lymphatic channels drain retroperitoneally, together with those of the tubes and part of those from the uterus, to the lumbar nodes along the aorta inferior to the kidney. The distribution of lymph channels in the ovary is so extensive that it suggests the system may also provide additional fluid to the ovary during periods of preovulatory follicular swelling.
Nerves
The nerve supply of the ovaries arises from the lumbosacral sympathetic chain and passes to the gonad along with the ovarian artery.
Vagina
Anatomy
The vagina is a strong, hollow, fibromuscular canal approximately 7–9 cm long that extends from the uterus to the vestibule of the external genitalia, where it opens to the exterior. Its long axis is almost parallel with that of the lower part of the sacrum, and it meets the cervix of the uterus at an angle of 45–90 degrees. Because the cervix of the uterus projects into the upper portion, the anterior wall of the vagina is 1.5–2 cm shorter than the posterior wall. The circular cul-de-sac formed around the cervix is known as the fornix and is divided into 4 regions: the anterior fornix, the posterior fornix, and 2 lateral fornices. Toward its lower end, the vagina pierces the urogenital diaphragm and is surrounded by the 2 bulbocavernosus muscles and bodies, which act as a sphincter (sphincter vaginae).
Wall Structure
The vaginal wall is composed of a mucosal layer and a muscular layer. The smooth muscle fibers are indistinctly arranged in 3 layers: an outer longitudinal layer, circumferential layer, and a poorly differentiated inner longitudinal layer. In the lower third, the circumferential fibers envelop the urethra. The submucous area is abundantly supplied with a dense plexus of veins and lymphatics. The mucous layer shows many transverse and oblique rugae, which project inward to such an extent that the lumen in transverse section resembles an H-shaped slit. On the anterior and posterior walls, these ridges are more prominent, and the anterior column forms the urethral carina at its lower end, where the urethra slightly invaginates the anterior wall of the vagina. The mucosa of the vagina is lined throughout by nonkeratinized squamous epithelium. Even though the vagina has no true glands, there is a secretion present. It consists of cervical mucus, desquamated epithelium, and, with sexual stimulation, a direct transudate.
Relationships
Anteriorly, the vagina is in close relationship to the bladder, ureters, and urethra in succession. The posterior fornix is covered by the peritoneum of the rectovaginal pouch, which may contain coils of intestine. Below the pouch, the vagina rests almost directly on the rectum, separated from it by a thin layer of areolar connective tissue. Toward the lower end of the vagina, the rectum turns back sharply, and the distance between the vagina and rectum greatly increases. This space, filled with muscle fibers, connective tissue, and fat, is known as the perineal body. The lateral fornix lies just under the root of the broad ligament and is approximately 1 cm from the point where the uterine artery crosses the ureter.
The remaining lateral vaginal wall is related to the edges of the anterior portion of the levator ani. The vagina is supported at the introitus by the bulbocavernosus muscles and bodies, in the lower third by the levator ani (puborectalis), and superiorly by the transverse (cardinal) ligaments of the uterus. The ductus epoophori longitudinalis (duct of Gartner), the remains of the lower portion of the wolffian duct (mesonephric duct), may often be found on the sides of the vagina as a minute tube or fibrous cord. These vestigial structures often become cystic and appear as translucent areas.
Arteries & Veins
The chief blood supply to the vagina is through the vaginal branch of the uterine artery. After forming the coronary or circular artery of the cervix, it passes medially, behind the ureter, to send 5 main branches onto the anterior wall to the midline. These branches anastomose with the azygos artery (originating midline from the coronary artery of the cervix) and continue downward to supply the anterior vaginal wall and the lower two-thirds of the urethra. The uterine artery eventually anastomoses to the urethral branch of the clitoral artery. The posterior vaginal wall is supplied by branches of the middle and inferior hemorrhoidal arteries, traversing toward the midline to join the azygos artery from the coronary artery of the cervix. These branches then anastomose on the perineum to the superficial and deep transverse perineal arteries. The veins follow the course of the arteries.
Lymphatics
The lymphatics are numerous mucosal plexuses, anastomosing with the deeper muscular plexuses. The superior group of lymphatics joins those of the cervix and may follow the uterine artery to terminate in the external iliac nodes or form anastomoses with the uterine plexus. The middle group of lymphatics, which drain the greater part of the vagina, appears to follow the vaginal arteries to the hypogastric channels. In addition, there are lymph nodes in the rectovaginal septum that are primarily responsible for drainage of the rectum and part of the posterior vaginal wall. The inferior group of lymphatics forms frequent anastomoses between the right and left sides and either courses upward to anastomose with the middle group or enters the vulva and drains to the inguinal nodes.
Nerves
The innervation of the vagina contains both sympathetic and parasympathetic fibers. Only occasional free nerve endings are seen in the mucosa; no other types of nerve endings are noted.
SUMMARY
Even though the basic anatomy and structure of the human body is not changing, the evolution of surgical approaches and technologies is. This constantly ever-changing field requires the gynecologic surgeon to be well versed in female pelvic anatomy by constantly reviewing and studying its contents. Being knowledgeable and current with the female pelvis will allow even the most experienced, senior surgeon to adjust to situations where anatomy is altered secondary to disease processes, congenital malformation, or other unknown complications.
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