Last's Anatomy: Regional and Applied

Part eleven. Kidneys, ureters and suprarenal glands

Kidneys

The kidneys lie high up on the posterior abdominal wall (Fig. 5.43) behind the peritoneum, largely under cover of the costal margin. At best only their lower poles can be palpated in the normal individual. Each kidney lies obliquely, with its long axis parallel with the lateral border of psoas major. It lies well back in the paravertebral gutter, so that the hilum, a vertical slit-like depression at the medial border transmitting the renal vessels and nerves and the renal pelvis (the beginning of the ureter), faces somewhat forwards as well as medially (Fig. 5.44). As a result of this slight ‘rotation’ of the kidney an anteroposterior radiograph gives a somewhat foreshortened picture of the width of the kidney. The normal kidney measures about 12 × 6 × 3cm and weighs 130–150g. The hilum of the right kidney lies just below, and of the left just above, the transpyloric plane 5cm from the midline. The bulk of the right lobe of the liver accounts for the lower position of the right kidney. The upper pole of the left kidney overlies the eleventh rib, that of the right kidney the twelfth rib. Each kidney moves in a vertical range of 2cm during the full respiratory excursion of the diaphragm.

The surfaces of the kidney, covered by its capsule, are usually smooth and convex though traces of lobulation, normal in the fetus, are often seen. The pelvis emerges from the hilum, behind the vessels, to pass down as the ureter.

Posteriorly the relations of both kidneys are similar, comprising mostly the diaphragm and quadratus lumborum muscles, with overlap medially on to psoas and laterally on to transversus abdominis. The upper pole lies on those fibres of the diaphragm which arise from the lateral and medial arcuate ligaments. A small triangular part of the costodiaphragmatic recess of the pleura lies behind the diaphragm and is an important posterior relation (Fig. 5.48), which is at risk in the lumbar approach to the kidney (see p. 286). The subcostal vein, artery and nerve, on emerging from beneath the lateral arcuate ligament, lie behind the kidney, as do the iliohypogastric and ilioinguinal nerves as they emerge from the lateral border of psoas. The hilum of the kidney lies over psoas and the convexity of the lateral border lies on the aponeurosis of origin of transversus abdominis.

The suprarenal glands surmount the superior poles of both kidneys and overlap a small part of their anterior surfaces. The rest of the upper halves of each kidney lie in contact with peritoneum, which on the right kidney is the peritoneum of the hepatorenal pouch (part of the greater sac), and on the left is the peritoneum of the lesser sac (part of the stomach bed) medially, and the peritoneum of the greater sac laterally (between the kidney and the spleen), with the splenorenal ligament passing forwards between these areas (Fig. 5.49). The hilum is separated from the peritoneum, on the right side by the second part of the duodenum and on the left side by the body of the pancreas and splenic vessels (Fig. 5.26). The lateral part of the lower pole is separated from peritoneum by the hepatic and splenic flexures of the colon on the right and left sides respectively. The medial part of the lower pole, on each side, lies in contact with peritoneum which separates it from coils of jejunum; between peritoneum and kidney are ascending branches of the right and left colic arteries.

The perinephric fat lies outside the renal capsule (Fig. 5.49) and plays a part in retaining the kidney in position. Nephroptosis (‘floating kidney’) may develop after severe loss of weight. The renal fascia (of Gerota) surrounds the perinephric fat. It is not a very obvious membrane in the living, but appears more convincingly in the embalmed cadavre. It is a condensation of the areolar tissue between the parietal peritoneum and the posterior abdominal wall and restrains the extension of a perinephric abscess. It ascends as a dome over the upper pole of the kidney and the suprarenal. However, a fascial septum separates the two organs, which explains why in nephrectomy the latter gland is not usually displaced (or even seen). At the lateral renal border the anterior and posterior layers fuse, while at the hilum the fascia is attached to the renal vessels and the ureter. When traced downwards, the fascia fades into the extraperitoneal tissue around the ureter. Pus in the perinephric space and injections into it do not usually track downwards, but increasing pressure may force the fascia to rupture and allow such contents to flow downwards retroperitoneally towards the pelvis.

The renal pelvis is the funnel-shaped commencement of the ureter, and is normally the most posterior of the three main structures in the hilum (though an arterial branch or venous tributary may lie behind it). The capacity of the average pelvis is less than 5mL.

Blood supply and segments

The wide-bored renal arteries have a blood flow in excess of 1 litre per minute. They leave the abdominal aorta at right angles and lie behind the pancreas and renal veins.

Based on its blood supply, each kidney possesses five segments (Fig. 5.50). In the region of the hilum the artery typically gives rise to an anterior and a posterior division. The posterior division supplies the posterior segment, while the anterior division gives branches that supply the apical, upper, middle and lower segments. The pattern of branching of the vessels may vary, but there are always five segments with no collateral circulation between them. Abnormal or aberrant renal arteries, such as a vessel running from the aorta to the lower pole are, in fact, segmental vessels with an unusual origin (persistence of a fetal vessel, see below). They are not usually accompanied by veins.

Veins from the renal segments communicate with one another (unlike the arteries) and eventually form five or six vessels that unite at the hilum to form the single renal vein (see p. 277). The usual order of structures in the hilum of each kidney is vein, artery, ureter from front to back.

Lymph drainage

The lymphatics of the kidney drain to para-aortic nodes at the level of origin of the renal arteries (L2).

Nerve supply

Renal nerves are derived from both parts of the autonomic system. The sympathetic preganglionic cells lie in the spinal cord from T12 to L1 segments and they send preganglionic fibres to the thoracic and lumbar splanchnic nerves. These fibres synapse in the coeliac and renal ganglia. They are vasomotor in function. Afferent fibres, including those subserving pain, accompany the sympathetic nerves, as for most other viscera. The pathway for the pain of renal colic from a stone in the calyces or renal pelvis passes to the coeliac plexus and thence by the splanchnic nerves to the sympathetic trunk and via white rami communicantes to T12–L1 spinal nerves and so into the spinal cord by the posterior nerve roots. The pain may thus be referred to the back and lumbar region, and radiate to the anterior abdominal wall and down to the external genitalia. It is possible that some afferents run with the vagal fibres, and this could explain the nausea and vomiting that may accompany renal pain.

Structure

The internal structure of the kidney is displayed when the organ is split open longitudinally. A dark reddish cortex lies beneath the capsule and extends towards the pelvis as the renal columns, lying between a number of darker and triangular striated areas, the pyramids of the medulla. The apices of several pyramids open together into a renal papilla, each of which projects into a minor calyx. The minor calyces unite to form two or three major calyces which open into the renal pelvis.

The histological and functional unit of the kidney is the nephron, and there are about 1 million in each kidney. Each nephron consists of a glomerulus and a tubule system. The glomerulus is a tuft of capillaries surrounded by very thin epithelial cells (podocytes), the whole forming a mass which projects into a rounded capsule (of Bowman). The epithelium covering the capillaries is continuous with that forming the boundary of Bowman's capsule, which in turn continues into the epithelium of the tubule system. The part of the tubule adjacent to Bowman's capsule is the proximal convoluted tubule, and this leads into the thin-walled loop of Henle and so to the distal convoluted tubuleand finally to the collecting tubule and collecting duct. The glomeruli and convoluted tubules are in the cortex, and the loops of Henle and collecting tubules and ducts in the medulla. The collecting ducts unite with one another, and the largest open at the tip of a renal papilla in a minor calyx. The glomerular capillaries are supplied by an afferent arteriole, and leaving them is an efferent arteriole which breaks up into peritubular capillaries surrounding the proximal and distal convoluted tubules. Urine is a glomerular filtrate (deproteinized plasma) which passes into the space of Bowman's capsule and so into the tubule system where it is modified by selective absorption and secretion. Certain arteriolar cells and distal convoluted tubule cells constitute the juxtaglomerular apparatus which secretes renin.

The pelvis, like the ureter, is lined by transitional epithelium and there is smooth muscle in its wall. Specialized muscle cells in the walls of the minor calyces act as ‘pacemakers’ that initiate contractile waves which pass down into the ureter.

Development

Three separate excretory organs appear in vertebrate evolution: the pronephros; mesonephros; and metanephros (see p. 23). The first two consist of excretory tubules arranged segmentally and they empty into the same duct. The third consists of a mass of tubules having no segmental arrangement and it drains into a new duct that develops specifically for the purpose (the ureter).

The pronephros is very evanescent, but its duct persists. Mesonephric tubules then develop and open into the pronephric duct which is henceforth called the mesonephric (Wolffian) duct (see p. 231). Caudal to the mesonephros the intermediate cell mass gives rise to about a million new tubules, forming the metanephros. The latter induces a bud, the ureter, to grow from the caudal end of the mesonephric duct. The ureteric bud separates from the mesonephric duct, leaving the latter to form part of the bladder (see p. 298) and in the male the vas deferens and associated structures (see p. 301). The bud grows up and divides into the calyces of the pelvis (major and minor) and the collecting tubules of the medullary pyramids, into which the distal convoluted tubules of the metanephros come to drain. The fetal and neonatal kidney has a lobulated appearance, reflecting the way metanephric tissue overlies tubular budding from the calyces.

The definitive kidney (metanephros) develops in the pelvis and is supplied from the internal iliac artery. It subsequently migrates to its adult position, gaining successively new arteries of supply from the common iliac and then from the aorta. The older vessels degenerate as the new ones appear, until the (usually) single definitive artery forms. The hilum is at first anterior but the kidney rotates 90° medially.

Anomalies. Persistence of fetal lobulation is of no significance. Persistence of one of the fetal arteries is common (30% of individuals), especially a vessel from the aorta to the lower pole. Whether such vessels should be called accessory, abnormal, aberrant, supernumerary or whatever is debated. Fusion of the lower poles of the kidneys gives rise to horseshoe kidney (1 in 800); the ureters pass anterior to the isthmus of kidney substance, as does the inferior mesenteric artery which limits ascent of the horseshoe (Fig. 5.51). Polycystic disease (1 in 500) in which both kidneys are riddled with cysts is a hereditary disorder and may be associated with cysts in the liver, pancreas and lungs. One person in 500 has only one kidney (renal agenesis), a situation which must be excluded before considering nephrectomy.

Surgical approach

For many operations on the kidney including removal (nephrectomy) and removal of stones (nephrolithotomy) a lumbar approach is used (see p. 233). The renal fascia and perirenal fat are incised to expose the kidney, whose upper pole is freed leaving the suprarenal gland within its own compartment of the fascia. The overlying peritoneum is pushed away forwards and medially. The renal vessels can then be exposed, ligated and divided (the artery before the vein) to mobilize the organ further and transect the ureter. On the right a diseased kidney may adhere to the colon, duodenum, inferior vena cava or suprarenal gland, and on the left to the colon, spleen, pancreas or suprarenal. The right renal vein is only 2.5cm long, so the inferior vena cava is very near the operation area. Operations on the kidney are also conducted through minimal access utilising laparoscopic techniques.

For percutaneous renal biopsy, the lower pole of the kidney is entered by an approach 2.5cm below the twelfth rib and at a distance from the midline determined radiologically. Damage to a renal vessel or calyx is a potential hazard, and the needle is only advanced while the patient is holding the breath so that the kidney is not torn by respiratory movement.

For transplantation, the donor kidney is placed retroperitoneally in the iliac fossa with the hilum parallel to the external iliac vessels. The renal artery is anastomosed to the internal or external iliac artery and the renal vein to the external iliac vein. The ureter is implanted into the bladder.

Ureters

The ureter is 25cm long. Its points of narrowest calibre are at the pelviureteric junction, where it crosses the pelvic brim, and as it passes through the bladder wall.

The ureter passes down on psoas major under cover of the peritoneum and crosses in front of the genitofemoral nerve, being itself crossed anteriorly by the gonadal vessels. On the right the upper part is behind the third part of the duodenum, while lower down it is crossed anteriorly by the right colic and ileocolic vessels and by the root of the mesentery. On the left it is lateral to the inferior mesenteric vessels and is crossed anteriorly by the left colic vessels and, at the pelvic brim, by the apex of the sigmoid mesocolon. It leaves the psoas muscle at the bifurcation of the common iliac artery, over the sacroiliac joint, and passes into the pelvis (see p. 298). It adheres to the peritoneum of the posterior abdominal wall when that membrane is stripped off the posterior abdominal wall. It can be distinguished from vessels and nerves in the living body in that it is a whitish, non-pulsatile cord which shows peristaltic activity when gently pinched with forceps.

Its surface markings are of use in palpating it for tenderness and in identifying radiographic shadows. On the anterior abdominal wall it can be marked from the tip of the ninth costal cartilage (see p. 234) to the bifurcation of the common iliac artery (see p. 276).

More important is the line of projection of the ureter on a radiograph. It lies medial to the tips of the transverse processes of the lumbar vertebrae (Fig. 5.24 and 5.48) and crosses the pelvic brim at the sacroiliac joint. From here its pelvic shadow passes to the ischial spine and thence, foreshortened, to the pubic tubercle.

Blood supply

The upper end is supplied by the ureteric branch of the renal artery and the lower end by branches from the inferior and superior vesical and uterine arteries. The middle stretch of the ureter is supplied by branches from the abdominal aorta, the gonadal, common iliac and internal iliac arteries. All these vessels make a fairly good anastomosis with each other in the adventitia of the ureter, forming longitudinal channels. The blood supply is endangered if the ureter is stripped clean of its surrounding tissue.

Lymph drainage

The lymphatics run back alongside the arteries; the abdominal portion of the ureter drains into para-aortic nodes, the pelvic portion into common iliac and internal iliac nodes.

Nerve supply

Although sympathetic fibres from T10–L1 segments of the cord reach the ureter via the coeliac and hypogastric plexuses, together with parasympathetic fibres from the pelvic splanchnic nerves, their functional significance is not clear. Intact innervation of the renal pelvis or ureter is not necessary for the initiation or propagation of peristalsis from the calyceal pacemakers. There are no ganglion cells in or on the ureter. Pain fibres accompany sympathetic nerves, as from the kidney (see p. 285).

Structure

The ureter is a tube of smooth muscle lined internally by mucous membrane. The muscle often appears histologically to be arranged as a middle circular layer with inner and outer longitudinal layers. However, it is more accurate to consider the muscle as a single coat with fibres running in many different directions because they are parts of intertwining helices. The lax mucous membrane is lined by transitional epithelium; there is no muscularis mucosae.

Development

The ureter is of mesodermal origin; it is derived by a process of budding from the caudal end of the mesonephric duct (see p. 286). Its upper end divides into two or three (the major calyces of the renal pelvis) and further subdivisions produce the minor calyces and collecting tubules. Low division of the ureteric bud produces double ureter.

Suprarenal glands

These glands lie anterosuperior to the upper part of each kidney (Fig. 5.43). They are somewhat asymmetrical, yellowish in colour, and lie within their own compartment of the renal fascia. Adrenal glands is an alternative name.

The right suprarenal gland is pyramidal in shape and surmounts the upper pole of the right kidney. It lies on the diaphragm and encroaches on to the front of the right kidney. The anterior surface is overlapped medially by the inferior vena cava. The rest of the anterior surface is in contact above with the bare area of the liver, and is covered below by the peritoneum of the posterior wall of the hepatorenal pouch.

The left suprarenal gland is crescentic in shape and drapes over the medial border of the left kidney above the hilum. It lies on the left crus of the diaphragm and overlaps the front of the left kidney. The upper part of the anterior surface is covered by the peritoneum of the posterior wall of the lesser sac, forming part of the stomach bed; the lower part is in contact with the body of the pancreas and the splenic vessels.

Blood supply

Both glands receive blood from three sources: directly from the aorta and from the renal and inferior phrenic arteries, the last providing two or three small branches. In contrast there is usually a single vein. The right vein is only a few millimetres long and enters the vena cava; the left vein is longer and enters the left renal vein.

Lymph drainage

To para-aortic nodes.

Nerve supply

The main supply is by myelinated preganglionic sympathetic fibres from the splanchnic nerves via the coeliac plexus; the fibres synapse directly with medullary cells (see p. 18). Blood vessels receive the usual postganglionic sympathetic supply. Cortical control is not neural but by ACTH from the anterior pituitary.

Structure

The suprarenal gland has an outer yellow cortex completely enclosing a much thinner grey medulla. The cortex, whose principal products are cortisol, aldosterone, androgens and related hormones, consists of three layers or zones. They are, from the surface inwards, the zona glomerulosa (with small rounded cells), the zona fasciculata (parallel rows of pale-staining vacuolated cells) and the zona reticularis (a network of smaller and darker-staining cells). The rather small central medulla has larger cells secreting the catecholamines adrenaline (epinephrine) (80%) and noradrenaline (norepinephrine) (20%) and some dopamine. Many of the medullary cells exhibit the chromaffin reaction: they contain fine cytoplasmic granules (the catecholamine precursors) which are coloured brown by chromium salts. Dilated capillaries are usually prominent in the medulla but not in the cortex.

Development

The medulla is derived by migration of cells from the neural crest and is ectodermal in origin while the cortex is derived in situ from the mesoderm of the intermediate cell mass (see p. 23).

Surgical approach

For bilateral adrenalectomy the glands are usually approached from the front. A bilateral subcostal ‘rooftop’ incision provides appropriate transperitoneal access. For exposure of the right gland, after retraction of the right lobe of the liver, a Kocher manoeuvre (see p. 269) is employed to mobilize the second part of the duodenum and head of the pancreas from the upper pole of the kidney and inferior vena cava. For the left gland, after division of the phrenicocolic ligament to mobilize the splenic flexure of the colon, the posterior layer of the splenorenal ligament is incised and the spleen turned medially with the tail of the pancreas. On each side the suprarenal vein is ligated before the numerous small arteries; the right vein is particularly short and the vena cava is easily torn. The glands must be handled as little as possible before venous ligation to prevent surges of hormone release. The anterior, transperitoneal approach is also used for laparoscopic bilateral adrenalectomy.

A posterolateral extraperitoneal approach through the bed of the twelfth rib provides access for unilateral adrenalectomy. The removal of a large adrenal tumour may require a higher approach, through the bed of the eleventh or tenth ribs, and division of the diaphragm.