PERSPECTIVE, PATTERNS OF SPREAD, AND PATHOLOGY
Adenocarcinomas are more common in the duodenum, lymphomas in the jejunum, and sarcomas and carcinoids in the ileum, with the most favored site being the vermiform appendix.
PERSPECTIVE AND PATTERN OF SPREAD
Consider the contradictory paucity of neoplasms in the small intestine in view of the extreme length of the small bowel, which exceeds in its length all other regions of the digestive system combined. It has a rich variety of metabolically active cells, with high and rapid turnover rates of regenerative cells. Its stem cells are estimated to have cell turnover times of 24 hours and travel times of 5 to 7 days from the crypt of Lieberkühn to the tip of the villus. The absence of malignancy is attributed to the rapid transport of carcinogens in luminal contents, abundant surface immunoglobulin A expression, and active enzymes. The annual rate of new cases is 6,960, with high survival rate. The surface columnar epithelial cells have brush borders for absorption of fluids and chyme, with numerous lymphoid cells, neuroendocrine cells, goblet cells, and Paneth cells with loose connective tissue filling the microvilli with its lacteal. What the small intestine lacks in number of cancers, it makes up for by their variety. Table 30.1 lists them; one notes a predilection for specific tumors in different bowel segments: Adenocarcinomas are more common in the duodenum, lymphomas in the jejunum, and sarcomas and carcinoids in the ileum, with the most favored site being the vermiform appendix (T1 histopathology versus distribution). Predisposing factors include celiac disease, Crohn disease, familial adenomatosis polyposis, Gardner syndrome, and Peutz–Jaeger syndrome, all beginning with hyperplasia, then dysplasia, and finally neoplasia. The patterns of cancer spread follow the mucosal and muscle layers of the bowel wall (Fig. 30.2; Table 30.2).
PATHOLOGY
Although small bowel mucosa is the most extensive cellular surface, it accounts for 1.1% to 2.4% of gastrointestinal malignancies; there are approximately 2500 cases annually, and less than half of the patients die. Adenocarcinomas (35% to 50%) are most common, followed by carcinoids (20% to 40%). Small bowel adenomas progress to adenocarcinomas similar to what occurs in the colon. Small bowel obstruction (70%) is a common presentation, triggered by interception or volvulus. Bleeding (20% to 50%) is usually occult, but massive hemorrhage is more common with sarcomas (gastrointestinal stromal tumors).
Figure 30.1 | A. Serrated adenoma. B. Neuroendocrine tumor of small intestine. B. A photomicrograph of the lesion in A demonstrates cords of uniform small, round cells. Neuroendocrine tumors demonstrate cords of uniform small round cells with rare mitotic figures.
Figure 30.2 | A. Patterns of spread. B. T categories. The patterns of spread and the primary tumor classification are similarly color coded: Tis (cancer in situ of mucosa), yellow; T1 (infiltrates the submucosa), green; T2 (penetrates the muscularis externa), blue; T3 (reaches the subserosa), green; and T4 (invades through the serosa into a neighboring viscera), red. The concept of visualizing patterns of spread to appreciate the surrounding anatomy is well demonstrated by the six-directional pattern, i.e., SIMLAP Table 30.2.
What the small intestine lacks in numbers of cancers, it makes up for by their variety. Table 30.1 lists them succinctly and one notes a predilection for specific tumors in different bowel segments: Adenocarcinomas are more common in the duodenum, lymphomas in the jejunum and sarcomas, and carcinoids in the ileum with its most favored site being the vermiform appendix (T1 histopathology versus distribution) (Table 30.1; Fig. 30.1).
TNM STAGING CRITERIA
SUMMARY OF CHANGES SEVENTH EDITION AJCC
TNM Staging Criteria
There has been no change or revision, with depth of wall penetration determining the stage: T1, mucosal; T2, muscularis; T3, serosa; and T4 other viscera (Fig. 30.3).
Generally, there is no overarching principle or context design for the digestive system (gastrointestinal tract) or major digestive glands (MDGs). Stages are frequently expanded to six by subdividing stages into A and B. The T and N categories are assigned to a stage grouping, specifically for division of a stage into more (a) versus less (b) favorable groupings. This occurs at different stages for different sites.
Specifically, this site is staged in the same fashion as colorectal cancers. Stages I and II are due to T progression, whereas stages III and IV are related solely to N progression: >T4 = N1.
In the seventh edition of the American Joint Committee of Cancer AJCC Cancer Staging Manual changes are minor and mainly involve subdividing stages I and II.
CLASSIFICATION AND STAGING
• T1 lesions have been divided into T1a (invasion of lamina propria) and T1b (invasion of submuscosa) to facilitate comparison with tumors of other gastrointestinal sites (Fig. 30.3).
• Stage II has been subdivided into Stage IIA and Stage IIB.
• The N1 category has been changed to N1 (1–3 positive lymph nodes) and N2 (four or more positive lymph nodes), leading to the division of Stage III into Stage IIIA and Stage IIIB.
The TNM Staging Matrix is color coded for identification of stage group once T and N stages are determined (Table 30.3).
SMALL INTESTINE ADENOCARCINOMA
Figure 30.3 | TNM staging diagram presents a vertical arrangement with color bars encompassing TN combinations showing progression. Small intestine cancers are both uncommon and unique. They are simply staged I to IV without substages, an exception for the digestive system. Stage 0, yellow; I, green; II, blue; III, purple; IV, red; and IV (metastatic), black. Definitions of TN on left and stage grouping on right.
T-ONCOANATOMY
ORIENTATION OF THREE-PLANAR ONCOANATOMY
The anatomic isocenter for the small intestine is at L3 to L5 (Fig. 30.4).
T-oncoanatomy
The TNM Staging Matrix is color coded for identification of stage group once T and N stages are determined (Table 30.5).
The small intestine extends from the pylorus of the stomach to the ileocecal valve. It is approximately 25 feet long and is divided into three sections: the duodenum, the jejunum, and the ileum. The duodenum is essentially a midline structure, approximately 1 foot long. It provides some of the most complex anatomy in the upper abdomen, as it bends at two right angles and loops around the pancreas, accepting the insertion of the pancreatic main duct into its second portion via the ampulla of Vater. The visceral relationships of the stomach, duodenum, pancreas, and liver are in multiple layers, separated by the omental bursa, lesser omentum, and greater omentum (Fig. 30.4).
• Coronal: The jejunum starts in the left side of the abdomen as the duodenal loop terminates posteriorly and to the left side of the superior mesenteric artery and vein. It occupies the left upper quadrant of the abdomen mainly leading into the ileum, which, in turn, terminates in the cecum and occupies most of the right lower quadrant. The internal mucosal markings are like bowel fingerprints and when seen on film vary from the duodenum, which is relatively smooth to the jejunum with multiple circular folds that are narrow, feathery, and thin; they gradually thicken and separate in the ileum (Fig. 30.5A, B, C). The small intestine is mainly involved in fine absorption of the various products of digestion, the large intestine with fluid reabsorption.
• Proximal jejunum: The circular folds (plicae circulares) are tall, closely packed, and commonly branched. Proximal ileum: The circular folds are low and becoming sparse. The caliber of the gut is reduced, and the wall is thinner. Distal ileum: Circular folds are absent, and solitary lymph nodules stud the wall. Intestines in situ, greater omentum reflected: The ileum is reflected to expose the appendix in the lower right quadrant. The appendix usually lies posterior to the cecum (retrocecal) or, as in the case, projects over the pelvic brim. Note the extensive coiling of the jejunum and ileum of the small intestine (together approximately 6 m long). Also observe the distinguishing features of the large intestine: its position around the small intestine; the teniae coli or longitudinal muscle bands; the sacculations or haustra; and fatty omental appendices.
• Sagittal: The peritoneal cavity consists of the greater sac and omental bursa. The superior recess of the omental bursa is between the liver and the posterior attachment of the diaphragm. The inferior recess of the omental bursa is between the two double layers of the greater omentum. In adults, the inferior recess usually only extends inferiorly as far as the transverse colon because of fusion of the two double peritoneal layers at birth.
• Transverse: The small intestine loops fills most of the abdomen. The inferior vena cava and aorta are located anterior to the vertebral column.
Figure 30.4 | Orientation and overview of oncoanatomy. The anatomic isocenter for the small intestine is at L4 to L5. A. Coronal. B. Sagittal.
Figure 30.5 | T-oncoanatomy. Connecting the dots. Structures are color coded for cancer stage progression. A. Coronal. B. Sagittal. C. Transverse axial. The color code for the anatomic sites correlates with the color code for the stage group (Fig. 30.3) and patterns of spread (Fig. 30.2) and SIMLAP tables (Table 30.2). Connecting the dots in similar colors will provide an appreciation for the 3D oncoanatomy.
N-ONCOANATOMY AND M-ONCOANATOMY
N-ONCOANATOMY
Despite a large variety and number of regional lymph nodes following the superior mesenteric artery and vein, the lymph node classification is simply N1, positive regional node, without qualification as to number or size of lymph nodes (Fig. 30.6A; Table 30.4).
M-ONCOANATOMY
The entire portal circulation should be considered as a unit in regard to the venous anatomy of the gastrointestinal tract below the diaphragm (see Fig. 30.6B). The two major trunks are the inferior and superior mesenteric veins. The inferior mesenteric vein drains the left colon and sigmoid colon tributaries, which cover the vascular drainage to the left of the mid-line originating from the superior rectal veins. On the right side, the superior mesenteric vein originates from the tributaries draining the ileum, jejunum, and the ileocolic and right and middle colic veins. The inferior mesenteric vein usually joins the splenic vein, which coalesces with the superior mesenteric vein and forms the portal vein. The splenic vein, which is a major tributary of the portal system, also drains much of the stomach along its greater curvature and includes the short gastric veins and left and right gastroepiploic veins. The right gastroepiploic also flows into the superior mesenteric vein. The entire drainage of the lesser curvature of the stomach, including the left and right gastric veins, drains directly into the portal vein. Because the portal vein then drains directly into the liver, it is the target metastatic organ and the most commonly involved organ in hematogenous spread pattern from the venous system of the gastrointestinal tract, as compared with other parts of the body, where the drainage is directly into the lung by way of the caval system.
Venous drainage is by way of the tributaries of the superior mesenteric vein and fusion with the splenic vein to give rise to the portal vein. Liver metastases are the most common site.
The venous drainage of the small intestine is complex because of the length and its convolutions throughout the abdominal cavity. The first part of the small intestine, the duodenum, drains into the pancreaticoduodenum veins, into the portal vein, and superiorly and inferiorly into the superior mesenteric vein. The jejuneal and ileal veins drain directly into the superior mesenteric vein and then into the portal vein. Liver is the target organ.
Figure 30.6 | A. N-oncoanatomy. Sentinel nodes of small intestine include the mesenteric nodes. B. M-oncoanatomy. Along superior mesenteric artery.
STAGING WORKUP
RULES OF CLASSIFICATION AND STAGING
Clinical Staging and Imaging
Cancers of the small intestine are uncommon, and although imaging may be useful for staging, the diagnosis realistically is often uncovered at laparotomy. At the time of surgery and resection an accurate view of penetration of the bowel wall is possible. Computed tomography (CT) and magnetic resonance imaging (MRI) may be useful; however, most small bowel neoplasias are carcinoids, lymphomas, or leiomyosarcomas and are not applicable to the TNM staging system (Table 30.5; Fig. 30.7).
Pathologic Staging
The surgically resected small intestine and associated lymph nodes removed are assessed. Tumor extension and location of both primary and nodes should be documented. Accurate radial margins should be marked and recorded and are defined as the surgically dissected surface adjacent to the deepest point of tumor invasion beyond the wall of the small bowel. The completeness of resection depends on the clearing of the deepest point of invasion: R0, complete; R1, microscopic; and R2, macroscopic.
Figure 30.7 | Axial CTs of L4 and L5 level correlate with the T-oncoanatomy transverse section (Figure 30.5C). Oncoimaging with CT is commonly applied to staging cancers, often combined with PET to determine true extent of primary cancer and involved lymph nodes. 1. Descending colon. 2. Ascending colon. 3. Rectus abdominus muscles. 4. Transversus abdominus muscle. 5. Internal oblique muscle. 6. External oblique muscle. 7. Vertebral body laminae. 8. Vertebral body pedicles. J, jejunum; Ps, psoas muscles.
PROGNOSIS AND CANCER SURVIVAL
Oncoimaging Annotations
• Adenocarcinomas occur in the duodenum, decreasing in frequency in the jejunum and ileum.
• Enteroclysis has a 90% success rate in imaging small bowel tumors, although it is included in 30% to 40% of small bowel followthrough studies.
• CT is best for determining penetration of the bowel into surrounding viscera; MRI is useful for detecting liver metastases.
• CT is reported to have an accuracy of detection rate between 70% and 80%. CT misses tumors 2 cm. Mucosal detail is absent. CT is best for staging and follow-up.
• At present, the role of MRI is limited to the search for liver metastases, but enthusiasm for MRI enteroclysis is increasing.
• Camera capsule endoscopy is ideal for sites beyond routine endoscopy and can identify obstructing and bleeding foci of polypoid and ulcerating lesions.
PROGNOSIS
The limited number of prognostic factors are listed in Table 30.6.
CANCER STATISTICS AND SURVIVAL
The digestive system, or gastrointestinal tract, which includes MDGs, accounts for 275,000 new patients annually, with colon and rectum responsible for >50%, or about 140,000 new diagnoses annually. Approximately half of these patients eventually die of these cancers. MDG cancers as a group are more lethal; only a handful of patients become long-term survivors. Fortunately, colon and rectal cancers are the most common, with the majority of patients becoming 5-year survivors (63%) responding to chemoradiation programs, often with the sparing of the rectal sphincter with conservative surgery. Anal cancers are the most responsive to chemoradiation (5-fluorouracil and cisplatin), eliminating the need for surgery. The 5-year survival rate is >90%, with anal sphincter preservation. This regimen has been proven to be very effective in clinical trials and to result in more long-term survivors, which is currently reflected in the literature. Liver, bile duct, and pancreatic cancers are among the poorest in the terms of survival, which is often measured in months rather than years (Fig. 30.8).
Figure 30.8 | Five-year observed survival adenocarcinoma of small intestine. (Data from Edge SB, Byrd DR, and Compton CC, et al., AJCC Cancer Staging Manual, 7th edition. New York, Springer, 2010, p. 129.)