Clinical Presentation

The clinical presentation of jejunoileal NETs differs from those occurring in other sites of the gut in that there is often metastatic disease at the time of presentation. These tumors present in four distinct patterns: the first is local effects of tumor mass, the second is the carcinoid syndrome, the third is fibrosis, and the last but quite frequent pattern (about 50%) is a completely unanticipated finding by biopsy or surgery.30 Patients most commonly present with abdominal pain or obstructive signs.1012'59,60 Because these tumor cells secrete serotonin, tachykinins, and other peptides and amines, small bowel NETs are the most common cause of the carcinoid syndrome.60 Overall, about 20 to 50% of patients with small bowel NETs have the carcinoid syndrome.10,59 Most patients with carcinoid syndrome have liver metastases that release serotonin-

Figure 18-7. Small bowel barium enema showing a small bowel neuroendocrine tumor.

like substances into the systemic circulation, bypassing hepatic deactivation.30 Intestinal venous ischemia or congestion (occurs in about 30% of advanced midgut NETs) results from both compression of mesenteric vessels by tumor and fibrosis and to a specific angiopathy (elastic vascular sclerosis), consisting of elastic tissue proliferation in the adventitia of mesenteric arteries and veins. Aggravated diarrhea may be a likely result when ischemia affects a limited segment of the small intestine, and severe watery diarrhea can be expected if major mesenteric veins are involved.60 Because of the moderate size and submucosal location of the primary tumor, intestinal bleeding is uncommon and is generally encountered only with advanced bowel involvement.59

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