Gastrointestinal carcinoids

Dr.R.Rengarajan

• Gastrointestinal carcinoid, also called carcinoid tumor, is the most common primary tumor of the small bowel and appendix.

• Gastrointestinal carcinoid accounts for more than 95% of all carcinoids.

• The tumors arise from enterochromaffin cells of Kulchitsky, which are considered neural crest cells situated at the base of the crypts of Lieberkühn.

• Gastrointestinal carcinoids account for 1.5% of all gastrointestinal tumors.

• The tumors elaborate serotonin and other histamine like substances that normally are transported to the liver, where they are metabolized.

• Most tumors are clinically silent, but they may cause pain or intestinal obstruction, weight loss, a palpable mass, or, rarely, bowel perforation.

• Carcinoid syndrome occurs when the humoral load exceeds the capacity of monoamine oxidase (MAO) present in the liver and lung to metabolize serotonin.

• Most patients with carcinoid syndrome have liver metastases from a bowel carcinoid, although in rare cases, the humoral load from a primary tumor may overwhelm the liver and the capacity of the lungs to metabolize serotonin.

• Rarer still is carcinoid syndrome that develops in patients with noncarcinoid malignant tumors and dermatomyositis.

• Diagnosis is usually achieved by using several complementary imaging techniques.

• The most promising imaging technique is somatostatin receptor scintigraphy.

The technique can aid diagnosis by localizing primary and metastatic sites of gastro-enteropancreatic endocrine tumors. The degree of radionuclide uptake is related to somatostatin receptor density. In gastrointestinal carcinoids, the concentration at the receptor sites is high (90%).

• Plain radiographic findings (eg, soft-tissue mass, punctate calcification within a mass, signs of intestinal obstruction) are not specific for carcinoids. Plain radiographs are usually obtained in an acute setting, being taken, for example, in patients presenting with intestinal obstruction or perforation.

• Plain abdominal radiographs may reveal curvilinear calcification within the abdomen. These are usually smaller than 15 mm in diameter and result from calcification within the tumor.

• On barium studies, findings consist of fairly well-defined, round, intraluminal bowel-filling defects. These may be associated with thickening of the valvulae conniventes resulting from interference of the bowel blood supply by the tumor.

• With invasion of the mesentery, the mesenteric mass causes rigidity, displacement/stretching, and fixation of small-bowel loops. Desmoplastic reaction from mesenteric invasion causes sharp angulation of a bowel loop or a stellate or spokelike wheel arrangement of adjacent bowel loops.

• The tumor often infiltrates the mesentery, provoking an intense fibrotic reaction that results in kinking of the bowel segments; such kinking may in turn cause intestinal obstruction.

• On a small-bowel barium series, kinking of the small-bowel loops is considered the hallmark of a small-bowel carcinoid tumor.

• Ultrasonography of the bowel can depict bowel tumors, with a pseudokidney sign. Associated lymphadenopathy and liver metastases may be demonstrated on ultrasonograms.

• On ultrasonography, liver metastases vary from hypoechoic to hyperechoic and show strong enhancement with intravenous contrast media.

• Tumors demonstrate peripheral hypervascularity on color and power Doppler images.

• CT scanning reveals a mass with soft-tissue attenuation and variable size, with spiculated borders and radiating surrounding strands.

• Calcification may be noted in the tumor.

• Linear strands within the mesenteric fat probably are thickened and retracted vascular bundles and represent peritumoral desmoplastic reaction.

• Lymphadenopathy and liver metastases may be visualized on CT scans.

• Helical CT enteroclysis has been used to detect small-bowel carcinoids and has been found to be more sensitive than are conventional barium studies.

• Liver metastases are demonstrated well on MRIs and usually have low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.

• After the administration of a gadolinium-based contrast agent, liver metastases enhance peripherally in the hepatic arterial phase and appear as hypo-intense defects against the enhancing normal liver in the portal venous phase.

• Somatostatin-receptor scintigraphy performed with indium-111 (111 In) octreotide and111 In pentetreotide is used to image many neuro-endocrine tumors, including carcinoids with somatostatin-binding sites.

• Several studies have shown that somatostatin-receptor scintigraphy is a sensitive and noninvasive technique for imaging primary carcinoid tumors and carcinoid metastatic spread.

• A refinement of the technique that increases sensitivity is the addition of single photon emission CT (SPECT) scanning

• Scintigraphy performed with iodine-123 (123 I) meta-iodobenzylguanidine demonstrates a 44-63% uptake in gastrointestinal carcinoids.

• A higher frequency of radionuclide uptake is found in midgut carcinoids and tumors with elevated serotonin levels.

• [Fluorine-18]fluorodopa positron emission tomography (18 F-dopa–PET) scanning has been used to image primary gastrointestinal carcinoid tumors and lymph node and organ metastases with promising results.

• In general, FDG-PET scanning is useful in poorly differentiated carcinoids and other neuro-endocrine tumors, but it should not be used as a first-line imaging agent. FDG-PET scanning is primarily useful when the results of somatostatin-receptor scintigraphy are negative.

• Before the advent of cross-sectional imaging, mesenteric angiography provided useful information regarding characterization of small-bowel carcinoids.

• The angiographic appearances of small-bowel carcinoids encountered on angiograms produced for other indications, such as gastrointestinal bleeding, are worth noting.

• Foreshortening of the bowel occurring with desmoplastic reaction makes mesenteric arteries tortuous and frequently narrowed; it also draws the arteries into a stellate pattern.

• The areas involved appear hypervascular, but in reality, the number of arteries in the area does not increase. Instead, the arteries contract into a smaller area as a result of fibrosis.

• An additional arterial change associated with carcinoids is smooth, multifocal stenosis of the mesenteric arteries distant from the tumor.

• Tumors seldom show capillary blush or demonstrate early or dense venous drainage.

• Venous occlusion and mesenteric varices also have been reported.

• These findings are nonspecific and have been reported with sclerosing peritonitis and with a carcinoma of the pancreas invading the mesentery.

• Selective hepatic angiography can demonstrate hypervascular liver metastases by demonstrating capillary blush in involved areas, highlighting the potential response of tumors to embolization.

Thank you