Diagnosis - Duodenal Carcinoid with Carcinoid syndrome secondary to hepatic metastases.

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 histaminelike substances that normally are transported to the liver where they are metabolized. Most gastrointestinal carcinoid tumors arise from neural crest cells, which are believed to be part of the amine precursor uptake and decarboxylation system and are programmed for endocrine function.

The small bowel is the most common primary site giving rise to carcinoid syndrome resulting from liver metastases. Gastrointestinal carcinoids metastasize to the lymph nodes and liver. Liver metastases may produce carcinoid syndrome, although most liver metastases are clinically silent and found on images obtained before surgery or on images obtained for other reasons.

Duodenal carcinoid is rare, and the duodenum is the second least common site for carcinoid tumors, which are seen with decreasing frequency from the first to the third part of the duodenum. The tumors usually are slow growing and benign. An association with Zollinger-Ellison syndrome has been described. The liver is frequently involved as a result of metastatic disease from a gastrointestinal carcinoid; in fact, a liver metastatic deposit may be the presenting feature of a carcinoid. Although rare, primary hepatic carcinoid does occur and is classified as a foregut tumor that is presumed to arise from the biliary mucosa. Carcinoids metastatic to the liver are often multiple in number. They may be hypervascular, they may become calcified, and they are frequently associated with carcinoid syndrome.

USG - Sonography of the bowel can depict bowel tumors, with a pseudokidney sign. Associated lymphadenopathy and liver metastases may be demonstrated on sonograms.

Barium - On barium series, tumors appear as intraluminal polypoid lesions or infiltrating lesions that cause an irregular stricture.

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

Nuclear Medecine - Somatostatin-receptor scintigraphy performed with indium-111 octreotide and 111In pentetreotide is used to image many neuroendocrine 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 further refinement of the technique, which increases sensitivity further, is the addition of single photon emission tomography. Scintigraphy performed with iodine-123 metaiodobenzylguanidine 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.

Angiography - Before the advent of cross-sectional imaging, mesenteric angiography provided useful information regarding characterization of small bowel carcinoids. The angiographic appearances encountered with small-bowel carcinoid on angiography performed for other indications, eg, gastrointestinal bleeding, are worth noting. Foreshortening of the bowel occurring with desmoplastic reaction makes mesenteric arteries tortuous and frequently narrowed and 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 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 or 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.