Diagnosis

A specific diagnosis based on clinical suspicion of a neuroendocrine tumor is rare and in our own experience has been made in only 20% of the patients. The most important examinations are the serum level of serotonin and the 24-hour urine collection for 5-HIAA. Because the amount of hormone secreted varies, multiple assessments may be necessary. When a gastric neuroendocrine tumor is suspected, serum 5-hydroxytryptophan should be measured instead of serotonin. In case of rare occasional flushing, pentagastrin can be infused to prevent flushing and confirm the diagnosis.37 Location of the neuroendocrine tumor determines whether endoscopic or radiologic examination is more useful. Endoscopic examination and biopsy are valuable in bronchial, gastric, and rectal neuroendocrine tumors. Gastric and rectal neuroendocrine tumors are often incidental findings when endoscopy is performed for other reasons. Because neuroendocrine tumors may grow in submucous areas, they may often be overlooked.

Primary midgut carcinoids are initially generally too small to be diagnosed with conventional bowel contrast studies, and localization of these tumors remains a problem. When patients present with symptoms related to obstruction or the carcinoid syndrome, the tumors are larger and unfortunately have usually metastasized to the mesenteric nodes and liver. Computed tomography (CT) scanning is helpful in

TABLE 86-3. Secreted Hormones and Neurotransmitters and Corresponding Clinical Symptoms in Carcinoid Tumors

Type

Kallikrein, bradykinin Tachykinin (substance P, neurokinin A, neuropeptide K) Prostaglandins

Diarrhea, fibrosis, bronchoconstriction, edema (hypoalbuminemia) Vasodilatation: flushing Vasodilatation: flushing

Diarrhea, flushing

FIGURE 86-3. A, Typical mesenteric fibrosis with isolated structure. B, Typical multiple hepatic metastasis of varying size.

localizing the primary tumor in about 55% of cases.3 The presence of a mesenteric mass with radiating densities is highly suggestive of mesenteric involvement of a midgut carcinoid. CT scanning of larger tumors often helps determine the size of the mesenteric tumor, its relation to the superior mesenteric artery, and possible extension retroperitoneally or above the pancreas. CT scanning is therefore recommended for appropriate planning prior to surgery. For patients with symptoms of intestinal obstruction, bowel contrast studies are recommended (Fig. 86-3).38

Somatostatin receptor scintigraphy has an accuracy of 80% and a positive predictive value of 100%. Because of its high sensitivity and ability to detect local and distant metastases, this examination is considered an essential imaging procedure.3'39 However, this localization study displays images that are usually inadequate for precise anatomic details to be of help preoperatively.38 Positron emission tomography scanning is recommended for patients whose neuroendocrine tumor fails to be identified with somatostatin scanning. Preliminary studies comparing somatostatin receptor scintigraphy and positron emission tomography seem to show a higher sensitivity for the latter.3'40 Somatostatin receptor scintigraphy can also predict whether

FIGURE 86-4. Somatostatin receptor scintigraphy of large ileal carcinoid tumor with extensive mesenteric infiltration and local lymph node metastases.

the hormonal hypersecretion can be controlled by somatostatin analogs (Fig. 86-4).41

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