Enteropancreatic neuroendocrine tumors spread first locally and to regional lymph nodes and from there generally to the liver. The single most impor-
tant factor affecting prognosis is liver metastases. Bone metastases occur late, and other distant metastases are rare. A cross-sectional study (CT or MRI) is the most useful initial test to identify tumors. The localizing rate of MRI is similar to that of ultrasonography and CT for pancreatic lesions (Figure 16-8) but has an increased sensitivity for diagnosis of liver metastases. There are almost always liver metastases before bone metastases, but bone scanning is useful if there are symptoms or biochemical abnormalities that suggest the presence of bone metastases. Angiography can be useful prior to surgery to localize disease and can be combined with stimulatory infusions to provide functional as well as anatomic data (Figure 16-9). The limiting factor in localizing tumors using ultrasonography, CT, angiography, or MRI is tumor size, with < 10%
of tumors < 1 cm, 30 to 40% of 1 to 3 cm, and 70 to 80% of > 3 cm detected. Current provocative hormonal testing includes angiography with selective intra-arterial secretin injection and gastrin determination in hepatic venous samples, which permits selective provocation for gastrinoma during localization with a standard angiogram. Similarly, calcium can be used to stimulate insulin from insulinoma.
SRS is critical in the imaging of patients with MEN type I (Figure 16-10). In addition to demonstrating the extent of enteropancreatic tumors, SRS can identify previously unsuspected disease in the chest or abdomen.63 Although SRS is useful in identifying otherwise occult neuroendocrine tumors in patients with MEN type I, and this can alter management substantially, it also has significant false-positive and false-negative rates, thus necessitating correlation with conventional imaging studies.
Finally, intraoperative ultrasonography and transillumination of the duodenum are extremely helpful to a experienced surgeon in localizing duodenal and pancreatic islet tumors.
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