Gastroenteropancreatic neuroendocrine tumors: multimodality imaging features with pathological correlation.

Neuroendocrine tumors of the gastrointestinal tract are rare entities. Functioning neuroendocrine tumors tend to present early because of hormone-induced clinical symptoms, but detection of the primary lesion may be difficult owing to their small size. Neuroendocrine tumors are typically hypervascular and show enhancement after contrast administration on computed tomography (CT) or magnetic resonance imaging (MRI). Large nonfunctioning tumors may be found in asymptomatic patients. In such cases, the synchronous presence of hypervascular hepatic metastases should be explored. This pictorial review illustrates imaging features of functioning and nonfunctioning neuroendocrine tumors arising in the gastrointestinal tract and the pancreas. Modalities included are CT, MRI, ultrasonography, and nuclear medicine. Characteristic histological specimens of these lesions are presented.