Neuroendocrinoma of the jejunum: electron microscopic and biochemical analysis

A 56-year-old woman presented with a sudden, severe hemorrhage per rectum. Angiography localized a jejunal tumor, which was excised. Light microscopy suggested a neuroendocrine tumor, but neither a smooth muscle tumor nor a lymphoma could be excluded. Electron microscopy showed dense cored, single membrane bound secretory granules 150--220 nm in diameter; myofilaments were not observed. Biochemical analysis of tumor tissue yielded considerable amounts of catecholamines. VMA, 5-HIAA, and metanephrines. These combined ultrastructural and biochemical observations establish the diagnosis of neuroendocrine tumor; however, in this case neither type of information is sufficiently specific to define the tumor as either a paraganglioma or a carcinoid. Although paraganglia and mucosal endocrine cells in the GI are currently thought to constitute distinct cell types, they share numerous structural and functional properties, and they are both thought to be part of the APUD cell system. These parallels and similarities are shared by the neoplasms derived from them which often display features of both. In the absence of specific granule types or specific substances isolated from tumor tissue, only the application of specific immunocytochemistry techniques may allow the precise "functional" classification of such tumors.