Carcinoid tumor of the middle ear. An immunohistochemical and electron microscopic study. Report of a case.

A primary tumor of the middle ear was examined histologically, histochemically, immunohistochemically and ultrastructurally. Neuroendocrine cell differentiation, a carcinoid feature, was demonstrated by the presence of numerous argyrophil granules, as well as positive serotonin, glicentin, glucagon, and human pancreatic polypeptide (hPP) granules in some of the Grimelium-positive cells. Chromogranin A was also detected in the cells, but much less frequently than Grimelius-positive staining. Neither neuron-specific enolase (NSE) nor epithelial membrane antigen (EMA) was demonstrated in the tumor. Mucin was demonstrated only intraluminally. Electron microscopy revealed many typical neurosecretory granules in tumor cells, but no apical mucin granules. The tumor appeared to be benign, and there has been no sign of recurrence during a postoperative period of one year.