Carcinoid tumor of the middle ear.

A primary tumor of the middle ear with histologic, histochemical, and ultrastructural features of a neuroendocrine neoplasm is described. This neoplasm superficially resembles the so-called adenomatous tumor of the middle ear, and potential relationships and differences between these tumors are discussed. Although the histogenesis of the carcinoid tumor of the middle ear is not well understood, it most likely originates from pre-existing neuroendocrine cells or a primitive precursor cell. This neoplasm should be considered in the differential diagnosis when biologically low-grade tumors with prominent acinar or trabecular architectures are encountered in the middle ear. Since the carcinoid tumor of the middle ear is presumably of foregut derivation, stains for argyrophilic granules and electron-microscopic identification of neurosecretory granules are important diagnostic aids.