Adenomatous tumor of the middle ear. An ultrastructural and immunocytochemical study.

An adenomatous tumor of the middle ear was examined by light microscopy, ultrastructural and immunocytochemical technics. It demonstrated the typical histologic growth pattern and featured ultrastructural evidence of glandular differentiation with two distinct types of secretory granules, apically oriented mucus granules and basally located uniformly condensed neurosecretory granules. In support of its neuroendocrine differentiation was the detection of neuron-specific enolase and positive reaction with monoclonal antibody to chromogranin. These findings are compared with previously reported cases and with middle ear mucosa. It is suggested that this bidirectional differentiation is analogous to that seen in other endodermally derived neuroendocrine tumors.