The spectrum of olfactory neural tumors. A light-microscopic immunohistochemical and ultrastructural analysis.

Twenty-eight malignant olfactory neural tumors representative of the histologic spectrum commonly designated as olfactory neuroblastoma were subdivided into two groups: Group I closely resembling classical neuroblastoma (20 cases), and Group II exhibiting neuroendocrine features (eight cases). Immunohistochemically, the tumors were analyzed by using antibodies to keratin, neurofilament protein, S-100, and neuron specific enolase. Neuron specific enolase was the most consistently positive in both groups. Single S-100 positive cells, within or at the edges of tumor nests, often corresponded ultrastructurally to Schwann cells at the tumor-stroma interface. Keratin and neurofilament proteins were expressed singly or together by a small number of cases in both groups. All 11 tumors examined ultrastructurally exhibited neuronal processes containing dense-core granules. The results indicate the following: (a) the reliable diagnostic utility of electron microscopy; (b) the frequent occurrence of Schwann cells in these tumors despite their inconspicuousness by light microscopy; and (c) the unexpected expression of keratin by tumors in both groups. The single or coexpression of keratin-neurofilament protein may define a subset of these tumors for which the clinical significance is presently unclear.