Olfactory neuroepithelioma: an immunohistochemical and ultrastructural study.

Three cases of olfactory neuroepithelioma are presented in this report. Histologically, these tumors were composed of small cells with round to oval, relatively hyperchromatic nuclei and scanty cytoplasm. The tumor cells were occasionally observed in tubular formations or rosette-like arrangements. Immunohistochemically, the tumor cells showed a positive reaction for cytokeratin AE1, cytokeratin CAM5.2, Ber-EP4, antisynaptophysin and anti-S100 protein in all cases. In two cases, LH-RH was detected in the tumor cells. Ultrastructurally, the tumor cells had the differentiation features of olfactory epithelium. Olfactory neuroepithelioma is a rare occurrence and it can be very difficult to distinguish olfactory neuroepithelioma from small cell carcinoma, neuroendocrine carcinoma and so-called "olfactory neuroblastoma" on the basis of hematoxylin and eosin stained sections alone. In controversial cases, a diagnosis of olfactory neuroepithelioma must be substantiated by ultrastructural and immunohistochemical findings, particularly regarding the detection of Ber-EP4 and LH-RH immunoreactivity.