Olfactory ensheathing cell tumor: a case report.

A 31-year-old Japanese woman was referred to our hospital after experiencing a convulsion. Upon radiological examination, a heterogeneously enhanced tumor was found on the anterior skull base. The tumor was surgically removed. On light microscopy, the tumor cells appeared spindle-shaped, forming an interwoven pattern. The nuclei were arranged partially parallel mimicking a palisading pattern. At first, the tumor was thought to be schwannoma. However, it was positive for S-100 and negative for both epithelial membrane antigen (EMA) and Leu7. The final diagnosis was olfactory ensheathing cell (OEC) tumor. OECs are similar to Schwann cells in microscopic appearance and upon immunohistochemical staining. However, the OECs are negative for CD57 (Leu7), while the Schwann cells are positive for it. Our patient's tumor had immunological characteristics identical to those of OEC. In the English and Japanese literature, 21 cases of solitary schwannoma on the anterior skull base have been reported. Although several theories have been suggested, the pathogenesis of subfrontal schwannoma has not been clarified. Also, OECs have never been considered as their origin. However, as in our case, OECs, rather than Schwann cells, are suspected as the origin in some of the cases.