Olfactory ensheathing cell tumor: case report.

Subfrontal schwannomas, sometimes referred to as olfactory groove schwannomas, are rare tumors (34 cases reported to date). Despite the name and several theories proposed in the literature, there is no officially recognized description of the tumor's cell origin. Yasuda proposed the concept of an olfactory ensheathing cell (OEC) tumor in 2006. Olfactory ensheathing cells are glial cells that ensheath the axons of the first cranial nerve. Microscopically, both olfactory ensheathing cells and Schwann cells have similar morphological and immunohistochemical features. However, immunohistochemically olfactory ensheathing cells are negative for Leu7 and Schwann cells positive. A 30-year-old woman presented with a subfrontal, extraaxial, enhancing tumor, and underwent gross total resection. Immunohistochemical reactivity data suggested a schwannoma (positive for S-100 and negative for epithelial membrane antigen). However, the tumor was negative for Leu7. Accordingly, our final diagnosis was that of an OEC tumor. Subfrontal schwannoma immunohistochemical staining, if negative for Leu7, is indicative of an OEC tumor. It is possible that schwannoma-like extraaxial tumors at the anterior skull base are OEC tumors, which negative Leu7 staining can confirm.