Subfrontal schwannoma without hyposmia--case report

A 44-year-old man presented with a rare subfrontal schwannoma with headache. He had undergone radiation therapy for a pineal lesion 30 years previously, but the histology was not verified. On admission, neurological examination revealed no focal deficits including hyposmia. Computed tomography demonstrated a mass measuring 5 x 3 cm in the right anterior cranial fossa. Magnetic resonance imaging revealed a heterogeneously enhanced mass with multiple cysts. The tumor, which was clearly separable from the surrounding normal brain, was totally resected through a right frontal craniotomy. There was no adhesion between the tumor and the olfactory groove or cribriform plate. The frontal base dura was suspected to be the tumor attachment. The patient was discharged without hyposmia. Histological examination revealed a typical pattern of schwannoma consisting of Antoni type A and type B. Immunohistochemical staining was positive for S-100 protein but negative for epithelial membrane antigen. Subfrontal schwannoma not associated with the olfactory groove or cribriform plate is extremely rare. The operative findings and absence of hyposmia suggest that the meningeal branch of the trigeminal nerve was the origin of the tumor. However, the possibility of radiation-induced reactive Schwann cells cannot be excluded.