Olfactory groove schwannoma masquerading as an orbital mass.

Olfactory groove schwannoma is a very rare tumor breaking through the skull base and orbit. The tumor may also extend to the subfrontal region intradurally. A case of olfactory groove schwannoma in a 35-year-old female, originating from the left olfactory groove with left proptosis, diplopia, supra-orbital mass, and gross intracranial extension is reported. The presence of bony scalloping on CT and absence of meningeal tail on contrast enhanced MRI are in favor of the diagnosis. Histological examination and immuno-histochemical evaluation for S-100 protein, showed the tumor as a schwannoma. Total excision through a frontal craniotomy and skull base reconstruction are the main therapeutic steps.