Aneurysm mimicking intracranial growth of optic nerve sheath meningioma.

A patient with a 30-year history of blindness in the right eye developed progressive temporal visual loss in the left eye. Examination showed right optic atrophy with optociliary shunts and left band atrophy. These clinical findings suggested that the visual deficit was caused by a right optic nerve sheath meningioma that had grown intracranially to involve the chiasm. Magnetic resonance imaging and surgical exploration revealed a perioptic meningioma extending from the orbit through the optic canal and over the tuberculum sellae. The tumor did not impinge on the optic chiasm or the left optic nerve. The chiasm was compressed by a thrombosed giant right internal carotid artery aneurysm.