Cysts of the optic nerve three cases associated with meningioma.

Cystic enlargement of the optic nerve sheath is extremely rare. Two cases secondary to a small meningioma in the orbital apex and one secondary to an intraorbital optic nerve sheath meningioma are described, a previously unreported association. High resolution CT scans or MRI can delineate quite small lesions in the orbital apex but a small meningioma within the dural sheath may be missed. Patients with an optic nerve cyst without an apparent cause should therefore be scanned over a number of years to exclude the presence of a meningioma.