Optic nerve penetration by a carotico-ophthalmic artery aneurysm.

Fenestration of a cranial nerve by an internal carotid artery aneurysm is rarely identified at surgical repair of intracranial aneurysms. Classically this condition is associated with visual disturbance in either acuity, fields or diplopia. We describe a patient with optic nerve fenestration by a carotico-ophthalmic artery aneurysm and discuss its likely pathophysiology. It is important to consider this anatomical variation during microsurgical approaches to the pericarotid and perioptic cisterns to prevent inadvertent damage to the optic apparatus.