Splitting and penetration of the optic nerve by an aneurysm arising from the anterior wall of internal carotid artery: case report.

Aneurysms arising from the anterior wall of the internal carotid artery (ICA) are uncommon. There have not been any reports demonstrating the anatomical relation of such aneurysms to the optic nerve. An aneurysm arising from the anterior wall of the ICA splitting and penetrating the optic nerve is reported. A 73 year old woman presented with severe headache due to subarachnoid haemorrhage. She had never experienced a visual disturbance. At surgery, the aneurysm was shown to arise from the anterior wall of the left internal carotid artery and to split and penetrate the left optic nerve. The aneurysm was not related to arterial bifurcation of any branches and was safely neck clipped. Given the evidence of a split and penetration of the optic nerve, the pathogenesis of such an aneurysm may be due to the persistence of an embryonic vessel.