Walsh & Hoyt: Location and Laterality

Aneurysms may originate from any of the intracranial arteries. Although there is some discrepancy not only between clinical (angiographic) and autopsy studies but also among individual clinical or autopsy studies, it is clear that about 85% of all intracranial aneurysms originate from the ICA or one of its branches. The most frequent site of origin is the ICA itself. About 2540% of all intracranial aneurysms arise from the main trunk of this vessel, usually at the origin of the posterior communicating artery, but also at its terminal bifurcation, at the origin of the ophthalmic artery, or within the cavernous sinus. Another 2530% of aneurysms originate from the anterior communicating artery. The MCA is the site of origin of about 1330% of all intracranial aneurysms. Thus, nearly all intracranial aneurysms originate from the internal carotid, anterior communicating, or middle cerebral arteries. The remaining vessels from which a significant number of aneurysms arise are the basilar artery (3%9%), the distal ACA (5%), and the vertebral artery (4%5%). In most series, aneurysms that occur on paired vessels are randomly distributed on the right or left side.