Embolization from a fusiform middle cerebral artery aneurysm.

A 34-year-old man had a transient ischemic attack and subsequently a completed stroke. Arteriography revealed a large fusiform aneurysm of the left middle cerebral artery with intraluminal thrombus. At surgery, the thrombus was seen within the lumen of the aneurysm. Absolute evidence for embolization is lacking as no examination for this could be done. Embolization from intracranial aneurysms seems to occur exclusively in large or giant aneurysms. Turbulent flow and a "stagnant zone" probably promotes thrombus formation. The reasons for the relative rarity of subsequent embolization are discussed. Because embolization from intracranial aneurysm is so uncommon and because aneurysms usually produce focal deficit by other mechanisms, 4 criteria are presented to determine whether embolization is likely.