Extracranial-intracranial arterial bypass and basilar artery ligation in the treatment of giant basilar artery aneurysms.

Two patients with giant aneurysms of the basilar artery treated with prophylactic extracranial-intracranial arterial bypass (EIAB) to the rostral brain stem before basilar artery ligation are presented. In both cases, the bypass provided considerable collateral flow to the upper basilar, posterior cerebral, and superior cerebellar arteries. Basilar artery ligation has been shown to be an effective, albeit dangerous, means of treating giant aneurysms of the basilar artery. The risk of significant brain stem ischemia after ligation is at least 30%. EIAB to the rostral brain stem should be considered whenever basilar artery ligation is performed, especially in cases where angiography demonstrates poor collateral circulation to the distal basilar artery.