C HAPTER External Carotid Endarterectomy : 53 Indications , Techniques , and Results

Naturally occurring collatera l pathways con necting the external carotid artery branches and the intracran ial cerebral circulation are well recognized and have been demonstrated anatomically, angiographically, and physiologically by vari­ ous flow detection devices. Under normal c ircumstances, all internal carotid artery blood flow is direc ted intracranially, and flow through the co ll ateral pathways is from intracranial vessels to the external carotid artery branches , Similarly, ocular blood supply is derived predominantly from the inter­ nal carotid artery via the ophthalmic artery, Thus, normally the external carotid arteries do not contribute significantly to intracranial or ocular blood flow. In the case of internal carotid artery occlusion, the direction of flow in the collateral pathways reverses , and flow courses from the external ca­ rotid branches to the intracranial branches of the internal carotid artery, Thus, with occlusion of the internal carotid artery, the ex ternal carotid artery may become an important source of blood flow to the brain. Occlusive or atheromatous changes in the ex ternal carotid artery can lead to transient ischemic episodes or amaurosis fugax w hen they are ips ilateral to an occluded internal ca­ rotid artery. These sym ptoms arise by the same physiologic mechanisms observed with the internal carotid artery , that is, embolization or hypoperfusion. A number of investigators have demonstrated the potential for increas ing cerebral blood fl ow in patients with ipsilateral internal carotid artery occlu­ sion and external carotid artery stenosis by external carotid endarterec tomy .'-' Emboli zation to the external caro tid artery from the blind cul-de-sac of an occluded inte rnal carotid artery can al so be re lieved by external carotid artery endar­ terectomy. Thi s chapter focu ses on the indications, techniques, and results for external carotid endarterectomy pelformed alone for symptoms of cerebral or ocular ischemia with ipsi lateral internal carotid artery occlusion,