Can a patent extracranial-intracranial bypass provoke the conversion of an intracranial arterial stenosis to a symptomatic occlusion?

Although extracranial-intracranial (EC-IC) artery anastomosis seems to result in symptomatic improvement in certain types of cerebrovascular ischemic disease, this procedure can also be associated with significant morbidity, some of which paradoxically may be the direct result of a patent bypass. A review of the last 5 1/2 years at the Oregon Health Sciences University shows that 50 patients underwent 51 superficial temporal artery to middle cerebral artery bypass procedures with an angiographic patency rate of 91%. Of the 50 patients, 17 had intracranial stenotic lesions of either the middle cerebral artery (7 patients) or the internal carotid artery (10 patients). One patient had posterior cerebral artery stenosis. Five of the 18 patients with stenosis and a patent bypass developed a symptomatic occlusion of the stenotic lesion within 30 days after the anastomosis. It is hypothesized that the EC-IC bypass may have contributed to the occlusion in some of these patients by causing a change in the hemodynamic state. Possibly the bypass reversed the direction of flow distal to the stenosis to result in stasis and subsequent occlusion at the site of the stenosis or in some other manner affected hemostasis (i.e., the coagulation cascade).