The Role of Extracranial–Intracranial Bypass in Current Practice

Historical Perspective

The first EC-IC bypass was reported by Donaghy and colleagues in 1967, and the procedure was in widespread use during the following decade. The most commonly performed variation was the superficial temporal artery–to–MCA bypass. Initial nonrandomized retrospective and prospective studies supported the safety and efficacy of the procedure. In addition to studies demonstrating an improvement in cerebral hemodynamics following EC-IC bypass based on functional imaging, improved clinical outcomes were demonstrated as well, especially in patients with poor collateral circulation. One study demonstrated that in 49 patients who presented with an ICA occlusion, treatment that included performing an EC-IC bypass was particularly effective for patients who were symptomatic or who had significant contralateral carotid artery stenosis.

Two randomized trials have been performed since the inception of the procedure. The first and larger was the EC-IC Bypass Study Group trial that was conducted in the mid-1980s. The EC-IC Bypass Study Group trial was designed as an international multicenter prospective randomized trial that evaluated the use of EC-IC bypass for treating symptomatic cerebrovascular stenosis or occlusion. Patients were evaluated who presented with one or more transient ischemic attacks (TIAs), or strokes with associated stenosis, or occlusion in the affected ICA or MCA distributions. Cerebrovascular lesions were stratified according to the following anatomic landmarks: ICA occlusion, stenosis of the ICA above the second cervical vertebrae (C2), and MCA stenosis or occlusion.

A total of 1377 patients were randomized to either EC-IC bypass ( n = 714) or best medical management ( n = 663). Best medical management at the time consisted of acetylsalicylic acid (325 mg up to four times per day) with appropriate control of hypertension. The mean follow-up interval was 56 months. In the surgical group, postprocedural angiographic patency was achieved in 96% of patients. Within the surgical group, the postoperative mortality and stroke rates were 0.6% and 2.5%, respectively. There was a nonsignificant trend toward increased nonfatal and fatal strokes in the surgical group as compared with the medically treated group. Subset analyses suggested that patients with severe MCA stenosis or occlusion of the ICA fared worse. Regardless, statistical significance was not achieved for any of the primary outcomes within the study. The study concluded that EC-IC bypass failed to demonstrate benefit in preventing ischemic events postoperatively as compared with medical management.

The most recently completed randomized trial was the Japanese EC-IC bypass trial (JET). The trial studied 195 patients who were symptomatic and who exhibited cerebrovascular hemodynamic compromise as measured by functional imaging; these patients were randomized to EC-IC bypass or to best medical care. The average follow-up was 25 months, and mortality rates were low for both groups (surgery, n = 2; medical, n = 1). Moreover, there were no significant differences between the surgical and medical treatment groups in all other adverse events measured. The trial concluded that there were no significant differences in outcomes between the surgical and medical groups.

Multiple criticisms were raised against both trials. The EC-IC Bypass Study Group was criticized for having inadequate randomization with regard to baseline criteria. Only stable low-risk patients were included in the study, which did not necessarily reflect the group that was being treated in the general population. In addition, there was no stratification for cerebrovascular hemodynamic compromise. More specifically, patients with embolic strokes but adequate collateral flow from the contralateral circulation as evidenced by functional imaging were not differentiated from stroke patients with compromised cerebrovascular hemodynamics. Despite these criticisms, EC-IC bypass procedure volume diminished significantly in subsequent years.

The Carotid Occlusion Surgery Study (COSS) is a randomized control trial that is under way to reassess outcomes for EC-IC bypass. The study is designed to evaluate patients specifically with cerebrovascular hemodynamic compromise ipsilateral to a symptomatic carotid occlusion as measured by oxygen extraction fraction using positron emission tomography (PET). The hypothesis is that patients with impaired hemodynamics, whose strokes result from a low-flow state, might benefit preferentially from an EC-IC bypass.

Procedural Characteristics