Extracranial-intracranial (EC-IC) arterial bypass has been used in the treatment of various neurosurgical pathologies including skull base tumors requiring sacrifice of a large intracranial artery; complex intracranial aneurysms requiring trapping; and distal revascularization, moyamoya disease, and symptomatic cerebrovascular stenoocclusive disease. The latter indication has been the subject of intense investigations in several large randomized controlled trials, most recently the Carotid Occlusion Surgery Study (COSS). In the present literature review and synthesis, the authors examine the current evidence available for EC-IC arterial bypass for the treatment of ischemic cerebrovascular disease including both extracranial carotid artery occlusive disease and intracranial atherosclerotic disease. They focus particular attention on EC-IC arterial bypass for the treatment of symptomatic hemodynamic cerebral ischemia and how lessons learned from the COSS might guide future investigations into the treatment of this disease.
Matthew R. Reynolds, Colin P. Derdeyn, Robert L. Grubb Jr., William J. Powers and Gregory J. Zipfel
Matthew R. Reynolds, Robert L. Grubb Jr., William R. Clarke, William J. Powers, Gregory J. Zipfel, Harold P. Adams Jr., Colin P. Derdeyn and for the Carotid Occlusion Surgery Study Investigators
The Carotid Occlusion Surgery Study (COSS) was a large, prospective clinical trial that examined whether superficial temporal artery–middle cerebral artery (STA-MCA) bypass, in addition to best medical therapy, reduced the risk of ipsilateral ischemic stroke in patients with carotid artery occlusion and hemodynamic cerebral ischemia. Despite improved cerebral hemodynamics and excellent bypass graft patency rates, COSS failed to show a benefit for the surgical group with respect to ipsilateral stroke recurrence at 2 years after treatment. This was due to a lower than expected rate of recurrent ipsilateral stroke in the medically treated group and a high rate of perioperative ipsilateral strokes in the surgical group. Critics of the trial have cited surgeon inexperience and technical difficulties related to the performance of the bypass graft as a leading cause of failure of the trial.
The authors retrospectively identified all patients from the COSS with an ipsilateral, perioperative (< 30 days) ischemic stroke after STA-MCA cortical branch anastomosis. Study records, operative notes, stroke adjudication forms, and imaging studies were reviewed. Ischemic strokes were characterized as bypass graft related or non–bypass graft related based on clinical and radiographic findings.
Fourteen of 93 surgically treated patients experienced an ipsilateral, perioperative ischemic stroke. Postoperatively, the mean oxygen extraction fraction (OEF) ratio between the symptomatic and asymptomatic cerebral hemisphere significantly improved in these patients (1.30 ± 0.18 preoperative vs 1.12 ± 0.11 postoperative; p = 0.02), but did not normalize. In this cohort, total MCA occlusion time during the anastomosis (54.3 ± 23.5 minutes) was no different from the MCA occlusion time in those surgical patients who did not have a perioperative stroke (45.4 ± 24.2 minutes, p = 0.2). Bypass graft patency rates in patients with a perioperative stroke were 92% at 30 days (11 of 12 patients with patency data) and 83% at last follow-up visit (10 of 12 patients with patency data). These patency rates were not significantly different from those achieved at 30 days (100%; 76 of 76 patients with patency data; p = 0.14) and at last follow-up (99%; 71 of 72 patients with patency data; p = 0.052) in patients without a perioperative stroke. Eighty-six percent (12 of 14 patients) of strokes were likely attributable to factors unrelated to the STA-MCA anastomosis. Only 21% of strokes (3 of 14 patients) were in the territory of the recipient vessel and likely related to technical performance of the anastomosis itself. One patient was thought to have dual stroke mechanisms.
Only a small minority of ipsilateral, perioperative ischemic strokes in the COSS could be attributed to technical problems of the bypass anastomosis. The majority of ischemic strokes could not be ascribed to this cause and were most likely due to patient hemodynamic fragility and the inability of patients to tolerate surgery.