Fatal complication of the "bonnet bypass": case report.

A patient with transient ischemic attacks and an occluded right common carotid artery underwent a left superficial temporal artery to right middle cerebral artery vein graft (bonnet bypass). One week after operation, minor trauma to the scalp caused avulsion of the anastomosis and a massive fatal acute subdural hematoma. The mechanism of the vascular avulsion and precautions to be taken to avoid such problems in other patients undergoing this procedure are discussed.