Subdural hemorrhage caused by de novo aneurysm complicating extracranial-intracranial bypass surgery: case report.

A case of a de novo aneurysm leading to subdural hemorrhage after right extracranial-intracranial bypass surgery is described. After an uneventful 2-month postoperative course, the patient experienced sudden onset of occipital headache with vomiting. Radiological study disclosed an acute subdural hematoma in the right temporo-occipital region and a newly formed aneurysm at the site of patent superficial temporal artery-middle cerebral artery anastomosis. The anastomotic portion with the ruptured aneurysm was resected en bloc after alternative occipital artery-middle cerebral artery bypass, and the cut end of the superficial temporal artery was successfully used for end-to-side reanastomosis to the other middle cerebral artery branch. The histological examination of the ruptured aneurysm revealed the features of a true aneurysm.