Dissecting aneurysms of the anterior circle of Willis arteries. Report of two cases.

Two cases of spontaneous dissecting aneurysm extending from the supraclinoid portion of the internal carotid artery to the middle cerebral artery are reported in two teenaged patients. Both patients collapsed with a headache on the right side, left hemiparesis, and altered consciousness due to cerebral ischemia. One patient became alert in 2 days; however, his condition rapidly deteriorated 4 days later and he died on the 8th day from massive cerebral infarction. The other patient received a right superficial temporal artery (STA)-middle cerebral artery (MCA) anastomosis 50 hours after his initial symptoms. He improved gradually and is able to walk without help. Cerebral angiograms 3 months after the operation disclosed progressive attenuation of the MCA and dilatation of the anastomosed STA. Artificial collateral flow demonstrated in the postoperative angiogram may have been useful in preventing massive cerebral infarction.