Accessory middle cerebral artery as a source of collateral blood flow.

A previously healthy 15-month-old girl became pale and lethargic. CT showed subarachnoid hemorrhage. Cerebral angiography showed a 5-mm aneurysm in the M1 segment of the left middle cerebral artery (Fig. 1 A). The anterior cerebral artery was not visualized on the left carotid artery angiogram. Both anterior cerebral arteries filled from the right carotid injection. An additional vessel originated near the anterior communicating artery and extended into the left sylvian cistern (Fig. 1 B). Intraoperatively, one of the lenticulostriate arteries was detected arising from the aneurysm. The aneurysm was clipped. No intraoperative complications were reported. Postoperatively the patient was neurologically intact. CT performed the day after surgery showed a small lentiform nucleus infarction. An angiogram performed 6 days after surgery showed a clip at the site of the aneurysm. The left middle cerebral artery did not fill from the left carotid artery injection (Fig . 1 C). Delayed filling of peripheral middle cerebral artery branches through posterior cerebral artery collaterals was seen. Injection of the right carotid artery showed increased opacification of the left insular vessels via the accessory left middle cerebral artery (Fig. 1 D). One month after discharge, the patient was examined again . She was doing well clinically .