The anatomy of the circle of Willis as a predictive factor for intra-operative cerebral ischemia (shunt need) during carotid endarterectomy.

The collateral flow to the cerebral hemisphere after carotid cross clamping during carotid endarterectomy is mainly through the circle of Willis, and the circle is incomplete in the majority of cases. A correlation between the status of the circle of Willis and the necessity of shunting was evaluated in 67 carotid endarterectomies with pre-operative four-vessel cerebral angiogram. All carotid endarterectomies were performed with selective shunting, based on the change of consciousness and motor function after carotid test clamping under regional anesthesia. Of the 55 patients with either an anterior or a posterior communicating artery, only four (7.3%) required shunting. Twelve patients had neither anterior nor posterior communicating artery, and 10 (83.3%) showed signs of cerebral ischemia necessitating shunting. Mandatory shunt was significantly higher in patients with absence of collaterals (p = 0.00). The rate of intraoperative cerebral ischemia was significantly higher in patients with poor collateral circulation defined by the anatomy of the circle of Willis.