Collateral variations in circle of Willis in atherosclerotic population assessed by means of transcranial color-coded duplex ultrasonography

Background and Purpose-Transcranial color-coded duplex ultrasonography comb ined with common carotid artery (CCA) compression can be used to assess the collateral function of the circle of Willis. The aim of this study was to assess the unknown fraction of hemodynamic functional anterior and posterio r communicating arteries (AcoA and PcoA, respectively) in an atheroscleroti c population with no cerebrovascular symptoms. Methods-In 76 patients with a mean age of 61 (35 to 89) years, the blood fl ow velocity changes in the precommunicating parts (Al and PI, respectively) of the anterior and posterior cerebral arteries were measured during CCA c ompression The AcoA was defined as functional if blood flow was reversed in the ipsilateral Al and enhanced in the contralateral Al during CCA. compre ssion. The PcoA was defined as functional if the flow velocity in the P1 wa s enhanced >20% during ipsilateral CCA compression. Results-It was possible to assess cross flow through the anterior part of t he circle of Willis in 95% of the subjects. Failure of this collateral path way was caused by a hypofunctional AcoA in 4% and a hypofunctional Al in 1% of the subjects. Anomalies in the posterior part of the circle of Willis h ampering collateral flow from the basilar to the internal carotid artery we re found in 45% of the hemispheres. Thirty-eight percent of PcoAs were hypo functional, and 7% of the posterior cerebral arteries had a persistent feta l anatomy. Conclusions-We found that in subjects with no cerebrovascular symptoms, the anterior collateral pathway of the circle of Willis was nearly always func tional. In contrast, the posterior collateral pathway was nonfunctional in almost half of the total number of hemispheres. Comparing these basic data with data from patients with cerebral ischemic disease might further help t o elucidate the importance of the collateral capacity of the circle of Will is.