Microanatomic Variations of the Posterior Circulation of the Circle of Willis

Aim: To study the variation in microsurgical anatomy of posterior circulation of the Circle of Willis in Chinese adult population to provide anatomical guide for high-risk vascular and cranial base surgery. Methods: Forty-six Chinese adult cadaveric brain specimens fixed in formalin were dissected, examined, measured, and photographed under light microscopy. Results: Over 60% of the posterior communicating arteries (PCoAs) in 46 cases (92 samples, both sides) were found to have differences in diameter between the 2 sides. About 50% of cases showed variation in length of >2 mm. Approximately 50% of the samples appeared to have a normal anatomic relationship between posterior communicating artery and the posterior cerebral artery (PCA). The occurrence rate of perforating branches from the precommunicating segment of the PCA (P1) was 98%. The angle of the basilar artery with bilateral PCA was measured as 45 to 150 degrees (mean 105 degrees). Conclusions: Variation in diameter, length, and/or other anatomic factors occurred in more than 50% of cases in the posterior circulation of the Circle of Willis.