A multitude of variations in the configuration of the circle of Willis: an autopsy study.

The circle of Willis (CW) is an anastomotic system of arteries located at the base of the brain. The aim of the study was to evaluate the anatomic configuration of the CW in the Polish population and to compare results with previously conducted research. Brains were obtained from 100 recently deceased human adults, and the diameters of cerebral vessels were measured using a slide caliper. Cerebral vessels were observed, paying attention to their origin, diameter, typical configuration and variations. Twenty-seven percent of cases presented the typical literature pattern. The remaining 73 % of all cases were atypical; in 16 % the CW was incomplete and in 57 % complete. Atypical findings involved the posterior communicating artery (PcomA), 62 %; anterior communicating artery (AcomA), 22 %; anterior cerebral artery (ACA), 14 %; posterior cerebral artery (PCA), 8 %. The most common variations were bilateral hypoplastic PcomAs (27 % of cases) and unilateral hypoplastic PcomAs (19 % of cases). Only 9 of the 22 types of CW variations classified previously in the literature were observed, and 26 variations (36 cases) in our study were labeled as 'other' type. Mean diameter values for typical CW patterns were internal carotid artery = 3.6 mm, ACA = 2.3 mm, AcomA = 1.9 mm, PCA = 2.2 mm and PcomA = 1.4 mm. Circle of Willis variations have a large impact on clinical practice. This study shows many rare variations that should be taken into consideration to avoid any unexpected complications during surgical procedures involving cerebral vessels.