Morphological evaluation of completeness of Circle of Willis

The cerebral vascular supply has always stirred interest among researchers since ischemic stroke in 30% cases can be managed by early intervention and reperfusion of brain tissue. Variations of collateral arterial circle at the base of brainor Circle of Willis are not uncommon which can be dated back to embryological causes. The aim of the study is to update the variations and to propose a clinically applicable simple classification for completeness of Circle of Willis. The present study was done on 65 formalin fixed adult human brains of both genders. Each component of the circle was observed carefully and the external diameters were measured. Accordingly, the vessels were defined into different categories as classical, narrow and hypoplastic as per their diameter. Absence of any segment was taken into account. Consequently, the circles were classified into Type I, II, III and IV as per presumed functional competence. 30.8% of the circles were found to be complete. In anterior segment fused cerebral artery and aplastic communicating artery were the commonest variations. In the posterior segment, narrow cerebral artery and fetal type of communicating artery were encountered most frequently. Hypoplasia and aplasia were more on the right posterior segment of the circle. P value for means of right and left side variations was statistically significant (p < 0.0001). Fetal PCoA was the most common variation noted. Incidence of hypoplasia was more common in cerebral arteries as opposed to aplasia, which was more common in communicating arteries. Type II was the most common variant. Left posterior quadrant had the highest incidence of incompleteness.