Variations in the circulus arteriosus cerebri in a South African cadaveric sample
The circulus arteriosus cerebri (CAC) or Circle of Willis is a highly variable arterial system at the base of the brain that allows for collateral blood flow, granting a protective effect during ischaemic events. Owing to variations, it may not compensate sufficiently during such events. Some CAC variations have been associated with aneurysm formation with subsequent rupture and subarachnoid haemorrhage. It is important to know the prevalence of these variations in a population. This is a cross-sectional, observational and quantitative study approved by the UCT Human Research Ethics Committee (645/2022) and the Cadaver Research Governance Committee (2022/009) in the Department of Human Biology. The brains of 94 bodies were analysed. Patency of hypoplastic arteries was investigated and Fiji® software was used to measure the lengths and diameters of arteries. Brain volumes were compared to arterial lengths and diameters and a correction factor for human variation was determined. The intact samples (n=40) were classified according to the 5-group system of Ayre et al. (2021) and 22.5% of the sample displayed the conventional anatomical pattern. The most common pattern of variation was group 5, comprising 15 different variations not matching the descriptions of groups 1-4. Individual variations were observed (n=64 brains; 81 variations). The most frequent variations were posterior communicating artery hypoplasia (17.3%) and aplasia (14.8%). The anterior communicating artery was the most variable artery (44.4% of individual variations). The narrowest artery was usually the right posterior communicating artery (PcoA) and the artery with the greatest variation in diameter was the left PcoA. Statistically significant associations were found for arterial diameter with age and length with age. Associations that were not statistically significant included variations with age, variations with sex and arterial dimensions with sex. There were too few intracranial aneurysms to perform analyses. These variations may result in an increased risk and severity of stroke and intracranial aneurysm formation. Knowledge about CAC variations will aid neurosurgeons when planning and executing a range of neurosurgical procedures. There is little published data on this topic in a South African setting and further studies are recommended.
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