Anatomical Variations of the Circle of Willis as seen at the University Teaching Hospital,Lusaka,Zambia

Abstract

ABSTRACT

BACKGROUND: The ideal distribution of blood to the brain and the collateral potential of the Circle of Willis (CW) is believed to be dependent largely on the morphology and the presence of all the component vessels of the CW. However, there is a considerable individual variation in the pattern and calibre of vessels that make up the CW. The anatomical variations of the CW that have been observed may affect the occurrence and severity of symptoms of cerebrovascular disorders such as stroke, aneurysms, infarctions among others. The study aimed to determine the anatomical variations of the CW as seen at the University Teaching Hospital, Zambia.

METHODS: A cross-section design was used to ascertain variations in 185 postmortem brains with respect to completeness of the circle, aneurysms and external diameter of the posterior communicating arteries (PcoA). The circle completeness was observed whereas the external diameter of the PcoA was measured using a digital vernier caliper. The median diameter was chosen to describe hypoplasia with a cutoff point at less than 1mm chosen based on earlier reports from other autopsy studies. Photographs were taken after dissection using a digital camera Canon power shot SX400IS 16 mega pixels. The brain specimen was placed back into the cranium upon completion of the examination. STATA version 12.0 was used for data analysis.

RESULTS: Out of a sample of 185, the proportion of males 149 (80.5%) were significantly higher (p < 0.0001) than females 36 (19.5%). Complete CW was found in 90.3% of the cadavers. Hypoplasia of the PcoA was noted in 30.3% on the right and 36.2% on the left side. The median age for individuals with hypoplasia (<1.0mm) of the right PcoA was 48 years (range; 17-86) and those without it was 34 years (1772); the medians were statistically different (p < 0.0001). In case of hypoplasia of the left PcoA, the median age for the affected was 46 years (range; 17-86) and for those unaffected was 33 years (range; 17-75); there was a statistical difference, p < 0.0001. Multivariate analysis showed that one unit increase in age statistically increased the likelihood of having hypoplasia of the left and right PcoA by 9% (OR 1.09; 95%CI 1.06, 1.12; p < 0.001) and 10% (OR 1.10; 95%CI 1.06, 1.13; p < 0.001) respectively.

CONCLUSION: The study revealed significant variations in the CW in the brain specimens studied at the University Teaching Hospital, Zambia. Hypoplasia in the PcoA was the most common noted variation with CW incompleteness in a few cases. No aneurysm was observed. These anomalies could predispose one to developing neurological deficit especially in patients with internal carotid artery (ICA) occlusion. Studying the variability of the CW is important academically and for clinical reasons because such considerations can influence the mode of presentation, plan of investigation and treatment of various neurological disorders.

Key Words: Circle of Willis, Anatomical Variations, Hypoplasia, Posterior communicating arteries.