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Anatomical variations of the circle of Willis and their prevalence, with a focus on the posterior communicating artery: A literature review and meta-analysis

Jones, Joshua D.; Castanho, Pedro; Bazira, Peter; Sanders, Katherine


Joshua D. Jones

Pedro Castanho

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Dr Kat Sanders
Senior Lecturer in Clinical Anatomy


The circle of Willis is an anastomotic network of arteries surrounding the base of the brain, providing collateral circulation to prevent ischemia. It has, however, long been established that it exhibits considerable anatomical variation when compared to Thomas Willis' originally described circle. This study aimed primarily to determine an accurate prevalence of the variation of the circle of Willis in the general population and the prevalence of common posterior communicating artery variations. Additional aims were to explain why such a wide range of reported variations exist, and whether different types of studies report significantly different prevalence of variation. A comprehensive literature search identified 764 papers. A three-phase screening process was undertaken, involving a critical analysis of papers, and a total of 33 papers were selected for analysis and literature review. A descriptive statistics test with bootstrap was performed to estimate the average prevalence of variations. The estimated prevalence of general variation, unilateral, and bilateral posterior communicating artery hypoplasia or aplasia was 68.22 ± 14.32%, 19.45 ± 8.63%, and 22.83 ± 14.58%, respectively. Over half of the population exhibit a circle of Willis with some form of variation. To provide a more accurate estimation for the prevalence of variations, a universal classification system needs to be established, collating all the work from high-quality studies, to provide a comprehensive database of the circle's variations. Knowing the prevalence of variations and how they can impact neurosurgical approaches or patterns of ischemic pathology can be crucial in providing effective patient care.


Jones, J. D., Castanho, P., Bazira, P., & Sanders, K. (2021). Anatomical variations of the circle of Willis and their prevalence, with a focus on the posterior communicating artery: A literature review and meta-analysis. Clinical Anatomy, 34(7), 978-990.

Journal Article Type Review
Acceptance Date Jul 20, 2020
Online Publication Date Jul 26, 2020
Publication Date 2021-10
Deposit Date Jan 4, 2022
Publicly Available Date Jan 5, 2022
Journal Clinical Anatomy
Print ISSN 0897-3806
Electronic ISSN 1098-2353
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 34
Issue 7
Pages 978-990
Keywords Cerebral arterial circle; Circle of Willis; Communicating; Hypoplasia; Posterior; Variation
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Copyright Statement
© 2020 The Authors. Clinical Anatomy published by Wiley Periodicals LLC on behalf of American Association of Clinical Anatomists.

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

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