Abstract
The main arteries that supply blood to the brain originate from the Circle of Willis (CoW). The CoW exhibits considerable anatomical variations which may have clinical importance, but the variability is insufficiently characterised in the general population. We assessed the anatomical variability of CoW variants in a community-dwelling sample (N = 1,864, 874 men, mean age = 65.4, range 40–87 years), and independent and conditional frequencies of the CoW’s artery segments. CoW segments were classified as present or missing/hypoplastic (w/1mm diameter threshold) on 3T time-of-flight magnetic resonance angiography images. We also examined whether age and sex were associated with CoW variants. We identified 47 unique CoW variants, of which five variants constituted 68.5% of the sample. The complete variant was found in 11.9% of the subjects, and the most common variant (27.8%) was missing both posterior communicating arteries. Conditional frequencies showed patterns of interdependence across most missing segments in the CoW. CoW variants were associated with mean-split age (P = .0147), and there was a trend showing more missing segments with increasing age. We found no association with sex (P = .0526). Our population study demonstrated age as associated with CoW variants, suggesting reduced collateral capacity with older age.
Highlights
The primary blood supply to the brain originates from the left and right internal carotid arteries and the basilar artery
The large sample size and recruitment of participants from the general population provide prevalence estimates of the anatomical variation in the Circle of Willis (CoW) according to our classification scheme for people between 40 to 90 years of age
Main findings were that only 11.9% had a complete textbook CoW variant, while the remaining 88.1% had one or more missing segments in the CoW
Summary
The primary blood supply to the brain originates from the left and right internal carotid arteries and the basilar artery. These arteries anastomose to form the Circle of Willis (CoW) at the base of the brain (S1 Fig in S1 File). The circular arrangement of the arteries enables the redistribution of blood flow when arteries in or upstream of the CoW experience reduced flow. This collateral ability of the CoW provides redundancy in the blood supply to the brain.
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