Circle of Willis Configuration as a Determinant of Intracranial Dolichoectasia

Abstract

Background: Circle of Willis (COW) variants might influence arterial caliber in the brain. We hypothesized that these variants would be associated with the prevalence of intracranial dolichoectasia (DE). Methods: We examined COW variants and DE in a sample of stroke-free participants (n = 436) undergoing magnetic resonance angiography (MRA) as part of a population-based study. Large intracranial arterial diameters were obtained when available; if not, the artery was defined as hypoplastic or absent according to its visibility on MRA. Subscores for the anterior and the posterior circulations were created. DE was defined as arterial diameters ≥2 SD above the population mean for that artery, adjusting for intracranial volume. Generalized linear models with a Poisson distribution were used to evaluate predictors of both absent and hypoplastic vessels, and logistic regression was used to assess the odds ratio (OR) and 95% confidence interval (95% CI) of DE depending on COW variants. Results: Only 44% of the sample had all 14 arteries present, 32% lacked 1 artery, 18% lacked 2 and 6% lacked 3 or more. DE of at least 1 artery was not associated with the total number of hypoplastic or absent arteries, but DE in a posterior circulation artery was weakly associated with the number of absent arteries in the posterior circulation (β coefficient = 0.36, p = 0.06). DE of at least 1 artery was more frequent in those with 1 or more absent arteries (OR 1.27, 95% CI 1.03-1.57). Posterior circulation DE was more frequent in participants with at least 1 or more absent arteries at any location (OR 1.35, 95% CI 1.02-1.78). Participants with an incomplete posterior COW were more likely to have DE in the anterior circulation (OR 1.52, 95% CI 1.01-2.33). Having an absent left anterior cerebral artery (ACA) A1 segment was associated with right ACA DE (OR 34.1, 95% CI 3.16-368.2); an absent right ACA was associated with left ACA DE (OR 14.1, 95% CI 1.69-118.28). Absence of 1 (OR 1.9, 95% CI 1.1-3.4) or 2 (OR 3.0, 95% CI 1.4-6.6) of the 2 arteries connecting the anterior to the posterior circulation was associated with basilar artery DE. Conclusion: The COW is a pleomorphic structure that allows collateral flow to compensate for an insufficient or absent arterial component at the base of the skull. By presumed flow diversion, arteries might undergo outward remodeling. Whether this compensatory arterial dilatation is beneficial or not remains unknown.

Brain Arterial Diameters and Cognitive Performance: The Northern Manhattan Study

“…This hypothesis is supported by the fact that in the presence of a fetal PCA the anterior circulation dominates the hippocampal blood flow and function (Hendrikse, van Raamt, van der Graaf, Mali, & van der Grond, 2005) and in the reciprocal relationship between left PCA with left Pcomm. (Gutierrez et al, 2013)…”

Basilar Artery Diameter Is Inversely Associated with Fetal Type Circle of Willis

“…While the study showed that BA diameter was associated with an increased risk of adverse vascular outcomes, that evaluation was done only in participants with non-fetal types CoW, and the relevance of having lower BA diameter related to fetal type CoW was not assessed. Likewise, in the Northern Manhattan Study, smaller BA diameters were noticed in individuals with fetal type CoW, but as the authors correctly noticed, the relevance of this finding is still unknown [3]. …”

“…In this view, it is possible that a BA that is not required to provide blood supply to territories irrigated by one or both posterior cerebral arteries – as it occurs in the fetal type Circle of Willis (CoW) – is not submitted to flow-induced outward vascular remodeling, and hence has a smaller diameter. However, the influence of CoW variants in BA diameter has been evaluated only in 2 studies [3, 4], and more information is needed to confirm these findings. In this study, we aimed to assess whether BA diameter associates with the presence of fetal type CoW in community-dwelling older adults living in rural Ecuador.…”

Letter by Gutierrez et al Regarding Article, “Differential Vascular Pathophysiologic Types of Intracranial Atherosclerotic Stroke: A High-Resolution Wall Magnetic Resonance Imaging Study”

“…First, it does not take into account that the contralateral homonymous arterial diameter is affected by the collateral flow on that side, that is, if there is a large anterior cerebral artery branching off from the same internal carotid artery, the middle cerebral artery would be expected to be smaller. 2 Second, it does not take into account the normal arterial taper in size as the artery extends further into the skull, and thus the use of the proximal arterial segment as a referent may falsely lead to an overestimation of positive remodeling. Using the distal poststenotic segment is also problematic as poststenotic dilatation may occur.…”