Anomalies and Normal Variants of the Cerebral Arterial Supply: A Comprehensive Pictorial Review with a Proposed Workflow for Classification and Significance

Abstract

Cerebral arteries may exhibit a wide range of variation from normal anatomy, which can be incidentally discovered during imaging. Knowledge of such variants is crucial to differentiate them from pathologies, to understand the etiology of certain pathologies directly related to a vascular variant, and to depict the changes in collateral circulation in patients with certain variants. Detection of particular variants may lead to the discovery of other nonvascular or vascular anomalies, especially aneurysms, and may also affect planning of endovascular or neurosurgical interventions. In this review, we summarize the variants and anomalies of cerebral arteries seen on cross-sectional imaging classified by a morphological approach and categorize their significance from a clinical perspective. This structured review is intended to serve as a guide for daily use in clinical practice.

Standardized Evaluation of Cerebral Arteriovenous Malformations Using Flow Distribution Network Graphs and Dual‐venc 4D Flow MRI

“…The distribution of CoW variants is consistent with population studies showing about a 0.6% prevalence of unilaterally absent PCOM, but 34% prevalence of unilaterally hypoplastic PCOM, which may contribute little hemodynamically. Notably, a previous 4D flow study found a 24–29% prevalence of variant anatomies in healthy controls (middle‐aged and older) vs. 38% in Alzheimer's disease patients in addition to significant differences in arterial PI between the groups .…”

“…The two symmetric groups had right transverse sinus predominance, which is most common on a population level 25 and consistent with previously published 4D flow results that did not distinguish between CoW morphologies, while the asymmetric left-PCOM group had reversed, left transverse sinus predominance. 26 The distribution of CoW variants is consistent with population studies showing about a 0.6% prevalence of unilaterally absent PCOM, but 34% prevalence of unilaterally hypoplastic PCOM, 27 which may contribute little hemodynamically. Notably, a previous 4D flow study found a 24-29% prevalence of variant anatomies in healthy controls (middle-aged and older) vs. 38% in Alzheimer's disease patients in addition to significant differences in arterial PI between the groups.…”

Association between the posterior part of the circle of Willis and the vertebral artery hypoplasia

“…The posterior collaterals are usually classified as one of the three variants: an adult configuration, a transitional configuration and a fetal configuration. The main difference between these variants is the relation between the diameter of P1 segment of the posterior cerebral artery (PCA) and the diameter of the posterior communicating artery (PCoA) [1], [2], [3]. The most common configuration of the posterior part of CW is described as adult configuration (Figs 1 and 2).…”

“…The presence of PCoA enables to redistribute the blood flow in both directions through PCoA in cases of diminished blood supply in the internal carotid artery (ICA) or vice versa in the vertebrobasilar system. However in more than 30% of individuals PcoA is hypoplastic or absent [3], Fig 2. In the transitional configuration which is observed in about 7% [2] of subjects the PCoA and P1 have an equal diameter.…”

“…In the minority of cases the configuration of the posterior part of CW is the so called fetal-type of the posterior circle of Willis (FCW) (or fetal PCA). FCW (Fig 3) is a morphological variant of the cerebrovascular anatomy in which P1 is smaller than PCoA and PCA arises directly from the terminal ICA, with (partial fetal) or without (full fetal) an intact P1 segment connecting PCA to the basilar artery [1], [2], [3]. In this variant, the larger brain area is dependent on ICA and could be more prone to develop large ischemic strokes in cases of carotid artery stenosis or occlusion.…”