Anatomical Variations of the Circle of Willis and Their Clinical Significance: A Systematic Review
Anatomical Variations of the Circle of Willis and Their Clinical Significance
DOI:
https://doi.org/10.54393/pjhs.v7i6.3889Keywords:
Circle of Willis, Anatomical Variation, Collateral Circulation, Ischemic Stroke, Intracranial Aneurysm, Magnetic Resonance Angiography, Computed Tomography AngiographyAbstract
The Circle of Willis (CoW) is the principal intracranial collateral network connecting the anterior and posterior cerebral circulations. Anatomical variations of the CoW are common and may influence cerebral hemodynamics, collateral capacity, ischemic stroke outcomes, and aneurysm development. However, contemporary imaging-based evidence regarding their clinical significance has not been systematically synthesized. Objectives:
To systematically review recent human imaging studies (2020–2025) evaluating anatomical variations of the Circle of Willis and their reported clinical associations. Methods: A systematic search of PubMed, Scopus, and the Cochrane Library was conducted following PRISMA 2020 guidelines. Original human studies assessing CoW anatomy using computed tomography angiography (CTA), magnetic resonance angiography (MRA), or conventional angiography were included. Data extracted included study design, population characteristics, imaging modality, prevalence of major variants, and clinical associations. Risk of bias was assessed using a qualitative domain-based approach. Due to methodological heterogeneity, findings were synthesized narratively. Results: Eighteen imaging-based studies were included. Incomplete CoW configurations and posterior communicating artery hypoplasia/aplasia were the most frequently reported variants, with incomplete configurations reported in 30–70% of participants. Several studies demonstrated associations between incomplete configurations and poorer ischemic stroke outcomes, vulnerable intracranial plaque features, and increased odds of intracranial aneurysm. Fetal-type posterior cerebral artery and A1 segment asymmetry were linked to distinct hemorrhagic and aneurysmal patterns. Conclusions: Anatomical variations of the Circle of Willis are highly prevalent and clinically relevant. Standardized reporting of CoW configuration may enhance cerebrovascular risk stratification and inform neurovascular decision-making.
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