Circle of Willis Anatomical Variations on CT Angiography: Prevalence and Clinical Associations in a Turkish Cohort

Background and Objectives: Anatomical variations in the Circle of Willis (CoW) may influence cerebral collateral pathways and the interpretation of vascular imaging. This study characterized their prevalence and clinical associations in a Turkish computed tomography angiography (CTA) cohort using complementary patient-level and component-level classifications. Materials and Methods: This retrospective, single-center study included 248 patients who underwent cranial CTA during 2024. Two radiologists independently assessed CoW anatomy, with disagreements resolved by consensus. Mutually exclusive patient-level configurations and non-exclusive arterial components were recorded. Associations with demographic and clinical characteristics were evaluated using logistic regression. Results: A normal configuration was identified in 142 patients (57.3%), and 106 (42.7%) had at least one variant. Isolated posterior communicating artery (PComA) hypoplasia/aplasia was the most frequent configuration (14.5%); PComA involvement reached 19.0% when mixed configurations were included. Isolated fetal-type posterior cerebral artery, P1 hypoplasia, and A1 hypoplasia occurred in 7.3%, 6.5%, and 4.8%, respectively. Older age (adjusted odds ratio [aOR] per 10 years, 1.57; 95% confidence interval [CI], 1.23–2.01) and migraine (aOR, 5.67; 95% CI, 2.06–15.56) were associated with variant anatomy. Previous stroke/transient ischemic attack and carotid stenosis showed inverse associations. Conclusions: CoW variants were common in this Turkish clinical cohort, particularly in the posterior circulation. Reporting both overall configurations and individual arterial components provides complementary information relevant to anatomical assessment, vascular imaging interpretation, and procedural planning.