Anatomical Variations of the Circle of Willis on Noncontrast Time-of-flight Magnetic Resonance Angiography in Ischemic Stroke Patients

Background: The circle of Willis (CoW) is the principal intracranial collateral arterial network. Variations in its configuration may influence cerebral perfusion and stroke distribution. Data correlating CoW variants with ischemic stroke patterns in large Indian cohorts remain limited. Aim: The aim of this study was to evaluate anatomical variations of the CoW using noncontrast three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography in ischemic stroke patients and assess their clinical relevance in relation to stroke distribution. Materials and Methods: This prospective cross-sectional study with retrospective image analysis included 2000 adult patients with magnetic resonance imaging-confirmed ischemic stroke (January 2022–June 2025). Noncontrast 3D-TOF MR angiography was performed on a 1.5 T scanner. CoW configurations were classified using standardized criteria. Vessel diameters were measured on source images. Stroke territories were categorized as anterior or posterior circulation infarcts. Statistical analysis included Chi-square and Mann–Whitney U tests. Results: A complete CoW was observed in 54% of patients, while 46% demonstrated partially complete and incomplete configurations. Posterior circulation incompleteness (43%) was significantly associated with posterior circulation infarcts ( P = 0.02). The mean vessel diameter was significantly greater in complete CoW configurations (1.20 ± 0.3 mm) compared to incomplete configurations (0.81 ± 0.2 mm; P < 0.001). Conclusion: Incomplete posterior CoW configurations are significantly associated with posterior circulation infarcts and reduced vessel caliber, highlighting their hemodynamic and clinical relevance in ischemic stroke. Routine reporting of CoW anatomy may improve risk stratification and management planning.