Patterns of Circle of Willis Variants among Patients Undergoing 3 Tesla Magnetic Resonance Angiography at a Tertiary Care Hospital: An Observational Study

Abstract

Introduction: The Circle of Willis (CoW) is a crucial cerebral arterial network, and its anatomical variations may influence cerebrovascular health. This study aimed to determine the prevalence and patterns of CoW variants using 3 Tesla magnetic resonance angiography.

Methods: This retrospective cross-sectional study was conducted at the Department of Radiology, of a tertiary care center, Nepal, from October 2022 to September 2024 following ethical approval (IRC- 16/2024). Inclusion required adequate 3T MRI imaging using a TOF MRA protocol. (TR 20 ms, TE 3.5 ms, flip angle 15°, slice thickness 0.5 mm). Patients with cerebrovascular disease, prior interventions, or contraindications were excluded. Circle of Willis morphology was analyzed for prevalence, variants, and age/gender correlations using SPSS and Excel.

Results: The study included 384 participants of which 206 (53.65%) were male. The mean age was 59.20±16.30 years. A complete Circle of Willis (COW) was observed in 139 (36.19%), while 220 (57.39%) were incomplete. Anterior anomalies 126 (32.81%) primarily consisted of hypoplasia 95 (75.40%), right A1 dominance and absence 24 (19.05%). Posterior variants 345 (89.84%)  involved hypoplasia 155 (44.93%) or absence 189 (54.78%) of the posterior communicating artery, with fetal PCA origin in 121 (31.51%).
Conclusions: This study found common Circle of Willis variations, especially in older adults. Hypoplasia of the posterior communicating artery was the most frequent variation, with differences observed by gender.