Background: The Circle of Willis (CoW) is the principal collateral arterial network at the base of the brain, yet fewer than half of individuals exhibit its textbook complete configuration. Anatomical variation of the CoW has been repeatedly implicated in cerebrovascular risk, stroke topography, and intracranial aneurysm formation, but the evidence remains scattered across heterogeneous case studies and primary research designs.

Methods: This scoping review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) framework. PubMed, Google Scholar, Taylor & Francis Online, Scopus, and ScienceDirect were searched for English-language case studies and primary research articles published between 2000 and 2026. Screening and eligibility assessment were conducted in duplicate against predefined inclusion and exclusion criteria.

Results: Forty-eight primary studies met inclusion criteria, comprising cadaveric dissections, magnetic resonance and computed tomography angiography cohorts, case-control investigations, and individual case reports. Pooled findings indicate that CoW variation occurs in approximately 50–70% of individuals, with posterior communicating artery hypoplasia/aplasia and anterior communicating artery anomalies being the most frequent configurations. Incomplete configurations were consistently associated with larger infarct volumes, altered stroke topography, and increased odds of anterior communicating and posterior communicating artery aneurysms.

Conclusion: CoW anatomical variation is common, clinically consequential, and population-dependent. Standardized preoperative angiographic characterization of the CoW is recommended to guide cerebrovascular risk stratification, stroke management, and neurosurgical or endovascular planning.