Anatomical variations of cerebral blood vessels and their clinical significance in cerebrovascular diseases: A narrative review

Cerebral arterial anatomy exhibits substantial interindividual variation, particularly within the circle of Willis and the branching patterns of the anterior, middle, and posterior cerebral arteries. Such differences are relevant to collateral circulation, interpretation of vascular imaging, planning of endovascular or microsurgical procedures, and assessment of selected cerebrovascular disorders. This narrative review synthesizes anatomical and clinical literature on developmental mechanisms, common configurations, diagnostic visualization, and potential implications of cerebral arterial variants. Particular attention is given to hypoplasia or absence of communicating segments, fetal-type posterior cerebral artery, anterior cerebral artery variants, and middle cerebral artery branching patterns. Available studies demonstrate marked heterogeneity in the reported frequency of these configurations, partly because definitions, imaging techniques, and sampled populations differ. An incomplete circle of Willis may limit certain collateral pathways under hemodynamic stress, but the presence of an anatomical variant does not, by itself, establish an individual risk of stroke or aneurysm. A clinically meaningful assessment therefore requires integration of vascular morphology with vessel caliber, collateral function, clinical presentation, and imaging findings. The review highlights the need for standardized anatomical terminology and cautious interpretation of observational associations.