ANATOMICAL AND CLINICAL FEATURES OF THE CIRCLE OF WILLIS: VARIATIONS AND THEIR ROLE IN CEREBROVASCULAR DISORDERS

The Circle of Willis is a major arterial anastomotic network located at the base of the brain and plays an essential role in maintaining cerebral perfusion when blood flow through one of the principal cerebral arteries is reduced or interrupted. Although the classical configuration of the Circle of Willis is frequently described in anatomical textbooks, complete and symmetrical anatomy is not present in all individuals. Variations such as hypoplasia, aplasia, duplication, fenestration, fetal-type posterior cerebral artery, asymmetry, and incomplete arterial connections are common and may influence cerebral collateral circulation. The aim of this study was to analyze the anatomical variants of the Circle of Willis and evaluate their clinical significance in cerebrovascular disorders, including ischemic stroke, intracranial aneurysm, carotid artery stenosis, and cerebral hypoperfusion. A narrative literature review was conducted using anatomical, radiological, and clinical studies focusing on the morphology of the Circle of Willis, computed tomography angiography, magnetic resonance angiography, digital subtraction angiography, cerebrovascular disease, and cerebral collateral circulation. The available evidence indicates that complete classical anatomy is present only in a proportion of the population, while hypoplastic or absent communicating arteries are among the most frequent variations.