Development, Anatomical Variations, and Clinical Implications of The Circle of Willis: A Review Article | ||
| The Egyptian Journal of Hospital Medicine | ||
| Volume 101, Issue 1, October 2025, Pages 5403-5408 PDF (722.32 K) | ||
| Document Type: Original Article | ||
| DOI: 10.21608/ejhm.2025.463875 | ||
| Abstract | ||
| The Circle of Willis (CW) (also known as Willis’ circle, loop of Willis, Willis’s polygon, or cerebral arterial circle) is a polygonal arterial network that forms a vital anastomotic system at the base of the brain, ensuring collateral blood flow between the anterior and posterior cerebral circulations. It is conserved across several vertebrate species, including birds, reptiles, and mammals, and is named after the English physician Thomas Willis (1621–1675). Its embryological development involves a coordinated sequence of vascular remodeling events derived from the primitive internal carotid and vertebrobasilar systems, establishing the mature cerebral arterial configuration during early gestation. However, substantial anatomical variations exist, with the classical complete configuration found in only about one-third of individuals. These variations significantly influence cerebral hemodynamics, affecting compensatory mechanisms in vascular occlusion and susceptibility to pathological changes. Consequently, they hold major clinical implications in the pathophysiology and management of aneurysm formation, ischemic stroke, subarachnoid hemorrhage, and other cerebrovascular disorders. Understanding the developmental origins, morphological diversity, and functional consequences of these variations is therefore crucial for improving diagnostic accuracy, guiding neurosurgical and endovascular interventions, and enhancing patient outcomes. This review aims to summarize the embryological development of the CW, delineate common and rare anatomical variants, and explore the clinical implications of these differences in stroke, aneurysm pathogenesis, and neurosurgical or interventional practice. | ||
| Keywords | ||
| Circle of Willis; Embryological development; Anatomical variation; Aneurysm; Ischemic stroke | ||
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