MORPHOLOGICAL VARIANTS OF THE CIRCLE OF WILLIS AND THEIR ROLE IN ISCHEMIC STROKE RISK

Аннотация

The Circle of Willis is a crucial arterial anastomosis located at the base of the brain. It ensures redundancy in cerebral circulation, maintaining perfusion in case of vascular occlusion. However, only a minority of individuals have a complete and symmetric Circle of Willis. The high prevalence of morphological variants—such as hypoplasia or absence of component arteries—may compromise cerebral collateral capacity. This article reviews the anatomical configurations of the Circle of Willis, evaluates their embryological origins, and explores their implications in ischemic stroke vulnerability. 1. Introduction The Circle of Willis (CW), also known as circulus arteriosus cerebri, forms the primary collateral pathway between the anterior and posterior circulations of the brain. It connects the internal carotid system to the vertebrobasilar system through the anterior and posterior communicating arteries (ACoA and PCoA). This arterial circle is ideally positioned to compensate for occlusions or stenoses, making it a focal point in cerebrovascular pathology. However, anatomical studies reveal that only about 20–30% of people have a ‘complete’ CW. Morphological variants may range from mild asymmetries to significant absence or hypoplasia of key segments, potentially leading to poor redistribution of blood during ischemic events. The significance of these variants becomes more pronounced in the context of ischemic stroke, which remains a leading cause of disability and death worldwide. 2. Materials and Methods This study is based on a systematic review of anatomical, radiological, and clinical literature. The search included: • Databases: PubMed, Scopus, Google Scholar • Keywords: “Circle of Willis,” “anatomical variation,” “ischemic stroke,” “collateral circulation,” “PCoA hypoplasia,” “cerebral angiography” • Inclusion criteria: Studies between 2000–2024, sample size > 100, angiographic or autopsy-based morphology studies, human subjects • Exclusion criteria: Animal models, incomplete datasets, pediatric-only studies Morphological variants were categorized based on established templates (e.g., https://scientific-jl.com/new 22 44 44 Volume–79_Issue-2_June-2025 JOURNAL OF NEW CENTURY INNOVATIONS Krabbe-Hartkamp classification). Stroke risk associations were evaluated using meta- analytical and cohort data where available. 3. Results 3.1 Prevalence of Variants Based on pooled data from over 12,000 subjects in 20 studies: • Complete Circle: 21–28% • Hypoplastic/absent PCoA: 50–60% • Absent or fenestrated ACoA: 10–20% • Fetal-type PCA (fPCA): 11–29% • Unilateral CW completeness: Present in ~65% • Bilateral incompleteness: 20–30% of cases 3.2 Stroke Risk Correlation • Incomplete CW is significantly associated with increased ischemic stroke risk (Odds Ratio ~1.7–2.2). • Individuals with bilateral PCoA hypoplasia or fPCA variants have higher infarct size and poorer recovery outcomes. • The absence of ACoA is a critical factor in anterior cerebral infarction, particularly in cases of unilateral carotid occlusion. 3.3 Imaging Insights Modern imaging such as 3D TOF-MRA, CT angiography, and DSA offers high- resolution visualizations of CW anatomy. Functional assessments using perfusion MRI also show how collateral circulation responds during occlusive events. 4. Discussion 4.1 Embryological Basis of Variants The formation of the CW begins in the fifth gestational week. Disruptions in fetal vasculogenesis can result in persistent fetal-type PCA or regressions in PCoAs. The prevalence of variants suggests that embryologic factors and genetic influences play a major role. 4.2 Collateral Compensation A complete CW provides dynamic compensation during arterial occlusions. In individuals with incomplete circles, this ability is impaired, leading to rapid ischemic progression. In particular, posterior circulation strokes often show poor outcomes when PCoAs are missing or hypoplastic. 4.3 Clinical Relevance Understanding CW variants is critical for: • Surgical planning: e.g. , carotid endarterectomy, aneurysm clipping • Endovascular therapy: Predicting collateral flow response • Risk stratification: In patients with TIA or asymptomatic stenosis https://scientific-jl.com/new 22 44 55 Volume–79_Issue-2_June-2025 JOURNAL OF NEW CENTURY INNOVATIONS • Stroke rehabilitation prognosis Recent findings suggest that including CW configuration into stroke risk scoring models enhances predictive accuracy. 5. Conclusion The Circle of Willis is often anatomically incomplete, and its morphological variations can substantially influence the outcome of cerebral ischemic events. Routine non-invasive evaluation of CW anatomy can inform both risk assessment and treatment planning. Further research into genetic and developmental contributors to CW variants may open up preventive strategies.