Abstract DP259: Posterior Circle of Willis Variants Are Associated with Infarct Laterality and Anterior-Posterior Distribution in Patients with Small Vessel Disease

Background: Anatomical variants of the Circle of Willis (CoW) may alter compensatory perfusion during ischemia, but their contribution to small vessel disease (SVD) remains poorly characterized. This study investigated whether posterior CoW variants are associated with infarct laterality and anterior-posterior (A-P) distribution in patients with MRI-confirmed acute lacunar infarcts. Methods: A retrospective cross-sectional study was conducted among 245 patients admitted to a tertiary care hospital for acute lacunar stroke due to SVD from 2020-2024. CoW anatomy was manually adjudicated on MRA or CTA scans from institutional registries and categorized by side and presence of posterior cerebral artery (PCA), posterior communicating artery (PCoM) and fetal PCA (fPCA). Multivariable logistic regressions assessed associations of CoW variants with infarct side and A-P location, adjusting for age, sex, hypertension, diabetes, smoking, and hyperlipidemia. Results: 245 patients (102 M, 143 F; age 65.3 ± 13.3 years) were included. In multivariable logistic regression, complete left posterior circulation (intact PCA and PCoM) was associated with lower odds of left-sided infarct (OR= 0.39, p= 0.004) compared to bilaterally incomplete posterior circulation ( Table 1 ). Similarly, presence of left PCA was associated with lower odds of left-sided infarction (OR= 0.27, p = 0.016), Neither presence of left PCoM nor right sided CoW variants were significantly associated with laterality. For A-P distribution ( Table 2 ), left posterior circulation completeness was associated with lower odds of posterior infarcts (OR = 0.44, p = 0.018), as were presence of left PCoM and bilateral PCoM (OR= 0.16, p < 0.001) and (OR = 0.49, p = 0.032), respectively. Left-sided fPCA and bilateral fPCA were also associated with lower posterior infarct odds (OR = 0.17, p = 0.007) and (OR = 0.25, p = 0.006). Conclusion: In this MRI-confirmed lacunar stroke cohort, posterior CoW anatomy influenced both infarct laterality and AP distribution. Posterior circulation completeness, presence of PCoM, and fetal-type PCA were strongly associated with lower infarct risk, whereas absence of CoW vessel segments may increase vulnerability to ipsilateral infarction. These findings suggest that posterior CoW variations may contribute to hemodynamic risk in SVD. Identifying the role of CoW in collateral perfusion may improve stroke risk stratification and guide mechanistic studies.