Association Between an Incomplete Circle of Willis and Acute Ischemic Stroke Severity at Admission: A Computed Tomography Angiography Study From Nepal

Background The Circle of Willis (CoW) is an important collateral pathway during arterial occlusion, but the clinical relevance of common anatomical variants in acute ischemic stroke remains uncertain. This study evaluates whether an incomplete CoW is associated with greater neurological severity at admission and describes CoW morphology on computed tomography angiography (CTA). Methods This hospital-based cross-sectional observational analytic study included 190 patients aged >50 years with first-ever acute ischemic stroke presenting within seven days of symptom onset and undergoing head-and-neck CTA at a teaching hospital in Kathmandu, Nepal. CoW morphology was classified using the Hartkamp framework; Type I was considered complete and Types II-IV incomplete. National Institutes of Health Stroke Scale (NIHSS) score at admission was the primary outcome, and NIHSS >15 was a secondary outcome. Multivariable linear and logistic regression and sensitivity analyses were performed. Results Among 462 patients assessed, 190 were enrolled and analyzed. Median age was 65 years (interquartile range (IQR) 60-70), and 109 (57.4%) were male. A complete CoW was present in 47 patients (24.7%) and an incomplete CoW in 143 (75.3%); Type II was most frequent (55.3%). Median NIHSS score was higher with incomplete than complete CoW, 10 (IQR 6-16) versus 8 (IQR 6-11), p=0.027. In the adjusted linear model, incomplete CoW was associated with a 1.877-point higher NIHSS score (95% CI 0.164-3.590; p=0.032), although the effect was modest and model explanatory power was limited (adjusted R²=0.073). There was no significant NIHSS gradient across Hartkamp Types I-IV (p=0.167). In the anterior-circulation-only analysis, the adjusted coefficient was 1.810 (95% CI -0.023 to 3.643; p=0.053). Timing-restricted analyses showed similar or slightly larger coefficients. Exploratory regional morphology analysis was not significant overall (p=0.079). For NIHSS score >15, incomplete CoW was associated with higher odds in both the five-predictor model (aOR=3.79, 95% CI 1.23-11.64; p=0.020) and parsimonious model (aOR=3.65, 95% CI 1.20-11.14; p=0.023), although CIs were wide. Conclusions Incomplete CoW anatomy was common and was associated with higher NIHSS score at admission after adjustment, but the primary continuous effect was modest. The absence of a monotonic Hartkamp severity gradient, non-significant regional analyses, and attenuation in the anterior-circulation model argue against using binary CoW completeness as a stand-alone marker of collateral capacity. The NIHSS score >15 association was imprecise and should be interpreted cautiously. CoW morphology should be considered within the broader vascular and clinical context.