Abstract Body: Introduction
Patients with chronic carotid occlusion (CCO) may present as either symptomatic or asymptomatic, with significant differences in prognosis and treatment strategies between these groups. Anterograde collateral circulation, particularly through the Circle of Willis (CoW), is essential for sustaining adequate cerebral blood flow in CCO patients. This study aimed to evaluate the association between collateral pathways within the CoW and the symptomatic status of patients with CCO.

Methods
This retrospective cohort study was conducted across two large comprehensive stroke centers in Turkey and the US, and included patients with CCO treated between January 2018 and December 2023. The Circle of Willis (CoW) was assessed using a combination of CTA, MRA, and DSA, focusing on the visualization and diameter of the following arteries: the anterior communicating artery (AcoA), the first segment of the anterior cerebral artery (A1), the posterior communicating artery (PcoA), the first segment of the posterior cerebral artery (P1), the ophthalmic artery (OA), and the fetal posterior cerebral artery (FPCA). Symptomatic status was defined as any TIA/stroke ipsilateral to the occluded ICA. Multivariable logistic regression was employed to evaluate the independent association between the visualization/presence and size of these arteries and symptomatic status.

Results
205 patients were included in the study, of whom 153 were symptomatic and 52 asymptomatic. The median age was 67 yrs. [IQR 59–76], and 26.8% were women. Patients in the symptomatic group were younger (median age 64 yrs. [58-72] vs. 75 [68-80], p<0.001), and had lower rates of prior treatment with antiplatelets (63.4% vs. 84.6%, p=0.04) and contralateral ICA severe stenosis (16.5% vs. 30%, p=0.010). Patients with symptomatic status had significantly smaller diameters of the AcoA (median diameter 1.64 vs. 1.91 mm, aOR 0.09, p=0.003), A1 (median diameter 1.81 vs. 1.91 mm, aOR 0.20, p=0.017), and PcoA (median diameter 1.28 vs. 1.49 mm, aOR 0.21, p=0.029), compared to patients in the asymptomatic group (Figure 1).

Conclusion
The size of the arteries within the Circle of Willis, serving as a surrogate for anterograde flow, may represent an important parameter to consider in identifying high-risk patients who may not respond adequately to medical therapy.