ABSTRACT NUMBER: ESOC2026A349 NOVEL FOUR-TYPE CLASSIFICATION OF CIRCLE OF WILLIS COLLATERALS: PROGNOSIS IN MT FOR ACUTE TERMINAL ICA OCCLUSION

Abstract Background and aims Acute terminal internal carotid artery (ICA) occlusion has a poor prognosis despite successful mechanical thrombectomy (MT), due largely to inadequate Circle of Willis collaterals. Existing classifications fail to capture functional collateral sufficiency. We aimed to propose and validate a novel four-type anatomical-functional classification to stratify prognosis after MT. Methods In this retrospective study, 142 patients with acute terminal ICA occlusion and successful reperfusion (mTICI 3) were classified using pre-interventional CTA/DSA: Type A (patent ACoA), B (non-patent ACoA), C (absent contralateral A1), and D (absent A1 with fetal-type PCA). A compromised Type A-C subtype was defined by hypoplastic A1 (diameter <30% of ipsilateral) or ACoA providing ASITN/SIR grade ≤2 flow. The primary outcome was favorable 90-day functional outcome (mRS ≤3). Results Type A demonstrated the highest rate of favorable outcome (54.29%), significantly superior to Types B (10.81%) and C (7.69%) (all P<0.0083). Type D had a numerically lower rate (11.11%). Malignant cerebral edema and 90-day mortality were significantly higher in Types B, C, and D versus Type A. Within Type A, the compromised subgroup (A-C) had significantly worse outcomes than the non-compromised (favorable mRS: 14.29% vs. 64.29%; malignant edema: 64.29% vs. 5.36%). Conclusions This four-type classification based on functional Circle of Willis integrity effectively stratifies post-MT prognosis. It identifies Type A (especially non-compromised) patients as optimal candidates, while Types B, C, D, and the compromised Type A-C subtype represent high-risk phenotypes for futile recanalization, emphasizing hemodynamic sufficiency over mere anatomical connectivity. Conflict of interest The authors report no conflicts of interest relevant to this abstract. This work was supported by a grant from the Key Scientific Research Projects of Jinhua Science and Technology Bureau (2022-3-044) and Medical Science and Technology Project of Zhejiang Province (2024XY078).