Background: Endovascular thrombectomy (EVT) has established efficacy across a wide range of patient age, radiological findings, and clinical features. However, EVT may be less effective in extreme scenarios (e.g., large established infarction in later treatment windows), where there are currently limited data. Methods: A heterogeneous, multinational observational cohort (CLEAR registry) of consecutive adult patients ≥18 years old who underwent EVT for acute occlusion (2014-2022) of the internal carotid or proximal middle cerebral (M1 or M2) arteries was queried (n=64 sites). A high-fidelity model for predicting good functional outcome at 90 days (return to pre-stroke modified Rankin Scale [mRS] or mRS 0-2 after EVT) was developed using a binary, multivariable logit model with adaptive double lasso adjustment, which was validated using 5-fold cross validation and 1000 bootstrap sampling for confidence intervals. Results: At the time of the analysis, we evaluated 2953 patients from the registry treated with EVT, of which 1855 (63%) had complete covariate data for inclusion. The median National Institutes of Health Stroke Scale (NIHSS) score was 15 (IQR 9-20), with 14.0% having a pre-stroke mRS >2, 8.3% having a NIHSS <6, and 17.8% having an Alberta Stroke Program Early Computed Tomography Scale (ASPECTS) score ≤6. A good functional outcome occurred in 813 (43.8%) patients. Independent predictors of the primary outcome, with points allocated toward the final score, included younger age, higher ASPECTS, lower NIHSS, and time from last known well to arterial puncture. The areas under the curve for derivation and validation cohorts were 0.72 (95% CI 0.70-0.75) and 0.74 (95% CI 0.71-0.80), respectively. Discussion: The CLEAR thrombectomy score provides a simple, validated means of predicting good functional outcome following late-window, anterior circulation thrombectomy using routinely acquired clinical and imaging data. External validation is warranted.
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