Association of pre-mechanical thrombectomy collateral scores with functional outcomes in the early versus extended window for thrombectomy.

Introduction: Cerebral collateral circulation refers to the anastomoses that reroute the blood flow to the ischemic penumbra in the event of a large vessel occlusion (LVO). We aim to determine the utility of pre-mechanical-thrombectomy (MT) collateral scores in the early (<6 h from onset) versus extended (6-24 h from onset) window for MT with respect to a 3-month functional outcome, 3-month mortality, and early neurological improvement. Methods: We performed a retrospective chart review of patients who underwent MT for an anterior circulation LVO at a comprehensive stroke center from 7/2014 to 12/2020. A board-certified neuroradiologist, who was blinded to the clinical outcomes, used the collateral grading scales of Miteff (ordinal), Maas (ordinal), and modified-Tan (dichotomous) to designate collateral scores on the pre-MT CT Angiogram. The patients were divided into early (<6 h from onset) versus extended (6-24 h from onset) window groups depending on their timing of presentation to the emergency department. A regression analysis was performed, controlling for the baseline parameters, with the pre-MT collateral grading scores as predictors. The outcome measures were a good functional outcome (3-month mRS 0-2), mortality, and early neurological improvement. Results: A total of 220 patients met the inclusion criteria. In the overall cohort, the pre-MT scale of Maas was associated with a good functional outcome (OR, 0.58; 95% CI, 0.34-0.99; P 0.047) and mortality (OR, 0.55; 95% CI, 0.31-0.97; P 0.036). For the 162 patients who presented in the early window for MT, all of three pre-MT scales of Maas (OR, 0.39; 95% CI, 0.2-0.77; P 0.006), Miteff (OR, 0.43; 95% CI, 0.19-0.97; P 0.042) and modified-Tan (OR, 5.62; 95% CI, 1.16-27.37; P 0.033) were associated with a good functional outcome, whereas the Maas (OR, 0.48; 95% CI, 0.26-0.9; P 0.021) and the Miteff scale (OR, 0.4; 95% CI, 0.22-0.74; P 0.003) were associated with mortality. For the 58 patients who presented in the extended window for MT, none of the collateral grades were associated with functional outcome, mortality, or early neurological improvement. Conclusions: Our study demonstrates that while several collateral grades are helpful to predict outcomes in patients presenting in the early window, none of the pre-MT collateral scores were associated with outcomes in patients who presented in the extended window for MT. Thus, the current strategy of using perfusion imaging for the selection of patients for MT in the extended window should continue.