Collateral Grade Modifies the Association Between Pretreatment Infarct Core Volume and 90-day Functional Independence After Mechanical Thrombectomy for Anterior-Circulation Large-Vessel Occlusion

Background. Outcomes after mechanical thrombectomy vary widely despite high rates of angiographic reperfusion. Pretreatment infarct core volume is a major determinant of recovery, yet the functional impact of a given core burden may differ by collateral physiology. Therefore, this study aimed to determine whether baseline angiographic collateral grade modifies the association between pretreatment infarct core volume and 90-day functional independence, defined as modified Rankin Scale score 0–2, among adults with anterior-circulation large-vessel occlusion undergoing attempted mechanical thrombectomy. Methods. This retrospective observational cohort included consecutive adults who underwent attempted mechanical thrombectomy at a comprehensive stroke centre. Infarct core volume was quantified on diffusion-weighted magnetic resonance imaging with apparent diffusion coefficient confirmation, or on computed tomography perfusion when magnetic resonance imaging was not feasible, using semi-automated volumetry with artifact correction. Collaterals were graded on baseline angiography using the ASITN/SIR scale (0 to 4) by a reader blinded to core volume and outcomes. The primary endpoint was 90-day functional independence (modified Rankin Scale 0 to 2). Multivariable logistic regression in anterior-circulation strokes evaluated core volume (per 10 cc), collateral grade (per 1 grade), and a prespecified interaction term, adjusting for clinical and workflow covariates. Results. Sixty-nine patients were included (mean age 67.4 ± 10.2 years), with successful reperfusion (final mTICI 2b or higher) in 91.3%. Functional independence occurred in 47.8% overall and 53.8% among anterior-circulation strokes (28/52). Any intracranial haemorrhage occurred in 31.9%, symptomatic intracranial haemorrhage in 13.0%, and 90-day mortality in 20.3%. In anterior-circulation modelling, larger core volume reduced the odds of independence (adjusted OR 0.79 per 10 cc, 95% CI 0.66 to 0.93), higher collateral grade increased the odds (adjusted OR 2.24 per grade, 95% CI 1.18 to 4.25), and the interaction term was significant (adjusted OR 1.12, 95% CI 1.01 to 1.28), with good discrimination (AUC 0.81). Conclusions. Collateral physiology modifies the association between established infarct core burden and 90-day recovery after thrombectomy in anterior-circulation large-vessel occlusion, supporting integrated tissue-plus-physiology prognostication.