Liquid Embolic Volume Does Not Predict Outcome After Middle Meningeal Artery Embolization for Chronic Subdural Hematoma

Purpose Middle meningeal artery embolization (MMAE) is increasingly used for chronic subdural hematoma (CSDH), but the relationship between injected liquid-embolic volume and outcomes is unclear. We evaluated dose–outcome associations and searched for a minimum effective dose. Methods This retrospective multicenter cohort included 313 patients treated with liquid embolic agents at 12 MESH Registry centers from 2016 to 2024. MMAE was performed alone in 172 patients (55.0%) and adjunctively with surgical evacuation in 141 (45.0%). Dose was assessed as total injected volume per patient and normalized to middle meningeal artery diameter, baseline hematoma thickness, and estimated hematoma volume. The primary outcome was a 180-day composite of retreatment, residual or recurrent hematoma > 10 mm, or death. Logistic regression with multiple imputation, restricted cubic splines, and sensitivity analyses evaluated associations and nonlinearity. Results Median injected volume was 0.60 mL (interquartile range, 0.50–0.90). Center accounted for 44.5% of variation in log volume, whereas hematoma burden accounted for 0.3%. No dose metric was significantly associated with the primary outcome or 90-day recurrence/reoperation. For absolute volume, the odds ratio per interquartile-range increment was 0.80 (95% confidence interval, 0.56–1.16; p = 0.24). No reliable minimum effective dose was identified. Findings remained consistent across sensitivity analyses and treatment indications (interaction p = 0.30). Procedural complications occurred in 6.4% and were not dose-associated. Conclusion Within the observed range, injected volume alone was not a consistent determinant of outcome and should not be a procedural target after a satisfactory angiographic endpoint. Future studies should evaluate embolic distribution, distal penetration, and vascular territory coverage.