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Background Middle meningeal artery embolization (MMAE) is increasingly used for subdural hematoma (SDH), yet optimal embolic dose remains undefined. We aimed to determine whether higher liquid embolic volume improves clinical outcomes after MMAE using propensity-weighted analysis.Methods We analyzed 345 patients from the MESH Registry who underwent MMAE with liquid embolic agents at 12 international centers (2016-2024). The primary outcome was treatment failure (any post-MMAE surgical evacuation). Secondary outcomes included radiographic SDH improvement, favorable mRS (0-2), and mortality. Inverse probability of treatment weighting (IPTW) based on generalized propensity scores adjusted for 14 confounders served as the primary analysis. Restricted cubic splines modeled nonlinear dose-response relationships. Doubly-robust augmented IPTW (AIPTW) served as sensitivity analysis. Associations are reported per interquartile range (IQR) increment (0.50 cc).Results Mean (SD) embolic volume was 0.72 (0.40) cc (IQR 0.50-0.90). Patients in the high-dose tertile (0.90-2.10 cc, n=95) were older (76.6 vs 72.0 years; P=0.003) and more likely to have bilateral SDH (45.3% vs 24.4%; P=0.001) than those in the low-dose tertile (0.10-0.50 cc, n=164), confirming confounding by indication. Treatment failure rates were identical across tertiles (44.5%, 45.3%, 44.2%; P=0.99). After IPTW adjustment, absolute volume was not associated with treatment failure (IPTW-adjusted OR per IQR, 0.861; 95% CI, 0.64-1.16; P=0.33). Restricted cubic spline analysis confirmed a flat dose-response curve (C-statistic 0.50-0.55). Higher dose was associated with radiographic SDH improvement in unadjusted analysis (OR, 1.69; P=0.002), but substantially attenuated after IPTW adjustment (OR, 1.361; 95% CI, 1.01-1.84; P=0.04), consistent with confounding. No association was observed with favorable mRS (P=0.59) or mortality (P=0.70). AIPTW doubly-robust estimation confirmed the null primary finding (OR, 0.92; 95% CI, 0.69-1.27).Conclusions In this multicenter IPTW-adjusted analysis, liquid embolic dose was not associated with treatment failure after MMAE for SDH. Apparent radiographic associations were attributable to confounding by indication. Within the observed dose range, embolic volume does not meaningfully influence the need for surgical evacuation.Disclosures A. Alsalama: None. A. Karandish: None. H. Salim: None. M. Collaborators: None.Abstract P-004 Figure 1