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Background Chronic subdural hematoma (cSDH) disproportionately affects elderly patients. Middle meningeal artery embolization (MMAE) is increasingly used alone or combined with surgical evacuation, yet whether patient age modifies the comparative effectiveness of these strategies remains unknown. We investigated age-by-treatment interactions across clinical outcomes in a large multicenter registry.Methods Using the MESH Registry (22 centers, 2015-2024), we compared outcomes between MMAE alone (n=860) and MMAE+surgery (n=692) across quartile-based age groups (<65, 65-74, 75-84, ≥85 years) in 1,552 patients with cSDH. The primary outcome was rescue surgical evacuation; secondary outcomes included radiographic resolution, functional independence (mRS 0-2), and mortality. Inverse probability of treatment weighting (IPTW) with 21 confounders addressed selection bias within each age stratum. Treatment-by-age interaction was assessed using likelihood ratio tests. All comparisons were corrected for multiplicity using the Benjamini-Hochberg procedure.Results Mean age was 73 years; 71.3% were male. Treatment allocation was uniform across age groups (42-46% receiving surgery; P=0.65). Rescue surgical evacuation occurred in 5.7% overall with consistent rates across age groups (trend P=0.98). IPTW-weighted analyses showed no significant difference between MMAE alone and MMAE+surgery for rescue surgery in any age group (ORs 0.35-1.85; all P>0.20). No treatment-by-age interaction was detected for any outcome (all interaction P>0.17). Radiographic resolution was uniformly high (91-93%). Functional independence declined with age (84% in <65 to 59% in ≥85; adjusted OR 0.36, 95% CI 0.16-0.81; P=0.01) but was independent of treatment modality (interaction P=0.56). Mortality showed a non-significant trend with age (9.2% to 14.2%; P=0.06). No comparison survived Benjamini-Hochberg correction for multiplicity ( figure 1).Conclusions In this large multicenter registry, age did not modify the comparative effectiveness of MMAE alone versus MMAE+surgery for cSDH across any outcome examined. The uniformly low rescue surgery rate (~6%) regardless of age or treatment strategy supports MMAE as a viable approach across the full age spectrum, without evidence that elderly patients differentially benefit from the addition of surgical evacuation.Disclosures B. Demessie: None. A. Karandish: None. H. Salim: None. V. Mendes Pereira: None. M. Collaborators: None.Abstract E-327 Figure 1