Bilateral Versus Unilateral Middle Meningeal Artery Embolization for Standalone Treatment of Unilateral Chronic Subdural Hematoma

BACKGROUND AND PURPOSE: Contralateral dural supply may leave residual membrane perfusion after unilateral middle meningeal artery embolization (MMAE) for unilateral chronic subdural hematoma (cSDH). We compared unilateral and bilateral MMAE selected as initial standalone treatment, focusing on index-admission surgical rescue and other clinically relevant outcomes. MATERIALS AND METHODS: This retrospective cohort included patients treated at 16 centers worldwide from 2018 through 2025. The primary endpoint was index-admission surgical rescue. The original 3:1 and confirmatory 1:1 propensity-matched analyses used prespecified baseline covariates. A composite sensitivity outcome of any retreatment was also examined post hoc. RESULTS: Among 600 patients, 546 underwent unilateral and 54 bilateral MMAE. Bilateral cases had lower baseline radiographic severity and more often underwent general anesthesia and selective distal embolization. Index-admission surgical rescue occurred in 9.5% of unilateral and 0% of bilateral cases (p<0.001), with corresponding rates of 10.6% versus 0% after 3:1 matching (p<0.001) and 11.1% versus 0% after 1:1 matching (p<0.001). The post-hoc composite of any retreatment did not differ in the unmatched cohort (p=0.37), 3:1 cohort (p=0.56), or 1:1 cohort (>0.99). Other outcomes showed no statistically significant between-group differences, but postdischarge follow-up was incomplete. CONCLUSIONS: Overall retreatment did not differ between groups, although bilateral MMAE was associated with fewer index-admission surgical rescues. These observational data identify, but do not validate, angiographically documented contralateral supply as a candidate selection marker for prospective evaluation but do not establish a benefit of bilateral treatment or support routine bilateral MMAE.