Background <p>Middle meningeal artery embolization (MMAE) is a novel minimally invasive technique that has been proven effective in reducing the recurrence and reoperation risk of chronic subdural hematoma (cSDH). However, the specific association of embolization branch location and the number of embolized branches on efficacy and safety remains unclear.</p> Methods <p>This secondary analysis was based on data from the multicenter, randomized MAGIC-MT trial, including 349 patients with cSDH treated with MMAE. Patients were categorized according to embolization site into distal branch group, proximal trunk group, and combined group; and according to the number of embolized branches into single-branch and multi-branch groups. The primary efficacy outcome was the proportion of patients with ≥ 50% hematoma volume reduction at 90 days postoperatively. The primary safety outcome was the incidence of serious adverse events within 90 days. Secondary outcomes included the proportion of patients with ≥ 50% reduction in maximum hematoma thickness and midline shift, changes in EQ-5D utility scores, the proportion of patients with stable or improved modified Rankin Scale (mRS) scores, hematoma recurrence or progression, incidence of adverse events, and reoperation rates. Outcomes were compared across different embolization sites and numbers of embolized branches to evaluate their association on the efficacy and safety of MMAE.</p> Results <p>Among the 349 enrolled patients (median age 69 years; 81.1% male), the primary efficacy outcome (≥ 50% hematoma volume reduction at 90 days) was achieved in 97.1% of patients, while the incidence of the primary safety outcome (serious adverse events) was 12.0%. Univariate analysis showed no significant differences in these efficacy or safety outcomes between groups stratified by embolization site or number of embolized branches. After adjustment for potential confounders, multivariable analysis confirmed that the embolization site was not significantly associated with serious adverse events, recurrence/progression, or reoperation. Similarly, the number of embolized branches showed no significant association with any outcomes after adjustment.</p> Conclusions <p>This secondary analysis indicates that neither embolization site nor number of branches demonstrates a significant association with 90-day postoperative efficacy or safety outcomes in MMAE for cSDH.</p>