Current Status of Middle Meningeal Artery Embolization for Chronic Subdural Hematoma: An International Perspective Including Japan

Middle meningeal artery embolization (MMAE) for chronic subdural hematoma (CSDH) is gaining global prevalence as a minimally invasive treatment aimed at serving as an adjunct to or method of avoiding surgery; however, its optimal positioning remains unclear. This study outlines the current status of MMAE in Japan, Germany, and the United States based on nationwide survey reports, recently published consensus guidelines, and meta-analyses including randomized controlled trials (RCTs) reported in the New England Journal of Medicine (NEJM; EMBOLISE, STEM, and MAGIC-MT) and examines its efficacy and limitations. Real-world clinical data from Japan, Germany, and the United States indicate that MMAE is primarily used as an adjunctive therapy following surgery for older and high-risk or recurrent cases, or as a stand-alone therapy in selected cases to safely reduce the risk of recurrence and reoperation. While a multidisciplinary consensus statement takes a cautious stance that limits MMAE to recurrent or inoperable cases such as those at high risk associated with interrupting antithrombotic medication, the Society of Vascular and Interventional Neurology guidelines published after the RCTs strongly recommend the concurrent use of MMAE with standard therapy in de novo cases. Meta-analyses integrating the 3 NEJM trials and other RCTs showed that MMAE suppressed recurrence and reoperation versus standard treatment, with particularly pronounced effects in the nonsurgical (conservative treatment) group; however, the additive effect was limited in the surgical adjunct group. No improvement in functional outcomes (modified Rankin Scale score) was observed. Cost-effectiveness analyses suggest that, while MMAE reduces reoperations, routine implementation for all cases is difficult to justify economically because of high procedural costs, indicating the need to narrow the indication to populations at high risk of recurrence. In conclusion, although MMAE is an effective treatment option, the current evidence does not support its uniform introduction in all patients with CSDH. Thus, it is necessary to individualize and adapt the indications for specific patient subgroups, such as those at high risk of recurrence or those for whom surgery is difficult. Finally, we propose a pragmatic treatment strategy for MMAE stratified by disease stage (de novo vs. recurrent) and clinical severity to guide the individualized selection of adjunctive and stand-alone embolization.