Recurrence of chronic subdural hematoma (cSDH) has been suggested to involve angiogenesis and leakage from the fragile neovasculature within the outer membrane of the hematoma, which is primarily supplied by the distal branches of the middle meningeal artery. Middle meningeal artery embolization (MMAE) has recently gained recognition as an effective treatment, either as a standalone procedure or as an adjunct to burr-hole drainage, to reduce recurrence and reoperation rates. Various embolic materials are used in MMAE, including ethylene-vinyl alcohol copolymer (EVOH)-based agents (Onyx [Medtronic, Irvine, CA, USA], Squid [Balt, Montmorency, France]), polylactide-co-glycolide (PLGA) and polyhydroxyethyl methacrylate (HEMA)-based agent (PHIL; Terumo Neuro, Aliso Viejo, CA, USA), n-butyl cyanoacrylate (NBCA), particulates such as polyvinyl alcohol (PVA) and trisacryl gelatin microspheres (TGM), and coils. EVOH-based and PLGA-HEMA-based agents provide controlled deep distal penetration and durable occlusion, providing the strongest evidence in recent randomized controlled trials. NBCA enables rapid and cost-effective embolization but requires precise technique to prevent complications such as catheter entrapment. Particulates (PVA and TGM) are inexpensive and widely available, yet carry a higher recanalization risk and are often combined with coils or liquid embolics. Coils alone have limited efficacy, although they serve a protective role during liquid embolic injection. In Japan, NBCA is the predominant material, often combined with coils or particles, due to insurance coverage and guideline recommendations. Comparative evidence among embolic agents remains limited, highlighting the need for further studies to define optimal material selection and standardize MMAE strategies.

Middle meningeal artery embolization (MMAE) for chronic subdural hematoma (CSDH) is increasingly performed to reduce recurrence. Several recent randomized controlled trials, such as EMBOLISE, MAGIC-MT, and STEM, have shown significant interest in endovascular treatment of CSDH. Many studies have demonstrated clinical and radiographic outcomes following MMAE in different patient populations and treatment strategies, including stand-alone or adjunctive MMAE combined with surgical evacuation. Most studies have shown the efficacy of MMAE in reducing hematoma recurrence, reoperation rates, and even several adverse events compared with surgery alone. Moreover, stand-alone MMAE can be an efficacious and minimally invasive treatment option for some patients. However, its benefits on functional or radiographic outcomes vary depending on patient selection and treatment strategy. Furthermore, knowledge of periprocedural radiographic findings associated with hematoma resolution or reaccumulation after MMAE may contribute to a sufficient follow-up period after treatment, as well as to medical economics, and thus has clinical implications. In this review, we focus on the clinical and radiographic outcomes of MMAE for CSDH.

Chronic subdural hematoma (cSDH) is among the most common neurosurgical conditions, particularly affecting older adults and patients receiving anticoagulation. While burr-hole evacuation has long been the standard therapy, recurrence rates and associated morbidity remain significant. Middle meningeal artery (MMA) embolization has recently emerged as a promising alternative or adjunctive treatment, offering durable hematoma control with reduced recurrence. To understand the rationale and safety of this endovascular approach, detailed knowledge of MMA anatomy, embryology, and variations is essential. This review synthesizes current understanding of the MMA from gross and microvascular perspectives, integrating embryological origins, common and rare anatomical variants, and dural angioarchitecture, with emphasis on how these factors inform embolization strategies for cSDH. By bridging historical anatomical insights with contemporary angiographic and clinical evidence, we aim to provide a comprehensive resource for clinicians and researchers involved in neuroendovascular therapy.

Chronic subdural hematoma (CSDH) is becoming increasingly common in the aging population, and preventing its recurrence after standard surgical drainage remains a significant clinical challenge. Middle meningeal artery embolization (MMAE) has emerged as a promising therapeutic option to interrupt the supply of neovessels to the outer membrane, thereby halting the cycle of inflammation and rebleeding. This review summarizes the latest findings on the therapeutic outcomes of MMAE, with a particular focus on 3 major randomized controlled trials reported in 2024: the STEM, EMBOLISE, and MAGIC-MT trials. Although these studies collectively suggest that MMAE can reduce the risk of treatment failure and recurrence, the results vary in terms of efficacy across different patient populations and study designs. The EMBOLISE trial demonstrated a significant reduction in recurrence requiring reoperation, whereas other trials adopted broader outcome definitions, which may partly explain the heterogeneity in reported efficacy. Consequently, MMAE may not be suitable for universal adoption across all patient populations. The procedure has a favorable safety profile and a low complication rate. Technical factors influencing success include the use of liquid embolic agents for distal penetration and the potential benefits of the transradial approach in reducing postoperative delirium in older patients. In conclusion, although MMAE is a valuable addition to CSDH management, a comprehensive evaluation is essential to optimize clinical outcomes.

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.