Embolic Materials in Middle Meningeal Artery Embolization for Chronic Subdural Hematoma

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.