Abstract Number ‐ 44: Middle Meningeal Artery Embolization: 294 Non‐Acute Subdural Hematomas with Outcomes and Risk Factors for Recurrence

Introduction Treatment of non‐acute subdural hematoma (NASDH) remains challenging due to recurrence ranging from 2–37%. Middle meningeal artery embolization (MMAe) has emerged as a minimally invasive procedure uniquely poised to improve outcomes in NASDH. The goal of this study is to evaluate the clinical and radiographic characteristics of patients undergoing MMAe for NASDH, and how outcomes for MMAe differ when utilized upfront, prophylactically, or as a salvage modality after surgical evacuation. Furthermore, we investigated how independent patient risk factors, such as oncologic history and anticoagulant/antiplatelet (ACAP) medication use, may impact MMAe and NASDH outcomes. Methods This prospective study followed patients undergoing MMAe for NASDH from 2016–2021. All patients were diagnosed with a NASDH on non‐contrast CT imaging and underwent MMAe by the lead neurosurgeon. The primary outcome was NASDH recurrence post‐MMAe requiring surgical evacuation, repeat MMAe, or both within the one‐year follow up period. Additional radiographic outcomes included reduction of hematoma width and midline shift at longest follow‐up. Subgroup analyses stratified outcomes by MMAe indication: upfront (previously untreated and nonoperative NASDH), prophylactic (MMAe 1–5 days after surgical evacuation), or salvage (individuals with radiographic and clinical NASDH recurrence). Outcomes among oncologic, coagulopathic, and ACAP patients were also assessed. The modified Rankin scale (mRS) quantified post‐MMAe clinical outcomes. Results A total of 236 NASDH patients underwent 294 MMAe. Of these, 115 (48.7%), 92 (39.0%), and 29 (12.3%) patients received upfront, prophylactic, and salvage MMAe, respectively. Upfront MMAe was performed more frequently than prophylactic and salvage for patients with co‐existing malignancy (29.6%, 12.0%, 20.7%; P < 0.01) and coagulopathy (17.4%, 4.3%, 10.3%; P = 0.01). Prophylactic MMAe was more commonly performed for subacute SDH compared with upfront or salvage (15.2%, 2.6%, 0%; P < 0.001); no differences in utilization were seen for chronic or acute on chronic SDH. Sixteen (5.4%) patients presented with hematoma recurrence after MMAe requiring repeat intervention, of which 5 (1.7%) received a craniotomy, 7 (2.4%) received repeat MMAe, and 4 (1.3%) underwent both MMAe and surgical evacuation. Risk of overall NASDH recurrence requiring re‐intervention did not differ among prophylactic, upfront, and salvage groups (6.5%, 7.0%, 6.9%; P > 0.99). Clinical outcomes did not differ between MMAe indications at longest follow‐up. Within the prophylactic group, radiographic and clinical outcomes were similar between MMAe paired with twist‐drill craniostomy or with craniotomy. Subgroup analysis revealed MMAe also effectively decreased NASDH recurrence in ACAP, oncologic, and coagulopathic patients. However, patients with both an oncologic history and concurrent ACAP use less frequently achieved improved clinical status at follow‐up compared with those harboring ACAP/coagulopathic history alone, oncologic history alone, or neither (31.4%, 45.9%, 50.0%, 57.3%; P = 0.049). Conclusions MMAe is emerging as a viable treatment for curtailing recurrence and improving NASDH outcomes, with similar clinical outcomes when performed prophylactically, upfront, or as salvage treatment. NASDH patients presenting with an oncologic history and concurrent ACAP use may be less likely to achieve improved clinical status after MMAe.