Abstract Number ‐ 99: Middle Meningeal Artery Embolization for Acute‐on‐Chronic Subdural Hematomas.
Authors: Fana Michael , Jum'ah Ammar , Gable Jessica , Rehman Mohammed 
Published: April 2023

Introduction
Chronic subdural hematomas (cSDH) are a challenge in management due to recurrent bleeds caused by focal inflammation and angiogenesis that produces frail vasculature. One intervention under investigation is endovascular embolization of the middle meningeal artery (MMA) for dura de‐vascularization. While there is increasing evidence for its utility, few investigations have been made into its role for acute‐on‐chronic SDHs and the timeline to intervention. Here, we identify 19 patients undergone MMA embolization to highlight preliminary trends in radiological and morbidity outcomes associated with time‐to‐intervention and hematoma size.

Methods
A retrospective cohort study of 19 patients undergone embolization of the anterior frontal and posterior parietal branches of the MMA for chronic or acute‐on‐chronic SDHs. Data retrieved is presented in Table 1 and includes: presenting symptoms; radiological features; surgical intervention(s); timeline to therapy and embolysate used; and procedural complications and outcomes.

Results
Preliminary findings suggests greater utility of MMA embolization for large‐sized subdural hematomas or when performed after 3–4 weeks of initial acute‐on‐chronic bleeds. We note 11 patients with complete or near‐complete resolution of the hematoma after several weeks without peri‐procedural complications or post‐surgical recurrence. In four of these cases (patients 7, 9, 18, and 19), there was resolution of the hematoma after only a brief interval of 2–14 days between radiographic evidence of the acute bleed and embolization. In these cases, the hematoma was noted to be considerably large in volume with a maximal width measuring between 18–30mm with resolution after 2–9 weeks post‐embolization. Conversely, we note poor outcomes in 4 cases (patients 6, 12, 13, and 15) when embolization was performed early (i.e. between 2–10 days) for smaller hematomas measuring between 5–12mm in maximal width.

Conclusions
MMA embolization functions to de‐vascularize capillary‐rich dura membranes to prevent re‐bleeds and allow for resorption of blood. However, the timeline for embolization of acute hematoma bleeds currently remains elusive. Here, we find preliminary evidence that suggests MMA embolization may be most appropriate for acute‐on‐chronic SDHs after a 3–4 week interval since time of radiographic evidence or for those with a large size hematoma when opting to treat sooner.These findings align with current understanding of the rapid angiogenetic formation of capillaries in the subacute phase (i.e. 0–3 weeks) with leaky vessels after the initial traumatic event. Occluding these vessels would prevent constant re‐bleeds and hematoma growth in the subacute phase. Theoretically, this would recede the hematoma, permit its resorption, and reduce angiogenesis. Moreover, in current literature there have been reports of contralateral hematoma formation in patients undergone surgical evacuation of an initial small acute hematoma. A similar pathogenic process may be implicit with an endovascular approach as well in which there is a natural tamponade effect of the larger coagulated chronic ematoma against frail vasculature causing acute bleeds.