Embolization of the Middle Meningeal Artery With ONYX™ Liquid Embolic System for Subacute and Chronic Subdural Hematoma

Inclusion Criteria:

• Pre-morbid Modified Rankin Score ≤3

• Confirmed diagnosis of subacute or chronic subdural hematoma

• Completed informed consent

• Meets criteria for Surgery or Observation Cohort

Exclusion Criteria:

• Life expectancy <1 year

• Unable to complete follow-up

• Pregnant, lactating, or has a positive pregnancy test at time of admission

• Diagnosed with acute SDH

• Potentially dangerous anatomic variations leading to increased procedural risk orunsafe access for MMA embolization

• Pre-randomized Markwalder Grading Scale score ≥ 3

• Unmanaged, uncontrolled bleeding disorders/blood diathesis

• Presumed septic embolus, or suspicion of microbial superinfection

• Known active COVID-19 infection

• CT or MRI evidence of intra-cranial tumor or mass lesion Contraindication toangiography

• Participation in another clinical trial

• Contraindicated for the use of Onyx™ LES

• Cannot be taken off corticosteroids (intended to treat subacute or chronic SDH) forat least 90 days post-randomization