Inclusion Criteria:

Candidates for this study must meet ALL of the following criteria:

1. Subject is 18 years of age or older.

2. Subject has a diagnosis of chronic subdural hematoma with mass effect Determined by brain imaging (CT or MRI) and correlated clinical symptoms.

3. Pre-randomization modified Rankin Score (mRS) ≤3

   a. Surgical Cohort: Assessment should reflect the subject's condition just prior to undergoing surgery. Assessment may be performed post-surgery using pre-surgical data.

4. Subdural Hematoma Size

   Medical Management Cohort:

   • Midline shift < 10mm and hematoma thickness > 10 mm as measured on coronal imaging perpendicular to the skull.
   • No focal deficit related to the chronic subdural hematoma requiring surgical intervention

   Surgical Cohort:

   • No requirement

5. A CT performed prior to randomization demonstrating stability of the hematoma. Stability is defined as no worsening of midline shift or increase in the size of the cSDH from the screening image that results in new or worsening clinical symptoms.

6. Patient or designated Legal Authorized Representative, confirms the patient has the mental capacity, willingness and ability to comply with protocol and follow-up requirements

7. In the opinion of the treating physician, MMA embolization is technically feasible, including evaluation of preoperative CTA, if available, or presence of a foramen spinosum bilaterally.

Exclusion Criteria:

• Candidates will be excluded from participation if ANY of the following apply:

  1. Patients presenting with an acute SDH (e.g. patient with presenting with a SDH due to trauma); mixed density is permitted.
  2. Subject presents with bilateral cSDHs requiring treatment (contralateral cSDH <5mm and not requiring treatment is permitted.
  3. Subject presents with Glasgow Coma Scale < 9
  4. Markwalder assessment >4
  5. cSDH that developed with underlying conditions such as vascular lesions, brain tumor, arachnoid cyst, spontaneous intracranial hypotension, end stage renal disease (ESRD) on hemodialysis, end stage liver disease or other comorbidities causing a coagulopathy
  6. Prior carotid stent placement that crosses the origin of the External Carotid Artery (ECA) ipsilateral to the subdural hematoma
  7. Presumed septic embolus, or suspicion of microbial superinfection
  8. CT or MRI evidence of intra-cranial tumor or mass lesion
  9. Significant contraindication to angiography (eg. kidney failure).
  10. Life expectancy of less than 1-year
  11. Women who are pregnant, lactating, plan on becoming pregnant during the course of the clinical investigation. We routinely do pregnancy tests prior to this procedure, to avoid radiation exposure to the fetus including radiation on follow up CT scans
  12. Current involvement in an investigational (drug, device, etc.) clinical trial that may confound study endpoints. Subjects in observational, natural history, and/or epidemiological studies not involving intervention are eligible
  13. Patient unwilling to follow SOC recommendations (e.g. refuses surgery or lifestyle modifications)