This is a prospective, randomized, controlled, open-label, blinded endpoint (PROBE) clinical investigation in which patients with non-emergent chronic subdural hematoma (cSDH) requiring treatment will be randomized (1:1) to either initial surgical evacuation (Control Arm) or initial MMAE with PHIL™ (investigational arm).

Inclusion Criteria:

• Age 22 years or older
• Diagnosis of chronic subdural hematoma
• Subject, or their legally authorized representative provides a signed and dated Informed Consent Form
• Pre-morbid mRS 0-1
• cSDH measures ≥ 10 mm in greatest thickness
• cSDH exerts mass effect upon the subjacent brain
• Imaging characteristics indicative of chronicity
• Negative urine pregnancy test for female subjects of child-bearing potential
• Subject is able and willing to comply with all study protocol requirements, including return to the investigational site for all follow-up visits
• Subject presents with one or more of the following neurological symptoms: headache/head pressure, cognitive decline, speech difficulty or aphasia, gait impairment or imbalance, focal neurological deficit (weakness, paresthesia or sensory deficit involving of one or more extremities or facial droop), and/or seizure

Exclusion Criteria:

• Prior ipsilateral craniotomy or burr hole evacuation of cSDH
• Prior embolization of either MMA
• Requires (in the opinion of the treating surgeon) full or mini-craniotomy at time of randomization
• Emergent subdural hematoma evacuation needed
• cSDH with a focal location
• cSDH developed due to underlying condition
• Life expectancy of <1 year
• Presents with an intracranial mass other than subdural hematoma
• Presents with a meningioma with mass effect and/or ≥1 cm or currently undergoing radiation therapy for carcinoma or sarcoma of the head or neck region
• Serum creatinine level > 3.0 mg/dL at time of enrollment and not on dialysis
• Life-threatening allergy to radiographic contrast (unless treatment for allergy is tolerated or can be managed medically)
• Currently enrolled in another investigational study protocol that could potentially confound the interpretation of the study endpoints/outcomes
• Known dangerous anatomic variations leading to increased procedural risk or unsafe access for MMAE
• Contraindicated for the use of PHIL™ liquid embolic system

Sponsor is blinded