MMA Embolization With NeoCast for Subacute and Chronic Subdural Hematoma

Inclusion Criteria: * Participant whose age is ≥ 18 and ≤ 90 years; * Pre-morbid mRS ≤ 2; * Confirmed diagnosis of subacute or chronic subdural hematoma that measures ≥10 mm in greatest thickness; * Participant presents with one or more of the following corroborating neurological symptoms: headache; cognitive decline; speech difficulty; gait impairment or imbalance; focal neurological deficit; and/or seizure, within the last 30 days; * Participant is planned for middle meningeal artery embolization within ±7 days of surgical evacuation of hematoma via burr hole or craniotomy; * Participant or Legally Authorized Representative/Person Responsible for consenting on their behalf understands the nature of the procedure, consents to participation in the study and provides a signed informed consent form; * Participant (woman of child-bearing potential) with a current negative pregnancy test who has agreed to an appropriate method of contraception throughout the trial; * Participant is willing to return to the investigational site for follow-up visits. Exclusion Criteria: * Diagnosed with acute SDH * Participant with prior embolization of either MMA * Participant with urgent or emergent (within 1 hour of assessment) subdural hematoma evacuation needed * Participant with bilateral SDH where both sides require surgery or contralateral SDH \>5mm in greatest thickness * Participant identified with potentially dangerous anatomic variations leading to increased procedural risk, risk of incomplete embolization, or unsafe access for MMA embolization (i.e., MMA originating from ophthalmic artery) * Participant who presents with a meningioma ≥1 cm or \< 1 cm with mass effect * Subjects with conditions placing them at high-risk for ischemic stroke who cannot be taken off anticoagulants for at least 7 days post-surgery * Participant currently undergoing radiation therapy for carcinoma or sarcomas of the head or neck region * SDH developed due to underlying condition or structure pathology (e.g., dural AV fistula, AVM, tumor, arachnoid cyst, ventriculoperitoneal shunt, spontaneous intracranial hypotension or previous craniotomy) * Presumed microbial superinfection * Participant who is breastfeeding * Participant with life expectancy of \<1 year * Participants with acute renal impairment that the investigator assesses could be at risk for contrast induced nephropathy * Participant with a life-threatening allergy to radiographic contrast (unless treatment for allergy is tolerated or can be managed medically) * Participant is allergic to any of the materials used in the NeoCast device or the Onyx LES commercial embolic device * Participant who is currently participating or planning to participate within 6 months in another clinical research study