The Onyx™ Trial For The Embolization Of The Middle Meningeal Artery For Chronic Subdural Hematoma

Inclusion Criteria: * Patient is ≥ 18 years old at inclusion (no upper age limit). * CSDH confirmed on cranial imaging (e.g. CT/magnetic resonance imaging \[MRI\]), as documented by a radiologist. * One or more symptoms attributable to CSDH including headache, cognitive impairment, gait instability, seizure, mild focal neurologic deficit, speech disturbance, or decreased consciousness. * No significant pre-morbid disability (baseline mRS score ≤3). * Decision of conventional therapy (neurosurgeon blinded to the randomization group) * Patient or patient's representative has received information about the study and has signed and dated the appropriate Informed Consent Form, or fulfilling the criteria for emergency consent. Exclusion Criteria: * CSDH developing with underlying conditions: vascular lesions, brain tumor, arachnoid cyst, or spontaneous intracranial hypotension. * CSDH that have a focal location (confined to the frontal or temporal base or the interhemispheric space without cerebral convexity involvement), is 10 mm or less in thickness, or have no mass effect (cortical flattening or midline shifting). * Known absence of vascular access or any local cause prohibiting femoral catheterization. * Known contrast or endovascular or anesthetic product allergy or contraindications. * Any contraindications to the use of the Onyx™. * Female who is known to be pregnant or lactating at time of admission. * Patient presenting severe or fatal co-morbidities or Life expectancy under 6 months that will likely interfere with improvement or follow-up or that will render the procedure unlikely to benefit the patient. * Patient unable to be present or available for follow-up * Pre-existing neurological or psychiatric disease that would confound the neurological or functional evaluations (e.g. severe dementia). * Current participation in another investigational drug or device study. * Major patients under court protection, guardianship or curatorship. * Not be affiliated to a French social security system or a beneficiary of such a system