Chronic Subdural Hematoma Treatment with Embolization vs Surgery or MedicalManagement Study (CHESS) - Chronic subdural hematoma (CSDH) is a common neurosurgical disease with a significant health burden.1,2 The outcomes of CSDH remain poor in up to 20% of patients treated with conventional surgery.12,13,15,16 Middle meningeal artery embolization (MMAE) is a minimally-invasive emerging therapy for patients with CSDH. Preliminary experience 46, 48, 51 suggests that compared with conventional surgery, MMAE has been associated with a reduced need for rescue operation. Thus far there is no randomized controlled trials comparing the safety and efficacy of MMAE vs. conventional surgery. We propose a multi-center, prospective, randomized, open- label, Phase III clinical trial in patients with convexity CSDH to determine superiority of MMAE versus conventional surgery in moderately symptomatic patients. We hypothesize that MMAE is a superior management strategy compared to conventional surgery in moderately symptomatic patients respectively. The aims of CHESS (Chronic Subdural Hematoma Treatment with Embolization vs Surgery Study) are as follows: Primary Aim: To determine if MMAE reduces the proportion of patients requiring rescue surgery or die within 180 days after randomization compared to conventional surgery in moderately symptomatic patients with CSDH. Safety Aim: To determine the 180-day rates of ischemic stroke, serious/life threatening adverse events, and worsening neurological status/development of new disabling neurological symptoms, seizures, and cranioneuropathy in moderately symptomatic CSDH patients, comparing MMAE to conventional surgery. Exploratory aims: To examine the radiographic benefit of MMAE and to assess the effects of MMAE on the quality of life, symptomatic relief, cognitive and functional outcomes compared to conventional surgery in moderately symptomatic CSDH patients. The results from this trial will contribute to the understanding of the appropriate strategies for the management of patients with moderate CSDH. Successful studies aiming to treat CSDH and to prevent its recurrence would have significant public health and cost-saving implications.