This condition is a buildup of clotted blood between the brain's outer layer and the membrane that covers the brain (called the dura). It usually results from a traumatic impact to the head, such as from a fall or car accident. The blood clot can result in pressure on the underlying brain which may require surgery to remove the blood from the surface of the brain. The blood clot can accumulate quickly (acute subdural hematoma) or slowly over a course of 3-6 weeks (subacute/chronic subdural hematoma).