Epidural or extradural hematoma (haematoma), also known as an epidural hemorrhage, is a type of traumatic brain injury (TBI) in which a buildup of blood occurs between the dura mater (the tough outer membrane of the central nervous system) and the skull. The spinal cord is also covered by a layer of dura mater, so epidural bleeds may also occur in the spinal column. Often due to trauma, the condition is potentially deadly because the buildup of blood may increase pressure in the intracranial space, compress delicate brain tissue, and cause brain shift. The condition is present in one to three percent of head injuries. Around 15% - 20% of epidural hematomas are fatal.