Epiural or extradural hematoma is a buildup of blood occurring between the dura mater (the brain's tough outer membrane) and the skull. Often due to trauma, the condition is potentially deadly because the buildup of blood may increase pressure in the intracranial space and compress delicate brain tissue. The condition is present in one to three percent of head injuries. Between 15 and 20% of patients with epidural hematomas die of the injury.