An epidural hematoma is a collection of blood between the dura mater and the skull. ("Epidural" means "on top of the dura;" a "hematoma" is a collection of blood.) Usually, injuries to the head cause epidural hematomas by tearing arteries in the dura. Because the arteries in the dura are large, they carry a lot of blood. If one of these arteries is injured, it can bleed very quickly, and an epidural hematoma can build up almost right away. 