Spinal epidural hematoma may occur as a result of trauma, but may also develop spontaneously in patients with bleeding disorders. They may occur with mild or trivial head trauma. Excessive movement of the brain causes rupture of these vessels which are anchored to the skull. Individuals with brain atrophy in whom the bridging veins are stretched and there is more room for the brain to move are especially prone to developing subdural hematoma. Less commonly, subdural hematomas results from rupture of arteries that accompany bridging veins, and from rupture of subarachnoid vessels or hemorrhagic contusions of the brain along with tears of the arachnoid membrane.
Subdural hematomas raise the intracranial pressure and compress the brain.
With arterial bleeding, symptoms develop rapidly. Sometimes the preceding injury is insignificant, or no history of trauma can be elicited. The subdural hematoma starts as a flat blood clot between the dura and the arachnoid membrane. Initially, it is not attached to the dura. Fibroblasts, growing from the dura into the clot, organize it.