Extra-axial hemorrhage

Extra-axial hematoma, or extra-axial hemorrhage is a subtype of intracranial hemorrhage, or bleeding within the intracranial space, that occurs within the skull but outside of the brain tissue itself. All intracranial hemorrhages constitute serious medical emergencies because they can increase intracranial pressure and crush delicate brain tissue, with potentially fatal results.

The category of extra-axial hematomas includes:
 * epidural, which occur between the dura mater (the outermost meninx) and the skull,
 * subdural, which occur in the subdural space between the dura and the arachnoid mater
 * subarachnoid, which occur between the arachnoid and pia meningeal layers

The other type of intracranial hemorrhages are intra-axial hemorrhages, which occur within the brain tissue itself.

Reference

 * 1) Wagner A.L. 2004. "Subdural Hematoma." Emedicine.com.