In an occipital epidural hematoma, the bleeding occurs between the skull and the dura (the brain cover). The bleeding is from an injury to a vein or a branch of the posterior meningeal artery. Occipital epidural hematoma is often caused by a full-on blow to the head and may be associated with a skull fracture.
In an occipital subdural hematoma, the bleeding is into the space between the dura and the brain itself. As the hematoma enlarges, it can put increasing pressure on the brain and cause neurological abnormalities including slurred speech, impaired gait, and dizziness and lead to coma and even death.
The diagnosis of an occipital hematoma, whether it be epidural or subdural, may be confirmed by MRI or CAT scan. Treatment may range from watchful waiting in the case of a small epidural bleed to trepanation -- drilling through the skull to drain the excess blood.