Epidural hematoma is when bleeding occurs between the tough outer membrane covering the brain (dura mater) and the skull.

[1] The cause is typically a head injury that results in a break of the temporal bone and bleeding from the middle meningeal artery.

[6] As blood accumulates, it starts to compress intracranial structures, which may impinge on the third cranial nerve, causing a fixed and dilated pupil on the side of the injury.

The trigeminal nerve may be involved late in the process as the pons is compressed, but this is not an important presentation, because the person may already be dead by the time it occurs.

[7] In the case of epidural hematoma in the posterior cranial fossa, tonsillar herniation causes Cushing's triad: hypertension, bradycardia, and irregular breathing.

[citation needed] The most common cause of intracranial epidural hematoma is head injury, although spontaneous hemorrhages have been known to occur.

Epidural hematoma is usually found on the same side of the brain which was impacted by the blow, but on very rare occasions it can be due to a contrecoup injury.

[3] Epidural bleeds from arteries can grow until they reach their peak size 6–8 hours post-injury, spilling 25–75 cubic centimeters of blood into the intracranial space.

It also increases intracranial pressure, causing the brain to shift, lose blood supply, be crushed against the skull, or herniate.

[15] In the hallmark of epidural hematoma, people may regain consciousness and appear completely normal during what is called a lucid interval, only to descend suddenly and rapidly into unconsciousness later.

If transfer to a facility with neurosurgery is unavailable, prolonged trephination (drilling a hole into the skull) may be performed in the emergency department.

If the volume of the epidural hematoma is less than 30 mL, the clot diameter less than 15 mm, a Glasgow Coma Score above 8, and no visible neurological symptoms, then it may be possible to treat it conservatively.

Age, pupil abnormalities, and Glasgow Coma Scale score on arrival to the emergency department also influence the prognosis.

The condition is more common in teenagers and young adults than in older people, because the dura mater sticks more to the skull as a person ages, reducing the probability of a hematoma forming.