Brain herniation occurs when pressure inside the skull (intracranial pressure) increases and displaces brain tissues. This is commonly the result of brain swelling from a head injury. It can also be caused by space-occupying lesions such as primary brain tumor, metastatic brain tumor, and hemorrhages or strokes that produce swelling within the brain.

Brain herniation itself often causes massive stroke, resulting from poor blood supply to some areas of brain and compression of vital structures that compromise cardiovascular and respiratory centers. This can rapidly lead to death or brain death.

Brain herniations are the most common secondary effect of expanding intracranial masses.

• Progressive loss of consciousness
• Coma
• Irregular breathing
• Respiratory arrest (no spontaneous breathing)
• Irregular pulse
• Cardiac arrest (no pulse)
• Loss of all brainstem reflexes (blink, gag, pupillary reaction to light)

A neurologic examination would show an impaired level of consciousness and, depending on the severity of herniation, one or several brainstem reflexes and cranial nerve functions will be impaired. The patient's respiratory patterns would show an inability to breathe consistently, and heart rhythms would be irregular.

Brain herniation is a medical emergency! The goal of treatment is to save the patient's life.

Treating increased intracranial pressure can help to prevent brain herniation.
Corticosteroids such as dexamethasone can reduce brain swelling and intracranial pressure, especially in cases where a tumor is involved, and this can help prevent herniation.

Mannitol or other osmotic diuretics may also be given to reduce intracranial pressure. Often, if a mechanical obstruction is causing herniation, a drain will be placed into the ventricle of the brain to drain off cerebrospinal fluid to try to prevent herniation. If a massive hemorrhage is present and causing herniation, it is sometimes possible to remove the blood; however, the outlook in these cases is poor.

Deliberate hyperventilation may also be used to reduce intracranial pressure. This often includes placing a tube in the airway (endotracheal intubation) and mechanically ventilating (forced breathing) at a rapid rate.

Once herniation in the brain's temporal lobe or the cerebellum occurs, death is often inevitable. Herniation of other brain areas has a variable prognosis (probable outcome).

• Permanent and profound neurologic problems
• Brain death

If decreased alertness or other symptoms develop suddenly, particularly if there is a known head injury or brain lesion, go to the emergency room or call the local emergency number (such as 911). A neurologist or neurosurgeon will ultimately be involved in the patient's care.

Prompt treatment of increased intracranial pressure and related disorders may reduce the risk of brain herniation.