Brain Herniation

How brain herniation happens

The skull is a closed box containing brain tissue, blood and cerebrospinal fluid (CSF). It is divided into compartments by stiff membranes: the falx between the two hemispheres, and the tentorium separating the upper brain from the brainstem and cerebellum below. The only large exit is the foramen magnum at the base of the skull.

When something adds volume, such as a blood clot, tumor or swelling, the body first compensates by pushing out CSF and venous blood. Once these reserves are used up, intracranial pressure rises steeply. Brain tissue is then squeezed toward lower-pressure areas, compressing itself, nearby blood vessels, cranial nerves and the brainstem, which controls breathing, heart rate and consciousness.

Causes

• Traumatic brain injury: epidural and subdural hematomas, contusions and diffuse swelling
• Intracerebral hemorrhage and subarachnoid hemorrhage
• Large ischemic stroke with swelling, peaking 2 to 5 days after the stroke
• Brain tumors and metastases with surrounding swelling
• Brain abscess and severe encephalitis or meningitis
• Cerebral edema from liver failure, low sodium, diabetic ketoacidosis in children, or lack of oxygen
• Hydrocephalus or a blocked shunt
• Lumbar puncture in someone with a mass lesion and raised pressure, which is why a CT scan is done first when there are warning signs

Types of brain herniation

Warning signs

Early signs of rising intracranial pressure:

• severe or worsening headache
• vomiting
• drowsiness, confusion, agitation
• blurred or double vision

Signs of herniation:

• one pupil dilated and slow to react, then fixed
• weakness or paralysis of one side
• abnormal posturing: arms bent toward the chest (decorticate) or rigidly extended (decerebrate)
• Cushing's triad: high blood pressure, slow heart rate and irregular breathing
• deep coma

Diagnosis

Herniation is diagnosed clinically and confirmed with an emergency CT scan of the head, which shows the cause (bleeding, swelling, mass) and the shift of brain structures, such as midline shift and compressed fluid spaces around the brainstem. MRI gives more detail when the person is stable. Intracranial pressure may be monitored directly with a probe or a drain placed in the brain.

Emergency treatment

Treatment begins immediately and focuses on lowering pressure and treating the cause.

1. Airway, breathing and circulation: intubation and ventilation for those who cannot protect their airway
2. Head of bed raised to 30 degrees, with the neck straight to help blood drain from the head
3. Hyperosmolar therapy: mannitol or hypertonic saline draw fluid out of the brain
4. Brief hyperventilation: lowers carbon dioxide and briefly reduces blood volume in the brain, used as a bridge to definitive treatment
5. Steroids (dexamethasone) for swelling around tumors and abscesses only. They are not used for head injury or stroke
6. Sedation, seizure control and normal temperature
7. Surgery: - removal of a blood clot (craniotomy) - decompressive craniectomy, where part of the skull is removed to let the swollen brain expand - external ventricular drain to remove CSF - removal of a tumor or abscess

Outlook

Brain herniation is often fatal, and many survivors have significant disability. Outcome depends on the cause, how quickly pressure is relieved, age and which structures were damaged. Early recognition of rising pressure, before herniation is complete, gives the best chance of recovery. Survivors usually need extended rehabilitation with physical, occupational and speech therapy.

Prevention

• wear seat belts and helmets
• prevent falls in older adults, especially those on blood thinners
• seek prompt assessment after any head injury in people taking anticoagulants, or with drowsiness, vomiting or worsening headache
• control blood pressure to reduce brain hemorrhage risk

Frequently asked questions

What is brain herniation?

Brain herniation is when high pressure inside the skull pushes brain tissue out of its normal compartment, compressing the brainstem and blood vessels. It is a medical emergency that can quickly cause coma and death without treatment.

What causes brain herniation?

The most common causes are severe head injuries with bleeding, strokes with swelling, brain hemorrhages, tumors, abscesses and conditions that cause brain swelling, such as severe liver failure or lack of oxygen. All raise the pressure inside the skull.

What are the signs of brain herniation?

Signs include a worsening headache, repeated vomiting, decreasing alertness, one enlarged pupil, weakness on one side, abnormal stiff posturing, irregular breathing, slow pulse and high blood pressure. Anyone showing these needs emergency care.

Can you survive brain herniation?

Some people do, particularly when treatment to lower pressure starts very early, before the brainstem is severely compressed. Survival rates vary widely with the cause and speed of treatment, and many survivors need long-term rehabilitation.

How is brain herniation treated?

Emergency treatment includes airway support, raising the head, medicines such as mannitol or hypertonic saline to reduce brain swelling, and surgery to remove blood clots or tumors, drain fluid, or remove part of the skull to relieve pressure.