A brain herniation, or cerebral herniation, occurs when brain tissue, blood, and cerebrospinal fluid (CSF) shifts from their normal position inside the skull. The condition is usually caused by swelling from a head injury, stroke, bleeding, or brain tumor. A brain herniation is a medical emergency and requires immediate medical attention. It’s often fatal if not treated right away.
A brain herniation can be classified by where the brain tissue has shifted. There are three main types of brain herniation:
- Subfalcine. The brain tissue moves underneath a membrane known as the falx cerebri in the middle of the brain. Brain tissue ends up being pushed across to the other side. This is the most common type of brain herniation.
- Transtentorial herniation. This type of brain herniation can be further broken down into two types:
- Descending transtentorial or uncal. The uncus, part of the temporal lobe, is shifted downward into an area known as the posterior fossa. This is the second most common type of brain herniation.
- Ascending transtentorial herniation. The cerebellum and the brainstem move upward through a notch in a membrane called the tentorium cerebelli.
- Cerebellar tonsillar. The cerebellar tonsils move downward through the foramen magnum, a natural opening at the base of the skull where the spinal cord connects to the brain.
A brain herniation can also occur through a hole that was created previously during surgery.
A brain herniation is considered a serious emergency. Signs and symptoms may include:
- dilated pupils
- difficulty concentrating
- high blood pressure
- loss of reflexes
- abnormal posturing, rigid body movements, and abnormal positions of the body
- cardiac arrest
- loss of consciousness
A brain herniation is typically the result of swelling in the brain. The swelling puts pressure on brain tissues (referred to as increased intracranial pressure), causing the tissue to be forced away from its normal positon.
The most common causes of a brain herniation include:
- head injury leading to a subdural hematoma (when blood collects on the brain’s surface beneath the skull) or swelling (cerebral edema)
- brain hemorrhage (bleeding in the brain)
- brain tumor
Other reasons for an increase in pressure in the skull include:
- abscess (collection of pus) from a bacterial or fungal infection
- buildup of fluid in the brain (hydrocephalus)
- brain surgery
- a defect in brain structure called Chiari malformation
People with brain tumors or blood vessel problems, such as an aneurysm, are at a higher risk of having a brain herniation. In addition, any activity or lifestyle choice that puts you at risk for a head injury can also increase your risk of a brain herniation.
Treatment is aimed at relieving the swelling and pressure inside the brain that is causing the brain to herniate from one compartment to another. Treatment will be necessary to save a person’s life.
To reduce swelling and pressure, treatment may involve:
- surgery to remove a tumor, hematoma (blood clot), or abscess
- surgery to place a drain called a ventriculostomy through a hole in the skull to get rid of fluids
- osmotic therapy or diuretics (medications that remove fluid from the body) to pull fluid out of the brain tissue, such as mannitol or hypertonic saline
- corticosteroids to reduce swelling
- surgery to remove a part of the skull to make more room (craniectomy)
While the cause of the brain herniation is being addressed, the person being treated may also receive:
- a tube placed in their airway to support breathing
- medications to control seizures
- antibiotics to treat an abscess or to prevent infection
In addition, a person with a brain herniation will require close monitoring through tests such as:
If not treated right away, the movement of brain tissue can impair vital structures in the body.
Complications of brain herniation include:
The outlook depends on the type and severity of the injury that caused the herniation and where in the brain the herniation occurs. A brain herniation can cut off the blood supply to the brain. For this reason, it will likely be fatal if not treated promptly. Even with treatment, a brain herniation can lead to serious, permanent problems in the brain, or death.
A brain herniation is considered a medical emergency. You should call 911 or go to the emergency room immediately if a person with a head injury or brain tumor becomes less alert or disoriented, has a seizure, or becomes unconscious.