A brain herniation, sometimes described as a cerebral herniation, occurs when brain tissue, blood, and cerebrospinal fluid (CSF) shift from their normal position inside the skull.
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. Often described as a midline shift, 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 brain stem 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 or blood pressure that’s too low
- loss of reflexes or increased reflexes
- shortness of breath or rapid breathing
- abnormal posturing, rigid body movements, and abnormal positions of the body
- cardiac arrest
- loss of consciousness
The time course of brain herniation symptoms varies.
For example, after a serious car accident, brain herniation may occur within an hour. For someone with a brain tumor, it can begin slowly and suddenly worsen. After a stroke, it may be erratic and happen within a few days.
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), pushing or compressing areas of the brain so they squeeze into other compartments, such as the foramen magnum.
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 that puts you at risk of a head injury can also increase your risk of a brain herniation.
The exams and tests to determine a brain herniation may include any of the following:
Because a brain herniation can be life threatening, a speedy diagnosis is essential.
To accurately diagnose a brain herniation, researchers suggest that healthcare professionals use an approach that includes:
- getting a comprehensive analysis of the person’s medical history and current symptoms
- identifying the brain structure that’s displaced to classify the hernia type
- evaluating other brain structures for possible herniation
Treatment is aimed at relieving the swelling and pressure inside the brain that’s causing the brain to herniate from one compartment to another. Treatment may prevent further brain damage or death.
To reduce swelling and pressure, treatment may involve:
- surgery to remove a tumor, blood clot, or abscess
- ventriculostomy, a surgery that places a drain through a hole in the skull to get rid of fluids
- osmotic therapy or diuretics, such as mannitol or hypertonic saline, to pull fluid out of the brain tissue
- corticosteroids to reduce inflammation
- craniectomy, a surgery that removes a part of the skull to make more room
Usually, a combination of these treatments is necessary.
While the cause of the brain herniation is being addressed, the person being treated may also receive:
If not treated right away, the disruption of brain tissue can impair vital structures in the body.
Complications of brain herniation include:
The outlook for a brain herniation 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 cut off the blood supply to a region of the brain.
A brain herniation is considered a medical emergency. 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.