A brain herniation occurs when a part of the brain pushes downward inside the skull through the opening that leads into the neck.
The brain is supported within the skull by a horseshoe-shaped piece called the tentorium. There is an opening in the tentorium where the brainstem connects to the brain. This is where most herniations occur.
Conditions that cause swelling in the brain or increased pressure in the skull can cause brain tissue to be pushed into this opening. This is called a herniation. For instance, if there is a mass, such as a tumor, in the head, the brain will swell. Since the skull is rigid, swelling will force the brain into the area of least resistance. This would be the hole in the center of the tentorium. The swelling may result in the brain shifting from its usual position to an abnormal position in the skull.
Anything that causes swelling in the brain might lead to herniation. Some common causes include:
Brain herniation can cause severe brain damage or even death. The brain tissue that is being squeezed through the opening and the brainstem tissue can be permanently damaged. The ability to breathe, keep the heart beating, be alert, and think can all be damaged.
Symptoms usually start with a loss of alertness that can progress into complete loss of consciousness. As the herniation increases, the pupil of the eye on the same side of the head as the swelling will dilate, which means it gets bigger. Weakness on the opposite side of the body will usually follow. Breathing will become irregular. The pulse will start to slow down. Finally, both pupils become dilated, breathing becomes labored, and the pulse rate steadily decreases.
Diagnosis is based on the person's medical history as well as characteristic signs and symptoms. Special tests that take pictures of the inside of the skull and brain, including cranial MRIs and cranial CT scans, can help confirm the diagnosis.
Some causes cannot be prevented. For instance, a brain tumor cannot be prevented. But other diseases that cause bleeding in the brain, such as stroke, can be controlled and treated to reduce the chance that they will cause herniation.
A person can help prevent injury to the head by following sports safety guidelines for adults, adolescents, and children. This would include wearing appropriate headgear, such as a helmet, when:
If brain herniation is left untreated, the person will stop breathing and die.
There are no risks to others.
This is a medical emergency, so treatment must be started right away. Treatment is aimed at reducing the brain's swelling. The person will be given different kinds of medicine through an intravenous line, called an IV. This treatment helps to get rid of excess water in the brain and reduce swelling. Treatment of the cause of the herniation is started next. The person will be kept in the hospital until the problem is solved.
Even with successful relief of symptoms, the herniation may return if the cause is not also fixed. For instance, sometimes brain tumors return. In some cases, surgery is needed to relieve the pressure. Medicines may cause side effects, such as allergic reactions and chemical imbalances, that need to be treated right away. Close monitoring is critical during treatment.
A person is often left with severe impairments, including:
If the person has significant impairments, it is important to begin rehabilitation with specialized therapists, nurses, and doctors who treat brain injuries.
All vital signs, such as heart rate, blood pressure, breathing rate, body temperature, and pressure inside the skull, should be monitored during treatment. After the crisis is over, ongoing monitoring of the problem that caused the herniation may be needed. Any new or worsening symptoms should be reported to the doctor.
Author:James Warson, MD
Editor:Crist, Gayle P., MS, BA
Reviewer:Karen Preston, PHN, MS, CRRN