Definition A brain herniation occurs when the brain pushes downward inside the skull. Part of the brain tissue is displaced down through the skull opening that leads into the neck.
What is going on in the body? The brain is supported within the skull by a horseshoe-shaped support piece called the tentorium. In the tentorium is the opening where the brainstem connects to the brain. This is where most herniations occur. Conditions that cause increased size of 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 tumour, 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 centre of the tentorium. The swelling may result in the brain shifting from its normal position to an abnormal position in the skull.
What are the signs and symptoms of the condition? 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, or get 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 laboured, and the pulse rate steadily decreases.
What are the causes and risks of the condition? Anything that causes swelling in the brain might lead to herniation. Some common causes include:
head injury from a blow to the head or other trauma
bleeding in the brain. Examples of bleeding in the brain are epidural haematoma, subdural haematoma, or subarachnoid haemorrhage.
Brain hernation 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 to think can all be damaged.
What can be done to prevent the condition? Some causes cannot be prevented. For instance, a brain tumour cannot be prevented. But other diseases that cause bleeding in the brain, such as stroke, can be controlled and treated to reduce the chance of them causing herniation. A person can 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:
riding a motorcycle or bicycle
playing baseball, football, or other physical sports
skiing or snowboarding
How is the condition diagnosed? Diagnosis is based on 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, will verify the problem.
What are the long-term effects of the condition? If brain herniation is left untreated, the person will stop breathing and die.
What are the risks to others? There are no risks to others.
What are the treatments for the condition? This is a medical emergency and treatment must be started right away. Treatment is aimed at reducing the brain's swelling. The person will be given different kinds of medication through an intravenous line, or IV, that will get rid of excess water in the brain and reduce swelling. Treatment of the cause of the herniation must be started. The person will be kept in the hospital until the problem is over.
What are the side effects of the treatments? Even with successful relief of symptoms, the herniation may return if the cause is not also fixed. For instance, sometimes brain tumours return. In some cases, surgery is needed to relieve the pressure. Medications may cause side effects, such as allergic reactions and chemical imbalances, that need to be treated right away. Close monitoring is critical during treatment.
What happens after treatment for the condition? A person is often left with severe impairments, including:
If the person has significant impairments, it is important to begin rehabilitation with specialised therapists, nurses, and doctors who treat brain injuries.
How is the condition monitored? 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, on-going monitoring of the problem that caused the herniation may be needed.
Author: Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 26/10/2004 Contributors Potential conflict of interest information for reviewers available on request
