Brain herniation occurs when pressure within the skull (intracranial pressure) is increased, causing the brain to be pushed sideways and downward through small natural openings in the relatively rigid sheets of tissue that divide the brain into compartments. Brain herniation is a medical emergency.
- Brain herniation may occur when a brain tumor, bleeding in the brain, another mass, or a disorder (such as liver or kidney failure) greatly increases pressure within the skull.
- Symptoms vary depending on which part of the brain is being compressed and can include abnormal breathing, abnormal muscle contractions, eye problems, impaired mental function, and coma.
- Computed tomography or magnetic resonance imaging is done to diagnose brain herniation.
- Doctors treat causes if possible and take measures to support breathing (such as mechanical ventilation) and to reduce the increased pressure within the skull.
A large mass, such as a brain tumor, an accumulation of blood (hematoma), or swelling can push the brain against the relatively rigid sheets of tissue that divide the brain in compartments. As a result, brain tissue may be damaged. If pressure is put on the areas of the brain that control consciousness, stupor or coma results. If the pressure is high enough, the brain may be forced through small openings in these dividers. This life-threatening disorder is called brain herniation. Herniation can further damage brain tissue, making an already dire condition worse.
There are two common types of herniation. They are named after the structure that the brain is pushed through:
- Transtentorial herniation: The upper part of the brain (cerebrum) is forced through the tentorial notch, which divides the cerebrum from the lower parts of the brain (cerebellum and brain stem). In people with this type of herniation, consciousness is reduced. The side of the body opposite the tumor may be paralyzed. The pupil of the eye on the side of the herniation may widen (dilate) and may not narrow (constrict) in response to bright light.
- Tonsillar herniation: A mass (tumor or bleeding) in the lower part of the brain pushes the lowest part of the cerebellum (cerebellar tonsils) through the opening at the base of the skull (foramen magnum). As a result, the brain stem, which controls breathing, heart rate, and blood pressure, is compressed and malfunctions.
Brain Herniation: The Brain Under Pressure
Bleeding or swelling in the brain can increase pressure within the skull. The pressure may force the brain sideways and downward in the skull through small openings in the relatively rigid sheets of tissue that separate the brain into compartments. The result is brain herniation. These dividers are extensions of the outer layer of tissue covering the brain (the dura mater.) Herniation compresses brain tissue and thus damages it.
Brain herniation results from disorders the can cause pressure within the skull to increase. They include
- Masses in the brain, such as brain tumors, areas of swelling (edema), an accumulation of blood (hematoma), or a pocket of pus (abscess)
- Widespread swelling caused by liver or kidney failure
- Increased pressure in the veins carrying blood away from the brain (such as the jugular veins)
- Blockages of cerebrospinal fluid (the fluid that flows through the tissues covering the brain and spinal cord and fills the spaces within the brain)
Increased pressure in the veins carrying blood from the brain may result from heart failure, blockages in the veins, or venous sinus thrombosis (a blood clot in the large veins that drain blood from the brain).
Symptoms of Brain Herniation
People with brain herniation may have symptoms of the disorder causing the problem. They may also have various symptoms depending on which part of the brain is being compressed. These symptoms include
- An abnormal pattern of breathing
- Unintended (involuntary) muscle contractions: For example, the head may be tilted back with the arms and legs extended—a position called decerebrate rigidity. Or the arms may be flexed with both legs extended—a position called decorticate rigidity. Or the entire body may be limp.
- Eye problems: One or both pupils of the eyes may be widened (dilated) and may not narrow (constrict) in response to light. Or the pupils may be tiny. The eyes may not move or may move in abnormal ways.
- Impaired consciousness, including stupor and coma
Other symptoms may include nausea, vomiting, a stiff neck, headache, and increasing sleepiness.
If not diagnosed and treated immediately, herniation can have catastrophic consequences, including paralysis, abnormal heart rhythms, and difficulty breathing. Breathing may stop (respiratory failure), the heart may stop pumping (cardiac arrest), causing death.
Diagnosis of Brain Herniation
- Imaging tests
Brain herniation is an emergency. Identifying it promptly is crucial to make life-saving treatment possible.
Doctors can usually tell that consciousness is impaired based on observation and a physical examination, with a focus on the nervous system (called the neurologic examination). Findings may suggest that the pressure within the skull (intracranial pressure) is increased before herniation occurs. If doctors suspect that it is increased, they do computed tomography (CT) or magnetic resonance imaging (MRI) immediately to check for possible causes, including swelling, bleeding, a structural abnormality, or a mass in the brain (such as a tumor, an accumulation of blood, or an abscess). If test results indicate increased pressure, doctors may drill a small hole in the skull and insert a device into one of the fluid-filled spaces (ventricles) in the brain. This device is used to reduce the pressure and monitor it during treatment.
CT or MRI can also show brain herniation and confirm the diagnosis.
Treatment of Brain Herniation
- Measures to help people breathe
- Treatment of the cause
- Measures to reduce the increased pressure within the skull
Prompt treatment of brain herniation is crucial. If a person is rapidly becoming less alert and more difficult to arouse, immediate treatment is required, often before the cause can be diagnosed.
Treatment is similar to treatment of coma. The cause of brain herniation is treated when possible.
The first steps in treatment, sometimes done by emergency medical personnel, are to check the following and treat them if needed:
- Whether the airway is open
- Whether breathing is adequate
- Whether pulse, blood pressure, and heart rate are normal (to make sure blood is reaching the brain)
People are treated first in an emergency department and then admitted to a hospital intensive care unit. In both places, nurses can monitor heart rate, blood pressure, temperature, and the oxygen level in the blood. Any abnormalities in these measurements are immediately corrected to prevent further damage to the brain. Oxygen is often given immediately, and a tube is inserted into a vein (intravenous line) so that drugs or sugar (glucose) can be given quickly.
If people have a very high or low body temperature, measures are taken to cool (heatstroke treatment) or warm them (hypothermia treatment). Any other disorders (such as heart or lung disorders), if present, are treated.
Treatment to control breathing
If doctors suspect that the pressure within the skull is increased, a breathing tube is inserted through the mouth so that mechanical ventilation can be used to make sure that enough carbon dioxide is exhaled and to maintain adequate oxygen levels in the blood. Most people with brain herniation need a mechanical ventilator to breathe for them. Mechanical ventilation is also used to quickly decrease the increased pressure within the skull.
The breathing tube is inserted through the nose or mouth and into the windpipe (trachea)—called endotracheal intubation. It prevents people from inhaling stomach contents after vomiting. The tube is then attached to a mechanical ventilator.
Mechanical ventilation can cause agitation, which can be treated with a sedative.
Treatment of increased pressure within the skull
If pressure within the skull (intracranial pressure) is increased, the following measures may be taken to lower it:
- The head of the bed may be elevated.
- Mechanical ventilation is used to make people breathe faster (called hyperventilation). Breathing faster removes carbon dioxide from the lungs and reduces the level of carbon dioxide in the blood. As a result, blood vessels in the undamaged part of the brain narrow, and less blood reaches the brain. This measure quickly but temporarily lowers pressure within the skull and temporarily stops herniation. The beneficial effect of hyperventilation lasts about 30 minutes. Doctors use this time to start treatments that can stop herniation, such as drugs and surgical procedures, which take more time.
- Diuretics or other drugs may be used to reduce fluids in the brain and rest of the body. Diuretics help eliminate excess fluid by causing the kidneys to excrete more sodium and water into urine.
- A sedative may be given to control excess involuntary muscle contractions or agitation caused by mechanical ventilation. These problems can increase pressure within the skull.
- Blood pressure is sometimes lowered, particularly if it was already high.
- Sometimes doctors insert a drain (shunt) in the ventricles of the brain to drain cerebrospinal fluid. Removing excess fluid can help lower pressure within the skull.
If pressure is increased because of a brain tumor or abscess, corticosteroids, such as dexamethasone, may help reduce pressure. However, corticosteroids are not used when increased pressure is caused by certain other disorders, such as bleeding within the brain or a stroke, because corticosteroids may make these conditions worse.
If other measures do not work, the following may be tried:
- When pressure within the skull is increased after a head injury or cardiac arrest, measures to lower body temperature may be tried. These measures may help some people who have had cardiac arrest.
- Pentobarbital (a barbiturate) may be used to reduce blood flow to the brain and brain activity. This treatment may improve the prognosis for some people. However, it is not beneficial for everyone, and it has side effects, such as low blood pressure and abnormal heart rhythms.
- The skull may be opened surgically (craniectomy), creating more room for the swollen brain and thus reducing pressure on the brain. This treatment can prevent death, but it may not improve a person's ability to recover function.
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