If you bump your knee, it's likely to swell. But what if you injure your brain?
Swelling -- also called edema -- is the body's response to many types of injury. It can result from overuse or infection. Usually, swelling happens quickly and is simple to treat with some combination of rest, ice, elevation, medication, or removal of excess fluid.
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Your brain can also swell as a result of injury, illness, or other reasons. Brain swelling, though, can quickly cause serious problems -- including death. It's also usually more difficult to treat. That's because as your body's master control system, the brain is critical to overall function. Yet, the thick, bony skull that snugly protects this vital organ provides little room for the brain to swell.
What Is Brain Swelling?
Brain swelling goes by many names:
Elevated intracranial pressure
Swelling can occur in specific locations or throughout the brain. It depends on the cause. Wherever it occurs, brain swelling increases pressure inside the skull. That's known as intracranial pressure, or ICP. This pressure can prevent blood from flowing to your brain, which deprives it of the oxygen it needs to function. Swelling can also block other fluids from leaving your brain, making the swelling even worse. Damage or death of brain cells may result.
What Causes Brain Swelling?
Injury, other health problems, infections, tumors, and even high altitudes -- any of these problems can cause brain swelling to occur. The following list explains different ways the brain can swell:
Traumatic brain injury (TBI): A TBI is also called a head injury, brain injury, or acquired brain injury. In TBI, a sudden event damages the brain. Both the physical contact itself and the quick acceleration and deceleration of the head can cause the injury. The most common causes of TBI include falls, vehicle crashes, being hit with or crashing into an object, and assaults. The initial injury can cause brain tissue to swell. In addition, broken pieces of bone can rupture blood vessels in any part of the head. The body's response to the injury may also increase swelling. Too much swelling may prevent fluids from leaving the brain.
Ischemic strokes: Ischemic stroke is the most common type of stroke and is caused by a blood clot or blockage in or near the brain. The brain is unable to receive the blood -- and oxygen -- it needs to function. As a result, brain cells start to die. As the brain responds, swelling can occur.
Brain (intracerebral) hemorrhages and strokes: Hemorrhage refers to blood leaking from a blood vessel. Hemorrhagic strokes are the most common type of brain hemorrhage. They occur when blood vessels anywhere in the brain rupture. As blood leaks and the body responds, pressure builds inside the brain. High blood pressure is thought to be the most frequent cause of this kind of stroke. Hemorrhages in the brain can also be due to head injury, certain medications, and unknown malformations present from birth.
Infections: Illness caused by an infectious organism such as a virus or bacterium can lead to brain swelling. Examples of these illnesses include:
Meningitis: This is an infection in which the covering of the brain becomes inflamed. It can be caused by bacteria, viruses, other organisms, and some medications.
Encephalitis: This is an infection in which the brain itself becomes inflamed. It is most often caused by a group of viruses and is spread usually through insect bites. A similar condition is called encephalopathy, which is due to Reye's syndrome.
Toxoplasmosis: This infection is caused by a parasite. Toxoplasmosis most often affects fetuses, young infants, and people with damaged immune systems.
Subdural empyem: Subdural empyema refers to an area of the brain becoming abscessed or filled with pus, usually after another illness such as meningitis or a sinus infection. The infection can spread quickly, causing swelling and blocking other fluid from leaving the brain.
Tumors: Growths in the brain can cause swelling in several ways. As a tumor develops, it can press against other areas of the brain. Tumors in some parts of the brain may block cerebrospinal fluid from flowing out of the brain. New blood vessels growing in and near the tumor can also lead to swelling.
High altitudes: Although researchers don't know the exact causes, brain swelling is more likely to occur at altitudes above 4,900 feet. This type of brain edema is usually associated with severe acute mountain sickness (AMS) or high-altitude cerebral edema (HACE).