Cerebral edema is a dangerous condition where the brain's water content rises, causing the pressure to rise in the skull. Unlike swelling in other parts of the body, where there is room for extra fluid (think of a sprained ankle), the brain is protected by a hard, inflexible skull that can expand very little. So, if the brain begins to swell because of illness or injury, its oxygen supply can quickly be cut off as the blood vessels become squeezed. Cerebral edema is a medical emergency that can even lead to death as brain cells become damaged and die.
There are many causes of cerebral edema. A head trauma, like in a car accident or a fall, can cause the brain to be knocked about and injured, leading to swelling. The brain might also begin to swell as a response to a stroke, where a blood clot prevents oxygen from reaching the brain. A brain hemorrhage, when bleeding from the brain's blood vessels causes the pressure in the skull to rise, is often caused by high blood pressure, but can also happen because of a head injury, medications or malformations of the brain's blood vessels. Infections like meningitis or encephalitis can make the brain swell, as can tumors and even high altitudes.
Usually, the symptoms of cerebral edema appear suddenly. Headache, neck stiffness, nausea, vomiting, dizziness, difficulty walking and talking, changes in breathing patterns, seizures, and even loss of consciousness could indicate that the pressure inside the skull is rising. Doctors would quickly assess someone with these symptoms, and would try to find the cause with a neurologic exam, and scans like a CT or MRI. Except in the case of minor cerebral edema, like after a slight concussion, treatment needs to be fast to prevent permanent damage or death. Doctors would give oxygen, intravenous fluids, and medications, and might even perform surgery to shunt the fluid out of the brain or remove a piece of skull to relieve the pressure.