"Head injuries" include trauma to the brain, scalp, and/or skull. A concussion is the most common type of brain injury. It results in a temporary dysfunction of the brain. In severe injuries, the brain swells, causing pressure in the head to rise, further damaging the brain. A pressure-measuring device is placed into the brains of patients who are at risk of severe swelling from head injury. Sometimes surgery is required if the pressure in the head does not respond to various medical treatments. This surgery involves temporarily removing large portions of the patient's skull to relieve pressure on the brain.