Traumatic brain injury (TBI) occurs when a sudden trauma causes brain damage. TBI can result from a closed head injury or a penetrating head injury. Parts of the brain that can be damaged include the cerebral hemispheres, cerebellum, and brain stem. TBI can cause a number of physical, cognitive, emotional, and social effects. Symptoms of a TBI can be mild, moderate, or severe, depending on the extent of the damage to the brain. Outcome can be anything from complete recovery to permanent disability or death.