TBI, a form of acquired brain injury, occurs when a sudden trauma causes damage to the brain. The damage can be focal – confined to one area of the brain – or diffuse – involving more than one area of the brain. TBI can result from a closed head injury* or a penetratinghead injury. A closed injury occurs when the head suddenly and violently hits an object but the object does not break through the skull. A penetrating injury occurs when an object pierces the skull and enters brain tissue.