A traumatic brain injury (TBI), also known as an intracranial injury, is an injury to the brain caused by an external force. TBI can be classified based on severity (ranging from mild traumatic brain injury to severe traumatic brain injury), mechanism (closed or penetrating head injury), or other features (e.g., occurring in a specific location or over a widespread area).  Head injury is a broader category that may involve damage to other structures such as the scalp and skull. TBI can result in physical, cognitive, social, emotional and behavioral symptoms, and outcomes can range from complete recovery to permanent disability or death.

Causes include falls, vehicle collisions and violence. Brain trauma occurs as a consequence of a sudden acceleration or deceleration within the cranium or by a complex combination of both movement and sudden impact. In addition to the damage caused at the moment of injury, a variety of events following the injury may result in further injury. These processes include alterations in cerebral blood flow and pressure within the skull. Some of the imaging techniques used for diagnosis include computed tomography (CT) and magnetic resonance imaging (MRIs).

TBI is a major cause of death and disability worldwide, especially in children and young adults.  Males sustain traumatic brain injuries around twice as often as females.  The 20th century saw developments in diagnosis and treatment that decreased death rates and improved outcomes.

TBI is usually classified based on severity, anatomical features of the injury, and the mechanism (the causative forces).  Mechanism-related classification divides TBI into closed and penetrating head injury. A closed (also called nonpenetrating, or blunt) injury occurs when the brain is not exposed. penetrating, or open, head injury occurs when an object pierces the skull and breaches the dura mater, the outermost membrane surrounding the brain.

Severity

Brain injuries can be classified into mild, moderate, and severe categories. The Glasgow Coma Scale (GCS), the most commonly used system for classifying TBI severity, grades a person’s level of consciousness on a scale of 3–15 based on verbal, motor, and eye-opening reactions to stimuli.  In general, it is agreed that a TBI with a GCS of 13 or above is mild, 9–12 is moderate, and 8 or below is severe.