Traumatic Brain Injury

traumatic brain injury, any damage to the brain from an applied force. The forces involved can be from direct contact, as in a blunt or penetrating head injury; from a gravitational source such as fierce shaking; or from rotational energy that produces shear stress between the brain and the skull. Often, a combination of forces is involved; for example, a motor vehicle collision can cause both direct blunt trauma and injury from rotational and rapid velocity changes. Those events cause a deformation of the brain tissue that results in several types of pathology. In addition to the primary injury (caused at the moment the force is applied), a series of events are set in motion that continue to cause cellular damage over the next days to weeks or even longer. Those secondary injury events include a complex set of biochemical reactions and molecular changes that extend cellular damage, brain edema (swelling), and inflammation in a self-perpetuating cycle that rapidly increases the extent of the brain damage.

Traumatic brain injury is broadly defined in terms of three categories of severity—mild, moderate, and severe—based on the Glasgow Coma Scale (GCS). The GCS is a 15-point scale designed to measure the patient’s ability to respond to visual, verbal, and motor stimuli after traumatic brain injury. The degree of impairment depends on the extent of damage to critical brain areas. The majority of traumatic brain injuries are mild. Nonetheless, traumatic brain injury is a significant cause of death. In the United States, for example, 40 percent of deaths from acute injury are due to traumatic brain injury. Traumatic brain injury is also a major source of disability, resulting in sometimes permanent impairment of physical and cognitive function.