Traumatic brain injury (TBI) is a form of nondegenerative acquired brain injury, resulting from an external physical force to the head (e.g., fall) or other mechanisms of displacement of the brain within the skull (e.g., blast injuries). Consistent with the diagnostic criteria detailed in the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; American Psychiatric Association [APA], 2013), TBI is associated with one or more of the following characteristics:
- Changes in levels of consciousness
- Memory disturbances
- Confusion associated with deficits in orientation
- Neurological signs, such as brain injury observable on neuroimaging, new onset or worsening of seizure disorder, visual field deficits, and hemiparesis
TBI can cause brain damage that is focal (e.g., gunshot wound) or widespread (e.g., diffuse axonal injury sustained in a motor vehicle accident). Damage can result from a primary injury or a secondary injury (see
common classifications of TBI for more details).
Severity of TBI is based on the extent and nature of the injury, duration of loss of consciousness, posttraumatic amnesia (PTA; loss of memory for events immediately following injury), and extent of confusion at initial assessment during the acute phase of the injury (APA, 2013; Centers for Disease Control and Prevention [CDC], 2015).
The Department of Defense (DOD) defines the following levels of severity (Defense Health Agency, 2019):
- Concussion/Mild TBI—loss of consciousness for up to 30 minutes; or confused or disoriented state lasting less than 24 hours; or memory loss lasting less than 24 hours. Excludes penetrating TBI. Results of a computed tomography (CT) scan, if obtained, are normal.
- Moderate TBI—loss of consciousness for more than 30 minutes, but less than 24 hours; or confused or disoriented state lasting more than 24 hours; or memory loss lasting more than 24 hours but less than 7 days; or meets criteria for concussion/mild TBI but with an abnormal CT. Excludes penetrating TBI. A structural brain imaging study may be normal or abnormal.
- Severe TBI—loss of consciousness for more than 24 hours; or confused or disoriented state lasting more than 24 hours; or memory loss lasting more than 7 days. Excludes penetrating TBI. A structural brain imaging study may be normal but usually is abnormal.
- Penetrating TBI—open head injury; scalp, skull, and dura mater (outer layer of meninges) are penetrated. Caused by high-velocity projectiles, objects of lower velocity such as knives, or bone fragments from a skull fracture that are driven into the brain.