U.S. flag

An official website of the United States government

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

O'Neil ME, Carlson K, Storzbach D, et al. Complications of Mild Traumatic Brain Injury in Veterans and Military Personnel: A Systematic Review [Internet]. Washington (DC): Department of Veterans Affairs (US); 2013 Jan.

Cover of Complications of Mild Traumatic Brain Injury in Veterans and Military Personnel: A Systematic Review

Complications of Mild Traumatic Brain Injury in Veterans and Military Personnel: A Systematic Review [Internet].

Show details


1.1. Definition of Traumatic Brain Injury

A traumatically induced structural injury and/or physiological disruption of brain function as a result of an external force that is indicated by new onset or worsening of at least one of the following clinical signs, immediately following the event:

  • Any period of loss of or a decreased level of consciousness (LOC)
  • Any loss of memory for events immediately before or after the injury (post-traumatic amnesia6)
  • Any alteration in mental state at the time of the injury (confusion, disorientation, slowed thinking, etc.) (Alteration of consciousness/mental state5)
  • Neurological deficits (weakness, loss of balance, change in vision, praxis, paresis/plegia, sensory loss, aphasia, etc.) that may or may not be transient
  • Intracranial lesion

External forces may include any of the following events: the head being struck by an object, the head striking an object, the brain undergoing an acceleration/deceleration movement without direct external trauma to the head, a foreign body penetrating the brain, forces generated from events such as a blast or explosion, or other forces yet to be defined.

The above criteria define the event of a TBI. Not all individuals exposed to an external force will sustain a TBI, but any person who has a history of such an event with immediate manifestation of any of the above signs and symptoms can be said to have had a TBI.

1.2. Severity of Brain Injury Stratification

TBI is further categorized as to severity into mild, moderate, or severe based on the length of LOC, AOC, or PTA (see Table A-1). Acute injury severity is determined at the time of the injury.

Table A-1. Classification of TBI Severity.

Table A-1

Classification of TBI Severity.

  • The patient is classified as mild/moderate/severe if s/he meets any of the criteria in Table A-1 within a particular severity level. If a patient meets criteria in more than one category of severity, the higher severity level is assigned.
  • If it is not clinically possible to determine the brain injury level of severity because of medical complications (e.g., medically induced coma), other severity markers are required to make a determination of the severity of the brain injury.
  • Abnormal structural imaging (e.g., Magnetic Resonance Imaging or Computed Tomography Scanning) attributed to the injury will result in the individual being considered clinically to have greater than mild injury.

In addition to traditional imaging studies, other imaging techniques such as functional magnetic resonance imaging, diffusion tensor imaging, positron emission tomography scanning; electrophysiological testing such as electroencephalography; and neuropsychological or other standardized testing of function have been used in the evaluation of persons with TBIs, but are not considered in the currently accepted criteria for measuring severity at the time of the acute injury outlined in Table A -1.

The severity level has prognostic value, but does not necessarily predict the patient's ultimate level of functioning. There is substantial evidence that the epidemiology, pathophysiology, natural history, and prognosis for concussion/mTBI are different than for moderate and severe TBI. For example, moderate and severe TBI are often associated with objective evidence of brain injury on brain scan or neurological examination (e.g., neurological deficits) and objective deficits on neuropsychological testing, whereas these evaluations are frequently not definitive in persons with concussion/mTBI. The natural history and prognosis of moderate and severe TBI are much more directly related to the nature and severity of the injury in moderate and severe TBI, whereas factors unrelated to the injury (such as co-existing mental disorders) have been shown to be the strong predictors of symptom persistence after a concussion/mTBI.


  • PubReader
  • Print View
  • Cite this Page
  • PDF version of this title (1.2M)

Other titles in this collection

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...