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Neurological Reports

Classifying Traumatic Brain Injury

Classifying Traumatic Brain Injury

18 December 2023   |   Gyrus Group


Accurate classification of traumatic brain injuries (TBIs) is important for the development and application of targeted treatments, and in understanding prognosis. There is no unified approach to TBI classification, and methods of classification are difficult to both develop and apply. Determining injury severity often relies on subjective determinations, symptoms which may not appear until beyond the acute stages of TBI, and symptoms which do not have an objectively measurable cause (such as a skull fracture, or a bleed identifiable on brain imaging). Systematic approaches to TBI classification include classifying by symptoms/severity (clinical presentation, often including level of consciousness and memory disturbance), physical mechanism (how the injury occurred), pathoanatomic features (identification of lesions, such as bleeds), or by prognosis (expected outcomes of TBI) (Saatman et al., 2008). The subjective nature of TBI symptom reporting and the use of different classifications of TBI can complicate medicolegal practice, which relies on objective truths and clear associations between cause and event (Kelly et al., 2023). Here, we describe three commonly used classification systems in both clinical and medicolegal practice.

The Glasgow Coma Scale

One of the most widely used systems, particularly in the acute stages of TBI, is the Glasgow Coma Scale (GCS; (Glasgow Coma Scale, n.d.; Saatman et al., 2008; Teasdale & Jennett, 1974). This is a measure of consciousness, where the lowest scores indicate unconsciousness or minimal consciousness, and higher scores indicate normal or close-to-normal consciousness. Scores can range from 3 (injuries with extremely high risk of fatality) to 15 (normal consciousness, highly survivable; Demetriades et al., 2004). TBI severity can be approximately categorised according to GCS, where severe brain injuries may result in lower GCS scores (3 to 8), moderate injuries may have middling scores (9 to 12), and mild brain injuries may result in higher GCS scores (13 to 15). GCS is a useful accompaniment to other objective measures, such as brain imaging, which may or may not initially show abnormalities. GCS classification measures the patient’s response in three domains: eyes, verbal, and motor responses.

Glasgow Coma Scale
Eyes Verbal Motor
4: Spontaneous opening 5: Oriented 6: Obeys commands
3: Open to verbal command 4: Confused speech 5: Localises pain
2: Open to pressure 3: Words 4: Normal flexion
1: None 2: Sounds 3: Abnormal flexion
1: None 2: Extension
1: None

ACRM Mild Brain Injury Definition

Mild TBI can be particularly difficult to assess, as there may be no associated loss of consciousness, post-traumatic amnesia, or abnormal brain imaging findings more commonly associated with moderate or severe TBI. Symptoms of mild TBI may not emerge in the acute stages, and due to the subjective nature of physical, cognitive, and behavioural symptoms, may not be immediately identified as being associated with a brain injury. The American Congress for Rehabilitation Medicine (ACRM) provide a definition to assist in identifying mild TBI (Kay et al., 1993):
“A patient with mild traumatic brain injury is a person who has had a traumatically induced physiological disruption of brain function, as manifested by at least one of the following:

  1. any period of loss of consciousness
  2. any loss of memory for events immediately before or after the accident
  3. any alteration in mental state at the time of the accident
  4. focal neurological deficit(s) that may or may not be transient

But where the severity of the injury does not exceed the following:

  • Loss of consciousness of 30 minutes or less
  • After 30 minutes, an initial Glasgow Coma Scale (GCS) of 13-15
  • Posttraumatic amnesia (PTA) not greater than 24 hours

The Mayo Classification System for Traumatic Brain Injury Severity

One of the most robust and holistic measures of TBI severity, the Mayo classification system (Malec et al., 2007) builds on features mention above, including Glasgow Coma Scale score, post-traumatic amnesia, and imaging findings. The Mayo classification system is particularly popular as it encapsulates objective and subjective measures, and provides three levels of injury classification: Moderate-Severe (Definite) TBI, Mild (Probable) TBI, and Symptomatic (Possible) TBI. Criticism of the Mayo is the lack of distinction between moderate and severe injury, however the distinction between ‘mild’ and ‘moderate-severe’ is often sufficient in clinical practice, particularly in management of the acute phase of brain injury. The Mayo traumatic brain injury severity criteria are as follows:

Criteria A (Moderate-Severe Definite). 

Classify as Moderate-Severe (Definite) TBI if one or more of the following apply:

Criteria B (Mild Probable). If none of Criteria A apply, class as Mild (probable) TBI if one or more of the following apply: Criteria C (Symptomatic Possible).

If none of Criteria A or B apply, classify as Symptomatic (probable) TBI if one or more of the following symptoms are present:

Death due to this TBI Loss of consciousness of momentary to less than 30 minutes
  • Blurred vision
  • Confusion
  • Dazed
  • Dizziness
  • Focal neurologic symptoms
  • Headache
  • Nausea
Loss of consciousness of 30 minutes or more Post-traumatic amnesia of momentary to less than 24 hours
Post-traumatic anterograde amnesia of 24 hours or more Depressed, basilar, or linear skull fracture (dura intact)
Worst Glasgow Coma Scale full score in first 24 hours (<13)
One or more of the following present:

  • Intracerebral haematoma
  • Subdural haematoma
  • Epidural haematoma
  • Cerebral contusion
  • Haemorrhagic contusion
  • Penetrating TBI (dura penetrated)
  • Subarachnoid haemorrhage
  • Brain stem injury


The Glasgow Coma Scale, ACRM definition of Mild Traumatic Brain Injury, and Mayo Classification System for traumatic brain injury each convey brain injury severity according to clinical presentation and objective findings, such as brain imaging. While these are sufficient for classifying brain injuries in medical practice, there are nuances within the classification systems that require expert neurologists and neuroradiologists to determine the most appropriate classification. Although recovery from TBI is often associated with early TBI classification, it is important to recognise – particularly in a medicolegal setting – that early classifications can be imperfect, and it often requires a significant period of recovery (generally around 2 years post-injury) to better understand the trajectory of recovery and any lasting disability that may have been caused by the TBI.


Demetriades, D., Kuncir, E., Velmahos, G. C., Rhee, P., Alo, K., & Chan, L. S. (2004). Outcome and Prognostic Factors in Head Injuries With an Admission Glasgow Coma Scale Score of 3. Archives of Surgery, 139(10), 1066–1068.

Glasgow Coma Scale. (n.d.). Retrieved December 13, 2023, from

Kay, T., Harrington, D. E., Adams, R., Anderson, T., Berrol, S., Cicerone, K., Dahlberg, C., Gerber, D., Goka, R., Harley, P., Hilt, J., Horn, L., Lehmkuhl, D., & Malec, J. (1993). Definition of mild traumatic brain injury (ACRM). Journal of Head Trauma Rehabilitation, 8(3), 86–87.

Kelly, N. A., Kelly, R. E., & Berkeley, R. P. (2023). The Glasgow Coma Scale: A disconnect between medical documentation and traumatic brain injury litigation in the United States.

Malec, J. F., Brown, A. W., Leibson, C. L., Flaada, J. T., Mandrekar, J. N., Diehl, N. N., & Perkins, P. K. (2007). The Mayo Classification System for Traumatic Brain Injury Severity. Https://Home.Liebertpub.Com/Neu, 24(9), 1417–1424.

Saatman, K. E., Duhaime, A. C., Bullock, R., Maas, A. I. R., Valadka, A., Manley, G. T., Brody, D., Contant, C., Dash, P., Diaz-Arrastia, R., Fertig, S., Gean, A., Goodman, C., Gordon, W., Hayes, R., Hicks, R., Langloi, J., Marmarou, A., Moore, D., … Wright, D. (2008). Classification of traumatic brain injury for targeted therapies. Journal of Neurotrauma, 25(7), 719–738.

Teasdale, G., & Jennett, B. (1974). ASSESSMENT OF COMA AND IMPAIRED CONSCIOUSNESS. A Practical Scale. The Lancet, 304(7872), 81–84.