Traumatic Brain Injury Types and Classification

Traumatic brain injuries are a leading cause of disability and death worldwide. In Canada, approximately 160,000 people sustain traumatic brain injuries each year with 11,000 deaths and over 6,000 cases of permanent disability. However, around 75% of all TBI incidents are considered mild, commonly referred to as a concussion, and are rarely fatal.

 

Classification

TBI can be classified into primary and secondary injuries. Primary injuries are those that occur at the time of injury as a result of the sustained impact and include hematomas or brain bleeds. Secondary injuries occur hours and days after the initial injury and typically result from the biochemical cascade that follows which could result in inflammation, decreased cerebral blood flow, and neuronal death. Some treatments and preventive measures are used to delay or decrease these secondary injuries and reduce their impact on brain structure and function.

 

Types of head injuries

Head injuries and TBI are often broken up into 2 types: open and closed head injuries. Open head injuries are ones that penetrate the skull and damage the brain and can be caused by objects such as bullets or knives. In contrast, closed head injuries are caused by blunt, overpressure, or accelerative forces that keep the skull intact but damage the brain.

 

Severity

The classification of initial severity of TBI is necessary in order to determine the level of care required and the prognosis of the injury. TBIs are categorized based on severity into mild, moderate, or severe TBI. The following criteria are used to make such classification:

  • The Glasgow Coma Scale (GCS) is commonly used to assess the level of consciousness in patients within 24 hours of injury and is composed of 3 response scores: eye opening, motor, and verbal scores. The total obtained determines the severity of the injury where a score of 13-15 is considered mild, 9-12 is diagnosed as moderate, and less than 8 is categorized as severe TBI.
  • Loss of Consciousness (LOC): if LOC lasts less than 30 minutes, then the TBI is classified as mild; 30 minutes to 24 hours of LOC is considered as moderate; and more than 24 hours of LOC counts as a severe TBI.
  • Alteration of consciousness/mental state (AOC) manifests as alteration in consciousness that leads to acute cognitive-behavioural changes. Similar to LOC, the duration of AOC helps determine the severity of TBI where less than 30 minutes of AOC is mild, 30 minutes to 24 hours is moderate, and more than 24 hours is severe TBI.
  • Post-traumatic amnesia (PTA) is a common symptom of TBI. The duration of memory loss helps determine the severity of TBI. Less than 24 hours of PTA is mild, 24 hours to 7 days is considered moderate, and more than 7 days of PTA is classified as severe TBI.
  • Structural imaging: Using standard neuroimaging techniques such as CT scans, mild forms of TBI show no structural abnormalities whereas moderate and severe TBI could show normal or abnormal brain images.

 

Written by Lea Farah

 

References

Najem, D., Rennie, K., Ribecco-Lutkiewicz, M., Ly, D., Haukenfrers, J., Liu, Q., Nzau, M., Fraser, D. D., & Bani-Yaghoub, M. (2018). Traumatic brain injury: Classification, models, and markers. Biochemistry and Cell Biology, 96(4), 391-406. https://doi.org/10.1139/bcb-2016-0160

Sussman, E. S., Pendharkar, A. V., Ho, A. L., & Ghajar, J. (2018). Mild traumatic brain injury and concussion: Terminology and classification. (pp. 21-24). Elsevier Health Sciences. https://doi.org/10.1016/B978-0-444-63954-7.00003-3

Swanson, T. M., Isaacson, B. M., Cyborski, C. M., French, L. M., Tsao, J. W., & Pasquina, P. F. (2017). Traumatic brain injury incidence, clinical overview, and policies in the US military health system since 2000. Public Health Reports (1974), 132(2), 251-259. https://doi.org/10.1177/0033354916687748

van Baalen, B., Odding, E., Maas, A. I. R., Ribbers, G. M., Bergen, M. P., & Stam, H. J. (2003). Traumatic brain injury: Classification of initial severity and determination of functional outcome. Disability and Rehabilitation, 25(1), 9-18. https://doi.org/10.1080/713813430