Blast-related TBI

Blast-related traumatic brain injury (TBI) is often associated with military conflicts and training but can also occur in the civilian world.

Blast-related TBI

Explosions generate a large amount of kinetic energy that can cause a range of injuries. Exposure to the complex, high-pressure blast waves released in an explosion (either direct or indirect) can result in a range of blast injuries to the body, including the brain. Blast-related traumatic brain injury (TBI) is often associated with military conflicts and training but can also occur in the civilian world, for example industrial and mining accidents.

What is a blast-related TBI?

Blast-related TBI is a traumatic brain injury caused by exposure to blast overpressure. Most blast-related TBI is mild TBI. Other terms for blast-related mild TBI include blast overpressure, military TBI1 or blast-induced neurotrauma (BINT)2.

Blast injuries occur with a sudden and significant increase in atmospheric pressure when an explosion happens. The change in atmospheric pressure creates an overpressure wave (blast wave), which moves outward from the source of the explosion at high speeds. This may cause significant damage to internal organs, including the brain.

Blast waves can cause TBI of all severities (i.e. subconcussive, mild, moderate, or severe), though mild TBI3 (concussion) is the most common.

There are many factors that can affect the severity of a blast injury. These include:
• Blast energy (i.e. the amount and type of explosives used)
• Distance from the blast wave
• Body position
• Use of body armour or helmets (these can amplify the effects of the blast wave)
• Environment (e.g. closed environments are usually worse than open spaces)
• Number of and time between blast exposures3,4
• Individual health and susceptibility (pre-existing conditions and overall health can influence injury severity)
• Blast wave duration and frequency (the length and frequency of the blast wave can affect the extent of the injury)
• Secondary projectiles (debris and shrapnel propelled by the blast can cause additional injuries)
• Protective measures (availability and use of protective measures other than armour, such as barriers or shields, can mitigate injury severity)

As with other types of blast injury, blast-related TBI can be classified into four subtypes1. These categories are based on mechanisms related to the explosion that cause injury. For blast-related TBI, these are:

1. Primary blast injury – TBI that is caused by the blast wave itself. Exposure to blast waves can cause concussion, diffuse axonal injury, and other forms of brain damage due to the rapid acceleration and deceleration of the brain tissue.

2. Secondary blast injury – TBI resulting from shrapnel or other debris hitting the head. Penetrating brain injuries may occur if objects pierce the skull and brain tissue.

3. Tertiary blast injury – TBI resulting from exposure to strong blast winds, which can propel people into objects or objects into people. For example, a TBI may result from blunt force trauma to the head when a person gets thrown into a solid object, such as a wall. Tertiary TBIs are the main type of blast TBI2.

4. Quaternary blast injury – This refers to other explosion-related factors such as burns, inhalation of toxic fire gases, or crush injuries. While these factors alone might not cause TBI, they can add to the physiological stress on the body and make brain injuries worse.

The US Department of Defense also recognises a fifth subtype of blast injury5–7. Called Quinary blast injury, this refers to longer-term effects and illnesses that can arise from exposure to toxic materials and environmental contaminants released by explosions. For example, bacterial agents dispersed by an explosion may lead to infections such as encephalitis (inflammation of the brain) or other secondary complications that can worsen blast-related TBI outcomes.

How does blast-related TBI occur?

Blast-related TBI most commonly occurs in military training and conflict zones. However, other ways that a person may sustain a blast-related TBI include3:

• Military and Police operations that involve breaching – a tactical technique used to enter closed or blocked buildings or areas, which involves the use of explosives
• Live firing during training exercises
• Terrorist attacks
• Mining accidents
• Industrial accidents
• Non-bomb blasts (e.g. chemical or fireworks explosions)

What parts of the brain are affected in blast-related TBI?

Each TBI, no matter what the cause, is unique. As such, any part of the brain can be injured when a person experiences a blast-related TBI, and there are many factors that determine the severity and extent of injury. However, studies that have used advanced neuroimaging techniques to better understand the structural and functional changes that happen in the brain following blast-related TBI have found evidence of:

• Decreased cortical thickness
• Decreased amygdala volume
• Decreased thalamus volume
• Differences in thalamic network architecture
• Irregularities in white matter tracts, including those that are commonly associated with TBI such as the corpus callosum and superior longitudinal fasciculus
• Changes in brain activity, especially in the frontal, parietal, temporal and cingulate regions8,9.

The cerebellum also appears to be particularly vulnerable to damage from blast-related TBI10,11. Although it is not yet clear why this is the case, microlesions in the blood-brain barrier and loss of Purkinje cells (a type of nerve cell found only in the cerebellum) are likely to play a role11.

* For more information on these parts of the brain, see the definitions at the bottom of the page.

Illustration of parts of the human brain
Illustration of parts of the brain

What are the consequences of blast-related TBI?

Blast injuries to the brain can cause a range of physical, emotional, cognitive and behavioural consequences. Amongst the most studied effects of blast-related TBI are post-traumatic stress disorder (PTSD), headache, depression, anxiety, sleep disorders, attention and cognitive disorders9. Most individuals will experience symptoms of blast-related TBI immediately after the injury has occurred. However, about 10-15% of people will have symptoms that persist over months and years12. In addition, military service members with a history or blast exposure have also been observed to have neuroimmune13 and hormonal14 changes. While mTBI and PTSD can co-occur, having a mild traumatic brain injury does not necessarily mean that a person will have post-traumatic stress disorder. They are distinct conditions, and it is possible to have one without the other.

 

Low-level blast exposure and TBI

Low-level blast (LLB) are explosions that involve lower blast pressures. Military personnel may be exposed to LLB from firing heavy weapon systems in combat or training environments, as well as some types of explosives used in combat.

In Australia, Military occupations and weapons systems that can increase risk of exposure to LLB include:
• Royal Australian Navy:
– Clearance Divers
– Naval Divers
• Australian Army Arms Corps (including instructors):
– Infantry
– Armour
– Artillery
– Combat Engineers
• Royal Australian Air Force:
– Combat Controllers
• Special Forces
• Australian Police Tactical Groups
• Any personnel working with breaching charges, grenades, shoulder-mounted recoilless weapons, large calibre weapons, indirect fire weapons (such as mortar weapon systems), artillery

LLB do not usually cause mild traumatic brain injury (concussion) from a single exposure. However, it may cause subconcussion – a type of head injury that does not present with any observable symptoms. Frequent exposure to LLB may result in cumulative effects and worsen outcomes from injury.

LLB exposure may cause the following symptoms:
• Neuropsychiatric Symptoms (e.g. irritability, depression, anxiety)
• Cognitive Impairments (e.g. concentration, memory, slowed thinking and reaction time)
• Decreased hand-eye coordination
• Headaches
• Tinnitus (ringing in the ears)
• Difficulty hearing/hearing loss
• Sleep disturbances15–18
• Brain-inflammation (e.g. may cause brain fog, low mood and above-mentioned symptoms)

To learn more about Traumatic Brain Injury Symptoms click here. 

 

Blast-related TBI and Chronic Traumatic Encephalopathy (CTE)

Though there have been numerous reports of CTE being found in military service members19, it is difficult to determine whether there is a relationship between blast-related TBI and CTE. This is partly because many individuals who donate their brains for post-mortem study also have a history of non-blast TBI (e.g. TBI from participating in contact sports or motor vehicle accidents). A recent study in which 225 brains of deceased military personnel were examined for the presence of CTE found evidence of CTE in only 3 out of 45 (6.67%) military members that had a known history of blast exposure20.

To learn more about CTE, click here.

 

Fact Sheets

Blast-related TBI

LLB exposure and TBI

 

 

Definitions

Cortical thickness The thickness of the outermost layer of the brain.

Amygdala Region of the brain that has a primary role in processing of memory, decision-making and emotional responses (including fear, anxiety and aggression).

Thalamus A pair of small, egg-shaped structures located within the brain, just above the brain stem and between the cerebral cortex. It plays an important role in sensation, movement, motivated behaviours and regulation of consciousness and alertness.

White matter tract A band/bundle of (mostly) myelinated axons that connect different parts of the brain.

Corpus Callosum A thick, white band of nerve fibres that connect the left and right hemispheres of the brain.

Superior longitudinal fasciculus A large, bidirectional white matter tract that links the prefrontal, temporal and occipital lobes.

Cerebellum The part of the brain that is located at the back of the head between the cerebrum and brain stem. It is mainly responsible for coordinating voluntary movement (e.g. walking) and balance.

Kinetic Energy Kinetic energy is the energy of motion such as the movement of an object or particle. A person walking, a basketball midflight, a pen falling from a desk and a charged particle in an electric field are all examples of kinetic energy.

Blast-related TBI references
  1. Kong, L. Z., Zhang, R. L., Hu, S. H. & Lai, J. B. Military traumatic brain injury: a challenge straddling neurology and psychiatry. Mil Med Res 9, 1–18 (2022).
  2. Cernak, I. & Noble-Haeusslein, L. J. Traumatic brain injury: An overview of pathobiology with emphasis on military populations. Journal of Cerebral Blood Flow and Metabolism 30, 255–266 (2010).
  3. Rosenfeld, J. V. et al. Blast-related traumatic brain injury. Lancet Neurol 12, 882–893 (2013).
  4. Cernak, I. Blast Injuries and Blast-Induced Neurotrauma. Brain Neurotrauma: Molecular, Neuropsychological, and Rehabilitation Aspects 631–644 (2015) doi:10.1201/b18126.
  5. US Department of Defense. Medical research for prevention, mitigation, and treatment of blast injuries (Directive Number 6025.21E). https://www.esd.whs.mil/Portals/54/Documents/DD/issuances/dodd/602521p.pdf?ver=2018-10-24-112151-983.
  6. Westrol, M. S., Donovan, C. M. & Kapitanyan, R. Blast Physics and Pathophysiology of Explosive Injuries. Ann Emerg Med 69, S4–S9 (2017).
  7. Bryden, D. W., Tilghman, J. I. & Hinds, S. R. Blast-Related Traumatic Brain Injury: Current Concepts and Research Considerations. J Exp Neurosci 13, (2019).
  8. Mu, W., Catenaccio, E. & Lipton, M. L. Neuroimaging in Blast-Related Mild Traumatic Brain Injury. Journal of Head Trauma Rehabilitation 32, 55–69 (2017).
  9. Phipps, H. et al. Characteristics and Impact of U.S. Military Blast-Related Mild Traumatic Brain Injury: A Systematic Review. Front Neurol 11, 559318 (2020).
  10. Mac Donald, C. et al. Cerebellar White Matter Abnormalities following Primary Blast Injury in US Military Personnel. PLoS One 8, e55823 (2013).
  11. Peskind, E. R. et al. Cerebrocerebellar hypometabolism associated with repetitive blast exposure mild traumatic brain injury in 12 Iraq war Veterans with persistent post-concussive symptoms. Neuroimage 54, S76–S82 (2011).
  12. Hicks, R. R., Fertig, S. J., Desrocher, R. E., Koroshetz, W. J. & Pancrazio, J. J. Neurological Effects of Blast Injury. J Trauma 68, 1257 (2010).
  13. Gilmore, N. et al. Impact of repeated blast exposure on active-duty United States Special Operations Forces. Proc Natl Acad Sci U S A 121, e2313568121 (2024).
  14. Hellewell, S. C., Granger, D. A. & Cernak, I. Blast-Induced Neurotrauma Results in Spatially Distinct Gray Matter Alteration Alongside Hormonal Alteration: A Preliminary Investigation. International Journal of Molecular Sciences 2023, Vol. 24, Page 6797 24, 6797 (2023).
  15. US Department of Defense Traumatic Brain Injury Center of Excellence. What is Low-Level Blast? DoD Provider Fact Sheet https://www.health.mil/Reference-Center/Fact-Sheets/2023/07/18/Low-Level-Blast-for-Providers-Fact-Sheet (2023).
  16. Carr, W. et al. Relation of repeated low-level blast exposure with symptomology similar to concussion. Journal of Head Trauma Rehabilitation 30, 47–55 (2015).
  17. Carr, W. et al. Repeated Low-Level Blast Exposure: A Descriptive Human Subjects Study. Mil Med 181, 28–39 (2016).
  18. St Onge, P., McIlwain, D., Hill, M., Walilko, T. & Bardolf, L. Marine Corps breacher training study: auditory and vestibular findings. The United States Army Medical Department Journal 97–107 (2011).
  19. Kim, P. S. & Beran, R. G. Chronic Traumatic Encephalopathy/Traumatic Encephalopathy Syndrome in Military Personnel. J Mil Veterans Health 30, 40–48 (2022).
  20. Priemer, D. S., Iacono, D., Rhodes, C. H., Olsen, C. H. & Perl, D. P. Chronic Traumatic Encephalopathy in the Brains of Military Personnel. New England Journal of Medicine 386, 2169–2177 (2022).

 

Disclaimer
Connectivity does not offer medical advice for individuals. If you have suffered a traumatic brain injury, please seek medical advice.

Created July 2024