The definition of a traumatic brain injury (TBI) has a long evolving history in the medical field. Some professionals might classify the problem as a “head injury,” a “concussion,” or a “traumatic brain injury.” No matter the name of the injury, the point of agreement for all definitions is that the brain is damaged. The most widely agreed upon definition is this: “A traumatic brain injury is an alteration in brain function, or other evidence of brain pathology, caused by an external force” (Menon et al., 2010).


“Alteration in brain function”

  • Any period of loss or decreased consciousness.
  • Any loss of memory for events immediately before (retro-grade amnesia) or after injury (PTA).
  • Neurologic deficits (weakness, loss of balance, change in vision, paralysis, sensory loss, etc).
  • Any alteration in mental state at the time of the injury (confusion, disorientation, slowed thinking, etc.)

“or other evidence of brain pathology”

  •  Confirmed damage to the brain via visual, neuroradiologic, or laboratory.

“caused by an external force” may include

  •  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 blasts or explosions
  • or other force yet to be defined


Traumatic brain injury is a growing health concern, with an annual incidence of 1.4 million people per year, of which 74% are mild TBIs (mTBI). mTBIs are often misdiagnosed and sent home, or properly diagnosed but discharged with no further brain treatment. The provided definition of traumatic brain injury is widely accepted – “A traumatic brain injury is an alteration in brain function, or other evidence of brain pathology, caused by an external force.” The difficulty for medical professionals is not one of definition, but rather one of identification. Severe traumatic brain injuries with multiple skull fractures, foreign objects stuck in the brain, and obvious MRI findings are easily diagnosed by medical professionals, but the TBI lacking these obvious signs does not rule out the TBI. These people likely have mild TBI (Fink, Mogil, & Lipton, 2016).

Depression is common after mTBI (15.3% risk). Depression, postconcussive syndrome and poor global outcomes are surprisingly worse for mTBI relative to severe TBI. Older mTBI persons are just as likely to experience depression as younger mTBI persons. Identification of mTBI occurs through process and will depend on symptoms, imaging, and diagnostic testing over a period of time  (Rao et al., 2010).

Phoenix, Arizona–The Department of Clinical Neuropsychology (2002) conducted a study on cognitive and affective sequelae in complicated and uncomplicated mild traumatic brain injuries. This raise two distinctions for mTBIs. The “complicated” mTBI has obvious brain tissue damage (lesions) that are shown on a CT scan or MRI, whereas “uncomplicated” mTBI lack these lesions, or they do not show up on a CT scan or MRI. While a complicated mTBI is more likely to have the worst cognitive function relative to an uncomplicated mTBI, some level of affective cognitive disturbances will exist in both groups, regardless of severity. Persons with uncomplicated mTBIs are typically denied admission into neurorehabilitation programs, even though they might need it.


  • Any force is sufficient to cause a TBI. A rotational force and axonal shear has the worst outcome typically (i.e. Figure 1).
  • Any alteration in consciousness.
  • Neurologic sequela may include headache, confusion, LOC, memory, finding words, loss of sensory abilities, balance, mood, behavior, learning, and any not otherwise listed alteration.
  • Gastrointestinal problems.
  • Vitamin deficiency.
  • Energy and will to perform at prior levels.
  • Biomarkers.
  • Blood work and other changes in the physiologic function.

Figure 1


Mayo Classification System

Mild (GCS, 13-15)

  • Brief, if any, loss of consciousness
  • Vomiting and nausea
  • Lethargic
  • Memory loss

Moderate (GCS, 9-12)

  • Unconscious up to 24 hours
  • Brain trauma
  • Contusions or bleeding
  • Signs of injury on neuroimaging tests

Severe (GCS, 3-8)

  • Unconsciousness exceeding 24 hours (coma)
  • No sleep/wake cycle during coma
  • Signs of injury on neuroimaging tests


  1. GCS is a single classification system.
  2. GCS is not predictive of long term outcome.
  3. Significant for severe TBI victims in terms of whether live or die.
  4. mTBI with GCS of 15 has no bearing on long term outcome (Journal of Neurotrauma, 24:1417-1424; September 2007).


Most symptoms of a TBI are highly volatile. The consequences of TBI are contingent upon many factors––such as the severity of the injury, the age and health of a person, where the brain is damaged, how much damage is done, and how long until treatment is received. One might receive a TBI on day X but not show symptoms until day Y or even day Z. Others might show symptoms immediately. A person can have a TBI, show symptoms, but overlook those symptoms and not get treated for the problem until later. Repeated damage to the brain, or just the right amount of damage in the right place, can lead to chronic traumatic encephalopathy (CTE). This article describes the risk of brain sequelae or CTE after any kind of head trauma, meaning the head trauma victim may be non-symptomatic initially, but the damaged neurons and axons in the bran an slowly degenerate over time leading to memory loss, depression, and risk of suicide. The most common symptom of a TBI is depression. There are four categories of symptoms for a TBI, all of which are subjective but still relevant:


* Clouded thinking
* Thinking slowly
* Trouble concentrating
* Difficulty remembering new information
* Epilepsy

* Abnormal headaches
* Fuzzy or blurry vision
* Nausea or vomiting (early on)
* Dizziness
* Sensitivity to noise or light (sensory issues)
* Balance issues
* Abnormally tired, less energized
* Slurred speech

* Irritability
* Sadness
* More emotional
* Nervousness or anxiety

* Sleeping more than usual
* Sleeping less than usual
* Trouble falling asleep


Neuroimaging (Fink AZ, Mogil LB, Lipton ML. Advanced neuroimaging in the clinic: critical appraisal of the evidence base. Br J Radiol 2016; 89: 20150753)

  1. Diffusion tensor imaging (DTI. This is the best test for proving a brain injury because it shows brain abnormalities far better than a standard CT or MRI, and is actually a higher form of an MRI.
  2. Magnetoencepholagraphy (MEG) is best for revealing/explaining cognitive deficits
  3. Dynamic Susceptibility Contrast (DSC–MRI) is good for identifying glioma (a brain tumor).
  4. Magnetic resonance imaging (MRI)
  5. Single photon emission computed tomography (SPECT)
  6. Electroencephalogram (EEG)
  7. Electromyography (EMG)

Physical alterations

  • Blood clots
  • Skull fractures
  • Penetration through head
  • One pupil larger than other


  • Convulsions or seizures


According to this study done in 2015 by the Annals of Neurology foundation, moderate to severe traumatic brain injuries can increase brain age (Figure 2, p.2). They found a correlation between increased brain age (atrophy) and cognitive impairment. This is why older people are more likely to get dementia than younger people. But with a traumatic brain injury, if severe enough, brain atrophy can start sooner than later (Tagge et al., 2018). The brain of a TBI person appears older, irrespective of the cause of injury (sports, cars, abuse, etc.). On average, the TBI person has a brain >4 years older than his or her chronological age. Persons with mild TBI are less likely to show brain aging or atrophy (Cole, Leech, Sharp, & Alzheimer’s Disease Neuroimaging, 2015).

Figure 2

A person with a single concussion, whether mild or severe, has a three times greater likelihood of committing suicide in the long term, according to this article. Nearly half of all patients with mild TBI have permanent cognitive impairments (McInnes, Friesen, MacKenzie, Westwood, & Boe, 2017).


When it comes to closed-head injuries, there is no apparent correlation between the intensity of impact and the level of acute neurobehavioral responses one will incur. In other words, the amount of force to the brain does not always indicate the amount of impairments.

  1. Prior concussion
  2. Prior tests (neurological or psychological)
  3. Gap between date of injury and date of treatment.
  4. Objective symptoms
  5. Type of injury (jolt, direct, indirect, blow, etc.)
  6. Witnesses
  7. Event/Context



Borgaro, S. R., & Prigatano, G. P. (2002). Early cognitive and affective sequelae of traumatic brain injury: a study using the BNI Screen for Higher Cerebral Functions. J Head Trauma Rehabil, 17(6), 526-534.

Cepelewicz, Jordana, Scientific American (2016). A Single Concussion May Triple the Long-Term Risk of Suicide. February 8, 2016.

Cole, J. H., Leech, R., Sharp, D. J., & Alzheimer’s Disease Neuroimaging, I. (2015). Prediction of brain age suggests accelerated atrophy after traumatic brain injury. Ann Neurol, 77(4), 571-581. doi:10.1002/ana.24367

Fink, A. Z., Mogil, L. B., & Lipton, M. L. (2016). Advanced neuroimaging in the clinic: critical appraisal of the evidence base. Br J Radiol, 20150753. doi:10.1259/bjr.20150753

McInnes, K., Friesen, C. L., MacKenzie, D. E., Westwood, D. A., & Boe, S. G. (2017). Mild Traumatic Brain Injury (mTBI) and chronic cognitive impairment: A scoping review. PLoS One, 12(4), e0174847. doi:10.1371/journal.pone.0174847

Menon, D. K., Schwab, K., Wright, D. W., Maas, A. I., Demographics, Clinical Assessment Working Group of the, I., . . . Psychological, H. (2010). Position statement: definition of traumatic brain injury. Arch Phys Med Rehabil, 91(11), 1637-1640. doi:10.1016/j.apmr.2010.05.017

Tagge, C. A., Fisher, A. M., Minaeva, O. V., Gaudreau-Balderrama, A., Moncaster, J. A., Zhang, X. L., . . . Goldstein, L. E. (2018). Concussion, microvascular injury, and early tauopathy in young athletes after impact head injury and an impact concussion mouse model. Brain, 141(2), 422-458. doi:10.1093/brain/awx350