Traumatic brain injury (TBI) is one of those medical conditions that we're hearing more about these days -- maybe because of increasing prevalence among soldiers in recent wars, and better research on the effects of TBI on athletes. However, TBI can affect anyone -- the problem leads to more than 1.7 million hospital stays and deaths each year. Because many people with mild TBI never go to a doctor, the true number of cases is probably larger.
The most common cause of civilian TBI varies by age. Between the ages of 0 to 4, the most common causes are falls or abuse. In adolescents, the most common causes are motor vehicle accidents or sports injuries. Falls are the most common cause in adults over the age of 65. Men are more commonly affected by TBI than women.
The costs of TBI are staggering. Treating someone with TBI can cost, on average, anywhere from $85,000 to $3 million, not including what is lost by the victim's inability to work. Total costs to society are currently thought to be about $60 billion a year. The cost in terms of suffering on behalf of the victim and their family is inestimable.
Phases of TBI
TBI can be caused by a number of different mechanisms. All involve some degree of stress on the tissues of the brain. The main two categories of injury are blunt (such as an explosion) or penetrating (such as a gunshot wound). There are two phases associated with TBI. The first is the direct consequence of the traumatic event. Examples include torn tissues and skull fractures. Head injuries also cause diffuse injury by accelerating and decelerating the entire brain. This can lead to the stretching of brain tissue, leading to diffuse axonal injury.
Damage to the brain due to this initial phase is usually thought to be complete by the time medical care arrives. In contrast, the second phase can last for days to weeks. This phase consists of a period of cell death due to low oxygen levels, inflammation, and toxic byproducts such as free radicals. This phase can be managed medically, allowing the brain to recover some of its previous functioning.
Classification of TBI
TBI is classified as mild, moderate, or severe. All degrees of TBI involve a traumatically induced disruption of brain function, which can appear as a loss of memory, loss of consciousness, a change in alertness, or other neurological deficits.
About 75% of cases of TBI are considered mild (mTBI). The term mTBI is often used interchangeably with concussion. In brief, a concussion involves a change in mental status shortly after a blow to the head. For TBI to be considered mild, the loss of consciousness must not have exceeded 30 minutes, and there can be no amnesia lasting more than 24 hours.
Moderate and severe TBI are serious conditions requiring urgent care in an advanced medical setting. Most penetrating head injuries, such as knife or gunshot wounds, lead to moderate or severe TBI. Moderate TBI is usually associated with prolonged loss of consciousness or neurological deficits, but does not automatically meet medical criteria for intubation, i.e. the Glascow Coma Score (GCS) is greater than 8. In severe TBI, the GCS is less than 8, meaning the patient is obtunded or comatose, and needs to be intubated to protect the airway.
In cases of severe traumatic brain injury, causes of confusion can be obvious, with clear evidence of sheared axons and bleeding that would disrupt normal cognition. The causes of the confusion following mild TBI such as a concussion are still being explored. After a concussive head injury, many neurons become randomly active. Recovering from this massive amount of activation takes time and energy that might otherwise be used to think clearly. Depending on the extent of the injury, blood flow may not be able to keep up with the brain's increased need for energy, leading to a higher risk of lasting injury.
Traumatic brain injury has been around for as long as people have existed, but we still have a lot to learn about exactly what goes wrong when the head is injured. Continuing to learn about these processes will lead to better treatments in the future.
Victoria C. Anderson-Barnes, Sharon R. Weeks, Jack W. Tsao. Continuum: Traumatic Brian Injury, Mild Traumatic Brain Injury Update Volume 16, Number 6, December 2010.
World Health Organization. International statistical classification of diseases and related health problems, 10th revision. Geneva, Switzerland; World Health Organization, 1992.