Traumatic brain injury

A traumatic brain injury (TBI) is damage to the brain that usually results from an accident. They can be classified according to several different criteria. One common system is to refer to them as either a “penetrating” or “closed-head” TBI. Penetrating head injuries occur when the skull has been compromised by a foreign object, as in the case of a gunshot wound. This type of injury is particularly destructive to the brain because, in addition to the damage to brain cells, it also causes bleeding and the possibility of infection. As a result, penetrating head injuries have the highest morbidity and mortality rates. Closed-head injuries are typically acceleration-deceleration injuries, caused by a person's head suddenly accelerating (such as from a blow to the head) or decelerating (such as in an automobile collision), which results in the brain striking the inside of the skull.

An estimated 36.4 to 39.8 million cases of traumatic brain injury (TBI) occurred worldwide in 2021, according to the Global Burden of Disease Study; although high, those statistics represented a decrease of almost 17 percent over 1990 figures.

Key Terms

Amnesia: A condition characterized by loss of memory

Aphasia: A condition characterized by loss of language abilities

Brain herniation: Shifting, dislocating, and/or squeezing of the brain due to high intracranial pressure

Cerebral edema: Buildup of fluid in the brain

Intracranial pressure: The pressure exerted within the skull, affecting brain tissue and cerebrospinal fluid

Causes and Symptoms

According to the 2021 Global Burden of Disease Study, the most common causes of TBI include falls, pedestrian road injuries, motor vehicle accidents, intentional assault, and unintentional blunt trauma, such as caused by collision with another person or an object. Falls and collisions related to sports and recreational activities—such as cycling, tackle football, basketball, and soccer—have been linked to TBIs, as has exposure to mortar fire and improvised explosive devices (IEDs) in military conflicts.

Young children and older adults are among the most vulnerable. Men are more likely than twice as likely as women to experience a severe TBI, with higher rates of TBI-related emergency-room visits and TBI-related deaths. Those who enter military service or who experience domestic violence are also at greater risk of incurring TBIs.

Symptoms of TBI often result from primary (focal) injuries as well as secondary (diffuse) injuries. Brain damage associated with primary injuries results from the initial impact of the skull hitting another object, as in a fall. The head striking the ground causes the brain to move within the cranium, which can cause bruising, tearing, and shearing injuries (referred to as the “shear-strain effect”) as it makes contact with the bony skull. The result is that brain cells expire.

Secondary injuries can occur within minutes or hours after the initial TBI. Symptoms include increased intracranial pressure (ICP) due to cerebral edema. If severe edema is not controlled, it can lead to death. Brain herniation can occur as a result of hemorrhages or an infection that has set in. This can also contribute to rising ICP, which can cause brain structures to be displaced and squeezed to the point that they no longer function properly. Compromising lower brain-stem structures is serious, since these areas control several components of the autonomic nervous system that keep the human body alive and functioning.

In addition to physical injuries, TBI can also bring about cognitive, emotional, and behavioral symptoms. Cognitive changes such as aphasia (deficits in language production and/or comprehension) can emerge. Amnesia is common, whether in the form of loss of memory of past events (retrograde amnesia) or a diminished ability to form new memories (anterograde amnesia).

Overall, people with TBIs may experience mental clouding and difficulty making decisions, preventing them from returning to their jobs and otherwise managing their affairs. Possible emotional symptoms include mood swings, irritability, depression, and anxiety. In instances of repeated concussions (a mild TBI), postconcussion syndrome can occur, bringing about symptoms such as headaches, irritability, dizziness, lack of concentration, and impaired memory.

According to the CDC, those who are incarcerated, detained, or unhoused are more likely to have experienced TBIs.

Treatment and Therapy

The severity of traumatic brain injury is often assessed using corresponding scores on the Glasgow Coma Scale (GCS). This scale provides a quick measure of the severity of TBI to medical professionals. The scale ranges from 3 to 15, with 3 being the most severe form of TBI and 15 being the mildest. A person with a score below 9 is considered to be in a coma with a diminished level of conscious awareness regarding their surroundings.

Intracranial monitoring is regarded as the cornerstone of medical therapy for TBI. Keeping intracranial pressure within normal levels is the most effective way to reduce the risk of developing additional injuries. One way to manage ICP is to ventilate cerebrospinal fluid that is building up within the brain cavity. This is done by drilling a small hole into the skull and inserting a tube, usually into a lateral ventricle.

In terms of medication, mannitol, an osmotic diuretic, can have significant effects on ICP, cerebral blood flow, and brain metabolism. The drug has two primary mechanisms of action. First, it expands plasma volume, thus reducing blood viscosity and increasing cerebral blood flow and oxygenation. Second and less immediately, it creates an osmotic gradient between the brain cells and the plasma, causing excess fluid to be drawn out of the brain. However, mannitol also contributes to the breakdown of the blood-brain barrier, and if the barrier is compromised while the mannitol is in the patient's system, it may exacerbate ICP instead of relieving it.

The range of therapeutic needs following a TBI can vary greatly. A neuropsychologist will be brought in to conduct neuropsychological testing to assess cognitive and behavioral deficits. Once an assessment has been completed, a treatment plan is developed to help the individual progress as far as he or she is capable. Because a brain injury can influence several systems in the body, it is common for an interdisciplinary team to work with TBI patients to provide not only cognitive therapy but also sensory-motor therapy, occupational therapy, speech and language therapy, and physical therapy, among others.

According to the US Centers for Disease Control and Prevention (CDC), TBI patients in rural areas, with low incomes, and/or of Indigenous, Hispanic, or non-Hispanic Black descent are less likely to receive adequate treatment for a TBI and thus more likely to experience adverse outcomes.

Prevention

To reduce TBIs, such as concussions, some government agencies and other entities have undertaken efforts to encourage the wearing of personal protective gear, such as helmets, during sports and recreational activities and the use of seat belts while driving or riding in motor vehicles. In the US, the CDC also launched efforts to improve TBI data collection and reporting, to increase healthcare providers' understanding of TBIs and other head injuries, and to reduce health disparities.

Perspective and Prospects

The study of TBI has helped neuroscientists learn more about the relationships between brain structures and their respective functions. In some instances, brain injury can be focused, leading to specific deficits. In 1861, French surgeon Paul Broca treated a patient who had been unable to speak for several decades. After the patient's death, Broca performed an autopsy and discovered a lesion in the left frontal lobe near the lateral fissure, which demarcates the brain's frontal lobe from the temporal lobe. After studying several other cases of patients with a similar language disturbance, Broca published his results in 1865. This paper supported the theory that language processes were localized to specific brain structures. The disorder now known as Broca's aphasia is a form of nonfluent aphasia, characterized by problems associated with the production of speech. However, if damage is only limited to the Broca area of the brain, speech comprehension remains intact. Additional language centers of the brain have been discovered. Depending on the extent of the TBI, multiple language problems can emerge.

Researchers continue to study TBI via clinical autopsy; however, it has become increasingly common to use brain-imaging technologies such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) to view the structure of the brain while simultaneously studying its functional properties in vivo. These imaging technologies provide neuroscientists with a window into the living brain that helps them understand the relationship between brain structures and function. They also provide medical doctors the ability to more accurately diagnose and treat several forms of head injury while the patient is still living.

One major development that has emerged within the literature on TBI recovery and rehabilitation is the concept of neuroplasticity, or the ability of the brain to reorganize itself after an injury has occurred. Neuroplasticity enables brain tissue that was genetically programmed to take charge of a particular set of responsibilities to take on new functions. Brain damage due to TBI could be mitigated by the recruitment of nearby healthy tissue.

Repeat concussions can lead to chronic traumatic encephalopathy (CTE), a neurodegenerative condition that has notably affected former professional athletes.

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