What is a concussion?

Quick Answer
Mild brain injury that briefly impairs neurological functions.
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Causes and Symptoms

Concussions can be caused by a variety of traumatic events: motor vehicle accidents, penetrating injuries, sports injuries, strikes, and falls. Recent studies indicate that the number of concussions from motor vehicle accidents and falls have decreased, while penetrating injuries (gunshot wounds) and sports-related injuries are on the increase. Concussion is a common athletic injury that often goes unreported. Recent information suggests that children heal more slowly than adults following head trauma. Although concussions are the mildest traumatic brain injuries, they can result in irreversible damage or death if a person suffers another head trauma prior to recovering from the initial injury.

People who have experienced head trauma that disrupts brain activity and sometimes causes brief unconsciousness, ranging from several seconds to minutes immediately after an impact, are considered to have sustained a concussion. Direct, sudden, powerful blows to the head or an impact to the body that jars the head cause the brain to bounce inside the skull and suffer tissue bruising. Nerve fibers tear, and chemical reactions are altered. The irregular interior surface of the skull can damage fragile brain tissues. Direct mechanical trauma can injure cortical tissue, while subdural hematomas can damage subcortical structures, potentially leading to vasospasm and ischemia.

Concussions are described as mild, moderate, or severe, though there is a lack of standardized definitions for each type of concussion. A mild concussion may or may not involve a brief period of unconsciousness; the brain generally recovers quickly and without long-term damage. However, approximately 15 percent of those injured will continue to experience symptoms one year after the initial injury. These symptoms may range from headaches to emotional or behavioral problems. The US Centers for Disease Control and Prevention (CDC) and the National Center for Injury Prevention and Control have developed recommendations for standardized terminology, treatment, and prevention of mild traumatic brain injuries. A severe concussion is considered an emergency and requires an extended period of time for recovery.

Headache, dizziness, nausea, and disorientation immediately following the injury are considered risk factors for long-term complications from the head injury. Each person’s brain and injury are unique. Therefore, a wide variety of symptoms may occur. Patients may experience blurred vision or suffer hearing problems. People with concussions also report becoming uncoordinated and sensitive to light and noises, and they may experience sensory changes in smell and taste. Patients may become moody, cognitively impaired, unable to concentrate, or fatigued.

Researchers have determined that the major neuropsychological complications of concussion may affect the brain’s memory, learning, and planning functions. Some concussion patients taking tests, such as the Wechsler Abbreviated Scale of Intelligence, have revealed decreased concentration, reaction, and processing skills in performing intellectual tasks. Their strategies to solve problems are impaired when compared to people who have not suffered concussions.

Medical professionals assess patients with a head injury by physical examination, radiological tests, and a standardized scale that measures level of consciousness called the Glasgow Coma Scale. Computed tomography (CT) and magnetic resonance imaging (MRI) scans may also be used. The American Academy of Neurology emphasizes the duration of loss of consciousness to determine the severity of concussions. Evaluations also consider orientation and posttraumatic amnesia. Medical professionals assess patients’ responses to stimuli and memory of incidents before their injury, defining the concussion according to the level of confusion, amnesia, and duration of loss of consciousness. Physicians ask patients questions about who and where they are and about the time and date. The duration of amnesia after the brain trauma helps medical professionals to determine the extent of the injury and treatments that would be most effective to heal the brain. The Colorado Medical Society developed a popular system, assigning grades 1 (mild), 2 (moderate), and 3 (severe) to concussions, to guide athletic personnel in examining players who suffer concussions during games and deciding how long they must refrain from participation in order to prevent additional damage.

Brain damage and death can result from serial concussions. Postconcussion complications may include second impact syndrome: If a patient suffers another concussion before healing is complete following the first injury, then the second concussion can be the catalyst for rapid cerebral swelling that causes increased pressure within the structure of the brain. This pressure can cause the brain to press on the brain stem and result in respiratory failure and death. This condition is usually fatal.

More common is postconcussive syndrome (PCS), which consists of such cognitive and physical symptoms as headache, anxiety, vertigo, nausea, and hallucinations. An estimated 30 percent of professional American football players suffer from PCS. Researchers have determined that people who experience several concussions, such as athletes and soldiers, are more vulnerable to becoming clinically depressed.

Treatment and Therapy

Patients who play sports should not be returned to play until symptoms of concussion have resolved completely, both during rest and exercise. A slow return to previous activities allows the brain to heal, resulting in fewer long-term complications than for patients who resume activities more quickly. Although most patients make a full recovery, some experience long-term concussion-related conditions, such as memory loss and neurological impairment.

Severe concussions with increased brain pressure require hospitalization, often in a neurological intensive care unit. The patient’s head is maintained in a neutral position. Immobilization should be continued until a full risk assessment indicates it is safe to remove. The patient may have suffered internal bleeding in the brain because of the injury, and blood clots can form there. Surgery may be required to remove these clots. Patients with preexisting conditions such as epilepsy and diabetes may develop complications related to those diseases and require longer recovery times.

Physicians recommend wearing helmets to absorb shocks sustained during athletic activities involving the risk of head injury in order to prevent or minimize concussions. The American Academy of Neurology has demanded a ban on boxing because the sport involves knocking out opponents by inflicting concussions. Boxers often suffer permanent brain damage and are at a heightened risk for neurological diseases.

Perspective and Prospects

Concussions were first described in medical literature by Muslim physician Rhazes (850–923). He differentiated between a head injury that caused neurological symptoms from those injuries that resulted in lesions and structural damage. In the nineteenth century, medical researchers developed hypotheses, often controversial, regarding the physical and emotional influences of concussion symptoms. Second impact syndrome was first defined in 1984.

The development of sports medicine increased the interest in studying concussions. The understanding of the internal brain damage involved in concussions did not significantly advance, however, until neuroimaging technologies such as CT scanning and magnetic resonance imaging (MRI) were developed in the late twentieth century. In the twenty-first century, medical professionals utilize those techniques to view brain tissues and to observe the physiological reactions to concussion-causing trauma. Positive emission tomography (PET) has been developed to measure chemical changes in the brain. In the case of concussion, the PET scan can be used to evaluate changes that signal areas of injury in the brain. These technologies will likely yield more accurate diagnostic exams for concussions.


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