Concussion is a transient disturbance in brain function caused by head injury, usually a blow. By definition, there are no structural brain abnormalities visible directly or on imaging studies, in contrast to more serious brain injuries (traumatic brain injuries [TBIs]).
Pathophysiology is still being clarified, but brain dysfunction is thought to involve excitotoxicity, which is neuronal damage caused by excessive release of excitatory neurotransmitters, particularly glutamate. For additional information, see Concussions: What a neurosurgeon should know about current scientific evidence and management strategies.
Estimates of the incidence of sports-related concussion in the US vary from 200,000 a year up to 3.8 million a year; the highest numbers include rough estimates of injuries that are not evaluated in a hospital or otherwise reported. The awareness and thus reporting of concussions has risen significantly in the past decade—the incidence of serious and fatal sports-related TBI has not increased similarly. Sports that routinely involve high-speed collision (eg, football, rugby, ice hockey, lacrosse) have the highest rates of concussion, but no sport, including cheerleading, is free of risk. An estimated 19% of participants in contact sports have a concussive injury over the course of a season.
Unlike with other causes of concussion (eg, vehicular crashes, falls), which are usually isolated events, sports participants are continually exposed to risk of concussion. Thus, repeat injury is common. Athletes are particularly vulnerable if the repeat injury occurs before they have fully recovered from a previous concussion, but even after recovery, athletes who have suffered one concussion are 2 to 4 times more likely to suffer another concussion at some point. Also, repeat concussions may occur after a less severe impact.
Furthermore, although most athletes eventually recover fully from a single concussion, about 3% of those who had multiple (even apparently minor) concussions develop chronic traumatic encephalopathy (CTE, initially described in boxers and termed dementia pugilistica). In CTE, patients have structural neurodegenerative changes, including cortical atrophy, somewhat similar to changes present in patients with Alzheimer disease. Symptoms can include
Several prominent retired athletes who had sustained recurrent TBI have committed suicide.
The Centers for Disease Control and Prevention (CDC) reports an average of 1.5 deaths a year from sports-related concussions. In most cases, a concussion, usually undiagnosed, had occurred before the fatal one.
Second-impact syndrome is a rare but serious complication of concussion. In this syndrome, acute, often fatal brain swelling occurs when a second concussion is sustained before complete recovery from a previous concussion. Vascular congestion is thought to lead to rapidly increased intracranial pressure (ICP) that is difficult or impossible to control.
The mortality rate approaches 50%.
The most obvious disturbance of brain function with a concussion is
However, many patients do not lose consciousness but instead manifest symptoms and signs such as
Confusion: Appears dazed or stunned, is unsure of opponent or score, answers slowly
Memory loss: Does not know plays or assignment, does not recall events before the injury (retrograde amnesia) or afterward (anterograde amnesia)
Vision disturbance: Has double vision or light sensitivity
Dizziness, clumsy movements, impaired balance
Nausea and vomiting
Loss of smell or taste
Postconcussive symptoms are symptoms that may be present for a few days to weeks after concussion; they include
Postconcussive symptoms typically resolve in a few weeks to several months.
Athletes with possible concussion should be evaluated by a clinician with experience in evaluation and management of concussions. Sometimes such clinicians are on site at high-level athletic events; otherwise, sideline staff should have training in recognizing concussive symptoms and protocols for referring patients for evaluation.
Diagnostic tools, such as the Standardized Assessment of Concussion (SAC), Sports Concussion Assessment Tool 2 (SCAT2), SCAT3, or SCAT5 (the version in current use), can help coaching staff, trainers, and inexperienced clinicians screen athletes on site. SCAT2 and SCAT3 are available free online and can be downloaded to handheld devices; SCAT5 is available free online. The CDC has tools and training information for anyone who needs to recognize, respond to, and try to prevent concussion and other serious brain injuries (CDC "Heads Up" programs).
Neuroimaging is not helpful to diagnose concussion itself but is done if more serious brain injury (eg, hematoma, contusion) is suspected. Typically, CT should be done if patients have any of the following:
Loss of consciousness
Glasgow Coma Score (GCS) < 15 (see table Glasgow Coma Scale)
A focal neurologic deficit
Persistently altered mental status
Other signs of deterioration
Formal neurocognitive testing can likely show abnormalities in symptomatic patients but is not typically done unless postconcussive symptoms last longer than expected or the patient has severe cognitive problems. However, some athletic programs do baseline neurocognitive tests on all participants and repeat them after concussion so that more subtle abnormalities can be identified and further participation deferred until the person returns to baseline. One of the more commonly used tests is a commercial computer-based tool called ImPACT.
Patients who had any concussive symptoms or signs should not return to play that day and are advised to rest. School and work activities, driving, alcohol, excessive brain stimulation (eg, using computers, television, video games), and physical exertion should be avoided during early recovery to prevent prolongation or exacerbation of the symptoms (1).
No drugs have been shown to improve recovery from concussion, but specific symptoms can be treated with appropriate drugs (eg, acetaminophen or nonsteroidal anti-inflammatory drugs [NSAIDs] for headache).
Family members are advised to watch for signs of deterioration and take the person to the hospital if they occur. These signs include
Typically, a graduated approach is recommended. Athletes should refrain from athletic activities until they are completely asymptomatic and require no medication. Then they may begin light aerobic exercise and advance through sport-specific training, noncontact drills, full-contact drills, and finally competitive play. Patients who remain asymptomatic at one level can be advanced to the next.
But however quickly they improve, patients are typically advised not to return to full play until they have been asymptomatic for 1 week. Those who had severe symptoms (eg, unconsciousness for > 5 minutes, > 24 hours of amnesia) should wait at least 1 month.
Athletes who have had multiple concussions in one season need to be fully advised of the risks versus benefits of continued participation. Parents of school-aged children should be involved in these discussions as well.
Concussion involves transient, traumatic brain dysfunction; consciousness may be lost, but sometimes patients manifest only confusion, memory loss, and gait or balance difficulties.
Symptoms may resolve quickly or persist for up to several weeks.
Athletes with possible concussion should be removed from play and evaluated; screening tools such as SCAT3 or SCAT5 may be helpful.
Neuroimaging is done if there is loss of consciousness, GCS < 15, focal neurologic deficits, persistently altered mental status, or clinical deterioration.
After concussion, patients are more susceptible to repeat concussion for a period of time and must refrain from sports activities until they have been asymptomatic for 1 week or more (depending on severity of injury).
Athletic activities are resumed gradually.