• Concussion is defined by short-term clinical symptoms and/or impairment of neurologic function after head/brain trauma, with or without loss of consciousness, and without abnormality on standard neuroimaging studies.
  • Concussion may be caused either by a direct blow to the head or a blow to the face, neck, or elsewhere on the body with an “impulsive” force transmitted to the head.
  • Concussion may result in pathologic changes, but the acute clinical symptoms largely reflect a functional rather than structural injury, and by definition, there is no evidence of intracranial injury (ICI) in imaging.
  • The symptoms of concussion typically resolve spontaneously over hours to days; however, postconcussive symptoms may be prolonged.


  • Concussion can occur after any type of head trauma, but sports-related concussions are of particular interest.
  • Since 2000, there has been an increase in diagnosis of sports-related concussions, which account for 25–50% of those reported to the emergency department (ED).
  • The Centers for Disease Control and Prevention (CDC) estimates that approximately 3.8 million recreation- and sport-related concussions occur annually in the United States.
  • Concussion may be underreported by athletes, trainers, and coaches.
  • Although concussion is overall more common in boys, girls have higher rates of concussion than boys in similar sports (e.g., soccer).

Risk Factors

  • Risk of sports concussion depends on sex, sport, position, and history of prior concussion.
  • For boys, concussions are most likely in rugby football, ice hockey, and lacrosse.
  • For girls, concussions are most likely in soccer, lacrosse, and field hockey.

General Prevention

  • Helmet use is the single most important preventive measure for serious traumatic brain injury. However, helmets have not been consistently shown to prevent concussion.
    • Helmets are not effective at preventing movement of the brain within the skull.
  • At preparticipation medical visits, providers should emphasize that reporting concussion immediately is essential and that loss of consciousness is not the only manifestation of concussion.
  • Children with more than one concussion should be cleared by a physician before returning to activity.
  • Baseline neuropsychological testing (prior to concussion) is being performed by many school athletic departments via widely available computerized testing modules.
    • Research is still needed regarding the optimum timing of this testing and whether baseline testing improves outcome.
Retirement should be considered when any athlete who has sustained three concussions in an individual season, when an athlete has had postconcussive symptoms for >3 months, when recovery requires an increasing amount of time, or when concussions occur with less forceful injury.


  • Concussion occurs with rapid rotational acceleration of the brain.
  • With acceleration–deceleration, the brain experiences continued momentum after impact and strikes against bone. The temporal and frontal lobes are particularly prone to injury because of their location adjacent to irregular parts of the skull.
  • Depressed level of consciousness is thought to be the result of rotational stretch injury to the reticular activating system in the dorsal aspect of the brainstem.
  • Pathologic changes after concussion include alterations in neuronal depolarization and neurotransmitter release, impaired axonal function, lactic acid accumulation, and decreased cerebral blood flow/autoregulation and glucose metabolism.
  • Children may respond to brain trauma differently than adults due to developmental factors such as brain size, brain water content, myelination level, skull and suture geometry and elasticity, and differential skull to body proportions.

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