Second Impact Syndrome

Second impact syndrome is a very rare condition in which a second concussion occurs before a first concussion has properly healed, causing rapid and severe brain swelling and often catastrophic results. Second impact syndrome can result from even a very mild concussion that occurs days or weeks after the initial concussion.

What is Second Impact Syndrome?

In patients who sustains a second concussion when the first one has not fully healed, the brain loses its ability to auto regulate intracranial and cerebral perfusion pressure. This may lead to cerebral edema (severe swelling of the brain) and possible brain herniation. Loss of consciousness after the initial injury followed by secondary brain damage creates ionic fluxes, acute metabolic changes, and cerebral blood flow alterations.  All of these characteristics enhance the vulnerability of the brain and greatly increase the risk of death, even if the second injury was far less intense. 

Populations at Risk for Second Impact Syndrome

Most cases of second impact syndrome have occurred in young athletes, particularly those who participate in sports such as boxing, baseball, football, hockey, and skiing. If an athlete has suffered a concussion, it’s best if they don’t return to their sport until the symptoms of the initial head injury are gone.

Avoid Second Concussions

Any athlete, or person who has sustained a concussion, who shows signs of concussion should not be allowed to return to play or activities where impact is possible. Signs of concussion include the following:

  • Disorientation
  • Vomiting
  • Headache
  • Fatigue
  • Nausea
  • Temporary loss of consciousness
  • Confusion or feeling as if in a fog
  • Ringing in the ears
  • Slurred speech
  • Sleep disturbances
  • Concentration or memory problems
  • Irritability and other personality changes

If there are any doubts about whether the person is suffering from delayed effects of the concussion, it's crucial to keep them out of situations that could lead to another concussion resulting in second impact syndrome.

Symptoms of Second Impact Syndrome

Second impact injury can result within a matter of days or weeks, or it can occur in the same game or competition if the athlete isn’t removed and treated after the first concussion. Neither impact has to be severe for second impact syndrome to occur. Symptoms usually occur immediately following the second impact and progress rapidly. Common symptoms include:

  • Dilated pupils
  • Loss of eye movement
  • Unconsciousness
  • Respiratory failure
  • Death

Prognosis of Second Impact Syndrome

In many cases, second impact syndrome is fatal. True SIS involves brain herniation and death usually within minutes. However, a patient who is suspected of suffering from SIS should immediately be stablized with special emphasis on airway management.  Neurosurgery will also be considered depending on the severity of the injuries. In cases where SIS isn’t fatal, the long-term effects will likely be similar to those of severe traumatic brain injury.