Second Impact Syndrome: A Rare But Usually Fatal Condition

Second-impact syndrome (SIS) occurs when an athlete who sustains a head injury - often a concussion or worse injury, such as a cerebral contusion (bruised brain) - sustains a second head injury before symptoms associated with the first have cleared.

Typically, the athlete suffers post-concussion signs and symptoms after the first head injury, such as headache, visual, motor or sensory changes or mental difficulty, especially with the thought and memory process. Before these symptoms have cleared, which may take minutes, hours, days or weeks, the athlete returns to competition and receives a second blow to the head.

Sudden onset

The second blow may be unremarkable, perhaps only involving a blow to the chest that jerks the athlete's head and indirectly sends accelerating forces to the brain. Affected athletes may appear stunned, but do not suffer loss of consciousness (LOC) and often complete the play. They usually remain alert on their feet for 15 seconds to 1 minute or so but seem dazed. Often, affected athletes remain on the playing field or walk off under their own power. Usually within seconds to minutes of the second impact, the athlete - conscious but stunned - suddenly collapses to the ground, semi-conscious with rapidly dilating (widening) pupils and loss of eye movement, and stops breathing.

Vast majority of victims under age 18

Concussion experts agree that, in general, the younger the athlete, the longer it takes for the symptoms of a concussive event to clear.  The brains of young athletes are still developing, making them particularly susceptible to catastrophic injury if the brain has not healed before a second blow to the head.  Indeed, the vast majority of the victims of Second Impact Syndrome (95% by some estimates) are under the age of eighteen.