Second Impact Syndrome (SIS) is defined as what?

• A. a second concussion that occurs before the first signs have resolved
• B. a mild knee sprain
• C. a second concussion received before the signs and symptoms of the first concussion have been resolved; a life-threatening emergency
• D. dehydration-related illness

Answer: (C)

Second Impact Syndrome happens when a second concussion occurs before the signs and symptoms of the first concussion have resolved, leading to rapid brain swelling that can be life-threatening. The danger lies in hitting the brain while it’s still vulnerable after an initial concussion; even a minor additional impact can cause the brain to swell quickly, raise pressure inside the skull, and potentially result in severe damage or death. This is why immediate removal from play and medical clearance are essential, with a careful return-to-play process only after full recovery.

The other choices describe conditions that are not related to this brain-injury scenario—knee sprain and dehydration-related illness—so they don’t capture the specific, dangerous combination of timing and emergency risk that defines SIS.