Indiana University researchers say a clean brain scan isn't enough to send high school football players who suffer concussions back on the field.

A case study of a 17-year-old football player concludes he fell victim to what's called "second impact syndrome." A second hit after the player was cleared to play caused bleeding in the brain. Three years later, the player is still in a wheelchair, with impairment to verbal and thinking abilities.

IU neurosurgeon Michael Turner says the syndrome is very rare, but "devastating" when it happens.

Turner says if concussed players still have headaches, they should stay on the sidelines, no matter what their brain scan shows.