Cody Lehe was still having headaches sustained from a concussion several days earlier at a high school football game. But when his CT scan came back normal, the 17-year-old figured it was OK to play.

Five days after the helmet-to-helmet collision  that the Brookston, Ind., teen described as “the hardest I’ve been hit in my whole life,” he was back on the field practicing with his teammates. The Frontier High School Falcons were heading for the 2006 sectional finals and, as team captain, Lehe was determined to be there.

But in the fourth drill of the day, Lehe was hit once again and knocked to the ground. As he slowly pulled himself back onto his feet, the teen told a teammate that his head hurt, but he was OK.

Several plays later, though, Lehe dropped to one knee, dizzy, his legs numb. Then he collapsed, his body shaking with seizures.

Second-impact syndrome (SIS) is a big reason why there has been so much attention to concussions the past few years.  It is why we don’t let athletes return to their sport until we have objective evidence that they have recovered.  Linda Carroll explains:

Experts say that if the brain doesn’t have enough time to recover from the initial concussion, a second one can have a devastating, often fatal, effect  — even when the second jolt is no more than a light bump.

The second hit causes the brain to swell catastrophically, but it’s the first injury, experts say, that makes the player a walking time bomb.

The diagnosis of concussion is a clinical one — that is, based on signs and symptoms that occur after a head injury.  Loss of consciousness is a sign of a concussion, however, most kids who get concussions do not lose consciousness.  Other important signs include confusion, change in gait and balance, or disturbances in speech.  Common symptoms of concussion include headache, dizziness, nausea, vomiting, hypersensitivity to loud noises and bright lights, and difficulty concentrating.  When these signs and symptoms are severe, an emergency room visit is warranted.  A CT (computerized tomography or CAT) scan may be obtained in order to look for specific areas of intracranial bleeding that could have resulted from the head injury.  A CT scan does not help determine whether or not a concussion has occurred, nor does it help measure the severity of a concussion.  In fact, the use of CT scanning has been declining for the past several years in emergency settings, especially in the pediatric population.  Most kids who suffer concussions have not had and do not need a CT scan.

What does help physicians confirm a diagnosis of concussion and measure its severity, its progress with therapy, and, ultimately its resolution is computerized neurocognitive testing.  At Pediatric Alliance, we utilize ImPACT (Immediate Post-Concussion Assessment and Cognitive Testing) — a computerized tool developed at the University of Pittsburgh Medical Center (UPMC) and widely used nationally in high schools and colleges, for both young amateur and adult professional athletes.  A baseline test (done in the player’s preseason) is very helpful to treating clinicians, the results of which can be compared to any post-concussion test results.

Only when the concussed patient has no further signs AND complains of no further subjective symptoms AND gets back to baseline numbers on the ImPACT test can a concussion be considered resolved.  The player can then enter a “return-to-play” protocol of increasing intensity of activity over time to ensure that signs and symptoms don’t recur, as well as allowing time for reconditioning.  Then (and only then) will the player be allowed to return to full-contact.  Anything short of that puts the player at risk for a second, more significant event:

Second-impact syndrome appears to be relatively rare. The Centers for Disease Control and Prevention documented 17 deaths from the condition between 1992 and 1995 in a report that cautioned that those figures could be an underestimate.

A 2007 study in the American Journal of Sports Medicine found 94 incidents of severe football head injuries in high school and college players reported from 1989 through 2002. Nearly 60 percent of the players had a history of previous head injury and more than 70 percent occurred in the same season as the catastrophic injury, the report found. Nine percent of those players died and more than 50 percent suffered permanent neurological injuries.

Although SIS is rare, it is always devastating. Victims who don’t die are left with life-altering brain injuries.

Serious stuff.

Read Linda Carroll’s article on NBCNews.com here.

Previous posts about concussions on The PediaBlog here and here.