Among the nearly 2 million estimated concussions children and teenagers sustain each year in the United States, as many as half are thought to go unreported to emergency room or family physicians.

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The divide, highlighted this summer in a study published in Pediatrics, emphasizes a greater need for any such injury — or even the suspicion of one — to be taken seriously.

As for the reasons a concussion might go untreated?

"Sometimes, I think kids don't want to report those symptoms to their parents; they're afraid they won't be allowed to play (sports)," says Ingrid Ichesco, M.D., a pediatrician with a specialty in sports medicine at University of Michigan C.S. Mott Children's Hospital and a part of the NeuroSport team.

"I've also had some parents who might not see the injury as a big deal — they had concussions growing up and do not realize the potential dangers of not treating these injuries properly."

But without proper medical diagnosis and recovery time, Ichesco says, head trauma could hinder a person's capacity to fully heal and, in a far more severe outcome, put him or her at risk for another blow before shock from the prior collision has subsided.

Which is why it's crucial for families to know the warning signs of a concussion and react accordingly.

What happens after a hit

Concussions, according to the Centers for Disease Control and Prevention, are a type of traumatic brain injury caused by a blow or jolt to the head — or one to the body that causes the head to move rapidly back and forth.

Sudden jarring can cause the brain to bounce or twist inside the skull, resulting in shock Ichesco describes as "more at a cellular level … with neurometabolic changes rather than structural changes."

As such, diagnosis methods can't be likened to that of, say, a broken bone.

"A CT scan isn't going to show you a concussion; there isn't one perfect test," Ichesco says.

Instead, a coach or athletic trainer — and, ultimately, a doctor — will survey the injured individual with a 22-question checklist to gauge the likelihood of a concussion. A clinician will also ask the patient to walk through what he or she recalls about the accident, Ichesco says.

Among the symptoms that suggest a concussion: dizziness, nausea, headache, vomiting, memory or concentration issues, behavioral changes and sensitivity to light and noise.

In other words, "not thinking, feeling or acting the way you normally do," Ichesco says, noting that most patients can wait to see a primary care physician or a concussion specialist in the office within the next few days after injury. Reasons to go to the emergency room immediately include repetitive vomiting, loss of consciousness and significant worsening of symptoms such as headache.

If a concussion is suspected at all, the athlete should be removed from play immediately.

"In the past, when people 'got their bell rung,' they may have been down on the sidelines and put back to play in 15 minutes," Ichesco says. "What we don't want is for them to take a hit and try to tough it out for the rest of the game."

Treatment and recovery

Doctors once ranked the severity of a patient's concussion. Now, Ichesco says, they usually rely on a personalized approach when treating each case. Doctors no longer recommend waking up patients every few hours or keeping them in a dark room without any stimulation. Initial treatment now typically consists of rest and treatment of headache with Tylenol.

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Those on the mend can gradually adjust to a normal routine without exacerbating discomfort.

"I always tell patients that while recovering from a concussion, if you are doing an activity such as watching TV and you feel worse, that's your body's way of saying you're probably not ready to do this yet," Ichesco says.

What they shouldn't do: return to team sports or physical activity without a physician's approval.

All 50 states, per the CDC, enforce varying "Return to Play" laws that typically mandate specific hiatus periods, medical clearance from a doctor and informed consent before an athlete can compete again.

Still, because helmets, mouthguards and other protective gear aren't concussion-proof, a periodic reminder about safe, mindful participation is always a good idea, Ichesco says.

"You want to follow the rules of the game, be respectful of other players and aware of your surroundings," she says, adding that parents and players alike should recognize that not all concussion risks lie in contact sports such as football and hockey.

Injuries also can come from pursuits such as bicycling or synchronized swimming — as well as unexpected tumbles during casual recreation or inclement weather.