Sports Concussions & The Immature Brain(2)

Young Athletes May Be More Vulnerable to Mild Brain Injury
by Brenda Patoine

February, 2010

BRIEFING PAPER

              

Ann Whitman
(212)223-4040
awhitman@dana.org

             

Johanna Goldberg
(212)223-4040
jgoldberg@dana.org

Canadian freestyle aerialist Steve Omischl, the reigning World Cup champion, took a two-week break from skiing in early January after suffering a concussion during a training session, but is back competing in anticipation of the Winter Olympics.  Patrick Elias, captain of the Czech Republic’s Olympic ice hockey team, suffered a “slight concussion” Jan. 21 but still plans to lead his team’s charge for gold in Vancouver.  Alpine skier Robbie Dixon skipped a few competitions after slipping on ice and banging his head, but he’ll be heading to Whistler to ski for Canada in the Games.

In the last few weeks, sports headlines have been peppered with stories about Olympics-bound athletes suffering concussions.  And in recent months, the long-term neurological consequences of head trauma suffered during sports have been in the public eye due to a series of scientific reports finding unusually high rates of severe brain damage in former professional football players.  But the problem of sports concussions is by no means limited to NFL linebackers or Olympians.  Many brain experts are calling for greater attention to the neural consequences of sports-related concussions, especially when they occur in young athletes whose brains are still developing.

“Based on current neuroscience data, the assumption is that the brain does not fully mature until at least the mid-20s, so if a concussion occurs in a still-developing brain, the trajectory of that development will presumably be affected,” says Jordan Grafman, Ph.D., chief of cognitive neuroscience at the National Institute of Neurologic Disorders and Stroke and a member of the Dana Alliance for Brain Initiatives.  “Even a mild head injury can certainly cause impairments and create problems in day-to-day functioning, particularly in higher cognitive functions, which are last to develop, as well as in social cognitive functions.”

Such higher-order cognitive skills are largely processed in the forward regions of the prefrontal cortex and temporal lobes, at the front and sides of the brain.  “In head injuries, these regions are particularly susceptible to damage, partly because of where they reside in the brain.”  The prefrontal cortex is concerned with tasks such as reasoning, decision-making, problem-solving, planning, holding things in mind, switching between tasks, as well as social cognitive abilities, such as making moral judgments or understanding the subtle social intentions of other people. 

“All of those abilities are still developing in adolescents and young adults, so one or more of them can be affected by even a mild head injury,” Grafman says.

Robert Cantu, M.D., a neurosurgeon at Boston University and Brigham & Women’s Hospital, and one of the world’s leading researchers studying sports concussions, agrees that there are reasons to be concerned about mild head trauma in young people.  “The developing brain may indeed be more prone to injury than an adult, mature brain because neurons are growing faster and connections are still being made.  There is not the redundancy that there is in an adult brain.”

In addition, he says: “Younger children have proportionately bigger heads than adults, and weak necks, so the ability to sustain a blow to the head is not as great.”  A blow of the same degree exerts more acceleration force to a child (particularly one under the age of 12 or so) than to an adult, because of the relative weakness of the neck musculature, which essentially acts as a shock absorber.  Cantu says this may also explain why female athletes seem to be more susceptible to concussive injuries than men, whose necks tend to be stronger.

Misconceptions and Under-Recognition

One of the biggest misconceptions about concussions is that it involves loss of consciousness.  In a large study of concussions in high school and college football players conducted by Kevin Guskiewicz, Ph.D., a sports-medicine researcher at the University of North Carolina, Chapel Hill, only nine percent of concussion injuries knocked the player unconscious.  When there is a loss of consciousness, it typically lasts only a few seconds and may not be noticed by referees, coaches, or even the athletes themselves.

Another dangerous myth is that a blow to the head – a “ding” or a “bell ringer” as many athletes call it – is no big deal.  A player may be eager to remain in the game or return to play and may downplay symptoms as a result.  A survey of high school soccer players by Jill Brooks, Ph.D., a neuropsychologist with Head-to-Head Consultants in Gladstone, N.J., found that the No. 1 reason for not reporting a concussion was because athletes didn’t think it was a serious problem.

The Centers for Disease Control and Prevention says that about 300,000 sports-related concussions are reported annually.  But since most concussions go unreported, that number is likely to be a huge under-estimate of the true scope of the problem.  Wes Rutland-Brown, M.P.H., an epidemiologist with the CDC, puts the number of unidentified sports concussions between 750,000 and 2.25 million.[i]

“Under-recognition is an absolutely huge issue,” says Cantu.  He points, for example, to recently published data from Dawn Comstock, Ph.D., of Nationwide Children’s Hospital in Columbus, Ohio, showing that 40 percent of athletes continued playing their sport despite having symptoms of a concussion.  “The numbers are unfortunately far larger than we ever thought,” Cantu says.

Compounding the problem of under-recognition is the fact that concussive injuries cannot be seen, making them difficult to diagnose.  X-rays or brain-imaging tools such as MRI can detect a problem only in the rare cases where internal bleeding has occurred. 

“If it is not an obvious bleed or lesion, current brain-scanning techniques are much less likely to be decisive in determining if somebody has a brain injury or not,” says Grafman.  “We just don’t yet have the fine resolution we need to look at brain structure to see whether it is temporarily or more permanently damaged.”

As a result, physicians must rely on symptoms that the athlete reports or on clinical signs of cognitive impairment, which can be subtle and difficult to detect.[ii]  Careful observation and testing of mental status is critical to accurate diagnosis, as is continued observation in the hours following an injury because of the low probability that a slow internal bleed could occur, which could cause death if not treated.

Unfortunately, such evaluations and follow-up care rarely happen in the heat of a game.  In contrast to Olympic or professional contests, team physicians are uncommon at elementary or high school sporting events. 

Moreover, not all symptoms of mild brain injury occur immediately; some are not evident until days or even weeks after the insult.  Changes in mental status tend to be most pronounced 24 to 48 hours after a concussive injury, according to studies by Guskewiecz’s group at UNC and by Ruben Echemendia, Ph.D., at the Pennsylvania State University.  In both studies, extensive baseline cognitive evaluations were taken at the time of study enrollment in order to compare an individual athlete’s normal cognitive function to his or her functioning after a concussion, should one be suffered.  Echemendia’s group found that brain-injured athletes’ cognitive test scores did not return to baseline levels until 10 to 30 days after the concussion.

Can Brain Trauma Ever Be ‘Mild’?

Even a “mild” concussion constitutes an injury to the brain – and in fact many experts scoff at the application of the descriptor “mild” to any kind of brain trauma.  Neural tissue is violently jostled within the skull, which can directly damage both brain cells and the blood vessels that feed them.  The initial insult triggers a cascade of biochemical reactions, flooding the brain with calcium and potassium ions that cause blood vessels to constrict and hamper the metabolism of glucose, which the brain uses for energy.[iii]  The end result has been described as an energy crisis in the brain that can last for weeks after an injury.

Energy-starved nerve cells are not able to perform at their peak, and are particularly vulnerable to further damage or death.  If another concussion occurs during the midst of this neural energy blight, the consequences can be catastrophic.  “Second-impact syndrome” describes a rare, life-threatening condition in which a subsequent brain injury occurs before the brain is fully recovered from an earlier injury, no matter how “mild” the first may have been. 

“That combination – a second concussive episode before total recovery from a first – is particularly bad,” says Cantu.  He says it is common to see “very profound cognitive problems” in such athletes, who “didn’t realize what the symptoms of concussion were, continued playing, and subsequently suffered an additional head trauma.” 

Second-impact syndrome (SIS) is fatal in up to half of the individuals who suffer it, and can cause major long-term brain damage and disability in the rest.  Adolescent and young adult males are disproportionately affected.  Experts have speculated various reasons why the immature brain may be more vulnerable to SIS, and to damage from mild trauma in general.  Children’s brains tend to fit more tightly within the skull, and have a higher concentration of water, two characteristics that may make the young brain less resilient to catastrophic swelling. 

Even a single concussion can spell trouble for the immature brain.  Animal studies suggest that young brains subjected to a mild injury have a decreased ability to learn, even when raised in enriched environments that normally hasten learning.  In adolescent children, Echemendia’s group found decrements in the capacity to learn new information after a concussion.  While the deficits generally disappeared after a short period of time, even short-term impairment to learning can have serious consequences to a child’s academic performance. 

‘Beating the Drum’

The popular media’s coverage of the controversy surrounding former NFL players who have gone on to suffer severe brain damage has helped raise awareness about the dangers of mild head injury more generally, a development brain experts have welcomed.  “It has drawn attention back to the younger athletes and efforts to limit their exposure to events that might create a head injury,” says Grafman.

Still, he and Cantu say more needs to be done.  “We need to keep beating the drum,” says Cantu.  “Coaches, parents, and medical personnel all need to be better educated about the symptoms and dangers of concussion, as do athletes themselves.”  In addition, he says, “the culture of collision sports – the idea of not letting down one’s teammates, or not having the coach bench you because he thinks you’re a wimp – needs to change.”

“We’re doing a better job, but we have a long way yet to go,” he adds.

Published February 2010


[i] Rutland-Brown, Wes.  Epidemiology: Defining the Problem.  PowerPoint presentation from Concussion and Youth Sports Summit, Feb. 24, 2006.  Coordinated by the Brain Injury Association of New Jersey.  http://www.sportsconcussion.com/information-for-coaches-teachers-and-parents (Accessed 1.21.2010)

[ii] For an overview of early and later symptoms of concussion, see: Concussion Symptoms, by MayoClinic.com.  http://www.mayoclinic.com/health/concussion/DS00320/DSECTION=symptoms (Accessed 1.21.2010)

[iii] For an overview of the pathophysiology of mild traumatic brain injury, see:  Rice, Stephen G.  What Really Happens When You Are Concussed: Pathophysiology.  PowerPoint presentation from Concussion and Youth Sports Summit, Feb. 24, 2006.  Coordinated by the Brain Injury Association of New Jersey.  http://www.sportsconcussion.com/information-for-coaches-teachers-and-parents (Accessed 1.21.2010)