CHICAGO—Repeatedly hitting the soccer ball with the head may lead to white matter abnormalities similar to those associated with traumatic brain injury (TBI), researchers reported here at the Radiological Society of North America annual meeting in December.
In a study of 38 amateur soccer players, those who headed the ball more than 1,320 times per year — which works out to just a few times a day — had microscopic white matter injuries consistent with TBI as detected by diffusion tensor imaging (DTI).
Young men who headed the ball less frequently did not show these abnormalities, said Michael Lipton, MD, PhD, associate director of the Gruss Magnetic Resonance Research Center at the Albert Einstein College of Medicine in Bronx, NY.
“I'm not advocating banning heading, but we identified a threshold below which you are less likely to have [TBI-associated brain abnormalities]. Therefore there may be a safe range where you can head the ball without adverse consequences to the brain,” he said.
Previous study of the same 38 soccer players showed that those who headed the ball more than 1,320 times a year scored about 20 percent worse on neuropsychological tests of verbal memory (p< .01) and processing speed (p< .03), he added.
Until more soccer players are studied for longer periods of time, however, there is insufficient evidence to state that a certain threshold of heading is either damaging or safe, Dr. Lipton continued.
His advice to patients, especially when children — whose brains are more vulnerable to injury — are involved, is to minimize heading, especially during practice drills where players often head the ball back and forth 30, 40 or more times without a break.
The cognitive consequences of heading have come under closer scrutiny by researchers. In a 1991 study in the American Journal of Sports Medicine, 81 percent of 37 adult soccer players in Norway who began playing soccer in youth leagues showed mild to severe deficits in attention, concentration, and memory on neuropsychological tests. Players who headed the ball more frequently during competition had higher rates of cognitive loss than players who used the technique less often.
According to current American Academy of Pediatrics (AAP) guidelines, there are insufficient published data to support a recommendation that young soccer players completely refrain from heading the ball. However, the AAP encourages that heading be minimized while the potential for permanent cognitive impairment is further delineated. The AAN published guidelines on sports concussion in 1997 but is in the process of updating them; the new guidelines are expected later this year.
Noting that a ball hit by the head reaches speeds of up to 35 mph during amateur play and 60 mph during professional games, Dr. Lipton said that a hard hit can cause symptoms of a concussion, including lightheadedness, confusion and headache, that require immediate attention.
Researchers have expressed concern about more subtle cognitive deficits presenting in youth soccer participants after heading the ball, he said, yet imaging has not been applied systematically to study soccer players.
DR. MEL B. GLENN The...Image Tools
So Dr. Lipton and colleagues used DTI to look for white matter injuries, as detected by fractional anisotropy, in healthy amateur soccer players.
Fractional anisotropy is a measure of diffusion of water across white matter, he explained. “Normally the movement of water through the brain is highly uniform. If the axons are injured, there will be more random movement of water,” he said.
The average age of the players was 31 years, and all had played soccer since childhood.
The researchers estimated how often each player headed the ball annually — a range that went from none to 5,600 — and divided them into quartiles. Then they compared DTI results of players in the highest quartile who headed the ball 1320 or more time a year to those in the lower three quartiles.
Results showed that players in the upper quartile had significantly lower fractional anisotropy in six regions of the brain, including the frontal, parietal and tempero-occipital lobes. “These regions are involved in attention, memory, executive functioning, and higher-order visual-spatial functions,” Dr. Lipton said.
“Lower fractional anisotropy in these regions suggests microstructural changes consistent with axonal injury, as seen in traumatic brain injury,” he said.
The relationship between heading and fractional anisotropy followed a reverse “S” shape, indicating a threshold effect. “It's not a simple linear relationship, with abnormalities continuing to rise as the frequency of heading rises,” Dr. Lipton explained.
Other researchers told Neurology Today that they were not surprised by the findings, while agreeing that further study is needed.
Max Wintermark, MD, chief of neuroradiology at the University of Virginia in Charlottesville, said, “These data are interesting, and the fact that the neuropsychological findings support the imaging findings gives strength to the study.
“It's not a surprise that repeatedly hitting a ball hard with your head could affect you. But we still have to be cautious. The sample size is small, and these findings need to be confirmed in a larger study,” he said. Dr. Wintermark said he would also like to see the imaging results correlated with clinical findings.
Noting that soccer is a seasonal game, Dr. Wintermark said that if the new findings are confirmed, it is possible that a repair mechanism kicks in when players have a few months off.
“It could be that the effect of heading is not cumulative because of some repair occurring between headings, which lessens or prevents permanent injury. That also needs to be studied further before we can make any recommendations,” he explained.
Calling the abstract “interesting,” Mel B. Glenn, MD, said, “I find it believable. It is similar to the frequent subclinical blows that boxers get, interspersed with an occasional concussion.” Dr. Glenn is director of outpatient and community brain injury rehabilitation at Spalding Rehabilitation Hospital and associate professor of physical medicine and rehabilitation at Harvard Medical School.
“The only caveat I would note is that a 1999 article in JAMA found that although heading frequency is associated with worse neuropsychological testing, the real culprit turns out to be the frequency of concussions. It was just that those who do more heading got more concussions, presumably because they hit heads with other players who were heading,” Dr. Glenn wrote in an e-mail.
Jeff J. Bazarian, MD, MPH, an associate professor of emergency medicine at the University of Rochester Medical Center in Rochester, who studies TBI, said, “I'm not surprised by the findings, especially if you have people hitting a ball thousands of times a year.”
He noted that his own study (published online Nov. 12 in Magnetic Resonance Imaging) as well one by another group that is in press in the Journal of Neurotrauma have linked blows to the head to subtle DTI changes similar to those seen in TBI. “Those studied didn't get concussions either,” he said.
While Dr. Bazarian said he is looking forward to reading the full manuscript if the findings get published, he agreed that this alone would not merit a change in recommendations.
“The work still needs to be reproduced by another group before we take action. But if validated, we should push for changes in recommendations [on heading],” he said.