Although young athletes who've had a concussion may seem to make a quick clinical recovery, physiologic changes in the brain may persist long after symptoms have resolved, researchers reported here.
In a case-control study, high school and college athletes who'd had a concussion had a significant drop in cerebral blood flow more than a week after their injury, while those who didn't sustain a concussion had no changes on MRI, Michael McCrea, PhD, of the Medical College of Wisconsin in Milwaukee, and colleagues reported during a press briefing at the Radiological Society of North America meeting here.
"The tail of physiologic recovery extends beyond the point of clinical recovery," McCrea said. "It's not reduced to what are the signs and symptoms manifested by this extended tail of physiologic recovery. It really pertains more to the discussion about that person's readiness to return to activity, where they're certain to sustain additional head impacts."
Other evidence has suggested that neurophysiologic abnormalities continue long after symptoms of concussion resolve, and that has been reflected in sports medicine practice. Gone are the days of same-day return-to-play -- which international guidelines now strongly recommend against -- and McCrea said the average time to get back in the game today is 15 days.
"Those extra days not only provide the athlete adequate rest and clinical recovery, but it's also going to put them in a better place in terms of physiologic recovery," he said.
But physicians still generally rely on symptoms and neurological and cognitive testing to guide their decision making about when to let athletes return to play. To get a better handle on neurophysiologic markers of recovery, McCrea and colleagues studied 27 high school and college athletes who had a concussion and compared them with 27 matched controls who weren't concussed.
All of them were imaged within 24 hours of their injury, and about 30% to 35% had a previous concussion, McCrea said.
He and colleagues used arterial spin labeling (ASL) MRI to evaluate cerebral blood flow changes immediately after the injury and then again 8 days later. ASL imaging doesn't involve radiation exposure; instead it uses arterial blood water as a contrast tracer to measure blood flow change. It has been highly associated with brain function, the researchers said.
Clinical assessments were made using the Sport Concussion Assessment Tool 3 (SCAT3) and the Standardized Assessment of Concussion (SAC) screens.
McCrea and colleagues found that controls didn't have any changes in cerebral blood flow at 24 hours or at 8 days -- but those with a concussion had significant declines in blood flow at 8 days.
Those declines come despite the fact that scores on clinical and cognitive tests had returned to normal by that time point, McCrea said.
"The end-game here, from a translational perspective, is that decision making around fitness to return to activity is dependent not only on what we observe to be their clinical recovery, but on their readiness from a physiologic standpoint to return to activities that may render them at risk for secondary injuries down the line."
But the findings are preliminary and more work needs to be done before MRIs help guide physicians in making decisions about a player's return to the game, said Salomao Faintuch, MD, of Beth Israel Deaconess Medical Center in Boston, who moderated the press briefing and wasn't involved in the study.
"We are at a very early stage in understanding how the brain recovers from concussions and injuries in general," Faintuch said. "Recovery time may be much slower, and we can't currently determine that based on clinical symptoms alone. We're looking forward to getting more data on how long it takes the brain to fully recover."
The work was supported by a grant from the National Football League and General Electric.
McCrea and Faintuch disclosed no financial relationships with industry.