Functional MRI may help settle an open question among pediatric neurologists over “second impact syndrome” in child and teen football players.

Does the syndrome exist as a discrete and unique injury brought on when a young athlete suffers a new concussion before a prior one has fully healed? Or is it the case, as some argue, that what sometimes gets diagnosed as second impact syndrome is simply diffuse cerebral swelling unrelated to the first concussion?

Part of the problem is that, as a review of the literature has now shown, reports of second impact syndrome are few.

A team led by Meredith Golomb, MD, MSc, Indiana University School of Medicine and Riley Hospital for Children in Indianapolis, searched the Ovid and PubMed databases spanning the years from 1946 to 2015 and using the terms “second impact syndrome,” “repeat concussion” and “catastrophic brain injury.”

They also found review articles using combinations of “concussion,” “second impact syndrome” and “repetitive head trauma.”

Golomb and colleagues found 17 patient cases in seven publications that met the criteria of having two hits to the head plus persistent symptoms from the first to the second concussion.

Among their key observations:

• Ten of the 17 (59 percent) were football players, all of them male, and ages ranged from 13 to 23 years.
• All patients with poor outcomes—death or permanent disability—were younger than 20, while four of the five players with good outcomes were older than 19.
• The lag time from first to second concussion ranged from one hour to four weeks. In many cases, at least one of the two hits appeared minor.

The study was published in Pediatric Neurology.

In search of risks and outcomes

In light of the dearth of clinical research into second impact syndrome, Golomb et al. call for prospective studies to clarify risk factors and document outcomes of the injury regardless of what it’s called.

The aim of the prospective inquiries would be to come up with return-to-play recommendations for young athletes.

The authors point to research hypothesizing several mechanisms for second impact syndrome. One study proposed that diffuse edema after the second hit “leads to compression of the parenchyma and vasculature, causing global brain injury.”

“A more widely accepted mechanism is that the brain’s vasculature loses its ability to autoregulate after the first traumatic brain injury,” they write. “This disruption of autoregulation leads to cerebral edema and engorgement of the vasculature after the second hit because the brain cannot compensate for the edema by decreasing blood flow.”

Looking to imaging

Golomb and co-authors stress the need to recognize which children have ongoing postconcussion symptoms, which is where fMRI could help.

“In addition to a thorough history and examination, newer forms of cranial imaging may become useful tools in identifying concussion,” they write. “Typical computed tomography and magnetic resonance imaging do not detect acute concussion in children. However, functional magnetic resonance imaging and magnetic source imaging have been shown to detect abnormalities.”

Future research, the authors add, should try to identify the risk factors for second impact syndrome.

“We believe that prothrombotic abnormalities and migraine warrant further investigation as risk factors,” they write. “There is also a need for further work on treatments for second impact syndrome because the outcome is often poor.”