By Gina McKlveen
A recent study published by the American Journal of Neuroradiology last month, revealed the ramifications of traumatic brain injuries for college athletes who not only experience sports-related concussions, but repetitive head injuries as well.
The authors of the study, Chung, Chen, Li, Wang, and Lui, titled “Investigating Brain White Matter in Football Players with and without Concussion Using a Biophysical Model from Multishell Diffusion MRI” began with the hypothesis that there may be subtle but significant changes in white matter microstructural damage due to sports-related concussions (SRC) and repetitive head injuries (RHI) exposure that could be detectable with advanced medical diffusion imaging. White matter, simply explained, is brain tissue located deep inside the brain that is composed of nerve fibers, also called axons, which are part of the brain’s nerve cells, or neurons. The name “white matter” is derived from the tissues’ white color which is caused by a myelin, a layer of the brain that aids in rate of speed for sending signals and electrical impulses quickly between neurons so that the brain can receive and respond to messages.
For these reasons, white matter plays an important part in brain functioning, as it effects internal body communications and the brain’s learning ability, which is why any damage or deterioration to this area of the brain can have traumatic, even potentially life-long, neurological impacts. Based on these growing concerns, especially around the risks posed to young, sometimes still developing minds, like those of student-athletes, associated with sports-related concussions and repetitive head injuries customary in most contact sports, this report investigated the key differences between collegiate football players, specifically, with and without sports induced head injuries.
To begin the research investigation, the authors collected and studied 78 collegiate level athletes, all males around the age of 19 years-old, with 24 being college football players that experienced a sports-related concussion within 48 hours, 26 being college football players that faced repetitive head injuries but lacked a history of any sports-related concussion during the study, and finally 28 being non-contact-sport athletes who played baseball, cross country, and a field event and served as a control group throughout the study. The results of the 24 student-athletes with sports-related concussions were analyzed in more detail, studying the longitudinal recovery trajectories across four different time points. First, student-athletes with sports-related concussions were observed in the 24 to 48 hours after the initial injury. Second was the asymptotic stage, in which student-athletes with sports-related concussions that were observed after passing an initial clearance and return-to-play protocol. Third, student-athletes with sports-related concussions were observed seven days post-concussion following unrestricted return-to-play and finally, the fourth time point observation occurred six months after the initial injury. For comparison purposes, the 28 student-athlete non-contact-sport control group and the 26 student-athletes subjected to repetitive head injuries were also observed at the same time intervals that matched the sports-related concussion group. All studies and participants were conducted over the 2016 to 2018 football seasons.
The data collected on the student-athlete participants in the study was obtained using magnetic resonance imaging (MRI) scanner technology and diffusion image processing. After scanning the student-athletes brains and capturing the diffusion images, the authors used Tract-Based Spatial Statistics (TBSS) a sophisticated set of tools used to analyze the voxelwise—or whole-brain—diffusion data to capture the statistics and maps to track the presence white matter metrics. “For TBSS, statistical tests were conducted with 5,000 permutations to identify statistically significant effects among [the] groups.” Once the data was collected, “post hoc sub-analyses were performed in an attempt to separate the effects of SRC from RHI. Specifically, the corpus callosum (CC) was studied to understand the temporal evolution of the SRC changes.”
One of the most notable results of the data collection of this study was that the TBSS analysis revealed a “diffusely higher” axial kurtosis, meaning the directional measure related to the normal distribution, in athletes that experienced a sports-related concussion compared to the control group at the first time point. Moreover, similar differences in axial kurtosis were found between the control group and the student-athletes that experienced repetitive head impacts. The authors propose that “[These] findings suggest that some of the diffuse measurable microstructural changes observed in the SRC group may related not to [a] sports-related concussion, but to a background of exposure to repeat subconcussive head impacts.” In fact, “[s]imilar changes of kurtosis have been reported in nonconcussed young football players with cumulative head impact exposure.”
Then, when the authors took a step back and observed the data collected over each of the four different time points established throughout the study, they found that the affected white matter regions of the brains of student-athletes that experienced sports-related concussions in comparison with the non-contact sport control group decreased across the time points, “suggesting partial recovery of microstructural changes during the study period.” Yet, what was most interesting to the authors revealed by the data was that “persistent higher [axial kurtosis] in the SRC group was observed compared with the non-contact-sport controls mainly in the [corpus callosum] on [the] 6-month follow up scans, suggesting longer-term persistence of microstructural changes associated with SRC,” which means that the damage to the brain from sports-related concussions can have lasting ramifications for student-athletes.
Finally, focusing on the student-athletes with repetitive head injuries, who unlike the student-athletes with sports-related concussions which were taken out of active play, experienced repetitive head injuries over the course of the study, the authors “persistently observed across all time points compared with the non-contact sport controls” increasing and higher axial kurtosis. For emphasis, the authors add, “[w]hile similar findings were present at the initial time point in the SRC group, these were no longer present at later time points after a recuperation period without RHI exposure, suggesting that at least some of the white matter microstructural changes associated with RHI exposure may be reversible early on.” In other words, the study found that repeated hits to the head can do increasing damage to white matter in the brain if subjected to those kinds of injuries over an extended length of time without any significant recovery period.
The study did also acknowledge some of its limitations such as the fact that the time points were established by clinical status instead of predefined follow-up intervals, that the small sample size of 78 student athletes may have explained some changes in diffusivity which other studies have shown, or that TBSS methods are sensitive to maximal deviations in diffusion metrics. But the authors of this study ultimately concluded, “[t]here are differences not only in concussed football athletes but also in nonconcussed football athletes compared with non-contact-sport control athletes in terms of microstructure measures. These findings reinforce previous work showing that corpus callosum is specifically implicated in football athletes with SRC and also suggest this to be true for football athletes with RHI.” Only further study will be able to reveal what is the matter when it comes to repetitive head injuries and the effect of lost white matter over time on student-athletes who have been impacted by these types of injuries and concussions that clearly have significant traumatic neurological repercussions.
The results of this study added to findings published previously from a larger sample population conducted by the National Collegiate Athletic Association-Department of Defense Concussion Assessment, Research and Education (CARE) Consortium study. The work of this study was supported by the National Institutes of Health, the Department of Defense, and the Leon Lowenstein Foundation.