Multimodal magnetic resonance imaging (MRI) in concussed athletes highlights persistent effects on cerebral blood flow (CBF) and mean diffusivity 1 year after medical clearance to return to play (RTP), according to a study published in Neurology.
In this longitudinal, observational study, 24 athletes with concussion received multimodal MRI scans during the early symptomatic phase of injury, prior to RTP, and 1 year after RTP. Imaging sessions assessed global functional connectivity and CBF, along with white matter fractional anisotropy and mean diffusivity. A control group of 122 athletes was also consecutively recruited and imaged at the start of their competitive seasons.
Assessment of global functional connectivity revealed elevated connectivity at symptomatic phase of injury, with clusters in frontal, temporal, and parietal regions, as well as in the posterior cingulate (mean effect 0.0275; 95% CI, 0.0175-0.0386); significant elevations in connectivity were also observed at RTP in similar brain regions, though frontal effects were found to be reduced (mean effect 0.0291; 95% CI, 0.0170-0.0423). No significant effect from concussion was observed 1 year after RTP for global functional connectivity.
For CBF, blood flow was elevated at symptomatic phase of injury, with more spatially limited effects vs global connectivity; effects were restricted to the superior frontal gyri. No significant effects of concussion were detected for CBF at RTP. A significant reductions in CBF, however, was observed within middle frontal and temporal regions.
For fractional anisotropy, concussion was associated with reductions in the posterior corona radiata at symptomatic phase of injury and at RTP — no significant effects were identified at 1-year post-RTP. For mean diffusivity, significant elevations were observed mainly in the posterior and superior corona radiata for symptomatic phase of injury, RTP, and 1 year after RTP, with increasingly spatially extensive effects seen at later time points.
The investigators note that gaps in our understanding of time-evolving pathophysiology in the brain may have limited these findings. They also note that potential transient brain changes between RTP and 1-year post-RTP were not observed in the study design and may further limit these findings. Moreover, the longitudinal effects of concussion during this time interval may be influenced by participant-dependent factors, such as detraining before RTP and the effects of exertion and subconcussive impacts after RTP. Despite potentially heterogenous post-RTP activities, significant effects of concussion were identified.
“The findings of this study may serve to refine our clinical understanding of concussion recovery, showing it to be a more complex, long-lasting process than previously thought,” concluded the researchers. “Current consensus guidelines for safe RTP are based primarily on the resolution of symptoms; however, the findings in this study indicate that more research is needed within the post-RTP time window to better understand optimal recovery time from a biological standpoint.”
Churchill NW, Hutchison MG, Graham SJ, Schweizer TA. Mapping brain recovery after concussion: from acute injury to 1 year after medical clearance [published online October 16, 2019]. Neurology. doi: 10.1212/WNL.0000000000008523