A diffusion tensor imaging study on the white matter skeleton in individuals with sports-related concussion

Abstract

Recognizing and managing the effects of cerebral concussion is very challenging, given the discrete symptomatology. Most individuals with sports-related concussion will not score below 15 on the Glasgow Coma Scale, but will present with rapid onset of short-lived neurological impairment, demonstrating no structural changes on traditional magnetic resonance imaging (MRI) and computed tomography (CT) scans. The return-to-play decision is one of the most difficult responsibilities facing the physician, and so far this decision has been primarily based on neurological examination, symptom checklists, and neuropsychological (NP) testing. Diffusion tensor imaging (DTI) may be a more objective tool to assess the severity and recovery of function after concussion. We assessed white matter (WM) fiber tract integrity in varsity level college athletes with sports-related concussion without loss of consciousness, who experienced protracted symptoms for at least 1 month after injury. Evaluation of fractional anisotropy (FA) and mean diffusivity (MD) of the WM skeleton using tract-based spatial statistics (TBSS) revealed a large cluster of significantly increased MD for concussed subjects in several WM fiber tracts in the left hemisphere, including parts of the inferior/superior longitudinal and fronto-occipital fasciculi, the retrolenticular part of the internal capsule, and posterior thalamic and acoustic radiations. Qualitative comparison of average FA and MD suggests that with increasing level of injury severity (ranging from sports-related concussion to severe traumatic brain injury), MD might be more sensitive at detecting mild injury, whereas FA captures more severe injuries. In conclusion, the TBSS analysis used to evaluate diffuse axonal injury of the WM skeleton seems sensitive enough to detect structural changes in sports-related concussion.

FIG. 1.

Results of the Tract-Based Spatial Statistics (TBSS) analysis of the white matter (WM) skeleton. Voxels demonstrating significantly (corrected p ≤ 0.05) increased mean diffusivity (MD) values for the concussion subjects compared to their age- and sex-matched control subjects are shown in red-yellow. Voxels are thickened into local tracts and overlaid on the WM skeleton (green), and the group mean fractional anisotropy (FA) image (grayscale). The two largest cluster divisions out of four are identified by an arrow with the cluster number. Further cluster details are given in Table 2. Images are shown in radiological convention (right = subject's left) for slice coordinates: x = −36 mm, y = −35 mm, z = 4 mm.

FIG. 2.

Comparison of concussion results to moderate and severe TBI data. Group averages are denoted by “X.” Differences in group averages of the diffusion values with increasing injury severity are highlighted with a dotted black line. Differences across the control groups are highlighted with a solid black line. (A) Average mean diffusivity (MD) for each individual subject, separated by group. Note that brain-injured subjects tend to have increased MD compared to controls. (B) Average fractional anisotropy (FA) values for each individual subject, separated by group. Note that brain-injured subjects tend to have decreased FA compared to controls. MD may be more sensitive at detecting mild injury, whereas FA captures more severe injuries (TBI, traumatic brain injury).