A Longitudinal Diffusion Tensor Imaging Study Assessing White Matter Fiber Tracts after Sports-Related Concussion

Abstract

The extent of structural injury in sports-related concussion (SRC) is central to the course of recovery, long-term effects, and the decision to return to play. In the present longitudinal study, we used diffusion tensor imaging (DTI) to assess white matter (WM) fiber tract integrity within 2 days, 2 weeks, and 2 months of concussive injury. Participants were righthanded male varsity contact-sport athletes (20.2 -1.0 years of age) with a medically diagnosed SRC (no loss of consciousness). They were compared to right-handed male varsity non-contact-sport athletes serving as controls (19.9 -1.7 years). We found significantly increased radial diffusivity (RD) in concussed athletes (n = 12; paired t-test, tract-based spatial statistics; p < 0.025) at 2 days, when compared to the 2-week postinjury time point. The increase was found in a cluster of right hemisphere voxels, spanning the posterior limb of the internal capsule (IC), the retrolenticular part of the IC, the inferior longitudinal fasciculus, the inferior fronto-occipital fasciculus (sagittal stratum), and the anterior thalamic radiation. Post-hoc, univariate, between-group (controls vs. concussed), mixed-effects analysis of the cluster showed significantly higher RD at 2 days ( p = 0.002), as compared to the controls, with a trend in the same direction at 2 months ( p = 0.11). Results for fractional anisotropy (FA) in the same cluster showed a similar, but inverted, pattern; FA was decreased at 2 days and at 2 months postinjury, when compared to healthy controls. At 2 weeks postinjury, no statistical differences between concussed and control athletes were found with regard to either RD or FA. These results support the hypothesis of increased RD and reduced FA within 72 h postinjury, followed by recovery that may extend beyond 2 weeks. RD appears to be a sensitive measure of concussive injury.

Subconcussive Head Impact Exposure and White Matter Tract Changes over a Single Season of Youth Football

“…This has some clinical implications for how the terminal fiber tracts respond to TBI compared with the core part of the fiber tracts. In this study, the observed alterations in the SLF are in agreement with current head impact literature (18,45,47) that demonstrates changes in the FA in the inferior and superior longitudinal fasciculus. Bendlin et al (18) showed decreased FA in the SLF of patients with TBI compared with healthy control patients.…”

“…These changes and abnormal findings in the whole left IFOF, terminals, and core part of IFOF suggests that subconcussive impacts can also contribute to alterations of varied segments of long-range WM tracts. Preliminary hypotheses suggest that IFOF and SLF may be preferentially susceptible to concussive and subconcussive forces because of the high degree of crossing and merging of WM fibers in these regions (45,47).…”

Evaluation of the protective capacity of baseball helmets for concussive impacts

“…Also of interest was that the upward angled impact (site 6) that represented a player ducking away from a ball impact had the largest strains in the white matter as opposed to grey matter. As the white matter is often suggested as a focal point for concussion (Wright et al, 2012;Murugavel et al, 2014;Shin et al, 2014) this impact site in particular might be of interest for future helmet designs. However, this methodology does indicate a significant risk of concussion for all the impact sites, which demonstrates the lack of protective capacity for this type of injury for all the helmets examined against these impacts from baseballs at high velocity.…”

White Matter Damage and Brain Network Alterations in Concussed Patients: A Review of Recent Diffusion Tensor Imaging and Resting-State Functional Connectivity Data

“…Although the number of published studies using DTI has more than quadrupled since 2002 [12], the utility of DTI for assessing white matter tract injury in concussion is still unclear. Several recent DTI studies have reported either high [13][14][15][16][17][18][19] or low [18,[20][21][22][23][24][25][26] FA following concussion, and one longitudinal study has shown both increases as well as decreases of anisotropy within the same individual over time [18] (see Table 1). These disparate findings in the recent concussion literature have spurred the hypothesis that anisotropic differences in concussed patients could differ depending on whether the patient is imaged immediately after the concussion or months/years postconcussion [13,14].…”

“…Several studies have noted high FA within 30 days post-concussion and have interpreted this 'surge' in FA following concussion as being reflective of intracellular edema [14,16,17,19]. However, other studies have shown contradictory findings of low FA in patients that were very recently concussed [18,21,22,25] Table 1.…”