Diffusion Tensor Imaging Findings in Semi-Acute Mild Traumatic Brain Injury

Abstract

The past 10 years have seen a rapid increase in the use of diffusion tensor imaging to identify biomarkers of traumatic brain injury (TBI). Although the literature generally indicates decreased anisotropic diffusion at more chronic injury periods and in more severe injuries, considerable debate remains regarding the direction (i.e., increased or decreased) of anisotropic diffusion in the acute to semi-acute phase (here defined as less than 3 months post-injury) of mild TBI (mTBI). A systematic review of the literature was therefore performed to (1) determine the prevalence of different anisotropic diffusion findings (increased, decreased, bidirectional, or null) during the semi-acute injury phase of mTBI and to (2) identify clinical (e.g., age of injury, post-injury scan time, etc.) and experimental factors (e.g., number of unique directions, field strength) that may influence these findings. Results from the literature review indicated 31 articles with independent samples of semi-acute mTBI patients, with 13 studies reporting decreased anisotropic diffusion, 11 reporting increased diffusion, 2 reporting bidirectional findings, and 5 reporting null findings. Chi-squared analyses indicated that the total number of diffusion-weighted (DW) images was significantly associated with findings of either increased (DW ≥ 30) versus decreased (DW ≤ 25) anisotropic diffusion. Other clinical and experimental factors were not statistically significant for direction of anisotropic diffusion, but these results may have been limited by the relatively small number of studies within each domain (e.g., pediatric studies). In summary, current results indicate roughly equivalent number of studies reporting increased versus decreased anisotropic diffusion during semi-acute mTBI, with the number of unique diffusion images being statistically associated with the direction of findings.

The role of the cervical spine in post-concussion syndrome

“…Studies examining acutely concussed patients have found significant decreases in FA and significant increases in MD compared to controls [51,52], particularly in the posterior corpus callosum according to a recent meta-analysis [49]. On the contrary, other studies have shown increases in FA and decreases in radial diffusivity and MD [51,54] in almost equal numbers [55]. This inverse relationship between FA and MD is thought to represent damage to the microfilaments and microtubules of the axon [56].…”

“…This inverse relationship between FA and MD is thought to represent damage to the microfilaments and microtubules of the axon [56]. However, like much of the research surrounding concussion injuries, as the scanning takes place further away from the initial injury most of the studies have shown variable results possibly attributed to inconsistent measurement methodology [49,53] or potential flaws within the measurement itself [55].…”

Functional and Structural Network Recovery after Mild Traumatic Brain Injury: A 1-Year Longitudinal Study

“…Complementary, classical diffusion tensor imaging (DTI) studies reported about equal evidence of both increased and decreased fractional anisotropy (FA) in adult samples during the semi-acute phase (Dodd et al, 2014). However, when focusing on studies conducted in acute mTBI rather increased FA has been revealed, while decreased FA findings are reported more frequently for post-acute studies (Eierud et al, 2014).…”

Increased Network Excitability Due to Altered Synaptic Inputs to Neocortical Layer V Intact and Axotomized Pyramidal Neurons after Mild Traumatic Brain Injury

“…[8][9][10][11][12] The cause of this morbidity associated with mTBI is not fully appreciated; however, the use of modern imaging has shown structural and functional changes in this patient population. [13][14][15] The use of diffusion tensor imaging (DTI) and susceptibility weighted imaging has shown regional changes in fractional anisotropy and microbleeds respectively that have been linked to more diffuse/ global axonal damage and disconnection. 15 These imaging signatures and their implications for axonal damage are also entirely consistent with limited pathological studies performed in patients who have sustained mTBI as well as numerous animal studies that have confirmed diffuse axonal injury (DAI) following various forms of mild injury.…”

“…While numerous studies have shown correlations between measures of fractional anisotropy and cognitive function following mTBI,13,14,[55][56][57] a recent report with a relatively large, healthy cohort of patients failed to identify any DTI-related changes associated with post-concussion symptoms 58. These differing results, perhaps related to the timing of imaging as Ilvesmä ki and colleagues obtained images acutely within 14 days of injury, at a minimum question the extent to which various imaging modalities can detect the most subtle of head injuries.…”