Are functional deficits in concussed individuals consistent with white matter structural alterations: combined FMRI & DTI study

Abstract

There is still controversy in the literature whether a single episode of mild traumatic brain injury (MTBI) results in short-term functional and/or structural deficits as well as any induced long-term residual effects. With the inability of traditional structural brain imaging techniques to accurately diagnosis MTBI, there is hope that more advanced applications like functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) will be more specific in diagnosing MTBI. In this study, 15 subjects who have recently suffered from sport-related MTBI and 15 age-matched normal controls underwent both fMRI and DTI to investigate the possibility of traumatic axonal injury associated with functional deficits in recently concussed but asymptomatic individuals. There are several findings of interest. First, MTBI subjects had a more disperse brain activation pattern with additional increases in activity outside of the shared regions of interest (ROIs) as revealed by FMRI blood oxygen level–dependent (BOLD) signals. The MTBI group had additional activation in the left dorsal-lateral prefrontal cortex during encoding phase of spatial navigation working memory task that was not observed in normal controls. Second, neither whole-brain analysis nor ROI analysis showed significant alteration of white matter (WM) integrity in MTBI subjects as evidenced by fractional anisotropy FA (DTI) data. It should be noted, however, there was a larger variability of fractional anisotropy (FA) in the genu, and body of the corpus callosum in MTB subjects. Moreover, we observed decreased diffusivity as evidenced by apparent diffusion coefficient (ADC) at both left and right dorsolateral prefrontal cortex (DL-PFC) in MTBI subjects (P < 0.001). There was also a positive correlation (P < 0.05) between ADC and % change of fMRI BOLD signals at DL-PFC in MTBI subjects, but not in normal controls. Despite these differences we conclude that overall, no consistent findings across advanced brain imaging techniques (fMRI and DTI) were observed. Whether the lack of consistency across research techniques (fMRI & DTI) is due to time frame of scanning, unique nature of MTBI and/or technological issues involved in FA and Apparent Diffusion Coefficient (ADC) quantification is yet to be determined.

Principal Component Analysis of Diffusion Tensor Images to Determine White Matter Injury Patterns Underlying Postconcussive Headache

“…1,10,15,16 These reports have demonstrated white matter abnormalities in patients with mTBI relative to controls [17][18][19] ; however, these differences have not correlated with symptoms. 20 Similarly, attempts to correlate structural injuries with postconcussive cognitive perfor- mance have shown mixed results without a strong anatomic/ pathologic correlation, with deficits detected in regions as diverse as the occipital cortex and corticospinal tracts.…”

Diffusion Measures Indicate Fight Exposure-Related Damage to Cerebral White Matter in Boxers and Mixed Martial Arts Fighters

“…Cubon et al 31 reported that college athletes with mild TBI (5 men and 5 women) who had concussion showed significantly increased MD in the left hemisphere, spanning the sagittal striatum, retrolenticular section of the internal capsule, and the posterior thalamic radiation (by use of tract-based spatial statistics), but there was no significant change in FA. In a recent study, Zhang et al 32 found no significant differences in fMRI and DTI results among patients with mild TBI versus control subjects; the authors suggested that these regional variations in FA and MD changes in patients with mild TBI might be the result of differing timeframes, technological issues involved in DTI, and different methodologic approaches.…”

Sports-related brain injuries: connecting pathology to diagnosis

“…10 In an effort to establish differences between the functionality of fMRI and DTI in the setting of mTBI, 1 study found a lack of consistent findings across both techniques. 149 This highlights the need for future research to establish a clearer difference in the diagnostic utility of each technique. Moreover, in addition to the architectural and microstructural changes highlighted with the use of DTI, magnetoencephalography has been used to identify changes in functional connectivity; patients with mTBI exhibited weakened local connections and strong long-range connections, displaying an inverse relationship relative to non-mTBI controls.…”