Extent of Microstructural White Matter Injury in Postconcussive Syndrome Correlates with Impaired Cognitive Reaction Time: A 3T Diffusion Tensor Imaging Study of Mild Traumatic Brain Injury

TLDR

Diffusion tensor imaging can detect microstructural white matter changes in mild traumatic brain injury that conventional MRI often misses. The study tested whether DTI-derived diffuse axonal injury metrics correlate with reaction time deficits, unlike conventional microhemorrhage counts. Thirty‑four symptomatic mild TBI patients underwent DTI and T2*-weighted GRE imaging, with fractional anisotropy values 2.5 SD below healthy controls in predefined regions flagged as diffuse axonal injury. DTI identified damage in key white matter tracts, and the number of affected structures correlated significantly with slower reaction times (r = 0.49, p = 0.012), whereas microhemorrhage counts did not.

Abstract

<b>BACKGROUND AND PURPOSE:</b> Diffusion tensor imaging (DTI) may be a useful index of microstructural changes implicated in diffuse axonal injury (DAI) linked to persistent postconcussive symptoms, especially in mild traumatic brain injury (TBI), for which conventional MR imaging techniques may lack sensitivity. We hypothesized that for mild TBI, DTI measures of DAI would correlate with impairments in reaction time, whereas the number of focal lesions on conventional 3T MR imaging would not. <b>MATERIALS AND METHODS:</b> Thirty-four adult patients with mild TBI with persistent symptoms were assessed for DAI by quantifying traumatic microhemorrhages detected on a conventional set of T2*-weighted gradient-echo images and by DTI measures of fractional anisotropy (FA) within a set of a priori regions of interest. FA values 2.5 SDs below the region average, based on a group of 26 healthy control adults, were coded as exhibiting DAI. <b>RESULTS:</b> DTI measures revealed several predominant regions of damage including the anterior corona radiata (41% of the patients), uncinate fasciculus (29%), genu of the corpus callosum (21%), inferior longitudinal fasciculus (21%), and cingulum bundle (18%). The number of damaged white matter structures as quantified by DTI was significantly correlated with mean reaction time on a simple cognitive task (<i>r</i> = 0.49, <i>P</i> = .012). In contradistinction, the number of traumatic microhemorrhages was uncorrelated with reaction time (<i>r</i> = −0.08, <i>P</i> = .71). <b>CONCLUSION:</b> Microstructural white matter lesions detected by DTI correlate with persistent cognitive deficits in mild TBI, even in populations in which conventional measures do not. DTI measures may thus contribute additional diagnostic information related to DAI.