To study the relation of loss of consciousness (LOC) to white matter integrity after mild traumatic brain injury (mTBI), we acquired diffusion tensor imaging (DTI) at 3 Tesla in 79 participants with mTBI and normal computed tomography (age 18 to 50 years) whom we imaged after a mean post-injury interval of 25.9 h (standard deviation = 12.3) and at 3 months. For comparison, 64 participants with orthopedic injury (OI) underwent DTI at similar intervals. Quantitative tractography was used to measure fractional anisotropy (FA) and mean diffusivity (MD) in the left and right uncinate fasciculus (UF), left and right inferior frontal occipital fasciculus (IFOF), and the genu of the corpus callosum. Generalized estimating equation models assessed the association between LOC and both MD and FA across time after mTBI and compared their DTI metrics with the OI group. LOC was significantly related to MD in UF and IFOF (p values ranged from p < 0.0001 to 0.0270) and to FA in left UF (p = 0.0104) and right UF (p = 0.0404). Between-group differences in MD were significant for left UF, left and right IFOF, and the genu of the corpus callosum on initial DTI, but not at 3 months post-injury, and these differences were specific to the mTBI subgroup with LOC. Groups did not differ in FA at either occasion. Early DTI may provide a biomarker for mTBI with LOC, even in patients whose consciousness recovers by arrival in the emergency department. MD better differentiates mTBI from OI than FA on early DTI, but this is specific to mTBI with LOC. DTI findings support a continuum of white matter injury in early mTBI.
Keywords: diffusion tensor imaging; loss of consciousness; mild traumatic brain injury.