Severe Traumatic Brain Injury Patients without Focal Lesion but with Behavioral Disorders: Shrinkage of Gray Matter Nuclei and Thalamus Revealed in a Pilot Voxel-Based MRI Study

After a traumatic brain injury (TBI), behavioral disorders can occur without major focal brain lesion, and in these situations, their pathophysiology remains unclear. The aim of this study is to examine whether TBI patients with behavioral disorders but without any focal damage, as observed from an initial clinical CT scan, present subtle volumetric alterations that could be measured voxel-by-voxel in the whole brain with MRI. Eight male adults with severe TBI who had behavioral sequela but not major focal cerebral lesion and 17 age-matched controls underwent a volumetric T1-weighted 1.5T MRI. A two step analysis was performed. First, gray matter (GM) and white matter (WM) volumes were compared between groups using voxel-based morphometry. Second, we examined brain regions systematically damaged using the sum of the individual binary maps obtained from z-maps thresholded at -1.75 for significant GM and WM atrophy. TBI patients had lower GM volume than controls (p<0.001, uncorrected) in the right parahippocampal gyrus; left and right superior, middle, and inferior temporal gyri; left superior frontal gyrus; right middle frontal gyrus; thalami; mammillary bodies; caudate nuclei; insulae; cerebellar cortex; and vermis. WM volume was lower (p<0.001, uncorrected) in the TBI group than in controls in the periventricular area and around the basal nuclei. We found shrinkage in the dorsomedial thalami in each of the TBI patients, and in the posterior part of the right putamen and caudate nuclei in seven TBI patients. Shrinkage in the dorsomedial thalami and in the posterior part of the right putamen and caudate nuclei may be a common effect of the disseminated microscopic lesions, and be associated with behavioral issues in severe TBI patients without major focal lesions.