Mild Traumatic Brain Injury Is Associated With Increased Thalamic Subregion Volume in the Subacute Period Following Injury

Structural vulnerability of the thalamus remains underinvestigated in mild traumatic brain injury (mTBI), and few studies have addressed its constituent nuclei using robust segmentation methods. This study aimed to investigate thalamic subnuclei volume in the subacute period following mTBI. Trauma control (TC) and mTBI patients aged 18-60 years old completed a magnetic resonance imaging (MRI) protocol including both high resolution structural (T1w) and diffusion-weighted sequences at 6-12 weeks following injury (mean: 57 days; SD 11). Each thalamus was segmented into its constituent subnuclei, which were grouped into eight lateralized subregions. Volumes of the subregions were calculated. Neurite Orientation Dispersion and Density (NODDI) maps with parameters optimized for gray matter were computed for the same subregions. Group differences in subregion volumes and NODDI parameters were investigated using Bayesian linear modeling, with age, sex, and estimated intracranial volume included as covariates. Comparisons of mTBI (n = 39) and TC (n = 28) groups revealed evidence of relatively increased gray matter volume in the mTBI group for the bilateral medial and right intralaminar subregions (BF₁₀ > 3). Of the subregions which showed volume differences, there was no evidence for differences in NODDI metrics between groups. This study demonstrates that in the subacute period following mTBI, there is evidence of increased volume in specific thalamic subregions. Putative mechanisms underpinning the increased volume observed here are disordered remyelination or myelin debris yet to be cleared.