Structural Brain Connectivity Correlates with Outcome in Mild Traumatic Brain Injury

We investigated the topology of structural brain connectivity networks and its association with outcome after mild traumatic brain injury, a major cause of permanent disability. Eighty-five patients with mild traumatic brain injury underwent magnetic resonance imaging (MRI) twice, about three weeks and eight months after injury, and 30 age-matched orthopedic trauma control subjects were scanned. Outcome was assessed with Extended Glasgow Outcome Scale on average eight months after injury. We performed constrained spherical deconvolution-based probabilistic streamlines tractography on diffusion MRI data and parcellated cortical and subcortical gray matter into 84 regions based on T1-weighted data to reconstruct structural brain connectivity networks weighted by the number of streamlines. Graph theoretical methods were employed to measure network properties in both patients and controls, and correlations between these properties and outcome were calculated. We found no global differences in the network properties between patients with mild traumatic brain injury and orthopedic control subjects at either stage. We found significantly increased betweenness centrality of the right pars opercularis in the chronic stage compared with control subjects, however. Further, both global and local network properties correlated significantly with outcome. Higher normalized global efficiency, degree, and strength as well as lower small-worldness were associated with better outcome. Correlations between the outcome and the local network properties were the most prominent in the left putamen and the left postcentral gyrus. Our results indicate that both global and local network properties provide valuable information about the outcome already in the acute/subacute stage and, therefore, are promising biomarkers for prognostic purposes in mild traumatic brain injury.