Corpus callosum and inferior forebrain white matter microstructure are related to functional outcome from raised intracranial pressure in child traumatic brain injury

In severe paediatric traumatic brain injury (TBI), a common focus of treatment is raised intracranial pressure (ICP). We have previously reported frontal cerebral vulnerability with executive deficits from raised ICP in paediatric TBI. Now, using diffusion tensor imaging (DTI) in a different population, we have examined fractional anisotropy (FA), and mean, axial and radial diffusivity (MD, AD, RD) in 4 regions of the corpus callosum (CC) and in both inferior frontal regions. Our aim was to examine during the chronic phase of TBI whether the CC cross-sectional area correlated with regional DTI metrics of white matter microstructure, with global outcome ratings of function (Functional Independence Measure and Multiattribute Health Status Classification) and with performance in the Rey-Osterrieth Complex Figure (ROCF) test. We examined 33 paediatric TBI cases who were followed, on average, 4.9 years after severe injury. All cases had received mechanical ventilation during their acute treatment and, a priori, they were assigned to a non-ICP or a raised ICP group. Twenty-two participants had mainly right-sided injury at the time of acute ictus. The findings confirm that severe TBI in childhood, complicated by intracranial hypertension, results in CC vulnerability. In the chronic phase of recovery, it is reduced in the cross-sectional area, it is more compact and thinned, and the anterior region is disproportionately small. Late after raised ICP, we have also found that individuals exhibit regional microstructural abnormality with combined reduced FA and increased MD, AD and RD. Smaller size and such microstructural changes in the anterior CC were associated with similar right-sided (rather than left-sided) frontal microstructural changes in the ICP group. Taken together, this evidence points to an interaction between raised ICP-related brain tissue perturbation and focal frontal extracallosal injury, leading to anterior CC regional vulnerability, most likely wallerian degeneration. At long-term follow-up, this lack of white matter integrity in the anterior CC is correlated with functional outcome, particularly in aspects of social interaction and the copy component of the ROCF test, which suggests that the CC-to-forebrain function warrants further study in chronic TBI.