Unravelling the organisation and microstructure of sensorimotor brain networks in children with congenital hemiparesis

Abstract

Cerebral palsy (CP) describes a group of non-progressive pathology of the developing foetal or infant brain. It is primarily characterised by deficits in motor function. Evidence from conventional imaging studies demonstrate that CP is often associated with lesions to the periventricular white matter (PWM), which consists of fibres that pass through the thalamus and posterior limb of the internal capsule (PLIC). This includes the descending corticospinal and ascending thalamocortical tracts. Although studies show altered integrity of these projections in children with CP, it remains unclear whether there are changes in the integrity of other white matter tracts that traverse through the thalamus and PLIC, and whether these are associated with deficits in clinical outcome. The project aimed to examine the organisation and integrity of PWM projections that traverse the thalamus and PLIC in typically developing children (TDC) and children with congenital hemiparesis (spastic motor type). If changes were present, a second aim was to examine whether white matter changes were associated with altered sensorimotor function in children with congenital hemiparesis. Structural and diffusion-weighted images (high-angular resolution diffusion imaging; HARDI) of the brain were acquired using a 3T magnetic resonance imaging (MRI). Structural images were anatomically parcellated into 34 cortical regions per hemisphere. Tractography of diffusion images was performed for white matter projections that connected each cortical region with the thalamus and the PLIC. This allowed parcellation of the thalamus and PLIC based on cortical connections of white matter projections. The integrity of these projections was quantified using an asymmetry index (AI) between hemispheres based on the number of tracts for each cortical region. Microstructure was also analysed using weighted fractional anisotropy (FA) and mean diffusivity (MD). Clinical measures of motor and sensory function were also completed. The AI, FA and MD for each thalamocortical and PLIC projection were compared between CP and TDC groups using a general linear model, and the association between brain measures and clinical outcome was assessed using linear correlations. The results showed that there is topographical organisation of white matter projections based on cortical connections at the thalamus and PLIC. This organisation appeared to be similar between children with congenital hemiparesis and TDC. For thalamocortical projections, connections with the paracentral lobule, pre-central and post-central gyri showed greater AI in the CP group when compared with children in the TDC group. This finding is consistent with reduced projections on the hemisphere contralateral to the impaired hand. Further, there was reduced FA, reduced tract volume and increased MD for these thalamocortical projections on the hemisphere contralateral to the impaired limb in children with congenital hemiparesis. For projections traversing the PLIC, there was greater AI for connections with the paracentral lobule and pre-central gyri in the CP group compared to the TDC group. In addition, reduced FA and increased MD for these PLIC projections were observed on the hemisphere contralateral to the impaired limb in children with congenital hemiparesis. Notably, changes in the AI and tract microstructure for thalamocortical and PLIC projections were associated with poorer sensorimotor function. The findings from this project aid to unravel the neuroanatomical correlates that underpin sensorimotor deficits in children with congenital hemiparesis secondary to lesions to the PWM. This improved understanding may help to optimise neurorehabilitation strategies that promote sensorimotor function, which may enhance the quality of life and reduce the burden associated with this debilitating condition.