Advanced fiber tractography in cerebral palsy suggests primary and secondary microstructural changes along the corticospinal tract and somatosensory projections

Introduction: Diffusion-weighted magnetic resonance imaging (MRI) and fiber tractography are increasingly used to investigate alterations in white matter tracts in cerebral palsy (CP). We employed a combined normalization and probabilistic fiber-tracking method of the corticospinal tracts (CST) and thalamocortical projections to the primary sensory cortices (TRS1) in patients with unilateral CP and focal brain lesions.

Patients and Methods: Cross-sectional study, including 15 children with unilateral CP and 24 typically developing controls. Data were collected using a 1.5-T MR scanner. A study-specific fractional anisotropy (FA) template was constructed; regions of interest were defined and mapped onto each subject's native space. Probabilistic fiber-tracking using a multifiber model was performed. Tract paths were qualitatively assessed, and diffusion tensor imaging (DTI) parameters were extracted in regions close to and distant from lesions and compared with measures in equivalent locations along the tracts in the controls.

Results: The method proved robust in reconstructing the tracts in both groups. Morphological changes were seen in lesion-affected areas in the patient group and included splitting, dislocation, or compaction of the tracts. Analysis of DTI parameters indicated primary neurodegeneration in lesion-affected areas and distant secondary neurodegeneration along the CST. In comparable parts of the CST and TRS1 on the lesion-affected side, mean diffusivity was increased in both tracts, whereas FA was decreased in the CST only.

Conclusions: The proposed method is sensitive for fiber tractography in patients with CP and focal brain lesions. The observed changes indicate that the primary injury in this patient cohort is located in the CST, but with possibly reactive changes in the TRS1.