Microstructural alterations of motor pathways in adolescents born preterm

Objectives: Preterm birth can be associated with long term neuromotor impairment. This is thought to be a consequence of injury to the white matter (WM) of the immature brain and subsequently altered brain development. Alterations in WM microstructure can be detected using diffusion-weighted magnetic resonance imaging (DW-MRI). Diffusion measures like fractional anisotropy (FA) and apparent diffusion coefficient (ADC) are often used to characterize the „integrity“ of WM pathways. This study attempts to assess the association of preterm birth with changes in the microstructure of the motor pathways.

Methods: 45 preterm adolescents (15.6 years±1.3), born before 32 weeks' gestation, treated in a single level III unit, were studied together with 31 term-born healthy controls of similar age. MRI included a DW-sequence with high angular resolution (64 directions, b-value 3000s/mm²). Three of the preterm children had cerebral palsy (CP), further 12 had unspecific neurological findings (such as mild muscular hypo- or hypertonia or clumsiness). Image analysis consisted of definition of seed and target regions for tractography in a template image generated from the subjects. These regions were then spatially warped to each individual's images. Tractography of motor pathways was performed using constrained spherical deconvolution and probabilistic streamlines. Diffusion parameters were then measured along the motor tracts at equivalent levels for all subjects as defined in template space.

Results: Diffusion parameters were significantly different between preterms and controls at several levels along the cortico-spinal, thalamo-cortical and transcallosal pathways. In the centrum semiovale, FA and ADC were significantly increased compared to controls. In contrast, within the highly organized WM regions of the corpus callosum and internal capsule, ADC was increased whilst FA was decreased. Fiber count in the corpus callosum was significantly lower in preterm children. All findings remained significant after excluding children with CP.