White matter microstructural abnormalities in children with spina bifida myelomeningocele and hydrocephalus: a diffusion tensor tractography study of the association pathways.

PURPOSE To quantify microstructural abnormalities in the major association pathways of children affected by spina bifida myelomeningocele (SBM) and shunted hydrocephalus using whole-brain diffusion tensor imaging (DTI). MATERIALS AND METHODS The institutional review board approved this Health Insurance Portability and Accountability Act (HIPAA)-compliant study and written informed consent/assent were obtained prior to the study. The 69 participants included 38 children with SBM and shunted hydrocephalus (age mean +/- SD = 12.30 +/- 2.10 years; 22 boys; 10 left-handed) and 31 age- and sex-matched normally-developing children (11.56 +/- 2.72 years; 15 boys, four left-handed). Diffusion tensor tractography (DTT) was performed to delineate and quantify bilaterally four major association pathways (arcuate, inferior longitudinal, inferior fronto-occipital, and uncinate fasciculi). RESULTS The group with SBM did not exhibit the pattern of age-related decreases in the diffusivities observed in the controls. The transverse and axial diffusivities were significantly elevated in most of the white matter pathways of the participants with SBM. The fractional anisotropy (FA) was significantly lower in most of the association pathways. Many of the association pathways were not traceable in some participants with SBM compared to the controls at the selected FA thresholds. CONCLUSION DTT revealed diffusion tensor characteristics of abnormal development (nonvisualization/poor visualization of tracts, downward arrow FA, upward arrow diffusivities), impairment in myelination (upward arrow transverse diffusivity) as well as abnormalities in intrinsic axonal characteristics and extraaxonal/extracellular space (upward arrow axial diffusivity) in the association pathways of the SBM children. The differences in the diffusion metrics observed in the children with SBM are suggestive of abnormal white matter development and persistent degeneration with increased age.