Tractography-based quantitation of corticospinal tract development in premature newborns

Objective: To evaluate the impact of early brain injury and neonatal illness on corticospinal tract (CST) development in premature newborns serially studied with diffusion tensor tractography.

Study design: Fifty-five premature newborns (median 27.6 weeks postmenstrual age) were scanned with magnetic resonance imaging (MRI) early in life and at term-equivalent age. Moderate-severe brain abnormalities (abnormal-MRI) were characterized by moderate-severe white matter injury or ventriculomegaly. Diffusion tensor tractography was used to measure CST diffusion parameters which reflect microstructural development: fractional anisotropy (FA) and average diffusivity (D(av)). The effect of abnormal-MRI and neonatal illness on FA and D(av) were assessed with multivariate regression for repeated measures adjusting for age at scan.

Results: Twenty-one newborns (38%) had abnormal-MRI on either scan. FA increased with age significantly slower in newborns with abnormal-MRI (0.008/week) relative to newborns without these MRI abnormalities (0.011/wk) (interaction term P = .05). D(av) was higher in newborns with abnormal-MRI (1.5 x 10(-5) mm(2)/sec; P < .001) for any given age at scan. In the 23 newborns (42%) with postnatal infection, FA increased more slowly (interaction term P = .04), even when adjusting for the presence of abnormal-MRI.

Conclusions: CST microstructural development is significantly impaired in premature newborns with abnormal-MRI or postnatal infection, with a pattern of diffusion changes suggesting impaired glial cell development.