Early postnatal development of corpus callosum and corticospinal white matter assessed with quantitative tractography

Abstract

Background and purpose: The early postnatal period is perhaps the most dynamic phase of white matter development. We hypothesized that the early postnatal development of the corpus callosum and corticospinal tracts could be studied in unsedated healthy neonates by using novel approaches to diffusion tensor imaging (DTI) and quantitative tractography.

Materials and methods: Isotropic 2 x 2 x 2 mm(3) DTI and structural images were acquired from 47 healthy neonates. DTI and structural images were coregistered and fractional anisotropy (FA), mean diffusivity (MD), and normalized T1-weighted (T1W) and T2-weighted (T2W) signal intensities were determined in central midline and peripheral cortical regions of the white matter tracts of the genu and splenium of the corpus callosum and the central midbrain and peripheral cortical regions of the corticospinal tracts by using quantitative tractography.

Results: We observed that central regions exhibited lower MD, higher FA values, higher T1W intensity, and lower T2W intensity than peripheral cortical regions. As expected, MD decreased, FA increased, and T2W signal intensity decreased with increasing age in the genu and corticospinal tract, whereas there was no significant change in T1W signal intensity. The central midline region of the splenium fiber tract has a unique pattern, with no change in MD, FA, or T2W signal intensity with age, suggesting different growth trajectory compared with the other tracts. FA seems to be more dependent on tract organization, whereas MD seems to be more sensitive to myelination.

Conclusions: Our novel approach may detect small regional differences and age-related changes in the corpus callosum and corticospinal white matter tracts in unsedated healthy neonates and may be used for future studies of pediatric brain disorders that affect developing white matter.

Fig 1.

Visualization of the 4 fiber tracts in axial and sagittal views, with overlay of location selected for statistical analysis. Genu (green), splenium (yellow), and left and right motor tracts (cyan) are shown in a 3D display combined with the DTI FA image. CS-12, central corticospinal tract; CS9, cortical corticospinal tract; G0, central genu; G21, cortical genu; S0, central splenium; S24, cortical splenium.

Fig 2.

Mean diffusivity, fractional anisotropy, T1w and T2w signal intensity in the major white matter tracts of the neonate (n = 47). See “Results” for details of statistical analysis.

Fig 3.

Maturation of mean diffusivity (MD) and fractional anisotropy (FA) in white matter tracts of the genu, splenium, and left corticospinal tract (n = 47). In the genu, MD was significantly correlated with age in the central (r² = 0.2392; P = .0005) and peripheral (r² = 0.3781; P < .0001) regions. FA also was significantly correlated with age in the central (r² = 0.1810; P = .0029) and peripheral (r² = 0.4219; P < .0001) regions. Unlike other fiber tracts studied, there were no significant correlations of age with MD in the central (r² = 0.05944; P = .0986) and peripheral (r² = 0.02135; P = .3271) regions of the splenium. In the splenium, FA also was not significantly correlated with age in the central (r² = 0.000027; P = .9720) and peripheral (r² = 0.00175; P = .7800) regions. In the left corticospinal tract, MD was significantly correlated with age in the central (r² = 0.3447; P < .0001) and peripheral (r² = 0.4727; P < .0001) regions. FA was significantly correlated with age in the central (r² = 0.2363; P = .0005) and peripheral (r² = 0.1138; P < .0204) regions.

Fig 4.

Age-related changes in T1W and T2W signal intensity in the white matter tracts of the genu, splenium, and left corticospinal tract. In the genu, T1W signal intensity was not significantly correlated with age in either the central (r² = 0.03823; P = .2461) or peripheral region (r² = 0.005794; P = .6543). T2W signal intensity significantly declined with age in both the central (r² = 0.09326; P = .0348) and peripheral regions (r² = 0.2891; P = .0001). A similar overall pattern is present in the left corticospinal tract. T1W signal intensity was not significantly correlated with age in either the central (r² = 0.02530; P = .3541) or peripheral region (r² = 0.005692, P = .6619) and T2W signal intensity decreases with age in both the central (r² = 0.5204, P < .0001.) and cortical peripheral (r² = 0.3975; P < .0001) regions. In the splenium, a different pattern is evident. T1W signal intensity decreases with age in the central (r² = 0.1207; P = .0352) but not the peripheral region (r² = 0.01349; P = .4937). T2W signal intensity significantly decreased with age in the peripheral region (r² = 0.1818; P = .0025), but not in the central region (r² = 0.01067; P = .4848).