Tract Profiles of the Cerebellar White Matter Pathways in Children and Adolescents

Abstract

Intact development of cerebellar connectivity is essential for healthy neuromotor and neurocognitive development. To date, limited knowledge about the microstructural properties of the cerebellar peduncles, the major white matter tracts of the cerebellum, is available for children and adolescents. Such information would be useful as a comparison for studies of normal development, clinical conditions, or associations of cerebellar structures with cognitive and motor functions. The goal of the present study was to evaluate the variability in diffusion measures of the cerebellar peduncles within individuals and within a normative sample of healthy children. Participants were 19 healthy children and adolescents, aged 9-17 years, mean age 13.0 ± 2.3. We analyzed diffusion magnetic resonance imaging (dMRI) data with deterministic tractography. We generated tract profiles for each of the cerebellar peduncles by extracting four diffusion properties (fractional anisotropy (FA) and mean, radial, and axial diffusivity) at 30 equidistant points along each tract. We were able to identify the middle cerebellar peduncle and the bilateral inferior and superior cerebellar peduncles in all participants. The results showed that within each of the peduncles, the diffusion properties varied along the trajectory of the tracts. However, the tracts showed consistent patterns of variation across individuals; the coefficient of variation for FA across individual profiles was low (≤20%) for each tract. We observed no systematic variation of the diffusion properties with age. These cerebellar tract profiles of the cerebellar peduncles can serve as a reference for future studies of children across the age range and for children and adolescents with clinical conditions that affect the cerebellum.

Keywords: Cerebellum; Development; Diffusion magnetic resonance imaging (dMRI); Premature birth; Tractography; White matter.

Figure 1

Location of anatomical reference ROIs used for tractography. Left hand columns display axial dMRI red-green-blue (RGB) color maps used to identify the ICP (A,B), MCP (D) and SCP (F,G) tracts. Right hand column displays results of the tracking approach in a representative subject for the left ICP (C-yellow), MCP (E-red) and left SCP (H-blue). The two way point ROIs used to identify the ICP (A,B), MCP (D) SCP (F,G) are indicated by white circles. Only left hemisphere ROIs are displayed for the ICP and SCP. Single pink arrow refers to first ROI (ROI1, white circle) used to initiate tracking. Single orange arrow indicates second ROI (ROI2) used to constrain tracts and interest tracking initiated from ROI1. (ICP = inferior cerebellar peduncle; MCP = middle cerebellar peduncle; SCP = superior cerebellar peduncle. L = left; R = right).

Figure 2

Tractography of the cerebellar peduncles. Two-dimensional rendering of the inferior (yellow), middle (red) and superior (blue) cerebellar peduncles displayed on a left sagittal section of a representative subject (A-B). Coronal view of all cerebellar peduncles in the same representative subject (C-D). White dashed lines represent location of each of two ROIs used to define individual cerebellar tracts. (ICP = inferior cerebellar peduncle; MCP = middle cerebellar peduncle; SCP = superior cerebellar peduncle. L = left; R = right).

Figure 3

FA tract profiles of the inferior and middle cerebellar peduncles in the sample of children and adolescents (N=19 ICP; N=18 MCP). Left hand column (A-C) shows renderings of 3 individual cerebellar tracts on sagittal (A,B) or axial (C) T1 images in the same representative subject shown in Figure 2. Right hand columns show FA tract profiles that are color-coded to match tract renderings in adjacent T1 images for the left (A) and right (B) ICP and MCP (C). FA values are plotted for 30 equidistant locations between two defining ROIs as indicated by dashed white lines. Location of ROIs correspond to pink and orange arrows in tract profiles. Boundaries of the 25th and 75th percentiles are indicated by dark gray shading. Boundaries of the 10th and 90th percentiles are indicated by light gray shading. (ICP = inferior cerebellar peduncle; MCP = middle cerebellar peduncle; L = left; R = right).

Figure 4

FA tract profiles of superior cerebellar peduncles in the sample of children and adolescents (N=19). Left hand column (A,B) shows renderings of 2 individual cerebellar tracts on sagittal T1 images in the same representative subject shown in Figure 2. Right hand columns show FA tract profiles that are color-coded to match tract renderings in adjacent T1 images for the left (A) and right (B) SCP. FA values are plotted for 30 equidistant locations between two defining ROIs as indicated by dashed white lines. Locations of ROIs correspond to pink and orange arrows in tract profiles. Boundaries of the 25th and 75th percentiles are indicated by dark gray shading. Boundaries of the 10th and 90th percentiles are indicated by light gray shading. (SCP = superior cerebellar peduncle; L = left; R = right).

Figure 5

Tract Mean Diffusivity (MD), Radial Diffusivity (RD) and Axial Diffusivity (AD) profiles of inferior, middle and superior cerebellar peduncles in the sample of children and adolescents. Columns show tract MD, RD and AD profiles that are color-coded to match tract renderings in T1 images presented in Figures 2-4. MD, RD and AD values are plotted for 30 equidistant locations between two defining ROIs. Locations of ROIs correspond to pink and orange arrows in tract profiles in Figures 2-4. Boundaries of the 25th and 75th percentiles are indicated by dark gray shading. Boundaries of the 10th and 90th percentiles are indicated by light gray shading. (ICP = inferior cerebellar peduncle; MCP = middle cerebellar peduncle; SCP = superior cerebellar peduncle; L = left; R = right).

Figure 6

Group and individual variance in Tract FA profiles. Group mean FA for the normative group is plotted for each tract for 3 locations corresponding to the average FA from nodes 1-10, 11-20, and 21-30 respectively (a-e). Error bars represent ±1 standard deviation of the normative group mean. (ICP = inferior cerebellar peduncle; MCP = middle cerebellar peduncle; SCP = superior cerebellar peduncle; L = left; R = right).