Alteration in the number and integrity of white matter tracts in the preterm: A quantitative diffusion tensor imaging and diffusion fibre tractography in children

Abstract

Purpose: Periventricular white matter is most commonly injured in preterm babies with hypoxia. To assess white matter damage, we decided to perform diffusion tensor imaging (DTI) in preterm children with history of hypoxia and magnetic resonance imaging (MRI) features of periventricular leukomalacia (PVL) (PTH). We hypothesized that the PTH have reduced number of white matter fibres compared to age matched pre term children without hypoxia (PTHO), and also depending on the severity of PVL, there could be reduction in the number of fibres as well.

Materials and methods: The present study was carried out at the Government Medical College, Thiruvananthapuram. DTI was performed on 15 PTH and 15 PTHO. We measured number of fibres and fractional anisotropy of corpus callosum (CC) and optic radiations (OR).

Results: There was significant difference between two groups with regard OR (P < 0.001). The mean number of OR fibres in cases and control was 104 ± 28.44 (mean ± SD) and 578 ± 286 (mean ± SD), respectively. The mean number of CC in cases was 953 ± 429 and in controls was 1625 ± 116 with a P value <0.56. No significant difference in FA was seen between cases and controls (P = 0.94).

Conclusions: Preterm children with history of hypoxia and MRI features of PVL show reduced number of CC and OR compared to preterm children without hypoxia. There was significant correlation between PVL severity and number of OR fibres which could be due to the preferential involvement of periventricular white matter, in which OR has a major contribution.

Keywords: Corpus callosum; diffusion tensor imaging; optic radiations; periventricular leukomalacia.

Figure 1(A and B)

(A) MRI template showing “sphere” ROI placement in lateral geniculate body (green ROI) and occipital cortex (yellow ROI); B and C shows optic radiations (yellow in C) from lateral geniculate body to occipital cortex (yellow arrows in B)

Figure 2(A-C)

(A and B) MRI template with “hand” ROI placement for drawing corpus callosum (red) and (C) showing normal corpus callosum tract

Figure 3

Bar chart shows reduced number of corpus callosum fibres (CC) and optic radiation fibres (OR) compared to controls-con CC (CC fibres in controls) and con OR (OR fibres in controls)

Figure 4(A and B)

Case 1 (A) MRI in a patient with PVL showing periventricular cysts and corpus callosal dysgenesis. (B) DFT of the same patient shows twisting and irregularity of corpus callosal fibers in a child with dysgenesis of corpus callosum

Figure 5(A and B)

Scatter plots showing (A) negative correlation between patients corpus callosal number (PT CCNO) and severity of PVL (Severity PVL) (P = 0.56) (B) significant correlation between patients optic radiation number (PT ORNO) and severity of PVL (Severity PVL) (P = 0.01)

Figure 6(A and B)

DFT showing reduced number of optic radiation fibres (OR) in (A) Mild variant of PVL and (B) Severe variant of PVL