Elsevier

Clinical Radiology

Volume 61, Issue 4, April 2006, Pages 358-364
Clinical Radiology

Potential of diffusion tensor MRI in the assessment of periventricular leukomalacia

https://doi.org/10.1016/j.crad.2006.01.001Get rights and content

AIM

To investigate magnetic resonance (MR) diffusion tensor imaging (DTI) and fibre tractography in the assessment of altered major white matter (WM) fibre tracts in periventricular leukomalacia (PVL).

MATERIALS AND METHODS

Twelve children (male:female=7:5, age range 3–10 years; mean age=6.5 years) who had suffered PVL were included in this study. Meanwhile, Twelve age-matched normal controls (male:female=6:6, age range 4–12 years; mean age=7.3 years) with normal MRI findings and no neurological abnormalities were recruited for comparison. DTI was performed with 15 different diffusion gradient directions and DTI colour maps were created from fractional anisotropy (FA) values and the three vector elements. To identify alteration of WM fibre tracts in patient of PVL quantitatively, FA values on diffusion tensor colour maps were compared between the patients and controls. Quantitative analysis was performed using the regions of interest (ROI) method settled on the central part of all identifiable WM fibres, including the corticospinal tract (CST) in the brainstem, middle cerebellar peduncle (MCP), medial lemniscus (ML), anterior/posterior limb of internal capsule (ICAL/ICPL), arcuate fasciculus (AF), posterior thalamic radiation (PTR), genu of corpus callosum (GCC), splenium of corpus callosum (SCC), corona radiata (CR), cingulum (CG), and superior longitudinal fasciculus (SLF). The averaged FA value of each WM fibre was measured and summarized as the mean±standard deviation (SD). All data were analysed by paired Student's t-test. A p-value of less than 0.05 was considered to indicate statistical significance.

RESULTS

Visual investigation of WM fibre tracts showed that the ICAL, brainstem CST, ML, MCP, and external capsule (EC) was similar in controls and subjects. However, the ICPL, AF, PTR, CR, CG, SLF and corpus callosum, were all attenuated in size. All 12 cases of PVL showed a significant mean FA reduction in the ICPL, AF, PTR, CR, CG, SLF, SCC, and GCC in comparison with the ipsilateral regions of healthy controls (p<0.05). However, there were no statistically significant differences of the ICAL, ML, MCP, and brainstem CST when analysed using a two-tailed Student's t-test for paired data (p>0.01).

CONCLUSION

DTI can provide more information for understanding the pathophysiology of motor disability and associated sensory handicap in PVL.

Introduction

Cerebral hypoxia–ischaemia during the perinatal period is the single most important cause of acute mortality and chronic disability in newborns. About 25% of infants suffering from a hypoxic–ischaemic insult will exhibit some sort of long-term consequence like encephalopathy, learning disabilities, epilepsy, and permanent motor deficits, such as cerebral palsy.1, 2 Periventricular leukomalacia (PVL), the leading cause of chronic motor disability in children after hypoxic insult, is due to the ischaemic infarction of the periventricular WM, the vascular watershed zone in the developing foetus.2 The primary long-term neurological finding of PVL is spastic diplegia or spastic quadriplegia, a form of cerebral palsy. Abnormalities in tone and movement associated with PVL, notably spasticity, have been attributed to loss of descending pyramidal corticospinal tracts.3 However, much less consideration has been given to damage of these pathways by conventional magnetic resonance imaging (MRI), due to its low resolution to white matter (WM) tracts, even though it is a major contributor to chronic neurological dysfunction in children.

MR diffusion tensor imaging (DTI), thought to be an indicator of the fibre tract integrity, reflecting coherence, organization, and density of the fibre bundles in WM regions of the brain, is one of the relatively newer, promising in vivo methods that have made it possible to investigate the neuroanatomical configuration of hemispheric WM fibre tracts in PVL.4 Although much of the work in this field remains experimental, DTI is currently making its way into the clinical realm. To our knowledge, DTI findings of PVL have not been fully reported, although visualization of altered sensory cortex WM pathways in PVL was proposed by Hoon et al.5 Our hypothesis was that DTI and fibre tractography could provide additional useful information in the assessment of major WM tracts after hypoxic insult.

Section snippets

Clinical data

In a prospective, hospital-based study, 12 children (male:female=7:5, age range 3–10 years; mean age=6.5 years) with cerebral palsy were examined neurologically and their perinatal history was reviewed. All patients had a history of hypoxic insult followed by coma or altered consciousness with or without convulsions in the neonatal period. Of the five preterm-born (gestational age: 30.5±2.1 weeks) and seven term-born children, eight had spastic diplegia; three had hemiplegia, and one had

Results

Characteristic imaging findings of PVL, including peritrigonal hyperintensities on T2-weighted image, focal reduced WM volume, irregular ventricle, and scalloped ventricular contours were present in all 12 patients on conventional MRI. Ten patients also showed the secondary atrophy of the posterior corpus callosum and six of them were present with thinning of the body of the corpus callosum. Meanwhile, porencephaly coexisted with PVL in one case.

Colour maps generated from axial DTI images

Discussion

PVL is a common finding after perinatal asphyxia, particularly in preterm infants. It is defined as focal necrosis in the periventricular WM of the cerebral hemispheres, associated with diffuse gliosis in adjacent WM.6 The ultimate consequences of PVL are injury and death of the developing oligodendrocytes, not only in the focally necrotic sites, but more importantly, in the surrounding gliotic WM.7 This widespread preferential WM injury leads to deficits in myelination, cerebral WM volume

Acknowledgements

The authors wish to thank Dr Bo Sun and Dr Hongzhan Sun for their expert neuroradiological opinion and assistance, and Prof. Liying Chen for helpful advice and discussion. The authors also thank Department of Paediatric Neurology of China Medical University for their fellowship.

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