Potential of diffusion tensor MRI in the assessment of periventricular leukomalacia
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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Diffusion tensor imaging of periventricular leukomalacia - Initial experience
2014, Egyptian Journal of Radiology and Nuclear MedicineCitation Excerpt :This is attributed to the fact that the microstructures of widespread WM tract fibers were significantly impaired in patients with PVL whose cause may be impairment of axonal development or in oligodendroglial ensheathment or both (15). The microstructure impairment of these projection, commissural and association tracts directly reduces the speed and capability of the information exchange among multiple cortical regions (16). Projection tracts, namely, corticospinal tract (CST), corona radiata (CR), posterior limb of the internal capsule (ICPL) and posterior thalamic radiation (PTR) encompass large areas of the brain and are responsible for the disturbance of motor and sensory functions.
Diffusion Imaging in the Developing Brain
2013, Diffusion MRI: From Quantitative Measurement to In vivo Neuroanatomy: Second EditionPotential of diffusion tensor MR imaging in the assessment of cognitive impairments in children with periventricular leukomalacia born preterm
2013, European Journal of RadiologyCitation Excerpt :Consequently, children with PVL showed various degree of cognitive and motor impairment in clinical findings. These findings are consistent with previous studies [14,15] and neuropathology [16]. Furthermore, the children with lower DQ scores showed more extensive and severe impairment of the WM microstructures based on reduced FA values.
Corpus callosum alterations in very preterm infants: Perinatal correlates and 2year neurodevelopmental outcomes
2012, NeuroImageCitation Excerpt :However, studies specifically examining PVL have found that the commissural fibers are frequently injured (Davatzikos et al., 2003; Nagae et al., 2007). Related studies have shown that PVL in children is associated with adverse CC tractography measures in the genu (Fan et al., 2006) and splenium (Davatzikos et al., 2003; Fan et al., 2006; Nagae et al., 2007). Furthermore, higher MD values are evident in the callosal tracts of children with mild ventriculomegaly (Gilmore et al., 2008).
Quantitative analysis of brain pathology based on MRI and brain atlases-Applications for cerebral palsy
2011, NeuroImageCitation Excerpt :With the detailed anatomy revealed by DTI, we now have access to a more complete picture of the patterns of white matter injury. Previously, DTI-based white matter analyses of CP patients have been reported, in which pre-defined and selected white matter structures were investigated using manually placed regions of interest or tractography (Fan et al., 2006; Hoon et al., 2009; Nagae et al., 2007; Panigrahy et al., 2005; Son et al., 2007, 2009; Thomas et al., 2005; Yoshida et al., 2010). In this study, we attempt to segment the brain into 110 sub-regions using an atlas-based 3D image transformation method (Oishi et al., 2008).
Neonatal neuroimaging: Going beyond the pictures
2009, Early Human Development