Potential of diffusion tensor MR imaging in the assessment of cognitive impairments in children with periventricular leukomalacia born preterm
Introduction
Cerebral palsy (CP) is defined as a group of non-progressive motor disorders of movement and posture due to a defect or lesion of the developing brain. The motor disorders of CP are often accompanied by disturbances in sensation, perception, cognition, communication, and behavior, and by epilepsy and secondary musculoskeletal problems [1]. Periventricular leukomalacia (PVL), which is the leading cause of CP, is a common finding after perinatal asphyxia, particularly in preterm infants. Cognitive deficits include mental retardation or subnormal intellectual function resulting in impaired language skills, learning, executive functions or social ability. A large proportion of CP has some kinds of cognitive impairment; the prevalence varies with the type of CP and especially increases when epilepsy is present. Increasing evidences suggest that children with moderate neonatal encephalopathy had cognitive deficits, such as memory impairments, visual-motor or visual-perceptive dysfunction, or increased hyperactivity, even in the absence of functional motor problems [2]. Children whose CP is due to PVL are more likely to have visual perceptual problems and up to 80% have some impairment of speech. Early accurate evaluation of individuals with CP is critical because certain developmental intervention programs can be initiated, and these offer the possibility of improving the neurological outcome.
Cognitive functions are supported by distributed networks of multiple interconnected cortical and subcortical regions. Efficient cognitive processing depends on fast communication between these regions. So the integrity of the connecting white matter (WM) fibers between them is of great importance [3]. Diffuse lesions in WM tracts are reported to be the cause of a general, lower efficiency of information processing with a potential impact on several cognitive functions.
MR diffusion tensor imaging (DTI) is a neuroimaging technique sensitive to degree and direction of water molecule permeability, which are related to WM microstructures. Fractional anisotropy (FA) is a frequently used intra-voxel metric characterizing degree of diffusion directionality sensitive to several neurobiological features, e.g. axon size, density, organization as well as degree of myelination [4]. Relations between DTI parameters and assessments of cognition have been investigated in samples with various neurological abnormalities, genetic disorders, developmental disorders, and healthy participants [5], [6]. Schmithorst et al. [7] have demonstrated positive correlations between IQ scores and FA values in WM association areas, including frontal and occipitoparietal areas in 47 normal children aged 5–18. In the very low birth weight (VLBW) group, low performers on the WISC-III test had low FA values in several white matter areas, all areas containing long association fibers [8]. Charlton et al. [9] reported that low FA values of damaged WM were correlated with cognitive decline of working memory function independently of age in 106 healthy middle-aged and elderly adults. Though the literature is limited, these studies suggest a relationship between WM microstructure as revealed by DTI and cognitive functions. However, to the best of our knowledge, no study has investigated in detail the relationships between maturation of the brain's WM fibers and development of cognitive functions in children with PVL.
Therefore, the purpose of our study is to evaluate the diffusion tensor characteristics of various WM fibers in children with PVL using DTI method and to investigate their relationship to the results of cognitive assessment.
Section snippets
Patients and controls
46 children (30 males and 16 females; age range 3–36 months; mean age 16 ± 4.7 months) with clinically definitive cerebral palsy were included in this study and their perinatal history was reviewed. All patients were preterm-born (gestational age: 32.5 ± 2.2 weeks) and had PVL, diagnosed by neuroradiological evaluation of conventional magnetic resonance imaging (MRI). Of all the patients, 23 children had spastic diplegia, 10 had hemiplegia, 6 had spastic tetraplegia and 7 had dyskinetic cerebral
Result
On conventional MRI, all participants had evidence of PVL, including peritrigonal hyperintensities on T2-weighted image, focal reduced WM volume, irregular ventricle, and scalloped ventricular contours. 21 patients also showed the secondary atrophy of the posterior corpus callosum and 12 of them were present with thinning of the body of the corpus callosum. Meanwhile, porencephaly coexisted with PVL in 9 cases, and microcephaly in one case.
Color maps generated from axial DTI images showed major
Discussion
PVL is defined as focal necrosis in the periventricular WM of the cerebral hemispheres, associated with diffuse gliosis in adjacent WM, a common finding after perinatal asphyxia, particularly in preterm infants. Dammann et al. [13] suggest that WM damage due to PVL involves both deficits of oligodendroglia, loss of axonal fibers, microgliosis and astrogliosis. Diffusion tensor MRI is a noninvasive in vivo method for mapping WM fiber tract trajectories in human brain. It measures FA values, an
Conclusion
Quantitative evaluation of DTI was able to detect differences in fractional anisotropy in specific white matters and provides more information for understanding the pathophysiology of cognitive impairments in children with PVL. The present study demonstrated that the disturbance of the cognitive ability including the language and visual abilities in preterm children with PVL was significantly correlated with WM microstructures in widespread areas of the brain. This may indicate the
Conflict of interest
All authors have no conflicts of interest.
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2014, Clinical RadiologyCitation Excerpt :Diffusion tensor imaging (DTI) is a relatively new technique useful for assessing changes in diffusion. Analysis of additional DTI metrics, such as fractional anisotropy (FA) and eigenvalues, may be useful for identifying microstructural abnormalities.7–10 It is unclear at present whether DTI can provide information regarding thalamus damage in patients with WD before abnormal signal is detected at conventional MRI.
Brain Development in Preterm Infants Assessed Using Advanced MRI Techniques
2014, Clinics in PerinatologyCitation Excerpt :Diffusion characteristics of WM in the developing preterm brain have been well described.24,42–47 FA values in the WM of preterm infants at term-equivalent age are significantly lower in comparison to term-born controls in several regions, suggesting widespread microstructural abnormalities, even in absence of major focal lesions.46,48,49 This decreased FA may reflect underlying reductions in myelination or decreased fiber coherence.
Diffusion tensor imaging of periventricular leukomalacia - Initial experience
2014, Egyptian Journal of Radiology and Nuclear MedicineCitation Excerpt :Moreover, long-term follow-up studies are recommended by us and Wang et al. (26) who proposed the fact that children’s development of cognitive functions is a dynamic process. It is not merely a consequence of an early brain lesion but also the result of the ongoing interaction between the child and his or her environment (26). Therefore, long-term follow-up studies will be necessary to clarify the relationship between altered WM anatomy and clinical outcome of cognitive function in children with PVL.