Thalamic atrophy in infants with PVL and cerebral visual impairment

Thalamic Volume Reduction in Cerebral Visual Impairment: Relationship to Visual Dysfunction

The thalamus is critical for the relay and modulation of visual information. As such, injury to the developing thalamus may result in cerebral visual impairment (CVI). This study investigated quantitative volume reductions of the thalamus in cerebral visual impairment compared to controls and probed the association between thalamic volume and the severity of cerebral visual impairment-related visual dysfunctions. Thalamic volumes were quantified using T1-weighted magnetic resonance imaging (MRI) data from 23 participants with cerebral visual impairment and 42 controls. Nineteen participants with cerebral visual impairment also completed the CVI Questionnaire. Cerebral visual impairment was associated with significant volume reductions of the global thalami, anterior, lateral, and ventral thalamic regions, as well as several nuclei, particularly in those with cerebral visual impairment due to periventricular leukomalacia. Within the cerebral visual impairment group, smaller volumes of the right thalamus and lateral pulvinar were significantly associated with more reported difficulties moving through space. Together, these results provide empirical evidence supporting aberrant thalamic development as a potential mechanism underlying cerebral visual impairment.

Automatic brain quantification in children with unilateral cerebral palsy

Assessing brain damage in children with spastic unilateral cerebral palsy (uCP) is challenging, particularly in clinical settings. In this study, we developed and validated a deep learning-based pipeline to automatically quantify lesion-free brain volumes. Using T1-weighted and FLAIR MRI data from 35 patients (aged 5-15 years), we trained models to segment brain structures and lesions, utilizing an automatic label generation workflow. Validation was performed on 54 children with CP (aged 7-16 years) using quantitative and qualitative metrics, as well as an independent dataset of 36 children with congenital or acquired brain anatomy distortions (aged 1-17 years). Clinical evaluation examined the correlation of lesion-free volumes with visual-based assessments of lesion extent and motor and visual outcomes. The models achieved robust segmentation performance in brains with severe anatomical alterations and heterogeneous lesion appearances, identifying reduced volumes in the affected hemisphere, which correlated with lesion extent (p < 0.05). Further, regional lesion-free volumes, especially in subcortical structures such as the thalamus, were linked to motor and visual outcomes (p < 0.05). These results support the utility of automated lesion-free volume quantification for exploring brain structure-function relationships in uCP.

The Impact of Cerebral Visual Impairment on Social Skills and Sensory Processing

Limited evidence exists on the impact of cerebral visual impairment (CVI) on developmental domains in toddlers. This study investigated whether CVI influences social skills and sensory processing in toddlers with cerebral palsy (CP). The study included toddlers with CP, with or without CVI, and typically developing (TD) toddlers. All parents completed the demographic information form. Social skills were assessed by the Brief Infant-Toddler Social and Emotional Assessment (BITSEA). Sensory processing was evaluated by the Infant/Toddler Sensory Profile (ITSP). Analysis of covariance was employed to assess the disparity in BITSEA and ITSP scores. Toddlers with CP and CVI group demonstrated lower social competence than the other groups (p < .05). Having CVI did not cause a statistically significant difference in sensory processing among toddlers with CP (p > .05). CVI significantly affects social competence in toddlers with CP but does not affect sensory processing.

The relation between neuroimaging and visual impairment in children and adolescents with cerebral palsy: A systematic review

OBJECTIVE

The structure-function relation between magnetic resonance imaging (MRI) and visual impairment (VI) in children with cerebral palsy (CP) has not been fully unravelled. The present systematic review aims to summarize the relation between brain lesions on MRI and VI in children and adolescents with CP.

METHODS

PubMed, Embase, Web of Science Core Collection, and Cochrane Database were systematically searched according to the PRISMA checklist. A total of 45 articles met the inclusion criteria.

RESULTS

White matter lesions were most frequently associated with VI. Only 25 studies described lesions within specific structures, mainly in the optic radiations. Only four studies reported on the thalamus. 8.4% of children with CP showed no brain abnormalities on MRI. Diffusion-weighted MRI studies showed that decreased structural connectivity in the optic radiations, superior longitudinal fasciculus, posterior limb of the internal capsule, and occipital lobe is associated with more severe VI.

CONCLUSIONS

All types of brain lesions lead to visual dysfunctions, arguing for a comprehensive visual assessment in all children with CP. Whereas white matter damage is a well-known contributor, the exact contribution of specific visual structures requires further investigation, to enable early prediction, detection, and intervention.

Visual impairment and periventricular leukomalacia in children: A systematic review

BACKGROUND

Thanks to Magnetic Resonance Imaging (MRI) it is now possible to diagnose lesions of the central nervous system (CNS) such as periventricular leukomalacia (PVL) from the first days of life. However, there are still few studies aimed at describing the relationship between MRI and the outcome of visual function in patients with PVL.

AIM

To systematically review and investigate the relationship between MRI neuroimaging and visual impairment arising from PVL.

METHODS AND PROCEDURES

Three electronic databases (PubMed, SCOPUS, Web of Science) were consulted from 15 June 2021-30 September 2021. Of the 81 records identified, 10 were selected for the systematic review. The STROBE Checklist was used to assess the quality of the observational studies.

OUTCOME AND RESULTS

PVL on MRI was found to have a strong association with visual impairment in the various aspects of visual function (visual acuity, ocular motility, visual field); in 60% of these articles, the selected subjects also reported damage to optical radiations.

CONCLUSION AND IMPLICATIONS

there is a clear need for more extensive and detailed studies on the correlation between PVL and visual impairment, in order to set up a personalized early therapeutic-rehabilitation plan. WHAT THIS PAPER ADDS?: Over the past decades numerous studies have reported increasing evidence that one of the most frequent sequelae in subjects with PVL, in addition to motor impairment, is the impairment of visual function even if it is still not clear what different authors mean with the term visual impairment. This systematic review presents an overview of the relationship between structural correlates of MRI and visual impairment in children with periventricular leukomalacia. Interesting correlations emerge between MRI radiological finding and consequences on visual function especially between damage to the periventricular white matter and the impairment of various aspects of visual function and also between the impairment of optical radiation and visual acuity. Thanks to this literature revision, it is now clear that MRI plays an important role in the screening and diagnosis of significant intracranial brain changes in very young children in particular about the outcome of visual function. This is of great relevance since that visual function represents one of the main adaptive functions in the development of the child.

The influence of visual deprivation on the development of the thalamocortical network: Evidence from congenitally blind children and adults

The thalamus is heavily involved in relaying sensory signals to the cerebral cortex. A relevant issue is how the deprivation of congenital visual sensory information modulates the development of the thalamocortical network. The answer is unclear because previous studies on this topic did not investigate network development, structure-function combinations, and cognition-related behaviors in the same study. To overcome these limitations, we recruited 30 congenitally blind subjects (8 children, 22 adults) and 31 sighted subjects (10 children, 21 adults), and conducted multiple analyses [i.e., gray matter volume (GMV) analysis using the voxel-based morphometry (VBM) method, resting-state functional connectivity (FC), and brain-behavior correlation]. We found that congenital blindness elicited significant changes in the development of GMV in visual and somatosensory thalamic regions. Blindness also resulted in significant changes in the development of FC between somatosensory thalamic regions and visual cortical regions as well as advanced information processing regions. Moreover, the somatosensory thalamic regions and their FCs with visual cortical regions were reorganized to process high-level tactile language information in blind individuals. These findings provide a refined understanding of the neuroanatomical and functional plasticity of the thalamocortical network.

Brain microstructural antecedents of visual difficulties in infants born very preterm

Infants born very preterm (VPT) are at risk of later visual problems. Although neonatal screening can identify ophthalmologic abnormalities, subtle perinatal brain injury and/or delayed brain maturation may be significant contributors to complex visual-behavioral problems. Our aim was to assess the micro and macrostructural antecedents of early visual-behavioral difficulties in VPT infants by using diffusion MRI (dMRI) at term-equivalent age. We prospectively recruited a cohort of 262 VPT infants (≤32 weeks gestational age [GA]) from five neonatal intensive care units. We obtained structural and diffusion MRI at term-equivalent age and administered the Preverbal Visual Assessment (PreViAs) questionnaire to parents at 3-4 months corrected age. We used constrained spherical deconvolution to reconstruct nine white matter tracts of the visual pathways with high reliability and performed fixel-based analysis to derive fiber density (FD), fiber-bundle cross-section (FC), and combined fiber density and cross-section (FDC). In multiple logistic regression analyses, we related these tract metrics to visual-behavioral function. Of 262 infants, 191 had both high-quality dMRI and completed PreViAs, constituting the final cohort: mean (SD) GA was 29.3 (2.4) weeks, 90 (47.1%) were males, and postmenstrual age (PMA) at MRI was 42.8 (1.3) weeks. FD and FC of several tracts were altered in infants with (N = 59) versus those without retinopathy of prematurity (N = 132). FDC of the left posterior thalamic radiations (PTR), left inferior longitudinal fasciculus (ILF), right superior longitudinal fasciculus (SLF), and left inferior fronto-occipital fasciculus (IFOF) were significantly associated with visual attention scores, prior to adjusting for confounders. After adjustment for PMA at MRI, GA, severe retinopathy of prematurity, and total brain volume, FDC of the left PTR, left ILF, and left IFOF remained significantly associated with visual attention. Early visual-behavioral difficulties in VPT infants are preceded by micro and macrostructural abnormalities in several major visual pathways at term-equivalent age.

Exploratory Investigation of Brain MRI Lesions According to Whole Sample and Visual Function Subtyping in Children With Cerebral Visual Impairment

Background: There is limited research on brain lesions in children with cerebral visual impairment (CVI) of heterogeneous etiologies and according to associated subtyping and vision dysfunctions. This study was part of a larger project establishing data-driven subtypes of childhood CVI according to visual dysfunctions. Currently there is no consensus in relation to assessment, diagnosis and classification of CVI and more information about brain lesions may be of potential diagnostic value.

Aim: This study aimed to investigate overall patterns of brain lesions and associations with level of visual dysfunction and to compare the patterns between the classification subgroups in children with CVI.

Methods: School-aged children with CVI received ophthalmological and neuro-psychological/developmental assessments to establish CVI-related subtyping. Other pediatric information was collected from medical records. MRI scans were coded according to a semi-quantitative template including brain regions (right hemisphere, left hemisphere, visual pathways) and summed for total scores. Non-parametric analyses were conducted.

Results: 28 children had clinical brain MRI scans available [44% of total sample, Group A (lower severity of visual dysfunctions) n = 16, Group B (higher severity) n = 12]. Total brain scores ranged between 0 and 18 (Group A mdn = 7, IQR = 0.8–10.0, Group B mdn = 10, IQR = 6.5–11.8) and were widespread across regions. 71 per cent had post-geniculate visual pathway damage. The median total brain and hemisphere scores of Group B were higher than subgroup A but differences did not reach statistical significance. No statistically significant associations were found between brain scores and vision variables (acuity, contrast sensitivity).

Conclusion: This study found a spread of lesions across all regions on the brain scans in children with congenital CVI. The majority had damage in the postgeniculate visual pathways and visual cortex region suggesting this is an area of interest and potentially informative for diagnosis. However the subtyping classification did not show differences in number or region of lesions though the trend was higher toward Group B. This study confirms the complex diffuse and variable nature of brain lesions in children with congenital CVI, many of whom have other neurological impairments.

Interaction between Preterm White Matter Injury and Childhood Thalamic Growth

OBJECTIVE

The purpose of this study was to determine how preterm white matter injury (WMI) and long-term thalamic growth interact to predict 8-year neurodevelopmental outcomes.

METHODS

A prospective cohort of 114 children born at 24 to 32 weeks' gestational age (GA) underwent structural and diffusion tensor magnetic resonance imaging early in life (median 32 weeks), at term-equivalent age and at 8 years. Manual segmentation of neonatal WMI was performed on T1-weighted images and thalamic volumes were obtained using the MAGeT brain segmentation pipeline. Cognitive, motor, and visual-motor outcomes were evaluated at 8 years of age. Multivariable regression was used to examine the relationship among neonatal WMI volume, school-age thalamic volume, and neurodevelopmental outcomes.

RESULTS

School-age thalamic volumes were predicted by neonatal thalamic growth rate, GA, sex, and neonatal WMI volume (p < 0.0001). After accounting for total cerebral volume, WMI volume remained associated with school-age thalamic volume (β = -0.31, p = 0.005). In thalamocortical tracts, fractional anisotropy (FA) at term-equivalent age interacted with early WMI volume to predict school-age thalamic volumes (all p < 0.02). School-age thalamic volumes and neonatal WMI interacted to predict full-scale IQ (p = 0.002) and adverse motor scores among those with significant WMI (p = 0.01). Visual-motor scores were predicted by thalamic volumes (p = 0.04).

INTERPRETATION

In very preterm-born children, neonatal thalamic growth and WMI volume predict school-age thalamic volumes. The emergence at term of an interaction between FA and WMI to impact school-age thalamic volume indicates dysmaturation as a mechanism of thalamic growth failure. Cognition is predicted by the interaction of WMI and thalamic growth, highlighting the need to consider multiple dimensions of brain injury in these children. ANN NEUROL 2021;90:584-594.

Structural brain damage and visual disorders in children with cerebral palsy due to periventricular leukomalacia

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There is a strong correlation between brain lesion severity and visual function, evident also with a Structural MRI.

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It is confirmed the validity of MRI semi-quantitative scale published by Fiori et al. (2014).

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There is a frequent association of PVL with thalamic lesions with important repercussion on visual function.

Aim

To systematically explore the relationship between type and severity of brain lesion on Magnetic Resonance Imaging (MRI) and visual function in a large cohort of children with periventricular leukomalacia (PVL).

Methods

94 children with bilateral cerebral palsy (CP) and history of PVL were recruited at Stella Maris Scientific Institute in Pisa (Italy). We included data of participants (72) with at least one MRI after the age of three years and an evaluation of visual function including fixation, following, saccades, nystagmus, acuity, visual field, stereopsis and color perception.

Brain lesions location and extent were assessed by a semi-quantitative MRI-scale for children with CP.

Results

Brain lesion severity strongly correlated with visual function total score (global MRI score p = .000; hemispheric score p = .001 and subcortical score p = .000). Moreover, visual acuity, visual field, stereopsis and colour were compromised when a cortical damage was present, while ocular motricity (and in particular fixation and saccades) were compromised in presence of subcortical brain damage.

Interpretation

Structural MRI is valuable for understanding the relationship between brain lesion severity and visual function in children with CP.

Correlation of lateral ventricular size and deep gray matter volume in MRI at term equivalent age with neurodevelopmental outcome at a corrected age of 24 months and with handedness in preterm infants

The aim of this study was to correlate ventricular size and volumes of deep gray matter (DGM) in MRI at term equivalent age (TEA) with outcome at a corrected age of 24 months in preterm infants and with handedness. Seventy-three infants born before 32 weeks of gestation or with birth weight < 1500 g  were included in this retrospective analysis and measurement of lateral ventricles, and DGM was performed on MRI scans. The left lateral ventricle was significantly larger than the right lateral ventricle (p = 0.001). There was no correlation between volumes of the right and left ventricles and the DGM volume (p = 0.207 and p = 0.597, respectively), nor with the head circumference at TEA (p = 0.177 and p = 0.976, respectively). The total volume of both lateral ventricles did not correlate with Mental Develomental Index (MDI, p = 0.336) or Psychomotor Developmental Index (PDI, p = 0.650) score (Bayley Scales of Infant Development, BSID II). However, a correlation of total DGM volume with birth weight (p = 0.0001; r = 0.437), head circumference at TEA (p < 0.0001; r = 0.640), MDI (p = 0.029; r = 0.310), and PDI (p = 0.002; r = 0.456) was observed. No significant difference between right- and left-handed infants was seen in relation to volumes of both lateral ventricles and of DGM.Conclusion: DGM volume at TEA was significantly associated with the outcome at a corrected age of 24 months. Handedness did not correlate with DGM or lateral ventricle size.What is Known:• White matter injury as well as altered development of deep gray matter is associated with neurodevelopmental disability in preterm infants.• No study analyzed the association between deep gray matter volume or volumes of lateral ventricle and handedness in former preterm infants so far.What is New:• Volume of deep gray matter, but not lateral ventricular size was significantly associated with outcome at a corrected age of 24 months in preterm infants.• There was no correlation of handedness with volumes of lateral ventricular size or with deep gray matter volumes.

Preterm brain Injury: White matter injury

Despite the advances in neonatal intensive care, the preterm brain remains vulnerable to white matter injury (WMI) and disruption of normal brain development (i.e., dysmaturation). Compared to severe cystic WMI encountered in the past decades, contemporary cohorts of preterm neonates experience milder WMIs. More than destructive lesions, disruption of the normal developmental trajectory of cellular elements of the white and the gray matter occurs. In the acute phase, in response to hypoxia-ischemia and/or infection and inflammation, multifocal areas of necrosis within the periventricular white matter involve all cellular elements. Later, chronic WMI is characterized by diffuse WMI with aberrant regeneration of oligodendrocytes, which fail to mature to myelinating oligodendrocytes, leading to myelination disturbances. Complete neuronal degeneration classically accompanies necrotic white matter lesions, while altered neurogenesis, represented by a reduction of the dendritic arbor and synapse formation, is observed in response to diffuse WMI. Neuroimaging studies now provide more insight in assessing both injury and dysmaturation of both gray and white matter. Preterm brain injury remains an important cause of neurodevelopmental disabilities, which are still observed in up to 50% of the preterm survivors and take the form of a complex combination of motor, cognitive, and behavioral concerns.

Correlation of morphological parameters and visual acuity with neurological development in former preterm children aged 4-10 years

PURPOSE

The objective of this study was to investigate the relationship between visual acuity, peripapillary retinal nerve fibre layer (pRNFL), retinal thickness at the fovea and other factors with the neurologic status of former preterm children.

METHODS

In this cross-sectional hospital based study in a maximum care tertiary centre, detailed anthropometric and ophthalmological data of former preterm children ranging from 4 to 10 years of age with a gestational age (GA) ≤32 weeks were assessed. Analyses of the correlation between pRNFL and foveal thickness, as well as visual acuity (VA) parameters at 4-10 years of age, with neurological development were evaluated at 2 years of age by Bayley Scales II of Infant Development, including Psychomotor Developmental Index (PDI) and Mental Developmental Index (MDI).

RESULTS

Data were available for 106 former preterm children. Univariate analysis revealed a correlation between PDI with pRNFL thickness (B = 0.43; p = 0.013), VA (B = -29.2; p < 0.001), GA (B = 2.7; p = 0.002), retinopathy of prematurity (ROP; B = -16.3; p < 0.001) and intraventricular haemorrhages (IVH; B = -22.9; p < 0.001) but not with strabismus or foveal thickness. In the multivariable analysis, the association remained for visual acuity and IVH, but not for pRNFL thickness or ROP. Mental Developmental Index (MDI) was associated with visual acuity (B = -34.3; p = 0.001), GA (B = 2.53; p = 0.02) and IVH (B = -15.4; p = 0.02), the latter also in the multivariable analysis.

CONCLUSION

This study revealed an association between PDI at 2 years of age and lower visual acuity later in childhood. However, there was no correlation between retinal morphology and neurologic outcome in former preterm children after adjusting for several potential confounders.

Neurological consequences of systemic inflammation in the premature neonate

Despite substantial progress in neonatal care over the past two decades leading to improved survival of extremely premature infants, extreme prematurity continues to be associated with long term neurodevelopmental impairments. Cerebral white matter injury is the predominant form of insult in preterm brain leading to adverse neurological consequences. Such brain injury pattern and unfavorable neurologic sequelae is commonly encountered in premature infants exposed to systemic inflammatory states such as clinical or culture proven sepsis with or without evidence of meningitis, prolonged mechanical ventilation, bronchopulmonary dysplasia, necrotizing enterocolitis and chorioamnionitis. Underlying mechanisms may include cytokine mediated processes without direct entry of pathogens into the brain, developmental differences in immune response and complex neurovascular barrier system that play a critical role in regulating the cerebral response to various systemic inflammatory insults in premature infants. Understanding of these pathologic mechanisms and clinical correlates of such injury based on serum biomarkers or brain imaging findings on magnetic resonance imaging will pave way for future research and translational therapeutic opportunities for the developing brain.

Early identification of cerebral visual impairments in infants born extremely preterm

AIM

Children born extremely preterm are at risk of visual processing problems related to brain damage. Damage in visual pathways can remain undetected by conventional magnetic resonance imaging (MRI) and functional consequences cannot always be predicted. The aim of this study was to assess the efficacy of processing visual information in infants born extremely preterm at a corrected age of 1 year using a communication-free visual function test based on eye tracking.

METHOD

Infants born extremely preterm (<29wks' gestation) without apparent white and grey matter damage on conventional MRI at 30 weeks' postmenstrual age were included (19 males, 1.01y [0.96-1.24] (median [25th-75th centiles]); 11 females, 0.99y [0.98-1.01]). At the corrected age of 1 year, reaction times to fixation (RTF) of specific visual properties displayed on an eye-tracker monitor were quantified and compared with results from a comparison group (eight males, 1.28y [1.01-1.33]; nine females, 1.10y [0.90-1.20]).

RESULTS

The infants in the preterm group had longer response times in detecting colour patterns (red-green) and motion compared with infants in the comparison group. No impairments were detected in oculomotor functions (saccades, pursuit, and fixations).

INTERPRETATION

The data suggest that delays in processing visual information can be identified in children born extremely preterm. The delays might be ascribed to deficits in neuronal connectivity in visual pathways at a microstructural level.

The Effects of the Severity of Periventricular Leukomalacia on the Neuropsychological Outcomes of Preterm Children

This study investigates the developmental outcomes of preterm children according to severity of periventricular leukomalacia. One hundred preterm children with periventricular leukomalacia evident on brain magnetic resonance imaging and who had undergone neuropsychologic evaluation were selected. Intellectual disability was noted in 27.8% of the children with mild periventricular leukomalacia, 53.2% with moderate periventricular leukomalacia, and 77.1% with severe periventricular leukomalacia. The rates of major neurodevelopmental impairments such as cerebral palsy or intellectual disability were related to the severity of periventricular leukomalacia but not to gestational age or epilepsy. There were significant differences in the intelligence quotient (IQ) and social maturity quotient between 3 groups of periventricular leukomalacia. The performance IQ was significantly lower than the verbal IQ. Behavioral problems were noted in about one-third of the children but the rate was not related with the severity of periventricular leukomalacia. Our study revealed the significant associations between severity of periventricular leukomalacia and cognitive and social adaptive functions in the preterm children.

Regional vulnerability of longitudinal cortical association connectivity: Associated with structural network topology alterations in preterm children with cerebral palsy

Preterm born children with spastic diplegia type of cerebral palsy and white matter injury or periventricular leukomalacia (PVL), are known to have motor, visual and cognitive impairments. Most diffusion tensor imaging (DTI) studies performed in this group have demonstrated widespread abnormalities using averaged deterministic tractography and voxel-based DTI measurements. Little is known about structural network correlates of white matter topography and reorganization in preterm cerebral palsy, despite the availability of new therapies and the need for brain imaging biomarkers. Here, we combined novel post-processing methodology of probabilistic tractography data in this preterm cohort to improve spatial and regional delineation of longitudinal cortical association tract abnormalities using an along-tract approach, and compared these data to structural DTI cortical network topology analysis. DTI images were acquired on 16 preterm children with cerebral palsy (mean age 5.6 ± 4) and 75 healthy controls (mean age 5.7 ± 3.4). Despite mean tract analysis, Tract-Based Spatial Statistics (TBSS) and voxel-based morphometry (VBM) demonstrating diffusely reduced fractional anisotropy (FA) reduction in all white matter tracts, the along-tract analysis improved the detection of regional tract vulnerability. The along-tract map-structural network topology correlates revealed two associations: (1) reduced regional posterior-anterior gradient in FA of the longitudinal visual cortical association tracts (inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, optic radiation, posterior thalamic radiation) correlated with reduced posterior-anterior gradient of intra-regional (nodal efficiency) metrics with relative sparing of frontal and temporal regions; and (2) reduced regional FA within frontal-thalamic-striatal white matter pathways (anterior limb/anterior thalamic radiation, superior longitudinal fasciculus and cortical spinal tract) correlated with alteration in eigenvector centrality, clustering coefficient (inter-regional) and participation co-efficient (inter-modular) alterations of frontal-striatal and fronto-limbic nodes suggesting re-organization of these pathways. Both along tract and structural topology network measurements correlated strongly with motor and visual clinical outcome scores. This study shows the value of combining along-tract analysis and structural network topology in depicting not only selective parietal occipital regional vulnerability but also reorganization of frontal-striatal and frontal-limbic pathways in preterm children with cerebral palsy. These finding also support the concept that widespread, but selective posterior-anterior neural network connectivity alterations in preterm children with cerebral palsy likely contribute to the pathogenesis of neurosensory and cognitive impairment in this group.

Developmental synergy between thalamic structure and interhemispheric connectivity in the visual system of preterm infants

Thalamic structural co-variation with cortical regions has been demonstrated in preterm infants, but its relationship to cortical function and severity of non-cystic white matter injury (non-cystic WMI) is unclear. The relationship between thalamic morphology and both cortical network synchronization and cortical structural connectivity has not been established. We tested the hypothesis that in preterm neonates, thalamic volume would correlate with primary cortical visual function and microstructural integrity of cortico-cortical visual association pathways. A total of 80 term-equivalent preterm and 44 term-born infants underwent high-resolution structural imaging coupled with visual functional magnetic resonance imaging or diffusion tensor imaging. There was a strong correlation between thalamic volume and primary visual cortical activation in preterms with non-cystic WMI (r = 0.81, p-value = 0.001). Thalamic volume also correlated strongly with interhemispheric cortico-cortical connectivity (splenium) in preterm neonates with a relatively higher severity of non-cystic WMI (p-value < 0.001). In contrast, there was lower correlation between thalamic volume and intrahemispheric cortico-cortical connectivity, including the inferior longitudinal fasciculus and inferior frontal orbital fasciculus. This study shows distinct temporal overlap in the disruption of thalamo-cortical and interhemispheric cortico-cortical connectivity in preterm infants suggesting developmental synergy between thalamic morphology and the emergence of cortical networks in the last trimester.

Microglia toxicity in preterm brain injury

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Microglia responses in the preterm human brain in association with injury.

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Microglia responses in animal models of preterm brain injury.

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Mechanisms of microglia toxicity from in vitro primary microglia cell culture experiments.

Microglia are the resident phagocytic cells of the central nervous system. During brain development they are also imperative for apoptosis of excessive neurons, synaptic pruning, phagocytosis of debris and maintaining brain homeostasis. Brain damage results in a fast and dynamic microglia reaction, which can influence the extent and distribution of subsequent neuronal dysfunction. As a consequence, microglia responses can promote tissue protection and repair following brain injury, or become detrimental for the tissue integrity and functionality. In this review, we will describe microglia responses in the human developing brain in association with injury, with particular focus on the preterm infant. We also explore microglia responses and mechanisms of microglia toxicity in animal models of preterm white matter injury and in vitro primary microglia cell culture experiments.

Neuropathologic studies of the encephalopathy of prematurity in the late preterm infant

It has been widely suggested that brain damage in survivors of late preterm deliveries is similar to that in early preterm infants, only less severe. This report addresses this concept through reanalysis of published neuropathologic data obtained according to late preterm in comparison with early preterm ages. Findings suggest that the spectrum of brain injury in the late preterm infant, as determined in an autopsy population, is similar to that found in early preterm infants, with potential differential susceptibility for different neuronal, glial, and vascular indices. Further research is needed to more clearly define developmental cellular susceptibilities in preterm populations.

Alterations in the optic radiations of very preterm children-Perinatal predictors and relationships with visual outcomes

Children born very preterm (VPT) are at risk for visual impairments, the main risk factors being retinopathy of prematurity and cerebral white matter injury, however these only partially account for visual impairments in VPT children. This study aimed to compare optic radiation microstructure and volume between VPT and term-born children, and to investigate associations between 1) perinatal variables and optic radiations; 2) optic radiations and visual function in VPT children. We hypothesized that optic radiation microstructure would be altered in VPT children, predicted by neonatal cerebral white matter abnormality and retinopathy of prematurity, and associated with visual impairments.

142 VPT children and 32 controls underwent diffusion-weighted magnetic resonance imaging at 7 years of age. Optic radiations were delineated using constrained spherical deconvolution tractography. Tract volume and average diffusion tensor values for the whole optic radiations and three sub-regions were compared between the VPT and control groups, and correlated with perinatal variables and 7-year visual outcome data.

Total tract volumes and average diffusion values were similar between VPT and control groups. On regional analysis of the optic radiation, mean and radial diffusivity were higher within the middle sub-regions in VPT compared with control children. Neonatal white matter abnormalities and retinopathy of prematurity were associated with optic radiation diffusion values. Lower fractional anisotropy in the anterior sub-regions was associated with poor visual acuity and increased likelihood of other visual defects.

This study presents evidence for microstructural alterations in the optic radiations of VPT children, which are largely predicted by white matter abnormality or severe retinopathy of prematurity, and may partially explain the higher rate of visual impairments in VPT children.

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This study compares optic radiations between very preterm and control 7-year-olds.

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There are microstructural alterations in the optic radiations of VPT children.

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The main risk factors are retinopathy of prematurity and white matter injury.

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Microstructural alterations associate with poor visual acuity and visual defects.

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This study elucidates neuroanatomical correlates of visual impairment in prematurity.

Reorganization of visual fields after periventricular haemorrhagic infarction: potentials and limitations

Visual functions are often impaired in preterm infants with periventricular haemorrhagic infarction, because of the involvement of the region where the optic radiations are located. In some cases an unexpected sparing of the visual fields has been described, and related to the plasticity of thalamo-cortical afferents that are supposedly able to bypass the lesion when it occurs in the early third trimester of gestation. We systematically reviewed the literature in the field to determine the limits and potentials of this type of reorganization. We found four studies meeting our criteria, from which we extracted case reports on 19 individuals with intraventricular haemorrhagic infarction. Eleven of the 19 did not have visual field defects, five had a bilateral visual field defect, and the remaining three had a unilateral visual field defect. The involvement of the optic radiations was often associated with normal visual fields as only one of the four individuals with damaged optic radiations showed visual field defects. Conversely, the presence of basal ganglia/thalamus involvement apparently prevented such reorganization, as the only two individuals with unilateral field restriction and available magnetic resonance imaging data both showed abnormalities in those structures. Consistent with this, we report on a further individual in which visual field restriction was associated with abnormal tractography on brain magnetic resonance imaging. Overall, this review supports the existence of effective mechanisms of plastic reorganization that allow a rewiring of geniculo-calcarine connections with restoration of full field vision but which are hindered by the involvement of the basal ganglia and thalamus.

Maternal endotoxin exposure results in abnormal neuronal architecture in the newborn rabbit

Maternal intrauterine inflammation/infection is a potential risk factor for the development of neurologic disorders such as cerebral palsy (CP) in preterm and term infants. CP is associated with white matter and grey matter injury. In the current study, we used a rabbit model of CP in which pregnant rabbits are administered intrauterine injections of the endotoxin lipopolysaccharide. We then investigated the extent of neuronal damage in the newborn kit brain. We observed an overall decrease in the number of MAP2-stained neurons and an increase in Fluoro-Jade C-stained cells in the anterior thalamus of 1-day-old rabbit brain. We also observed an overall decrease in the number of branching points and spine density in the retrosplenial cortex, a major output region of the anterior thalamus that is involved in cognition and memory. The loss of spines and dendritic atrophy in the retrosplenial cortex may be caused by loss of presynaptic input from the thalamus. Our study indicates that the cognitive impairments seen in patients with CP may be related to the degeneration of neurons and abnormal arborization of the thalamic and cortical neurons.

Visuospatial working memory in toddlers with a history of periventricular Leukomalacia: an EEG narrow-band power analysis

BACKGROUND

Periventricular Leukomalacia (PVL) affects white matter, but grey matter injuries have also been reported, particularly in the dorsomedial nucleus and the cortex. Both structures have been related to working memory (WM) processes. The aim of this study was to compare behavioral performances and EEG power spectra during a visuospatial working memory task (VSWMT) of toddlers with a history of PVL and healthy toddlers.

METHODOLOGY/PRINCIPAL FINDINGS

A prospective, comparative study of WM was conducted in toddlers with a history of PVL and healthy toddlers. The task responses and the EEG narrow-band power spectra during a VSWMT were compared in both groups. The EEG absolute power was analyzed during the following three conditions: baseline, attention and WM retention. The number of correct responses was higher in the healthy group (20.5 ± 5.0) compared to the PVL group (16.1 ± 3.9) (p = 0.04). The healthy group had absolute power EEG increases (p ≤ 0.05) during WM compared to the attention condition in the bilateral frontal and right temporal, parietal and occipital regions in frequencies ranging from 1.17 to 2.34 Hz and in the right temporal, parietal and occipital regions in frequencies ranging from 14.06 to 15.23 Hz. In contrast, the PVL group had absolute power increases (p ≤ 0.05) in the bilateral fronto-parietal, left central and occipital regions in frequencies that ranged from 1.17 to 3.52 Hz and in the bilateral frontal and right temporal regions in frequencies ranging from 9.37 to 19.14 Hz.

CONCLUSIONS/SIGNIFICANCE

This study provides evidence that PVL toddlers have visuospatial WM deficits and a very different pattern of absolute power increases compared to a healthy group of toddlers, with greater absolute power in the low frequency range and widespread neuronal networks in the WM retention phase.

Visual function in preterm infants: visualizing the brain to improve prognosis

Considerable development of the visual system occurs in the third trimester of life, a time when very preterm-born infants are in a neonatal intensive care unit (NICU). Their very early birth during a period of rapid and marked neurodevelopment and their clinical course makes them a very high-risk population. A range of different events impacts brain development and the visual system, leading to significant long-term visual dysfunction. Improved neuroimaging techniques provide an important window on the early brain and visual system development of these vulnerable infants. Greater understanding of the etiology of visual impairment subsequent to preterm birth and the timing of critical processes will allow early recognition and the earlier implementations of interventions. In the longer term, this will help clinicians optimize NICU practice to reduce the incidence of visual dysfunction in these children.

The influence of preterm birth on the developing thalamocortical connectome

INTRODUCTION

Defining connectivity in the human brain signifies a major neuroscientific goal. Advanced imaging techniques have enabled the non-invasive tracing of brain networks to define the human connectome on a millimetre-scale. During early development, the brain undergoes significant changes that are likely represented in the developing connectome, and preterm birth represents a significant environmental risk factor that impacts negatively on early cerebral development. Using tractography to comprehensively map the connections of the thalamocortical unit, we aim to demonstrate that premature extrauterine life due to preterm delivery results in significantly decreased thalamocortical connectivity in the developing human neonate.

METHODS

T1- and T2-weighted magnetic resonance images and 32-direction diffusion tensor images were acquired from 18 healthy term-born neonates (median gestational age: 41(+3)) and 47 preterm infants (median gestational age: 28(+3)) scanned at term-equivalent age. Using a novel processing pipeline for tracing connections in the neonatal brain we map and compare the thalamocortical macro-connectome between groups.

RESULTS

We demonstrate that connections between the thalamus and the frontal cortices, supplementary motor areas, occipital lobe and temporal gyri are significantly diminished in preterm infants (FDR-corrected, p < .001).

CONCLUSIONS

This supports the hypothesis that the thalamocortical system is vulnerable following preterm birth and the tractographic framework presented represents a method for analysing system connectivity that can be readily applied to other populations and neural systems.

Thalamic changes in a preterm sample with periventricular leukomalacia: correlation with white-matter integrity and cognitive outcome at school age

INTRODUCTION

Thalamic abnormalities have been well documented in preterms with periventricular leukomalacia (PVL), although their contribution to long-term cognitive dysfunctions has not been thoroughly investigated.

RESULTS

Significant differences between groups were observed for global thalamic volume. Neuropsychological assessments showed that preterms with PVL scored within the normal range, although significantly below controls in the full intelligence quotient and the specific cognitive domains of processing speed and working memory. Correlations of several thalamic regions with Working Memory Index and FIQ were found in the PVL group. Moreover, thalamic atrophy correlated with white-matter (WM) damage indexes (fractional anisotropy and radial diffusivity) assessed by diffusion tensor imaging.

DISCUSSION

The findings suggest that thalamic damage is a common correlate of WM microstructural alterations and might be involved in the cognitive deficits seen in premature infants with PVL at school age.

METHODS

We analyzed the impact of PVL-associated thalamic injury on cognitive status at school age and its correlation with WM integrity as measured by magnetic resonance imaging techniques. Thalamic volume and shape of 21 preterm children with PVL were compared with those of 11 preterm children of similar gestational age and birth weight with no evidence of focal WM abnormality.

Disruption of the serotonergic system after neonatal hypoxia-ischemia in a rodent model

Identifying which specific neuronal phenotypes are vulnerable to neonatal hypoxia-ischemia, where in the brain they are damaged, and the mechanisms that produce neuronal losses are critical to determine the anatomical substrates responsible for neurological impairments in hypoxic-ischemic brain-injured neonates. Here we describe our current work investigating how the serotonergic network in the brain is disrupted in a rodent model of preterm hypoxia-ischemia. One week after postnatal day 3 hypoxia-ischemia, losses of serotonergic raphé neurons, reductions in serotonin levels in the brain, and reduced serotonin transporter expression are evident. These changes can be prevented using two anti-inflammatory interventions; the postinsult administration of minocycline or ibuprofen. However, each drug has its own limitations and benefits for use in neonates to stem damage to the serotonergic network after hypoxia-ischemia. By understanding the fundamental mechanisms underpinning hypoxia-ischemia-induced serotonergic damage we will hopefully move closer to developing a successful clinical intervention to treat neonatal brain injury.

Diffuse periventricular leukomalacia in preterm children: assessment of grey matter changes by MRI

BACKGROUND

Preterm children may have cognitive deficits and behavioural disorders suggestive of grey matter (GM) injury. The prevalence is higher in preterm children with diffuse periventricular leukomalacia (dPVL).

OBJECTIVE

Evaluate changes in the volume of 116 GM areas in preterm children with dPVL.

METHODS AND MATERIALS

Eleven preterm children with dPVL, gestational age 32.8 ± 2.6 weeks, examined at corrected age 22.0 ± 18.2 months and 33 matched preterm controls with normal brain MRI were studied. Volumes of 116 individual GM areas, and white matter/cerebrospinal fluid (WM/CSF) ratio were calculated on T1-weighted high-resolution images after segmentation.

RESULTS

Relative to controls, children with dPVL had decreased GM volume of the hippocampus, amygdala, and frontal lobes and temporal middle gyrus (P < 0.05); increased GM volume of the putamen, thalamus, globus pallidum, superior temporal gyrus and of the parietal and occipital lobes (P < 0.05) and lower WM volume/higher CSF volume (P < 0.05). WM/CSF ratios also differed (P < 0.05).

CONCLUSIONS

Preterm children with dPVL have increased regional GM volume in some areas probably related with a process of brain plasticity-regeneration and reduced GM volume in areas associated with cognition and memory.

Visual perception in preterm children: what are we currently measuring?

Over the past two decades, cerebral visual impairment has been recognized as a principal deficit in preterm children, and in particular those with cerebral palsy. We review the current knowledge of visual processing deficits in these children, and provide an overview of the tools for assessing cerebral visual impairment. Commercially available instruments are usually directed at evaluating visuospatial skills rather than detecting object recognition difficulties. Particularly in children aged 3 years or younger and in children with multiple handicaps, cerebral visual impairment is difficult to diagnose. This difficulty may be attributable to limitations specific to the instrument, such as a test that is inappropriate for age, or to child-specific limitations such as motor impairment or speech delay. We therefore include an overview of relevant neuroimaging findings reported in these children, focusing on the most recent imaging modalities. Novel techniques such as diffusion tensor imaging may provide sensitive markers of cerebral visual impairment in situations where clinical diagnosis is difficult, and such approaches may allow for early intervention.

Gray matter volume decrements in preterm children with periventricular leukomalacia

Periventricular leukomalacia (PVL) is the prototypic lesion in the encephalopathy of prematurity. Although PVL is identified by targeting cerebral white matter (WM), neuropathological and MRI studies document gray matter (GM) loss in cortical and subcortical structures. This study aimed to investigate the distribution of GM changes in children with a history of premature birth and PVL. Voxel-based morphometry was used to examine regional GM abnormalities in 22 children with a history of preterm birth and PVL. Preterms with PVL were compared with 22 terms and 14 preterms without PVL of similar GA and birth weight. GM and WM global volumetric volumes were found to decrease in comparison with both control groups. Regional GM volume abnormalities were also found: compared with their term peers, preterm children with PVL showed several regions of GM reduction. Moreover, PVL differed from preterms without PVL in the medial temporal lobe bilaterally, thalamus bilaterally, and caudate nuclei bilaterally. In addition, in our preterm sample with PVL, birth weight showed a statistical significant correlation with decreased GM regions. In conclusion, the voxel-based morphometry methodology revealed that PVL per se does involve GM reductions.

Early visual assessment in preterm infants with and without brain lesions: correlation with visual and neurodevelopmental outcome at 12 months

BACKGROUND

Several studies have reported the development of various aspects of visual function in infancy and early childhood in both preterm and term-born infants, but only a few studies have focused on the predictive power of neonatal visual findings in infants with brain lesions.

AIMS

To explore visual findings at term age, and at 3 and 12 months corrected age in preterm infants (gestational age <33 weeks) with and without brain lesions; to compare the assessment at term age and at 12 months; and to assess the relationship between visual findings and neurodevelopmental outcome at 12 months.

STUDY DESIGN

Cranial ultrasound scans (US) were classified in normal, mild or major abnormalities. One-hundred and forty-five infants were assessed with age specific tests for visual function at term age, and at 3 and 12 months. Neurodevelopmental assessment (Griffiths' Scales) was performed at 12 months.

RESULTS

A good correlation was found between early and late visual assessment and neurodevelopment outcome. Of the 121 infants with normal neonatal visual assessment, 119 were also normal at 12 months and 116 had normal developmental quotient. Of the 24 infants with abnormal neonatal visual assessment, 12 were also abnormal at 12 months. All the false positives had normalised by 3 months. Of the 35 infants with major US abnormalities, 20 had normal and 15 abnormal scores on the neonatal assessment. At 1 year 17 had normal and 18 abnormal scores.

CONCLUSION

A normal visual assessment at term age is a good predictor of normal visual and neurodevelopmental outcome at 12 months. An abnormal visual examination in the neonatal period was a less reliable prognostic indicator, infant should be reassessed at 3 months.

Abnormal microstructure of the atrophic thalamus in preterm survivors with periventricular leukomalacia

BACKGROUND AND PURPOSE

The neuroanatomic substrate of cognitive deficits in long-term survivors of prematurity with PVL is poorly understood. The thalamus is critically involved in cognition via extensive interconnections with the cerebral cortex. We hypothesized that the thalamus is atrophic (reduced in volume) in childhood survivors of prematurity with neuroimaging evidence of PVL and that the atrophy is associated with selective microstructural abnormalities within its subdivisions.

MATERIALS AND METHODS

We performed quantitative volumetric and DTI measurements of the thalamus in 17 children with neuroimaging evidence of PVL (mean postconceptional age, 5.6 ± 4.0 years) who were born prematurely and compared these with 74 term control children (5.7 ± 3.4 years).

RESULTS

The major findings were the following: 1) a significant reduction in the overall volume of the thalamus in patients with PVL compared with controls (P < .0001), which also correlated with the severity of PVL (P = .001); 2) significantly decreased FA (P = .003) and increased λ(⊥) (P = .02) in the thalamus overall and increased axial, radial, and mean diffusivities in the pulvinar (P < .03), suggesting injury to afferent and efferent myelinated axons; and 3) a positive correlation of pulvinar abnormalities with those of the parieto-occipital white matter in periventricular leukomalacia, suggesting that the pulvinar abnormalities reflect secondary effects of damaged interconnections between the pulvinar and parieto-occipital cortices in the cognitive visual network.

CONCLUSIONS

There are volumetric and microstructural abnormalities of the thalamus in preterm children with PVL, very likely reflecting neuronal loss and myelinated axonal injury. The selective microstructural damage in the pulvinar very likely contributes to abnormal cognitive visual processing known to occur in such survivors.

Visual performance and brain structures in the developing brain of pre-term infants

The presence of abnormal visual function has been related to overt lesions in the thalami, peritrigonal white matter (such as cavitational-necrotic periventricular leucomalacia) and optic radiations, and also to the extent of occipital cortex involvement. The normal development of visual function seems to depend on the integrity of a network that includes not only optic radiations and the primary visual cortex but also other cortical and subcortical areas, such as the frontal or temporal lobes or basal ganglia, which have been found to play a topical role in the development of vision. Therefore, the complex functions and functional connectivity of the developing brain of premature infants can be studied only with highly sophisticated techniques such as diffusion tensor tractography. The combined use of visual tests and neonatal structural and functional neuroimaging, which have become available for newborn infants, provides a better understanding of the correlation between structure and function from early life. This appears to be particularly relevant considering the essential role of early visual function in cognitive development. The identification of early visual impairment is also important, as it allows for early enrolment in intervention programmes. The association of clinical and functional studies to newer imaging techniques, which are being increasingly used also in neonates, are likely to provide further information on early aspects of vision and the mechanisms underlying brain plasticity, which are still not fully understood. Early exposure to a difficult postnatal environment together with early and unexpected removal from a protective milieu are exclusive and peculiar factors of prematurity that interfere with the normal development of the visual system in pre-term babies. The problem is further compounded by the influence of different perinatal brain lesions affecting the developing brain of premature babies. Nevertheless, in the last few decades, there have been considerable advances in our understanding of the development of vision in pre-term infants during early infancy. This has mainly been due to the development of age-specific tests assessing various aspects of visual function, from ophthalmological examination to more cortical aspects of vision, such as the ability to process orientation or different aspects of visual attention [1-7]. Improvements in understanding very early and specific neurological impairments in neurological functions have been reported in pre-term infants, known to be at risk of developing visual and visual-perceptual impairment. These impairments are due not only to retinopathy, a common finding in premature infants, but also to cerebral (central) visual impairment, secondary to brain lesions affecting the central visual pathway.

Brain lesions in preterm infants: initial diagnosis and follow-up

Children surviving premature birth present with a wide spectrum of motor, sensory and cognitive disabilities, ranging from slight motor deficits, school difficulties and behavioural problems to cerebral palsy and mental retardation. The anatomic and functional substrate of these problems can be investigated using a variety of imaging techniques. Cranial US coupled with colour Doppler is a well-established method for the initial diagnosis of intraventricular haemorrhage, parenchymal haemorrhagic infarct and periventricular leukomalacia. MRI is useful for the follow-up study of brain maturation. Conventional T1- and T2-weighted sequences, magnetization transfer and diffusion tensor imaging coupled with sophisticated tools of tissue segmentation and analysis at a voxel level offer substantial anatomic and functional information on pathological conditions that define the prognosis of preterm infants.

Cortical visual function in preterm infants in the first year

OBJECTIVE

To assess visual function in low-risk preterm infants at 3, 5, and 12 months corrected age to determine whether the maturation of visual function in the first year is similar to that reported in term-born infants.

STUDY DESIGN

Seventy-five low-risk infants (25.0-30.9 weeks gestation) underwent ophthalmological examinations and a battery of tests (fix and follow, visual fields, acuity, attention at distance, and fixation shift) designed to assess various aspects of visual function at 3, 5, and 12 months corrected age.

RESULTS

The results were comparable with normative data from term-born infants in all tests but fixation shift, suggesting that maturation of most aspects of visual function is not significantly affected by preterm birth. In contrast, >25% of preterm infants failed the fixation shift test at 3 months, with a higher percentage of failing at 5 and 12 months.

CONCLUSIONS

There is a specific profile of early visual behavior in low-risk preterm infants, with a high percentage of infants failing a test that specifically assesses visual attention and provides a measure of cortical processing.

Periventricular leukomalacia in preterm children: assessment of grey and white matter and cerebrospinal fluid changes by MRI

BACKGROUND

Brain plasticity in patients with periventricular leukomalacia (PVL) may suggest grey matter (GM) changes.

OBJECTIVE

To assess the volume of 116 GM areas and total volume of GM, white matter (WM) and cerebrospinal fluid (CSF) in preterm children with PVL, using the Statistical Parametric Mapping (SPM5) and the Individual Brain Atlases Statistical Parametric Mapping (IBASPM) toolboxes.

MATERIALS AND METHODS

Ten preterm children (gestational age 31.7 +/- 4.2 weeks, corrected age 27.8 +/- 21.7 months) with PVL and 46 matched, preterm control subjects were studied using a three-dimensional T1-weighted sequence. Volumes were calculated using SPM5 and IBASPM.

RESULTS

GM volume in frontal superior orbital, posterior cingulum and lingual gyrus, the putamen and thalamus was significantly higher in children with PVL (3.6 +/- 0.6 cm(3), 2.0 +/- 0.5 cm(3), 9.7 +/- 1.7 cm(3), 2.5 +/- 0.6 cm(3), 2.6 +/- 0.9 cm(3), respectively) than in controls (3.1 +/- 0.7 cm(3), 1.5 +/- 0.2 cm(3), 8.2 +/- 1.3 cm(3), 1.7 +/- 1.4 cm(3), 1.8 +/- 0.4 cm(3), respectively). White matter volume was lower (182.1 +/- 40.5 cm(3)) and CSF volume was higher (300.8 +/- 56.2 cm(3)) in children with PVL than in controls (222.9 +/- 67.2 cm(3), 219.0 +/- 61.8 cm(3), respectively), P < 0.05. No significant difference was found in the total GM volume and the volume of neocortex.

CONCLUSION

Preterm children with PVL show regional GM volume increase, possibly explained by axonal sprouting, neuronal hypertrophy and neurogenesis, which in turn may reflect brain plasticity.

Magnetic resonance imaging in neonatal stroke

Neonatal stroke occurs in 1 in 2300-5000 live births, the incidence of which is lower than that in adults, but still higher than that in childhood. The higher incidence of perinatal stroke in preterm and term infants compared to stroke in childhood may be partly explained by higher detection rates using routine fetal ultrasound and postnatal cranial sonography. In addition, there is greater availability of magnetic resonance imaging (MRI) for neuroimaging in preterm and full-term infants, which is due in part to the availability of MR-compatible incubators and MR systems at or near the neonatal intensive care unit. In addition, the wide range of MR techniques, such as T2-, diffusion- and susceptibility-weighted imaging allows improved visualization and quantification of neonatal stroke or hypoxic-ischemic injury. This chapter reviews the MR neuroimaging modalities that actually assist the clinician in the detection of neonatal stroke.

Thalamic damage in periventricular leukomalacia: novel pathologic observations relevant to cognitive deficits in survivors of prematurity

Despite major advances in the long-term survival of premature infants, cognitive deficits occur in 30-50% of very preterm (<32 gestational weeks) survivors. Impaired working memory and attention despite average global intelligence are central to the academic difficulties of the survivors. Periventricular leukomalacia (PVL), characterized by periventricular necrosis and diffuse gliosis in the cerebral white matter, is the major brain pathology in preterm infants. We tested the novel hypothesis that pathology in thalamic nuclei critical for working memory and attention, i.e. mediodorsal nucleus and reticular nucleus, respectively, occurs in PVL. In 22 PVL cases (gestational age 32.5 +/- 4.8 wk) and 16 non-PVL controls (36.7 +/- 5.2 wk) who died within infancy, the incidence of thalamic pathology was significantly higher in PVL cases (59%; 13/22) compared with controls (19%; 3/16) (p = 0.01), with substantial involvement of the mediodorsal, and reticular nuclei in PVL. The prevention of thalamic damage may be required for the eradication of defects in survivors with PVL.

Diffuse axonal injury in periventricular leukomalacia as determined by apoptotic marker fractin

Periventricular leukomalacia (PVL), the major substrate of neurologic deficits in premature infants, is associated with reduced white matter volume. Using immunomarkers of axonal pathology [beta-amyloid precursor protein (beta-APP) and apoptotic marker fractin], we tested the hypothesis that widespread (diffuse) axonal injury occurs in the gliotic white matter beyond the foci of necrosis in PVL, thus contributing to the white matter volume reduction. In a cohort of 17 control cases and 13 PVL cases with lesions of different chronological ages, diffuse axonal damage in PVL was detected by fractin in white matter sites surrounding and distant from acute and organizing foci of necrosis. Using beta-APP, axonal spheroids were detected within necrotic foci in the acute and organizing (subacute) stages, a finding consistent with others. Interestingly, GAP-43 expression was also detected in spheroids in the necrotic foci, suggesting attempts at axonal regeneration. Thirty-one percent of the PVL cases had thalamic damage and 15% neuronal injury in the cerebral cortex overlying PVL. We conclude that diffuse axonal injury, as determined by apoptotic marker fractin, occurs in PVL and that its cause likely includes primary ischemia and trophic degeneration secondary to corticothalamic neuronal damage.