Imaging biomarkers of outcome in the developing preterm brain

Prematurity and brain perfusion: Arterial spin labeling MRI

Purpose

Abnormal brain perfusion is a critical mechanism in neonatal brain injury. The aim of the present study was to compare Cerebral Blood Flow (CBF) evaluated with ASL MRI in three groups of neonates: preterms without brain lesions on MRI (PN), preterms with periventricular white matter lesions (PNp) and term neonates with normal MRI (TN). The correlation between CBF and clinical outcome was explored.

Materials and methods

The institutional review board approved this prospective study and waived informed consent. The perfusion ASL data from 49 consecutive preterm neonates (PN) studied at term-equivalent age and 15 TN were evaluated. Statistically significant differences in gray matter CBF were evaluated by using a linear mixed-model analysis and Mann-Whitney U test. Logistic regression analysis was used to assess the relation between CBF and neuromotor outcome at 12 months.

Results

Comparison of means indicated that the CBF of the whole brain were significantly higher in PN compared to TN (P = 0.011). This difference remained significant when considering the frontal (P = 0.038), parietal (P = 0.002), temporal (P = 0.030), occipital (P = 0.041) and cerebellar (P = 0.010) gray matter. In the PN group, lower CBF in basal ganglia was associated with a worse neuromotor outcome (P = 0.012).

Conclusions

ASL MRI demonstrated differences in brain perfusion of the basal ganglia between PN and TN. In PN, a positive correlation between CBF and neuromotor outcome was demonstrated in this area.

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Different ASL cerebral perfusion between preterm and term neonates

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Global reduction of CBF values in preterm neonates with white matter lesions

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ASL identifies preterm neonates at higher risk for sub-optimal neuromotor development.

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Worst 12-months neuromotor outcome in preterm neonates with lower CBF of basal ganglia

Functional thalamocortical connectivity development and alterations in preterm infants during the neonatal period

The thalamus is one of the most commonly affected brain regions in preterm infants, particularly in infants with white matter lesions (WML). The aim of this paper is to explore the development and alterations of the functional thalamocortical connectivity in preterm infants with and without punctate white matter lesions (PWMLs) during the period before term equivalent age (TEA). In this study, twenty-two normal preterm infants (NP), twenty-two preterm infants with PWMLs and thirty-one full-term control infants (FT) were enrolled. Thalamus parcellation was performed based on partial correlation between the thalamus and seven well-recognized infant networks obtained from independent component analysis (ICA), and thalamocortical connectivity was further reconstructed between the defined thalamus clusters and the whole brain. Thalamo-salience (SA) and thalamo-sensorimotor (SM) connectivity were predominantly identified, while other types of thalamocortical connectivity remained largely limited during the neonatal period. Both preterm groups exhibited prominent development in thalamo-SA and thalamo-SM connectivity during this period. Compared with NP infants, PWML infants demonstrated increased connectivity in the parietal area in thalamo-SA connectivity but no significant differences in thalamo-SM connectivity. Our results reveal that compared with NP infants, PWML infants exhibit slightly altered thalamo-SA connectivity, and this alteration is deduced to be functional compensations for inefficient thalamocortical processing due to PWMLs.

Growth of Thalamocortical Fibers to the Somatosensory Cortex in the Human Fetal Brain

Thalamocortical (TH-C) fiber growth begins during the embryonic period and is completed by the third trimester of gestation in humans. Here we determined the timing and trajectories of somatosensory TH-C fibers in the developing human brain. We analyzed the periods of TH-C fiber outgrowth, path-finding, "waiting" in the subplate (SP), target selection, and ingrowth in the cortical plate (CP) using histological sections from post-mortem fetal brain [from 7 to 34 postconceptional weeks (PCW)] that were processed with acetylcholinesterase (AChE) histochemistry and immunohistochemical methods. Images were compared with post mortem diffusion tensor imaging (DTI)-based fiber tractography (code No NO1-HD-4-3368). The results showed TH-C axon outgrowth occurs as early as 7.5 PCW in the ventrolateral part of the thalamic anlage. Between 8 and 9.5 PCW, TH-C axons form massive bundles that traverse the diencephalic-telencephalic boundary. From 9.5 to 11 PCW, thalamocortical axons pass the periventricular area at the pallial-subpallial boundary and enter intermediate zone in radiating fashion. Between 12 and 14 PCW, the TH-C axons, aligned along the fibers from the basal forebrain, continue to grow for a short distance within the deep intermediate zone and enter the deep CP, parallel with SP expansion. Between 14 and 18 PCW, the TH-C interdigitate with callosal fibers, running shortly in the sagittal stratum and spreading through the deep SP ("waiting" phase). From 19 to 22 PCW, TH-C axons accumulate in the superficial SP below the somatosensory cortical area; this occurs 2 weeks earlier than in the frontal and occipital cortices. Between 23 and 24 PCW, AChE-reactive TH-C axons penetrate the CP concomitantly with its initial lamination. Between 25 and 34 PCW, AChE reactivity of the CP exhibits an uneven pattern suggestive of vertical banding, showing a basic 6-layer pattern. In conclusion, human thalamocortical axons show prolonged growth (4 months), and somatosensory fibers precede the ingrowth of fibers destined for frontal and occipital areas. The major features of growing TH-C somatosensory fiber trajectories are fan-like radiation, short runs in the sagittal strata, and interdigitation with the callosal system. These results support our hypothesis that TH-C axons are early factors in SP and CP morphogenesis and synaptogenesis and may regulate cortical somatosensory system maturation.

Sensory modulation in preterm children: Theoretical perspective and systematic review

BACKGROUND

Neurodevelopmental sequelae in preterm born children are generally considered to result from cerebral white matter damage and noxious effects of environmental factors in the neonatal intensive care unit (NICU). Cerebral white matter damage is associated with sensory processing problems in terms of registration, integration and modulation. However, research into sensory processing problems and, in particular, sensory modulation problems, is scarce in preterm children.

AIM

This review aims to integrate available evidence on sensory modulation problems in preterm infants and children (<37 weeks of gestation) and their association with neurocognitive and behavioral problems.

METHOD

Relevant studies were extracted from PubMed, EMBASE.com and PsycINFO following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Selection criteria included assessment of sensory modulation in preterm born children (<37 weeks of gestation) or with prematurity as a risk factor.

RESULTS

Eighteen studies were included. Results of this review support the presence of sensory modulation problems in preterm children. Although prematurity may distort various aspects of sensory modulation, the nature and severity of sensory modulation problems differ widely between studies.

CONCLUSIONS

Sensory modulation problems may play a key role in understanding neurocognitive and behavioral sequelae in preterm children. Some support is found for a dose-response relationship between both white matter brain injury and length of NICU stay and sensory modulation problems.

Histograms of Oriented 3D Gradients for Fully Automated Fetal Brain Localization and Robust Motion Correction in 3 T Magnetic Resonance Images

Fetal brain magnetic resonance imaging (MRI) is a rapidly emerging diagnostic imaging tool. However, automated fetal brain localization is one of the biggest obstacles in expediting and fully automating large-scale fetal MRI processing. We propose a method for automatic localization of fetal brain in 3 T MRI when the images are acquired as a stack of 2D slices that are misaligned due to fetal motion. First, the Histogram of Oriented Gradients (HOG) feature descriptor is extended from 2D to 3D images. Then, a sliding window is used to assign a score to all possible windows in an image, depending on the likelihood of it containing a brain, and the window with the highest score is selected. In our evaluation experiments using a leave-one-out cross-validation strategy, we achieved 96% of complete brain localization using a database of 104 MRI scans at gestational ages between 34 and 38 weeks. We carried out comparisons against template matching and random forest based regression methods and the proposed method showed superior performance. We also showed the application of the proposed method in the optimization of fetal motion correction and how it is essential for the reconstruction process. The method is robust and does not rely on any prior knowledge of fetal brain development.

Deficits in Top-Down Sensory Prediction in Infants At Risk due to Premature Birth

A prominent theoretical view is that the brain is inherently predictive [1, 2] and that prediction helps drive the engine of development [3, 4]. Although infants exhibit neural signatures of top-down sensory prediction [5, 6], in order to establish that prediction supports development, it must be established that deficits in early prediction abilities alter trajectories. We investigated prediction in infants born prematurely, a leading cause of neuro-cognitive impairment worldwide [7]. Prematurity, independent of medical complications, leads to developmental disturbances [8-12] and a broad range of developmental delays [13-17]. Is an alteration in early prediction abilities the common cause? Using functional near-infrared spectroscopy (fNIRS), we measured top-down sensory prediction in preterm infants (born <33 weeks gestation) before infants exhibited clinically identifiable developmental delays (6 months corrected age). Whereas preterm infants had typical neural responses to presented visual stimuli, they exhibited altered neural responses to predicted visual stimuli. Importantly, a separate behavioral control confirmed that preterm infants detect pattern violations at the same rate as full-terms, establishing selectivity of this response to top-down predictions (e.g., not in learning an audiovisual association). These findings suggest that top-down sensory prediction plays a crucial role in development and that deficits in this ability may be the reason why preterm infants experience altered developmental trajectories and are at risk for poor developmental outcomes. Moreover, this work presents an opportunity for establishing a neuro-biomarker for early identification of infants at risk and could guide early intervention regimens.

Mapping the critical gestational age at birth that alters brain development in preterm-born infants using multi-modal MRI

Preterm birth adversely affects postnatal brain development. In order to investigate the critical gestational age at birth (GAB) that alters the developmental trajectory of gray and white matter structures in the brain, we investigated diffusion tensor and quantitative T2 mapping data in 43 term-born and 43 preterm-born infants. A novel multivariate linear model-the change point model, was applied to detect change points in fractional anisotropy, mean diffusivity, and T2 relaxation time. Change points captured the "critical" GAB value associated with a change in the linear relation between GAB and MRI measures. The analysis was performed in 126 regions across the whole brain using an atlas-based image quantification approach to investigate the spatial pattern of the critical GAB. Our results demonstrate that the critical GABs are region- and modality-specific, generally following a central-to-peripheral and bottom-to-top order of structural development. This study may offer unique insights into the postnatal neurological development associated with differential degrees of preterm birth.

Effects of a Home-Based Family-Centred Early Habilitation Program on Neurobehavioural Outcomes of Very Preterm Born Infants: A Retrospective Cohort Study

Preterm children have an increased risk of neurodevelopmental impairments which include psychomotor and language retardation. The objectives of the present retrospective cohort study were to examine the effects of an individually adapted, home-based, and family-centred early developmental habilitation program on neurodevelopmental and behavioural outcomes of very preterm children compared with a standard follow-up at 2 years' corrected age. Enrolled infants were retrospectively assigned to the intervention group (61 subjects) or to the control group (62 subjects) depending on whether they had or had not carried out a home-based family-centred early developmental habilitation program focused on environmental enrichment, parent-guided environmental interaction, and infant development. Developmental outcome was assessed for both groups at 24 months' corrected age using the Bayley Scales of Infant Development 2nd Edition. Intervention significantly improved both cognitive and behavioural outcomes. In addition, males had significantly lower scores than females either before or after treatment. However, the treatment was effective in both genders to the same extent. In conclusion, a timely updated environment suitable to the infant's developmental needs could provide the best substrate where the parent-infant relationship can be practised with the ultimate goal of achieving further developmental steps.

Longitudinal change in white matter in preterm infants without magnetic resonance imaging abnormalities: Assessment of serial diffusion tensor imaging and their relationship to neurodevelopmental outcomes

PURPOSE

We used diffusion tensor imaging (DTI) to evaluate longitudinal changes in fractional anisotropy (FA) of white matter tracts in preterm infants without abnormal magnetic resonance imaging (MRI) findings. Imaging was conducted at term equivalent age (TEA) and 1year of corrected age. Furthermore, we assessed correlations between FA and neurodevelopmental outcomes at 3years of corrected age to investigate brain prematurity of preterm infants without MRI abnormalities.

METHODS

Preterm infants underwent serial MRI at TEA and 1year of corrected age. Of these, 13 infants entered a retrospective study, undergoing neurodevelopmental assessment at 3years of corrected age. These infants were divided into two groups depending on gestational age (GA): <26weeks and ⩾26weeks. DTI-based tractography was performed to obtain the FA of the motor tract, sensory tract, superior cerebellar peduncle, middle cerebellar peduncle, and corpus callosum. FA was compared between two groups, and correlations between FA and neurodevelopmental outcomes were assessed.

RESULTS

FA of the splenium at TEA was significantly different between the two groups divided according to GA. However, this difference was no longer observed at 1year of corrected age. There was no correlation between FA of the splenium at TEA and neurodevelopmental assessment scores at 3years of corrected age.

CONCLUSIONS

At TEA, FA of the splenium was lower in younger GA infants without MRI abnormalities, but this may not affect subsequent neurodevelopmental outcomes.

Creatine, Glutamine plus Glutamate, and Macromolecules Are Decreased in the Central White Matter of Premature Neonates around Term

Preterm birth represents a high risk of neurodevelopmental disabilities when associated with white-matter damage. Recent studies have reported cognitive deficits in children born preterm without brain injury on MRI at term-equivalent age. Understanding the microstructural and metabolic underpinnings of these deficits is essential for their early detection. Here, we used diffusion-weighted imaging and single-voxel 1H magnetic resonance spectroscopy (MRS) to compare brain maturation at term-equivalent age in premature neonates with no evidence of white matter injury on conventional MRI except diffuse excessive high-signal intensity, and normal term neonates. Thirty-two infants, 16 term neonates (mean post-conceptional age at scan: 39.8±1 weeks) and 16 premature neonates (mean gestational age at birth: 29.1±2 weeks, mean post-conceptional age at scan: 39.2±1 weeks) were investigated. The MRI/MRS protocol performed at 1.5T involved diffusion-weighted MRI and localized 1H-MRS with the Point RESolved Spectroscopy (PRESS) sequence. Preterm neonates showed significantly higher ADC values in the temporal white matter (P<0.05), the occipital white matter (P<0.005) and the thalamus (P<0.05). The proton spectrum of the centrum semiovale was characterized by significantly lower taurine/H2O and macromolecules/H2O ratios (P<0.05) at a TE of 30 ms, and reduced (creatine+phosphocreatine)/H2O and (glutamine+glutamate)/H2O ratios (P<0.05) at a TE of 135 ms in the preterm neonates than in full-term neonates. Our findings indicate that premature neonates with normal conventional MRI present a delay in brain maturation affecting the white matter and the thalamus. Their brain metabolic profile is characterized by lower levels of creatine, glutamine plus glutamate, and macromolecules in the centrum semiovale, a finding suggesting altered energy metabolism and protein synthesis.

Brain Volumes at Term-Equivalent Age Are Associated with 2-Year Neurodevelopment in Moderate and Late Preterm Children

OBJECTIVE

To explore the association between brain maturation, injury, and volumes at term-equivalent age with 2-year development in moderate and late preterm children.

STUDY DESIGN

Moderate and late preterm infants were recruited at birth and assessed at age 2 years using the Bayley Scales of Infant and Toddler Development, Third Edition. Brain magnetic resonance imaging (MRI) was performed at term-equivalent age and qualitatively assessed for brain maturation (myelination of the posterior limb of the internal capsule and gyral folding) and injury. Brain volumes were measured using advanced segmentation techniques. The associations between brain MRI measures with developmental outcomes were explored using linear regression analyses.

RESULTS

A total of 197 children underwent MRI and assessed using the Bayley Scales of Infant and Toddler Development, Third Edition. Larger total brain tissue volumes were associated with higher cognitive and language scores (adjusted coefficients per 10% increase in brain size; 95% CI of 3.2 [0.4, 5.6] and 5.6 [2.4, 8.8], respectively). Similar relationships were documented for white matter volumes with cognitive and language scores, multiple cerebral structures with language scores, and cerebellar volumes with motor scores. Larger cerebellar volumes were independently associated with better language and motor scores, after adjustment for other perinatal factors. There was little evidence of relationships between myelination of the posterior limb of the internal capsule, gyral folding, or injury with 2-year development.

CONCLUSIONS

Larger total brain tissue, white matter, and cerebellar volumes at term-equivalent age are associated with better neurodevelopment in moderate and late preterm children. Brain volumes may be an important marker for neurodevelopmental deficits described in moderate and late preterm children.

Imaging and serum biomarkers reflecting the functional efficacy of extended erythropoietin treatment in rats following infantile traumatic brain injury

OBJECTIVE Traumatic brain injury (TBI) is a leading cause of death and severe morbidity for otherwise healthy full-term infants around the world. Currently, the primary treatment for infant TBI is supportive, as no targeted therapies exist to actively promote recovery. The developing infant brain, in particular, has a unique response to injury and the potential for repair, both of which vary with maturation. Targeted interventions and objective measures of therapeutic efficacy are needed in this special population. The authors hypothesized that MRI and serum biomarkers can be used to quantify outcomes following infantile TBI in a preclinical rat model and that the potential efficacy of the neuro-reparative agent erythropoietin (EPO) in promoting recovery can be tested using these biomarkers as surrogates for functional outcomes. METHODS With institutional approval, a controlled cortical impact (CCI) was delivered to postnatal Day (P)12 rats of both sexes (76 rats). On postinjury Day (PID)1, the 49 CCI rats designated for chronic studies were randomized to EPO (3000 U/kg/dose, CCI-EPO, 24 rats) or vehicle (CCI-veh, 25 rats) administered intraperitoneally on PID1-4, 6, and 8. Acute injury (PID3) was evaluated with an immunoassay of injured cortex and serum, and chronic injury (PID13-28) was evaluated with digitized gait analyses, MRI, and serum immunoassay. The CCI-veh and CCI-EPO rats were compared with shams (49 rats) primarily using 2-way ANOVA with Bonferroni post hoc correction. RESULTS Following CCI, there was 4.8% mortality and 55% of injured rats exhibited convulsions. Of the injured rats designated for chronic analyses, 8.1% developed leptomeningeal cyst-like lesions verified with MRI and were excluded from further study. On PID3, Western blot showed that EPO receptor expression was increased in the injured cortex (p = 0.008). These Western blots also showed elevated ipsilateral cortex calpain degradation products for αII-spectrin (αII-SDPs; p < 0.001), potassium chloride cotransporter 2 (KCC2-DPs; p = 0.037), and glial fibrillary acidic protein (GFAP-DPs; p = 0.002), as well as serum GFAP (serum GFAP-DPs; p = 0.001). In injured rats multiplex electrochemiluminescence analyses on PID3 revealed elevated serum tumor necrosis factor alpha (TNFα p = 0.01) and chemokine (CXC) ligand 1 (CXCL1). Chronically, that is, in PID13-16 CCI-veh rats, as compared with sham rats, gait deficits were demonstrated (p = 0.033) but then were reversed (p = 0.022) with EPO treatment. Diffusion tensor MRI of the ipsilateral and contralateral cortex and white matter in PID16-23 CCI-veh rats showed widespread injury and significant abnormalities of functional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD); MD, AD, and RD improved after EPO treatment. Chronically, P13-P28 CCI-veh rats also had elevated serum CXCL1 levels, which normalized in CCI-EPO rats. CONCLUSIONS Efficient translation of emerging neuro-reparative interventions dictates the use of age-appropriate preclinical models with human clinical trial-compatible biomarkers. In the present study, the authors showed that CCI produced chronic gait deficits in P12 rats that resolved with EPO treatment and that chronic imaging and serum biomarkers correlated with this improvement.

Motor and cortico-striatal-thalamic connectivity alterations in intrauterine growth restriction

BACKGROUND

Intrauterine growth restriction is associated with short- and long-term neurodevelopmental problems. Structural brain changes underlying these alterations have been described with the use of different magnetic resonance-based methods that include changes in whole structural brain networks. However, evaluation of specific brain circuits and its correlation with related functions has not been investigated in intrauterine growth restriction.

OBJECTIVES

In this study, we aimed to investigate differences in tractography-related metrics in cortico-striatal-thalamic and motor networks in intrauterine growth restricted children and whether these parameters were related with their specific function in order to explore its potential use as an imaging biomarker of altered neurodevelopment.

METHODS

We included a group of 24 intrauterine growth restriction subjects and 27 control subjects that were scanned at 1 year old; we acquired T1-weighted and 30 directions diffusion magnetic resonance images. Each subject brain was segmented in 93 regions with the use of anatomical automatic labeling atlas, and deterministic tractography was performed. Brain regions included in motor and cortico-striatal-thalamic networks were defined based in functional and anatomic criteria. Within the streamlines that resulted from the whole brain tractography, those belonging to each specific circuit were selected and tractography-related metrics that included number of streamlines, fractional anisotropy, and integrity were calculated for each network. We evaluated differences between both groups and further explored the correlation of these parameters with the results of socioemotional, cognitive, and motor scales from Bayley Scale at 2 years of age.

RESULTS

Reduced fractional anisotropy (cortico-striatal-thalamic, 0.319 ± 0.018 vs 0.315 ± 0.015; P = .010; motor, 0.322 ± 0.019 vs 0.319 ± 0.020; P = .019) and integrity cortico-striatal-thalamic (0.407 ± 0.040 vs 0.399 ± 0.034; P = .018; motor, 0.417 ± 0.044 vs 0.409 ± 0.046; P = .016) in both networks were observed in the intrauterine growth restriction group, with no differences in number of streamlines. More importantly, strong specific correlation was found between tractography-related metrics and its relative function in both networks in intrauterine growth restricted children. Motor network metrics were correlated specifically with motor scale results (fractional anisotropy: rho = 0.857; integrity: rho = 0.740); cortico-striatal-thalamic network metrics were correlated with cognitive (fractional anisotropy: rho = 0.793; integrity, rho = 0.762) and socioemotional scale (fractional anisotropy: rho = 0.850; integrity: rho = 0.877).

CONCLUSIONS

These results support the existence of altered brain connectivity in intrauterine growth restriction demonstrated by altered connectivity in motor and cortico-striatal-thalamic networks, with reduced fractional anisotropy and integrity. The specific correlation between tractography-related metrics and neurodevelopmental outcomes in intrauterine growth restriction shows the potential to use this approach to develop imaging biomarkers to predict specific neurodevelopmental outcome in infants who are at risk because of intrauterine growth restriction and other prenatal diseases.

Altered Amygdala Development and Fear Processing in Prematurely Born Infants

Context: Prematurely born children have a high risk of developmental and behavioral disabilities. Cerebral abnormalities at term age have been clearly linked with later behavior alterations, but existing studies did not focus on the amygdala. Moreover, studies of early amygdala development after premature birth in humans are scarce.

Objective: To compare amygdala volumes in very preterm infants at term equivalent age (TEA) and term born infants, and to relate premature infants’ amygdala volumes with their performance on the Laboratory Temperament Assessment Battery (Lab-TAB) fear episode at 12 months.

Participants: Eighty one infants born between 2008 and 2014 at the University Hospitals of Geneva and Lausanne, taking part in longitudinal and functional imaging studies, who had undergone a magnetic resonance imaging (MRI) scan at TEA enabling manual amygdala delineation.

Outcomes: Amygdala volumes assessed by manual segmentation of MRI scans; volumes of cortical and subcortical gray matter, white matter and cerebrospinal fluid (CSF) automatically segmented in 66 infants; scores for the Lab-TAB fear episode for 42 premature infants at 12 months.

Results: Amygdala volumes were smaller in preterm infants at TEA than term infants (mean difference 138.03 mm³, p < 0.001), and overall right amygdala volumes were larger than left amygdala volumes (mean difference 36.88 mm³, p < 0.001). White matter volumes were significantly smaller (p < 0.001) and CSF volumes significantly larger (p < 0.001) in preterm than in term born infants, while cortical and subcortical gray matter volumes were not significantly different between groups. Amygdala volumes showed significant correlation with the intensity of the escape response to a fearsome toy (r_s = 0.38, p = 0.013), and were larger in infants showing an escape response compared to the infants showing no escape response (mean difference 120.97 mm³, p = 0.005). Amygdala volumes were not significantly correlated with the intensity of facial fear, distress vocalizations, bodily fear and positive motor activity in the fear episode.

Conclusion: Our results indicate that premature birth is associated with a reduction in amygdala volumes and white matter volumes at TEA, suggesting that altered amygdala development might be linked to alterations in white matter connectivity reported in premature infants. Moreover, our data suggests that such alterations might affect infants’ fear-processing capabilities.

Axon density and axon orientation dispersion in children born preterm

BACKGROUND

Very preterm birth (VPT, <32 weeks' gestation) is associated with altered white matter fractional anisotropy (FA), the biological basis of which is uncertain but may relate to changes in axon density and/or dispersion, which can be measured using Neurite Orientation Dispersion and Density Imaging (NODDI). This study aimed to compare whole brain white matter FA, axon dispersion, and axon density between VPT children and controls (born ≥37 weeks' gestation), and to investigate associations with perinatal factors and neurodevelopmental outcomes.

METHODS

FA, neurite dispersion, and neurite density were estimated from multishell diffusion magnetic resonance images for 145 VPT and 33 control 7-year-olds. Diffusion values were compared between groups and correlated with perinatal factors (gestational age, birthweight, and neonatal brain abnormalities) and neurodevelopmental outcomes (IQ, motor, academic, and behavioral outcomes) using Tract-Based Spatial Statistics.

RESULTS

Compared with controls, VPT children had lower FA and higher axon dispersion within many major white matter fiber tracts. Neonatal brain abnormalities predicted lower FA and higher axon dispersion in many major tracts in VPT children. Lower FA, higher axon dispersion, and lower axon density in various tracts correlated with poorer neurodevelopmental outcomes in VPT children.

CONCLUSIONS

FA and NODDI measures distinguished VPT children from controls and were associated with neonatal brain abnormalities and neurodevelopmental outcomes. This study provides a more detailed and biologically meaningful interpretation of white matter microstructure changes associated with prematurity. Hum Brain Mapp 37:3080-3102, 2016. © 2016 Wiley Periodicals, Inc.

Differentiating T2 hyperintensity in neonatal white matter by two-compartment model of diffusional kurtosis imaging

In conventional neonatal MRI, the T2 hyperintensity (T2h) in cerebral white matter (WM) at term-equivalent age due to immaturity or impairment is still difficult to identify. To clarify such issue, this study used the metrics derived from a two-compartment WM model of diffusional kurtosis imaging (WM-DKI), including intra-axonal, extra-axonal axial and radial diffusivities (D_a, D_e,// and D_e,⊥), to compare WM differences between the simple T2h and normal control for both preterm and full-term neonates, and between simple T2h and complex T2h with hypoxic-ischemic encephalopathy (HIE). Results indicated that compared with control, the simple T2h showed significantly increased D_e,// and D_e,⊥, but no significant change in D_a in multiple premyelination regions, indicative of expanding extra-axonal diffusion microenvironment; while myelinated regions showed no changes. However, compared with simple T2h, the complex T2h with HIE had decreased D_a, increased D_e,⊥ in both premyelination and myelinated regions, indicative of both intra- and extra-axonal diffusion alterations. While diffusion tensor imaging (DTI) failed to distinguish simple T2h from complex T2h with HIE. In conclusion, superior to DTI-metrics, WM-DKI metrics showed more specificity for WM microstructural changes to distinguish simple T2h from complex T2h with HIE.

Long-chain saturated and monounsaturated fatty acids associate with development of premature infants up to 18 months of age

Myelination is important perinatally and highly dependent on long-chain saturated and monounsaturated fatty acids. Long-chain polyunsaturated fatty acids, nowadays often supplemented, inhibit oleic acid synthesis. Using data from a premature cohort, we studied if nervonic, lignoceric and oleic acids correlated to growth and early development up to 18 months corrected age. Small for gestational age infants had lower concentrations than infants appropriate for gestational age. Only oleic acid was negatively correlated to long-chain polyunsaturated fatty acids. Oleic and lignoceric acids correlated to social interaction at one month, and nervonic acid to mental, psychomotor and behavioral development at 6, 10 and 18 months, also when adjusted for several confounders. Negative association between oleic acid and long-chain polyunsaturated fatty acids suggests inhibition of delta-9 desaturase, and nervonic acid´s divergent correlation to lignoceric and oleic acids suggests different metabolism in neonatal period. Our results may have implications for the supplementation of premature infants.

Brain injury in the international multicenter randomized SafeBoosC phase II feasibility trial: cranial ultrasound and magnetic resonance imaging assessments

BACKGROUND

Abnormal cerebral perfusion during the first days of life in preterm infants is associated with higher grades of intraventricular hemorrhages and lower developmental score. In SafeBoosC II, we obtained a significant reduction of cerebral hypoxia by monitoring cerebral oxygenation in combination with a treatment guideline. Here, we describe (i) difference in brain injury between groups, (ii) feasibility of serial cranial ultrasound (cUS) and magnetic resonance imaging (MRI), (iii) local and central cUS assessment.

METHODS

Hundred and sixty-six extremely preterm infants were included. cUS was scheduled for day 1, 4, 7, 14, and 35 and at term-equivalent age (TEA). cUS was assessed locally (unblinded) and centrally (blinded). MRI at TEA was assessed centrally (blinded). Brain injury classification: no, mild/moderate, or severe.

RESULTS

Severe brain injury did not differ significantly between groups: cUS (experimental 10/80, control 18/77, P = 0.32) and MRI (5/46 vs. 3/38, P = 0.72). Kappa values for local and central readers were moderate-to-good for severe and poor-to-moderate for mild/moderate injuries. At TEA, cUS and MRI were assessed in 72 and 64%, respectively.

CONCLUSION

There was no difference in severe brain injury between groups. Acquiring cUS and MRI according the standard operating procedures must be improved for future trials. Whether monitoring cerebral oxygenation during the first 72 h of life prevents brain injury should be evaluated in larger multicenter trials.

Perinatal MRI diffusivity is related to early assessment of motor performance in preterm neonates

Preterm neonates represent a high-risk population for abnormal neuropsychological development. But presently, an accurate method for identifying those at risk is not available. This study evaluated the association between the microstructural organization measured with Diffusion Tensor Imaging (DTI) in term-corrected preterm neonates and subsequent motor performance. Fractional anisotropy (FA), axial diffusion (AD), mean diffusivity (MD) and radial diffusivity (RD) were determined in two regions of interest (ROIs) corresponding to the posterior limb of the internal capsule (PLIC) and cortico-spinal tract (CST). The Griffiths Mental Developmental Scales (GMDS) were longitudinally administered at 3, 6 and 15 months; and correlations between the metrics of diffusivity and the motor subscale of the GMDS were assessed using the Spearman correlation. A statistically significant negative correlation was observed between the AD of PLIC of the left hemisphere and the 3-month GMDS Locomotor Subscale. These results suggested that AD is a valid indicator of the stage of maturation of the motor pathway in preterm neonates, but not of later motor outcome.

Brain network characterization of high-risk preterm-born school-age children

Higher risk for long-term cognitive and behavioral impairments is one of the hallmarks of extreme prematurity (EP) and pregnancy-associated fetal adverse conditions such as intrauterine growth restriction (IUGR). While neurodevelopmental delay and abnormal brain function occur in the absence of overt brain lesions, these conditions have been recently associated with changes in microstructural brain development. Recent imaging studies indicate changes in brain connectivity, in particular involving the white matter fibers belonging to the cortico-basal ganglia-thalamic loop. Furthermore, EP and IUGR have been related to altered brain network architecture in childhood, with reduced network global capacity, global efficiency and average nodal strength. In this study, we used a connectome analysis to characterize the structural brain networks of these children, with a special focus on their topological organization. On one hand, we confirm the reduced averaged network node degree and strength due to EP and IUGR. On the other, the decomposition of the brain networks in an optimal set of clusters remained substantially different among groups, talking in favor of a different network community structure. However, and despite the different community structure, the brain networks of these high-risk school-age children maintained the typical small-world, rich-club and modularity characteristics in all cases. Thus, our results suggest that brain reorganizes after EP and IUGR, prioritizing a tight modular structure, to maintain the small-world, rich-club and modularity characteristics. By themselves, both extreme prematurity and IUGR bear a similar risk for neurocognitive and behavioral impairment, and the here defined modular network alterations confirm similar structural changes both by IUGR and EP at school age compared to control. Interestingly, the combination of both conditions (IUGR + EP) does not result in a worse outcome. In such cases, the alteration in network topology appears mainly driven by the effect of extreme prematurity, suggesting that these brain network alterations present at school age have their origin in a common critical period, both for intrauterine and extrauterine adverse conditions.

Imaging the "At-Risk" Brain: Future Directions

OBJECTIVES

Clinical neuroscience is increasingly turning to imaging the human brain for answers to a range of questions and challenges. To date, the majority of studies have focused on the neural basis of current psychiatric symptoms, which can facilitate the identification of neurobiological markers for diagnosis. However, the increasing availability and feasibility of using imaging modalities, such as diffusion imaging and resting-state fMRI, enable longitudinal mapping of brain development. This shift in the field is opening the possibility of identifying predictive markers of risk or prognosis, and also represents a critical missing element for efforts to promote personalized or individualized medicine in psychiatry (i.e., stratified psychiatry).

METHODS

The present work provides a selective review of potentially high-yield populations for longitudinal examination with MRI, based upon our understanding of risk from epidemiologic studies and initial MRI findings.

RESULTS

Our discussion is organized into three topic areas: (1) practical considerations for establishing temporal precedence in psychiatric research; (2) readiness of the field for conducting longitudinal MRI, particularly for neurodevelopmental questions; and (3) illustrations of high-yield populations and time windows for examination that can be used to rapidly generate meaningful and useful data. Particular emphasis is placed on the implementation of time-appropriate, developmentally informed longitudinal designs, capable of facilitating the identification of biomarkers predictive of risk and prognosis.

CONCLUSIONS

Strategic longitudinal examination of the brain at-risk has the potential to bring the concepts of early intervention and prevention to psychiatry.

Altered resting-state whole-brain functional networks of neonates with intrauterine growth restriction

The feasibility to use functional MRI (fMRI) during natural sleep to assess low-frequency basal brain activity fluctuations in human neonates has been demonstrated, although its potential to characterise pathologies of prenatal origin has not yet been exploited. In the present study, we used intrauterine growth restriction (IUGR) as a model of altered neurodevelopment due to prenatal condition to show the suitability of brain networks to characterise functional brain organisation at neonatal age. Particularly, we analysed resting-state fMRI signal of 20 neonates with IUGR and 13 controls, obtaining whole-brain functional networks based on correlations of blood oxygen level-dependent (BOLD) signal in 90 grey matter regions of an anatomical atlas (AAL). Characterisation of the networks obtained with graph theoretical features showed increased network infrastructure and raw efficiencies but reduced efficiency after normalisation, demonstrating hyper-connected but sub-optimally organised IUGR functional brain networks. Significant association of network features with neurobehavioral scores was also found. Further assessment of spatiotemporal dynamics displayed alterations into features associated to frontal, cingulate and lingual cortices. These findings show the capacity of functional brain networks to characterise brain reorganisation from an early age, and their potential to develop biomarkers of altered neurodevelopment.

Normal development

Numerous events are involved in brain development, some of which are detected by neuroimaging. Major changes in brain morphology are depicted by brain imaging during the fetal period while changes in brain composition can be demonstrated in both pre- and postnatal periods. Although ultrasonography and computed tomography can show changes in brain morphology, these techniques are insensitive to myelination that is one of the most important events occurring during brain maturation. Magnetic resonance imaging (MRI) is therefore the method of choice to evaluate brain maturation. MRI also gives insight into the microstructure of brain tissue through diffusion-weighted imaging and diffusion tensor imaging. Metabolic changes are also part of brain maturation and are assessed by proton magnetic resonance spectroscopy. Understanding and knowledge of the different steps in brain development are required to be able to detect morphologic and structural changes on neuroimaging. Consequently alterations in normal development can be depicted.

Bäuml J, Meng C, M. Wohlschläger A, Sorg C, Busch B, Baumann N, Wolke D, Bartmann P, Hattingen E, Boecker H. White matter alterations of the corticospinal tract in adults born very preterm and/or with very low birth weight

White matter (WM) injury, either visible on conventional magnetic resonance images (MRI) or measurable by diffusion tensor imaging (DTI), is frequent in preterm born individuals and often affects the corticospinal tract (CST). The relation between visible and invisible white mater alterations in the reconstructed CST of preterm subjects has so far been studied in infants, children and up to adolescence. Therefore, we probabilistically tracked the CST in 53 term-born and 56 very preterm and/or low birth weight (VP/VLBW, < 32 weeks of gestation and/or birth weight < 1,500 g) adults (mean age 26 years) and compared their DTI parameters (axial, radial, mean diffusivity--AD, RD, MD, fractional anisotropy--FA) in the whole CST and slice-wise along the CST. Additionally, we used the automatic, tract-based-spatial-statistics (TBSS) as an alternative to tractography. We compared control and VP/VLBW and subgroups with and without CST WM lesions visible on conventional MRI. Compared to controls, VP/VLBW subjects had significantly higher diffusivity (AD, RD, MD) in the whole CST, slice-wise along the CST, and in multiple regions along the TBSS skeleton. VP/VLBW subjects also had significantly lower (TBSS) and higher (tractography) FA in regions along the CST, but no different mean FA in the tracked CST as a whole. Diffusion changes were weaker, but remained significant for both, tractography and TBSS, when excluding subjects with visible CST lesions. Chronic CST injury persists in VP/VLBW adults even in the absence of visible WM lesions, indicating long-term structural WM changes induced by premature birth.

Limited microstructural and connectivity deficits despite subcortical volume reductions in school-aged children born preterm with very low birth weight

Preterm birth and very low birth weight (VLBW, ≤1500 g) are worldwide problems that burden survivors with lifelong cognitive, psychological, and physical challenges. In this multimodal structural magnetic resonance imaging (MRI) and diffusion MRI (dMRI) study, we investigated differences in subcortical brain volumes and white matter tract properties in children born preterm with VLBW compared to term-born controls (mean age=8 years). Subcortical brain structure volumes and cortical thickness estimates were obtained, and fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) were generated for 18 white matter tracts. We also assessed structural relationships between white matter tracts and cortical thickness of the tract endpoints. Compared to controls, the VLBW group had reduced volumes of thalamus, globus pallidus, corpus callosum, cerebral white matter, ventral diencephalon, and brain stem, while the ventricular system was larger in VLBW subjects, after controlling for age, sex, IQ, and estimated total intracranial volume. For the dMRI parameters, group differences were not significant at the whole-tract level, though pointwise analysis found shorter segments affected in forceps minor and left superior longitudinal fasciculus - temporal bundle. IQ did not correlate with subcortical volumes or dMRI measures in the VLBW group. While the deviations in subcortical volumes were substantial, there were few differences in dMRI measures between the two groups, which may reflect the influence of advances in perinatal care on white matter development.

Impaired oligodendrocyte maturation in preterm infants: Potential therapeutic targets

Preterm birth is an evolving challenge in neonatal health care. Despite declining mortality rates among extremely premature neonates, morbidity rates remain very high. Currently, perinatal diffuse white matter injury (WMI) is the most commonly observed type of brain injury in preterm infants and has become an important research area. Diffuse WMI is associated with impaired cognitive, sensory and psychological functioning and is increasingly being recognized as a risk factor for autism-spectrum disorders, ADHD, and other psychological disturbances. No treatment options are currently available for diffuse WMI and the underlying pathophysiological mechanisms are far from being completely understood. Preterm birth is associated with maternal inflammation, perinatal infections and disrupted oxygen supply which can affect the cerebral microenvironment by causing activation of microglia, astrogliosis, excitotoxicity, and oxidative stress. This intricate interplay of events negatively influences oligodendrocyte development, causing arrested oligodendrocyte maturation or oligodendrocyte cell death, which ultimately results in myelination failure in the developing white matter. This review discusses the current state in perinatal WMI research, ranging from a clinical perspective to basic molecular pathophysiology. The complex regulation of oligodendrocyte development in healthy and pathological conditions is described, with a specific focus on signaling cascades that may play a role in WMI. Furthermore, emerging concepts in the field of WMI and issues regarding currently available animal models are put forward. Novel insights into the molecular mechanisms underlying impeded oligodendrocyte maturation in diffuse WMI may aid the development of novel treatment options which are desperately needed to improve the quality-of-life of preterm neonates.

Comparison of cortical folding measures for evaluation of developing human brain

We evaluated 22 measures of cortical folding, 20 derived from local curvature (curvature-based measures) and two based on other features (sulcal depth and gyrification index), for their capacity to distinguish between normal and aberrant cortical development. Cortical surfaces were reconstructed from 12 term-born control and 63 prematurely-born infants. Preterm infants underwent 2-4 MR imaging sessions between 27 and 42weeks postmenstrual age (PMA). Term infants underwent a single MR imaging session during the first postnatal week. Preterm infants were divided into two groups. One group (38 infants) had no/minimal abnormalities on qualitative assessment of conventional MR images. The second group (25 infants) consisted of infants with injury on conventional MRI at term equivalent PMA. For both preterm infant groups, all folding measures increased or decreased monotonically with increasing PMA, but only sulcal depth and gyrification index differentiated preterm infants with brain injury from those without. We also compared scans obtained at term equivalent PMA (36-42weeks) for all three groups. No curvature-based measured distinguished between the groups, whereas sulcal depth distinguished term control from injured preterm infants and gyrification index distinguished all three groups. When incorporating total cerebral volume into the statistical model, sulcal depth no longer distinguished between the groups, though gyrification index distinguished between all three groups and positive shape index distinguished between the term control and uninjured preterm groups. We also analyzed folding measures averaged over brain lobes separately. These results demonstrated similar patterns to those obtained from the whole brain analyses. Overall, though the curvature-based measures changed during this period of rapid cerebral development, they were not sensitive for detecting the differences in folding associated with brain injury and/or preterm birth. In contrast, gyrification index was effective in differentiating these groups.

[Formula: see text]Gestational age and gender influence on executive control and its related neural structures in preterm-born children at 6 years of age

Within preterm-born children, being born male and at a lower gestational age (GA) have both been associated with a heightened risk for developmental difficulties. However, in this population little is known about the combined effect and the influence of these risk factors on cortical structures and executive control. In the present study, 58 preterm-born children (GA ranging from 24.0 to 35.1 weeks) were administered the computerized Child Attention Network Task at 6 years of age. Brain magnetic resonance imaging was performed and analyzed using Voxel-Based Morphometry (VBM) in all children. At a behavioral level, boys born <28 weeks of GA had significantly less executive control than preterm-born girls <28 weeks (p = .001) and preterm-born boys ≥28 (p = .003). The reduced executive control in preterm-born boys <28 weeks gestation was related to lower cortical densities in the inferior frontal gyrus (IFG) and dorsolateral prefrontal cortex (DLPFC). The current study links the higher incidence of reduced executive control in preterm-born boys to a higher degree of prematurity (low GA) and identifies brain structural abnormalities in the prefrontal cortex related to these deficits. The implications of these results are discussed.

Controversies in preterm brain injury

In this review, we highlight critical unresolved questions in the etiology and mechanisms causing preterm brain injury. Involvement of neurons, glia, endogenous factors and exogenous exposures is considered. The structural and functional correlates of interrupted development and injury in the premature brain are under active investigation, with the hope that the cellular and molecular mechanisms underlying developmental abnormalities in the human preterm brain can be understood, prevented or repaired.

Hypoxia diminishes the protective function of white-matter astrocytes in the developing brain

OBJECTIVES

White-matter injury after surgery is common in neonates with cerebral immaturity secondary to in utero hypoxia. Astrocytes play a central role in brain protection; however, the reaction of astrocytes to hypothermic circulatory arrest (HCA) remains unknown. We investigated the role of astrocytes in white-matter injury after HCA and determined the effects of preoperative hypoxia on this role, using a novel mouse model.

METHODS

Mice were exposed to hypoxia from days 3 to 11, which is equivalent to the third trimester in humans (prehypoxia, n = 49). Brain slices were transferred to a chamber perfused by cerebrospinal fluid. Oxygen-glucose deprivation (OGD) was performed to simulate ischemia-reperfusion/reoxygenation resulting from circulatory arrest under hypothermia. Astrocyte reactions were compared with preoperative normoxia (prenormoxia; n = 45).

RESULTS

We observed astrocyte activation after 25°C ischemia-reperfusion/reoxygenation in prenormoxia (P < .01). Astrocyte number after OGD correlated with caspase-3(+) cells (rho = .77, P = .001), confirming that astrogliosis is an important response after HCA. At 3 hours after OGD, astrocytes in prenormoxia had already proliferated and become activated (P < .05). Conversely, astrocytes that developed under hypoxia did not display these responses. At 20 hours after ischemia-reperfusion/reoxygenation, astrogliosis was not observed in prehypoxia, demonstrating that hypoxia altered the response of astrocytes to insult. In contrast to prenormoxia, caspase-3(+) cells in prehypoxia increased after ischemia reperfusion/reoxygenation, compared with control (P < .01). Caspase-3(+) cells were more common with prehypoxia than with prenormoxia (P < .001), suggesting that lack of astrogliosis permits increased white-matter injury.

CONCLUSIONS

Preoperative hypoxia alters the neuroprotective function of astrocytes. Restoring this function before surgery may be a therapeutic option to reduce postoperative white-matter injury in the immature brain.

Machine-learning to characterise neonatal functional connectivity in the preterm brain

Brain development is adversely affected by preterm birth. Magnetic resonance image analysis has revealed a complex fusion of structural alterations across all tissue compartments that are apparent by term-equivalent age, persistent into adolescence and adulthood, and associated with wide-ranging neurodevelopment disorders. Although functional MRI has revealed the relatively advanced organisational state of the neonatal brain, the full extent and nature of functional disruptions following preterm birth remain unclear.

In this study, we apply machine-learning methods to compare whole-brain functional connectivity in preterm infants at term-equivalent age and healthy term-born neonates in order to test the hypothesis that preterm birth results in specific alterations to functional connectivity by term-equivalent age.

Functional connectivity networks were estimated in 105 preterm infants and 26 term controls using group-independent component analysis and a graphical lasso model. A random forest–based feature selection method was used to identify discriminative edges within each network and a nonlinear support vector machine was used to classify subjects based on functional connectivity alone.

We achieved 80% cross-validated classification accuracy informed by a small set of discriminative edges. These edges connected a number of functional nodes in subcortical and cortical grey matter, and most were stronger in term neonates compared to those born preterm. Half of the discriminative edges connected one or more nodes within the basal ganglia.

These results demonstrate that functional connectivity in the preterm brain is significantly altered by term-equivalent age, confirming previous reports of altered connectivity between subcortical structures and higher-level association cortex following preterm birth.

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Robust classification of preterm and term-born neonates using functional connectivity patterns.

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Discriminative pattern of alterations in basal ganglia and frontal connections.

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Reflects system-wide disruption of subcortical–cortical connections following preterm birth.

Disconnected neuromagnetic networks in children born very preterm: Disconnected MEG networks in preterm children

Many children born very preterm (≤32 weeks) experience significant cognitive difficulties, but the biological basis of such problems has not yet been determined. Functional MRI studies have implicated altered functional connectivity; however, little is known regarding the spatiotemporal organization of brain networks in this population. We provide the first examination of resting-state neuromagnetic connectivity mapped in brain space in school age children born very preterm. Thirty-four subjects (age range 7–12 years old), consisting of 17 very preterm-born children and 17 full-term born children were included. Very preterm-born children exhibited global decreases in inter-regional synchrony in all analysed frequency ranges, from theta (4–7 Hz) to high gamma (80–150 Hz; p < 0.01, corrected). These reductions were expressed in spatially and frequency specific brain networks (p < 0.0005, corrected). Our results demonstrate that mapping connectivity with high spatiotemporal resolution offers new insights into altered organization of neurophysiological networks which may contribute to the cognitive difficulties in this vulnerable population.

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We recorded resting-state magnetoencephalography in school-age children born very preterm and healthy children.

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We examine functional connectivity across a wide frequency spectrum in brain space.

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Global reductions in neural synchrony were detected in children born very preterm.

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These reductions encompass networks related to executive function and overall cognitive flexibility.

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These effects may be relevant to cognitive and behavioural difficulties reported in the ex-preterm population.

Preterm Birth and Poor Fetal Growth as Risk Factors of Attention-Deficit/ Hyperactivity Disorder

BACKGROUND

Previous studies have shown an association between prematurity and attention- abstract deficit/hyperactivity disorder (ADHD). Results concerning late preterm infants are controversial, and studies examining fetal growth represented by weight for gestational age are scarce. Our objective was to examine the association between gestational age by each week of fetal maturity, weight for gestational age, and ADHD.

METHODS

In this population-based study, 10 321 patients with ADHD, diagnosed according to the International Classification of Diseases and 38 355 controls individually matched for gender, date and place of birth, were identified from Finnish nationwide registers. Perinatal data were obtained from the Finnish Medical Birth Register. Conditional logistic regression was used to examine the association between gestational age, weight for gestational age, and ADHD after controlling for confounding factors.

RESULTS

The risk of ADHD increased by each declining week of gestation. The associations were robust after adjusting for confounders. An elevated risk also was seen among late preterm and early term infants. As for fetal growth, the odds ratio showed a U-shaped curve with an increased risk seen when the weight for gestational age was 1 SD below and 2 SD above the mean.

CONCLUSIONS

Our findings suggest that each gestational week has significance for child's subsequent neurodevelopment and risk for ADHD. We also showed that poor fetal growth increased the risk of ADHD. This highlights the importance of taking into account both prematurity and poor fetal growth when planning the timing of birth as well as later follow-up and support policies.

White matter abnormalities and impaired attention abilities in children born very preterm

While attention impairments are commonly observed in very preterm (<32weeks' gestational age) children, neuroanatomical correlates of these difficulties are unclear. We aimed to determine whether the microstructural organization of key white matter tracts thought to be involved in attention (cingulum bundle, superior longitudinal fasciculi, reticular activating system, and corpus callosum) were altered in very preterm children compared with term-born controls. We also aimed to determine whether alterations in microstructural organization of these tracts were associated with attention functioning in very preterm children. One hundred and forty-nine very preterm children and 36 term-born controls underwent neuroimaging and assessment of their attention abilities at 7years. Constrained spherical deconvolution and probabilistic tractography was used to identify the key white matter tracts. Altered microstructural organization and reduced tract volume within reticular activating system and corpus callosum were found in the very preterm group compared with the control group. Diffusion and volume changes in the cingulum bundle, superior longitudinal fasciculi, reticular activating system, and corpus callosum were related to variations in attention functioning in the very preterm children. These findings emphasize that white matter tract integrity is associated with later attentional abilities in very preterm children.

Prolonged White Matter Inflammation After Cardiopulmonary Bypass and Circulatory Arrest in a Juvenile Porcine Model

BACKGROUND

White matter (WM) injury is common after neonatal cardiopulmonary bypass (CPB). We have demonstrated that the inflammatory response to CPB is an important mechanism of WM injury. Microglia are brain-specific immune cells that respond to inflammation and can exacerbate injury. We hypothesized that microglia activation contributes to WM injury caused by CPB.

METHODS

Juvenile piglets were randomly assigned to 1 of 3 CPB-induced brain insults (1, no-CPB; 2, full-flow CPB; 3, CPB and circulatory arrest). Neurobehavioral tests were performed. Animals were sacrificed 3 days or 4 weeks postoperatively. Microglia and proliferating cells were immunohistologically identified. Seven analyzed WM regions were further categorized into 3 fiber connections (1, commissural; 2, projection; 3, association fibers).

RESULTS

Microglia numbers significantly increased on day 3 after CPB and circulatory arrest, but not after full-flow CPB. Fiber categories did not affect these changes. On post-CPB week 4, proliferating cell number, blood leukocyte number, interleukin (IL)-6 levels, and neurologic scores had normalized. However, both full-flow CPB and CPB and circulatory arrest displayed significant increases in the microglia number compared with control. Thus brain-specific inflammation after CPB persists despite no changes in systemic biomarkers. Microglia number was significantly different among fiber categories, being highest in association and lowest in commissural connections. Thus there was a WM fiber-dependent microglia reaction to CPB.

CONCLUSIONS

This study demonstrates prolonged microglia activation in WM after CPB. This brain-specific inflammatory response is systemically silent. It is connection fiber-dependent which may impact specific connectivity deficits observed after CPB. Controlling microglia activation after CPB is a potential therapeutic intervention to limit neurologic deficits after CPB.

Serial cranial ultrasonography or early MRI for detecting preterm brain injury?

OBJECTIVE

To investigate detection ability and feasibility of serial cranial ultrasonography (CUS) and early MRI in preterm brain injury.

DESIGN

Prospective cohort study.

SETTING

Level III neonatal intensive care unit.

PATIENTS

307 infants, born below 29 weeks of gestation.

METHODS

Serial CUS and MRI were performed according to standard clinical protocol. In case of instability, MRI was postponed or cancelled. Brain images were assessed by independent experts and compared between modalities.

MAIN OUTCOME MEASURES

Presence of preterm brain injury on either CUS or MRI and discrepant imaging findings on CUS and MRI.

RESULTS

Serial CUS was performed in all infants; early MRI was often postponed (n=59) or cancelled (n=126). Injury was found in 146 infants (47.6%). Clinical characteristics differed significantly between groups that were subdivided according to timing of MRI. 61 discrepant imaging findings were found. MRI was superior in identifying cerebellar haemorrhage; CUS in detection of acute intraventricular haemorrhage, perforator stroke and cerebral sinovenous thrombosis.

CONCLUSIONS

Advanced serial CUS seems highly effective in diagnosing preterm brain injury, but may miss cerebellar abnormalities. Although MRI does identify these lesions, feasibility is limited. Improved safety, better availability and tailored procedures are essential for MRI to increase its value in clinical care.

Predicting developmental outcomes in premature infants by term equivalent MRI: systematic review and meta-analysis

BACKGROUND

This study aims to determine the prognostic accuracy of term MRI in very preterm born (≤32 weeks) or low-birth-weight (≤1500 g) infants for long-term (>18 months) developmental outcomes.

METHODS

We performed a systematic review searching Central, Medline, Embase, and PsycInfo. Two independent reviewers performed study selection, data extraction, and quality assessment. We documented sensitivity and specificity for three different MRI findings (white matter abnormalities (WMA), brain abnormality (BA), and diffuse excessive high signal intensity (DEHSI)), related to developmental outcomes including cerebral palsy (CP), visual and/or hearing problems, motor, neurocognitive, and behavioral function. Using bivariate meta-analysis, we estimated pooled sensitivity and specificity and plotted summary receiver operating characteristic (sROC) curves for different cut-offs of MRI.

RESULTS

We included 20 papers published between 2000 and 2013. Quality of included studies varied. Pooled sensitivity and specificity values (95 % confidence interval (CI)) for prediction of CP combining the three different MRI findings (using normal/mild vs. moderate/severe cut-off) were 77 % (53 to 91 %) and 79 % (51 to 93 %), respectively. For prediction of motor function, the values were 72 % (52 to 86 %) and 62 % (29 to 87 %), respectively. Prognostic accuracy for visual and/or hearing problems, neurocognitive, and/or behavioral function was poor. sROC curves of the individual MRI findings showed that presence of WMA provided the best prognostic accuracy whereas DEHSI did not show any potential prognostic accuracy.

CONCLUSIONS

This study shows that presence of moderate/severe WMA on MRI around term equivalent age can predict CP and motor function in very preterm or low-birth-weight infants with moderate sensitivity and specificity. Its ability to predict other long-term outcomes such as neurocognitive and behavioral impairments is limited. Also, other white matter related tests as BA and DEHSI demonstrated limited prognostic value.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42013006362.

Advanced magnetic resonance spectroscopy and imaging techniques applied to brain development and animal models of perinatal injury

Magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) are widely used in the field of brain development and perinatal brain injury. Due to technical progress the magnetic field strength (B0) of MR systems has continuously increased, favoring (1)H-MRS with quantification of up to 18 metabolites in the brain and short echo time (TE) MRI sequences including phase and susceptibility imaging. For longer TE techniques including diffusion imaging modalities, the benefits of higher B0 have not been clearly established. Nevertheless, progress has also been made in new advanced diffusion models that have been developed to enhance the accuracy and specificity of the derived diffusion parameters. In this review, we will describe the latest developments in MRS and MRI techniques, including high-field (1)H-MRS, phase and susceptibility imaging, and diffusion imaging, and discuss their application in the study of cerebral development and perinatal brain injury.

Use of resting-state functional MRI to study brain development and injury in neonates

Advances in methodology have led to expanded application of resting-state functional MRI (rs-fMRI) to the study of term and prematurely born infants during the first years of life, providing fresh insight into the earliest forms of functional cerebral development. In this review, we detail our evolving understanding of the use of rs-fMRI for studying neonates. We initially focus on the biological processes of cortical development related to resting-state network development. We then review technical issues principally affecting neonatal investigations, including the effects of subject motion during acquisition and image distortions related to magnetic susceptibility effects. We next summarize the literature in which rs-fMRI is used to study normal brain development during the early postnatal period, the effects of prematurity, and the effects of cerebral injury. Finally, we review potential future directions for the field, such as the use of complementary imaging modalities and advanced analysis techniques.

Longitudinal measurement of the developing grey matter in preterm subjects using multi-modal MRI

Preterm birth is a major public health concern, with the severity and occurrence of adverse outcome increasing with earlier delivery. Being born preterm disrupts a time of rapid brain development: in addition to volumetric growth, the cortex folds, myelination is occurring and there are changes on the cellular level. These neurological events have been imaged non-invasively using diffusion-weighted (DW) MRI. In this population, there has been a focus on examining diffusion in the white matter, but the grey matter is also critically important for neurological health. We acquired multi-shell high-resolution diffusion data on 12 infants born at ≤ 28 weeks of gestational age at two time-points: once when stable after birth, and again at term-equivalent age. We used the Neurite Orientation Dispersion and Density Imaging model (NODDI) (Zhang et al., 2012) to analyse the changes in the cerebral cortex and the thalamus, both grey matter regions. We showed region-dependent changes in NODDI parameters over the preterm period, highlighting underlying changes specific to the microstructure. This work is the first time that NODDI parameters have been evaluated in both the cortical and the thalamic grey matter as a function of age in preterm infants, offering a unique insight into neuro-development in this at-risk population.

Recent advancements in diffusion MRI for investigating cortical development after preterm birth-potential and pitfalls

Preterm infants are born during a critical period of brain maturation, in which even subtle events can result in substantial behavioral, motor and cognitive deficits, as well as psychiatric diseases. Recent evidence shows that the main source for these devastating disabilities is not necessarily white matter (WM) damage but could also be disruptions of cortical microstructure. Animal studies showed how moderate hypoxic-ischemic conditions did not result in significant neuronal loss in the developing brain, but did cause significantly impaired dendritic growth and synapse formation alongside a disturbed development of neuronal connectivity as measured using diffusion magnetic resonance imaging (dMRI). When using more advanced acquisition settings such as high-angular resolution diffusion imaging (HARDI), more advanced reconstruction methods can be applied to investigate the cortical microstructure with higher levels of detail. Recent advances in dMRI acquisition and analysis have great potential to contribute to a better understanding of neuronal connectivity impairment in preterm birth. We will review the current understanding of abnormal preterm cortical development, novel approaches in dMRI, and the pitfalls in scanning vulnerable preterm infants.

Visual-motor deficits relate to altered gray and white matter in young adults born preterm with very low birth weight

Individuals born preterm and at very low birth weight (birth weight ≤ 1500 g) are at an increased risk of perinatal brain injury and neurodevelopmental deficits over the long term. This study examined whether this clinical group has more problems with visual-motor integration, motor coordination, and visual perception compared to term-born controls, and related these findings to cortical surface area and thickness and white matter fractional anisotropy. Forty-seven preterm-born very low birth weight individuals and 56 term-born controls were examined at 18-22 years of age with a combined cognitive, morphometric MRI, and diffusion tensor imaging evaluation in Trondheim, Norway. Visual-motor skills were evaluated with the Beery-Buktenica Developmental Test of Visual-Motor Integration-V (VMI) copying test and its supplemental tests of motor coordination and visual perception. 3D T1-weighted MPRAGE images and diffusion tensor imaging were done at 1.5 T. Cortical reconstruction generated in FreeSurfer and voxelwise maps of fractional anisotropy calculated with Tract-Based Spatial Statistics were used to explore the relationship between MRI findings and cognitive results. Very low birth weight individuals had significantly lower scores on the copying and motor coordination tests compared with controls. In the very low birth weight group, VMI scores showed significant positive relationships with cortical surface area in widespread regions, with reductions of the superior temporal gyrus, insula, and medial occipital lobe in conjunction with the posterior ventral temporal lobe. Visual perception scores also showed positive relationships with cortical thickness in the very low birth weight group, primarily in the lateral occipito-temporo-parietal junction, the superior temporal gyrus, insula, and superior parietal regions. In the very low birth weight group, visual-motor performance correlated positively with fractional anisotropy especially in the corpus callosum, inferior fronto-occipital fasciculus bilaterally, and anterior thalamic radiation bilaterally, driven primarily by an increase in radial diffusivity. VMI scores did not demonstrate a significant relationship to cortical surface area, cortical thickness, or diffusion measures in the control group. Our results indicate that visual-motor integration problems persist into adulthood for very low birth weight individuals, which may be due to structural alterations in several specific gray-white matter networks. Visual-motor deficits appear related to reduced surface area of motor and visual cortices and disturbed connectivity in long association tracts containing visual and motor information. We conjecture that these outcomes may be due to perinatal brain injury or aberrant cortical development secondary to injury or due to very preterm birth.