Adaptive mechanisms of developing brain. The neuroradiologic assessment of the preterm infant

European recommendations on practices in pediatric neuroradiology: consensus document from the European Society of Neuroradiology (ESNR), European Society of Paediatric Radiology (ESPR) and European Union of Medical Specialists Division of Neuroradiology (UEMS)

Pediatric neuroradiology is a subspecialty within radiology, with possible pathways to train within the discipline from neuroradiology or pediatric radiology. Formalized pediatric neuroradiology training programs are not available in most European countries. We aimed to construct a European consensus document providing recommendations for the safe practice of pediatric neuroradiology. We particularly emphasize imaging techniques that should be available, optimal site conditions and facilities, recommended team requirements and specific indications and protocol modifications for each imaging modality employed for pediatric neuroradiology studies. The present document serves as guidance to the optimal setup and organization for carrying out pediatric neuroradiology diagnostic and interventional procedures. Clinical activities should always be carried out in full agreement with national provisions and regulations. Continued education of all parties involved is a requisite for preserving pediatric neuroradiology practice at a high level.

Ultrasound imaging of preterm brain injury: fundamentals and updates

Neurosonography has become an essential tool for diagnosis and serial monitoring of preterm brain injury. Preterm infants are at significantly higher risk of hypoxic-ischemic injury, intraventricular hemorrhage, periventricular leukomalacia and post-hemorrhagic hydrocephalus. Neonatologists have become increasingly dependent on neurosonography to initiate medical and surgical interventions because it can be used at the bedside. While brain MRI is regarded as the gold standard for detecting preterm brain injury, neurosonography offers distinct advantages such as its cost-effectiveness, diagnostic utility and convenience. Neurosonographic signatures associated with poor long-term outcomes shape decisions regarding supportive care, medical or behavioral interventions, and family members' expectations. Within the last decade substantial progress has been made in neurosonography techniques, prompting an updated review of the topic. In addition to the up-to-date summary of neurosonography, this review discusses the potential roles of emerging neurosonography techniques that offer new functional insights into the brain, such as superb microvessel imaging, elastography, three-dimensional ventricular volume assessment, and contrast-enhanced US.

Routine Neuroimaging of the Preterm Brain

Neuroimaging of the preterm infant is a common assessment performed in the NICU. Timely and focused studies can be used for diagnostic, therapeutic, and prognostic information. However, significant variability exists among neonatal units as to which modalities are used and when imaging studies are obtained. Appropriate timing and selection of neuroimaging studies can help identify neonates with brain injury who may require therapeutic intervention or who may be at risk for neurodevelopmental impairment. This clinical report reviews the different modalities of imaging broadly available to the clinician. Evidence-based indications for each modality, optimal timing of examinations, and prognostic value are discussed.

Preterm neuroimaging and neurodevelopmental outcome: a focus on intraventricular hemorrhage, post-hemorrhagic hydrocephalus, and associated brain injury

Intraventricular hemorrhage in the setting of prematurity remains the most common cause of acquired hydrocephalus. Neonates with progressive post-hemorrhagic hydrocephalus are at risk for adverse neurodevelopmental outcomes. The goal of this review is to describe the distinct and often overlapping types of brain injury in the preterm neonate, with a focus on neonatal hydrocephalus, and to connect injury on imaging to neurodevelopmental outcome risk. Head ultrasound and magnetic resonance imaging findings are described separately. The current state of the literature is imprecise and we end the review with recommendations for future radiologic and neurodevelopmental research.

Brain changes on magnetic resonance imaging in school-age children who had been preterm infants with intracranial hemorrhage

Objective

To determine whether preterm infants diagnosed with intracranial hemorrhage (by transfontanellar ultrasound) at birth have cerebral lesions that are detectable by magnetic resonance imaging (MRI) upon reaching school age.

Materials and Methods

MRI scans of the brain were obtained in 22 school-age children. Fifteen had presented intracranial hemorrhage at birth, and seven had not. We calculated the odds ratio (OR) for the occurrence of brain alterations detectable by MRI and the kappa index for discrepancies among the radiological reports.

Results

The children without previous intracranial hemorrhage presented normal MRI findings. Of the 15 children with previous intracranial hemorrhage, 6 (40%) presented brain alterations on MRI: isolated ventricular alteration (dilation and asymmetry), in 2 (13.3%); and ventricular asymmetry accompanied by parenchymal lesion, in 4 (26.7%). The nine remaining children with previous intracranial hemorrhage (60%) presented normal MRI findings. The children with previous intracranial hemorrhage were more likely to present ventricular alteration (OR = 7.8) and parenchymal lesions (OR = 5.4).

Conclusion

Ventricular and parenchymal brain alterations detected by MRI suggest isolated morphologic alterations that do not result in neurological impairment detectable on physical examination in school-age children.

Echogenicity changes in the fetal brain, a 6-year follow-up study

OBJECTIVE

To asses the relation between echogenicity changes in the fetal brain and neurodevelopmental outcome until 6 years of age.

METHODS

Fetuses (n = 124) from pregnancies affected by hypertensive disorders (n = 64) or preterm labor (n = 60) at risk for preterm birth (26-34 weeks gestation) were studied. Moderate echogenicity changes (periventricular grade IB, II; intraventricular grade II-III; local basal ganglia/thalami) in the fetal and neonatal brain were related to neurological outcome and Griffiths mental developmental scales quotients at 1, 2 and 6 years. Multiple regression analysis tested the influence of moderate echogenicity changes and perinatal clinical characteristics on composite outcome (death or abnormal neurodevelopment).

RESULTS

Moderate echogenicity changes were present in 37/124 (30%) fetuses. Median gestational age and weight at birth were respectively 31 weeks (range 26-43), 1314 g (range 550-4330), mortality was 19%, follow-up loss 10%. Composite outcome was abnormal in 47/124 (38%). Fetal and neonatal moderate intraventricular echodensities were related to cerebral palsy at 6 years (p < 0.04). In the multiple regression analysis only gestational age was related to composite outcome (p = 0.005).

CONCLUSIONS

Moderate intraventricular echodensities in the fetal brain related to cerebral palsy at 6 years of age. Gestational age at birth was the main predictor of abnormal composite outcome.

Oligodendrocyte regeneration after neonatal hypoxia requires FoxO1-mediated p27Kip1 expression

Diffuse white matter injury (DWMI) caused by hypoxia is associated with permanent neurodevelopmental disabilities in preterm infants. The cellular and molecular mechanisms producing DWMI are poorly defined. Using a mouse model of neonatal hypoxia, we demonstrate a biphasic effect on oligodendrocyte development, resulting in hypomyelination. Oligodendrocyte death and oligodendrocyte progenitor cell (OPC) proliferation during the week after hypoxia were followed by delayed oligodendrocyte differentiation and abnormal myelination, as demonstrated by electron microscopy. Cdk2 activation was essential for the regenerative OPC response after hypoxia and was accompanied by reduced FoxO1-dependent p27(Kip1) expression. p27(Kip1) was also reduced in OPCs in human infant white matter lesions after hypoxia. The negative effects of hypoxia on oligodendrogenesis and myelination were more pronounced in p27(Kip1)-null mice; conversely, overexpression of FoxO1 or p27(Kip1) in OPCs after hypoxia promoted oligodendrogenesis. Our studies demonstrate for the first time that neonatal hypoxia affects the Foxo1/p27(Kip1) pathway during white matter development. We also show that molecular manipulation of this pathway enhances oligodendrocyte regeneration during a critical developmental time window after DWMI. Thus, FoxO1 and p27(Kip1) may serve as promising target molecules for promoting timely oligodendrogenesis in neonatal DWMI.

Low Rate of Cerebral Injury in Monochorionic Twins With Selective Intrauterine Growth Restriction

This study was conducted to determine the incidence of cerebral injury as detected by postnatal brain scan in monochorionic twins with selective intrauterine growth restriction. Having excluded cases complicated with twin-to-twin transfusion syndrome and one co-twin suffering intrauterine fetal death, a total of 73 monochorionic twin pregnancies divided into absence (group I,n= 46) or presence (group II,n= 27) of selective intrauterine growth restriction. Mild cerebral injury was defined as presenting one of the following abnormal cranial scan findings: intraventricular hemorrhage grade I, grade II, lenticulostiate vasculopathy and/or subependymal pseudocysts, while severe cerebral injury was defined as presenting intraventricular hemorrhage grade III, grade IV, cystic periventricular leukomalacia (PVL) grade II or higher, porencephalic cysts, and/or ventricular dilatation. The incidence of mild cerebral injury was not significantly different between these two groups (eight cases in group I and six cases in group II). Except for one case that later developed a seizure, the majority (13 out of 14) of cases with minor brain scan anomalies were only transient, without significant clinical impact. There was only one case diagnosed with a major brain scan anomaly (periventricular leukomalacia) in group II. One severe brain injury and three neonatal deaths all belonged to group II with abnormal umbilical artery Doppler in the growth restricted twin. In conclusion, the incidence of severe cerebral injury in monochorionic twin pregnancies with selective intrauterine growth restriction was low, at 3.7%.

Comparative analysis of perinatal and postnatal factors, and general movement in extremely preterm infants

STUDY AIM

To describe general movement in extremely premature infants and examine correlations with risk factors for antenatal, perinatal, and postnatal morbidity.

STUDY TYPE

Prospective, single-center study. Nineteen patients were followed up.

METHODOLOGY

The infants' general movement was analyzed using video recordings. Qualitative and quantitative assessments were performed during the writhing movement (WM) period and fidgety movement (FM) period. The quality of the general movements (GMs) and the scores achieved were then correlated with antenatal, perinatal, and postnatal factors.

RESULTS

Infants' motor activity fluctuated during the WM period, especially in extremely premature infants where poor repertoire is often observed. No correlations were found between WMs and obstetric factors. Gestational age correlated with WMs' quality (p=0.023). WMs correlated with factors of postnatal morbidity such as chronic lung disease (CLD) (p=0.034) and nosocomial infections (p=0.05). At 3 months corrected age, the spontaneous movement quality are correlated with neurological explorations such as US brain (p=0.032), MRI (p=0.039), EEG (p=0.036), and neurological follow-up assessments (p=0.015).

CONCLUSION

Prudence must be used when performing the analysis of general movement in extremely preterm infants. WMs may be influenced by perinatal morbidity, and possibly by the severe brain immaturity of these infants. WMs correlate with CLD and nosocomial infections. Analysis of general movement in infants of 3 months corrected age is a valuable means to detect neurological disorders.

Predictability of cerebral palsy and its characteristics through neonatal cranial ultrasound in a high-risk NICU population

The aim of the study is to evaluate the predictive value of various types of brain injury detected by ultrasound in the neonatal period for the occurrence of cerebral palsy and its characteristics in a large cohort of high-risk infants. Thousand twenty-one consecutively NICU-admitted high-risk infants were assessed up to the corrected age of at least 2 years. Cerebral palsy (CP) was categorised into spastic or non-spastic, bilateral or unilateral and mild, moderate or severe CP. Different types of brain injury were identified by serial cranial ultrasound (US) during the NICU stay: white matter disease (WMD), haemorrhage, cerebral infarction, deep grey matter and parasagittal cerebral injury. There is a significant overall association between different types of brain injury and gestational age. Only 4% of the children with normal US develop CP. In the presence of any abnormal US image, the likeliness to develop CP is at least seven times higher. Within the group of infants with WMD and haemorrhage, the degree of brain involvement has a clear impact on the occurrence of CP. Concerning the characteristics of CP, deep grey matter lesion predict non-spastic CP versus spastic CP (OR = 31, P < 0.001). Cerebral infarction and haemorrhage grade IV are strong predictors of unilateral spastic CP versus bilateral spastic CP (OR = 49 and 24, respectively, P < 0.001). Deep grey matter lesion is a significant predictor for severe versus mild and moderate CP (OR = 6). In conclusion, neonatal cranial US is a useful tool in predicting CP and its characteristics.

The Impact of Periventricular Brain Injury on Reading and Spelling Abilities in the Late Elementary and Adolescent Years

The present study was designed: (1) to investigate the long-term consequences of both the presence and the severity of periventricular brain injury (PVBI) on intellectual, academic, and cognitive outcome in extremely-low-birthweight (ELBW: < 1,000 grams) children at a mean age of 11 years; and (2) to determine the nature of the underlying difficulties associated with academic problems in these children. The results indicated that ELBW children without PVBI performed as well as full-term children on intelligence, academic, and cognitive ability tests. In contrast, ELBW children with mild and severe PVBI achieved significantly lower scores than either ELBW children without PVBI or children who were born at term. A second analysis indicated that, after accounting for Full Scale IQ, working memory and phonological processing were significant predictors of reading and spelling performance in ELBW children. These findings suggest that the presence and severity of PVBI, and not ELBW status alone, is associated with performance on tests of intelligence, and academic and cognitive functioning, and that some of the same factors known to be associated with learning disabilities in full-term children contribute to learning disabilities in ELBW children.

The association between early minor motor difficulties in extreme low birth weight infants and school age attentional difficulties

INTRODUCTION

Extremely premature infants of normal intellectual ability have an increased prevalence of motor and attentional difficulties. Knowledge of the relationship between early motor difficulties and measures of attention at school age would enhance understanding of these developmental pathways, their interrelationship and opportunities for intervention.

OBJECTIVE

This study examines whether an association exists between early findings of minor motor difficulties and school age clinical and psychometric measures of attention.

METHODOLOGY

45/60 eligible ELBW(1000 g) or preterm (< 27/40 gestation) infants born at the Mater Mother's Hospital were assessed at 12 and 24 months for minor motor deficits (using NSMDA) and at 7-9 years for attention, using clinical (Conners and Du Paul Rating Scales) and psychometric (assessing attention span, selective and divided attention) measures.

RESULTS

NSMDA at 12 months was only associated with the psychometric measures of verbal attention span. It was not associated with later clinical measures of attention. NSMDA at 24 months was strongly associated with specific clinical measures of attention at school age, independent of biological and social factors. It was not associated with psychometric measures of attention.

CONCLUSION

The major finding of this study is that motor difficulties in ELBW infants at 2 years are associated with later clinical measures of attention. Possible mechanisms underlying this relationship are considered.

Prevalence of neurological damage in monochorionic twins with selective intrauterine growth restriction and intermittent absent or reversed end-diastolic umbilical artery flow

OBJECTIVE

To assess the incidence of parenchymal lesions on early and late neonatal brain scans and its association with the presence or absence of intermittent absent or reversed end-diastolic umbilical artery flow velocity (A/REDV) in monochorionic twins complicated by selective intrauterine growth restriction (IUGR), as compared to dichorionic twins and monochorionic twins without selective IUGR.

METHODS

This was a prospective cohort study involving 42 monochorionic twins diagnosed with selective IUGR and managed expectantly. The presence or absence of intermittent A/REDV was recorded in all cases. This study group was compared to dichorionic twins (n = 29) and monochorionic twins without selective IUGR (n = 32) delivered at 26-34 weeks during the study period. All infants underwent an early neonatal brain scan (at or before the fourth day of postnatal life) and at least one follow-up scan during the first 28 days of postnatal life. Perinatal outcome and the incidence of neurological damage were compared between the study groups.

RESULTS

The incidence of intrauterine fetal death (IUD) and periventricular leukomalacia was significantly increased in monochorionic twins complicated with selective IUGR, as compared with the other study groups. Intermittent A/REDV was observed in 22/42 (52.4%) twin pairs, and was always present in the growth-restricted twin. The incidence of IUD (overall 9/44 (20.5%) vs. 0/40, P < 0.001; smaller twin 6/22 (27.3%) vs. 0/20, P < 0.05) and parenchymal brain damage (overall 7/35 (20.0%) vs. 2/40 (5.0%), P = 0.07; larger twin 7/19 (36.8%) vs. 1/20 (5.0%), P < 0.05) was significantly higher in pregnancies with intermittent A/REDV than in those without intermittent A/REDV. Brain damage usually occurred in the larger twin, irrespective of whether the smaller twin was liveborn or not.

CONCLUSIONS

The presence of intermittent A/REDV in monochorionic twins with selective IUGR identifies a subgroup with an elevated risk of intrauterine demise of the smaller twin and neurological damage in the larger twin; this latter finding is not restricted to cases with IUD of the cotwin.

School performance in adolescents with and without periventricular-intraventricular hemorrhage in the neonatal period

Long-term sequelae of preterm birth have been studied extensively up until the age of 5 to 8 years. However, the cognitive development of adolescents born preterm has received limited attention. The objective of this study is to determine school performance in adolescents born very preterm. We have followed up a cohort of 484 infants born before 32 weeks of gestation in whom cranial ultrasound was routinely and systematically performed. School performance was assessed in the surviving adolescents at 14 years of age. The outcome variable divided the adolescents into three groups: (1) normal, (2) slow learners, and (3) special education. School performance data were obtained from 278 of 304 surviving adolescents; 129 performed normally, while 107 were slow learners, and 42 needed special education. From the unadjusted odds ratios for the need of special education by the various perinatal factors, only the odds ratio for periventricular-intraventricular hemorrhage was significantly associated (2.56, 95% confidence interval 1.17-4.86). Logistic regression analysis revealed that, after correction for possible confounding factors, the odds ratios for special education were significantly higher for adolescents with all grades of periventricular-intraventricular hemorrhage. Less than 50% of adolescents born before 32 weeks gestation perform normally in school. Periventricular-intraventricular hemorrhage, including the lower grades,does have an unfavorable additional effect on school performance.

Serial head ultrasound studies in preterm infants: how many normal studies does one infant need to exclude significant abnormalities?

OBJECTIVE

We hypothesized that preterm infants with two normal head ultrasound (HUS) screening studies > or = 7 days apart would have subsequently normal follow-up studies.

POPULATION

We reviewed reports of all HUS studies performed in preterm infants < or = 32 weeks gestation admitted to our nursery between January 1998 and July 2000.

SETTING

Regional perinatal referral center.

DESIGN

A normal HUS screening study was defined as either no findings; or grade I intraventricular hemorrhage (IVH) (Papile classification), germinal matrix irregularity or cyst, or normal but unequal ventricular size. An abnormal study was defined as any with IVH > or = grade II, periventricular leukomalacia (PVL), ventriculomegaly (VM), or periventricular echogenicity (PVE).

RESULTS

Of 98 infants, 92 infants (94%) who had two normal HUS studies > or = 7 days apart had normal repeat studies subsequently, and six (6%) were abnormal. Four of the six abnormal infants were <25 weeks gestation at birth. One infant (27 weeks) became abnormal after culture-positive bacterial sepsis and necrotizing enterocolitis with bowel perforation requiring surgery. The remaining infant (29 weeks) had a question of PVE, and a normal repeat study. The positive predictive value for having a normal HUS after two previously normal studies > or = 7 days apart was 94% with a specificity of 86%.

CONCLUSION

Stable premature infants > or = 25 weeks gestation without intervening deterioration may not need repeat screening HUSs after having had two normal studies > or = 7 days apart. Unstable or extremely premature infants <25 weeks gestation may be subject to late severe IVH, VM, and PVL, and therefore need a repeat study before hospital discharge, even if two initial studies > or = 7 days apart were normal.

[Early cerebral MRI in preterm infants: correlations with EEG and outcome]

AIM OF THE STUDY

Assess the potential benefits of performing an early cerebral MRI to evaluate the gravity of cerebral lesions among premature neonates at risk of neurologic sequels and establish correlations between EEG findings, abnormal neuroimaging findings and neurodevelopment.

METHODS

A MRI was performed in 34 premature newborn babies with abnormal neurological clinical signs, and/or with two abnormal EEG and/or with two abnormal cerebral ultrasound scans. The mean age and the adjusted age of our population were 5 weeks (range 1-11 weeks) and 35 weeks of adjusted age (range 29-40 weeks) respectively. The neuroimaging findings were correlated to the results of three EEGs (recorded before 15 days old, between 15 days and one month old, and after the first month of life) and to neurodevelopment.

RESULTS

Two statically significant correlations were found between: 1) the severity of brain injuries observed in MRI and the results of the latest EEG (sensitivity 100%, specificity 60%), 2) the severity of brain injuries observed in MRI and abnormal neurodevelopment (sensitivity 75%, specificity 80%). There was no correlation between the abnormal development and the results of EEG recordings.

CONCLUSION

Early cerebral MRI is justified in a selected premature population. It is useful for the diagnosis, the evaluation of the severity of brain injury and for the management of these children. The correlation with EEGs traces allows the detection of the majority of prematures babies that will develop sequels.

Periventricular leukomalacia, inflammation and white matter lesions within the developing nervous system

Periventricular leukomalacia (PVL) occurring in premature infants, represents a major precursor for neurological and intellectual impairment, and cerebral palsy in later life. The disorder is characterized by multifocal areas of necrosis found deep in the cortical white matter, which are often symmetrical and occur adjacent to the lateral ventricles. There is no known cure for PVL. Factors predisposing to PVL include birth trauma, asphyxia and respiratory failure, cardiopulmonary defects, premature birth/low birthweight, associated immature cerebrovascular development and lack of appropriate autoregulation of cerebral blood flow in response to hypoxic-ischemic insults. The intrinsic vulnerability of oligodendrocyte precursors is considered as central to the pathogenesis of PVL. These cells are susceptible to a variety of injurious stimuli including free radicals and excitotoxicity induced by hypoxic-ischemic injury (resulting from cerebral hypoperfusion), lack of trophic stimuli, as well as secondary associated events involving microglial and astrocytic activation and the release of pro-inflammatory cytokines TNF-alpha and IL-6. It is yet unclear whether activated astrocytes and microglia act as principal participants in the development of PVL lesions, or whether they are representatives of an incidental pathological response directed towards repair of tissue injury in PVL. Nevertheless, the accumulated evidence points to a pathological contribution of microglia towards damage. The topography of lesions in PVL most likely reflects a combination of the relatively immature cerebrovasculature together with a failure in perfusion and/or hypoxia during the greatest period of vulnerability occurring around mid-to-late gestation. Mechanisms underlying the pathogenesis of PVL have so far been related to prenatal ischemic injury to the brain initiated within the third trimester, which result in global cognitive and developmental delay and motor disturbances. Over the past few years, several epidemiological and experimental studies have implicated intrauterine infection and chorioamnionitis as causative in the pathogenesis of PVL. In particular, recent investigations have shown that inflammatory responses in the fetus and neonate can contribute towards neonatal brain injury and development-related disabilities including cerebral palsy. This review presents current concepts on the pathogenesis of PVL and emphasizes the increasing evidence for an inflammatory pathogenic component to this disorder, either resulting from hypoxic-ischemic injury or from infection. These findings provide the basis for clinical approaches targeted at protecting the premature brain from inflammatory damage, which may prove beneficial for treating PVL, if identified early in pathogenesis.

Ethical aspects of cardiopulmonary resuscitation in premature neonates: where do we stand?

Advances in diagnosis, techniques, therapeutic interventions, organisation of perinatal care, and socio-economic factors have all contributed to the survival after resuscitation and intensive care of neonates with extremely low birth weight and gestational age. While morbidity during the first years of life in those infants does not increase, at school age multiple dysfunctions may become apparent. What are the limits of intensive care for the newborn? Is it right to use extreme technical and economic measures for neonates with a borderline chance of survival? What is justifiable for the neonate, the family, the society and how does legislation interfere in a decision process which involves starting, stopping or continuing intensive care? A short historical overview for the care of the newborn is given, followed by the outcome after resuscitation and treatment of the very low birth weight infant. Published management strategies and recommendations are discussed.