Early brain injury in premature newborns detected with magnetic resonance imaging is associated with adverse early neurodevelopmental outcome

Brain injury in premature infants: a complex amalgam of destructive and developmental disturbances

Brain injury in premature infants is of enormous public health importance because of the large number of such infants who survive with serious neurodevelopmental disability, including major cognitive deficits and motor disability. This type of brain injury is generally thought to consist primarily of periventricular leukomalacia (PVL), a distinctive form of cerebral white matter injury. Important new work shows that PVL is frequently accompanied by neuronal/axonal disease, affecting the cerebral white matter, thalamus, basal ganglia, cerebral cortex, brain stem, and cerebellum. This constellation of PVL and neuronal/axonal disease is sufficiently distinctive to be termed "encephalopathy of prematurity". The thesis of this Review is that the encephalopathy of prematurity is a complex amalgam of primary destructive disease and secondary maturational and trophic disturbances. This Review integrates the fascinating confluence of new insights into both brain injury and brain development during the human premature period.

Brain imaging findings in very preterm infants throughout the neonatal period: part II. Relation with perinatal clinical data

This study describes the relation between frequent and clinically relevant brain imaging findings in very preterm infants (GA<32 weeks), assessed with sequential cranial ultrasonography throughout the neonatal period and MRI around term age, and several potential perinatal risk factors. For ultrasound findings during admission the following independent risk factors were identified: male gender for periventricular echodensities and intraventricular haemorrhage, postnatal corticosteroid treatment for cystic white matter lesions, and lower gestational age for post-haemorrhagic ventricular dilatation. For MRI findings around term age, including punctate white matter lesions, ventricular dilatation, decreased cortical complexity, and diffuse and excessive high signal intensity, no independent risk factors were found. In very preterm infants, the risk factors for frequently found changes on cranial ultrasound have largely remained unchanged over the last decades, while no risk factors could be identified for subtle and diffuse white matter injury as seen on MRI around term age.

Comparison of computer tomography and magnetic resonance imaging scans on the third day of life in term newborns with neonatal encephalopathy

OBJECTIVE

Our goal was to compare the patterns of brain injury detected by computed tomography, conventional MRI (T1- and T2-weighted sequences), and diffusion-weighted MRI in a cohort of term newborns with neonatal encephalopathy studied uniformly with all 3 modalities on the third day of life.

METHODS

Term newborns (> or =36 weeks' gestation) admitted to our center with neonatal encephalopathy were scanned with computed tomography, MRI, and diffusion-weighted MRI at 72 (+/-12) hours of life (n = 48). Each modality was scored independently of the other with previously validated scoring systems. The predominant pattern of brain injury was classified as: normal, watershed, basal nuclei, total (maximal basal nuclei and watershed), and focal-multifocal (presence of strokes and/or white matter injury alone).

RESULTS

The agreement for the predominant pattern of injury was excellent between MRI and diffusion-weighted MRI (77% agreement). The agreement for the pattern of injury was also good for computed tomography and diffusion-weighted MRI (67% agreement). The extent of cortical injury and focal-multifocal lesions, such as strokes and white matter injury, were less apparent on computed tomography than diffusion-weighted MRI. In 19 newborns with a repeat MRI in the second week of life, the predominant pattern seen on the day 3 diffusion-weighted MRI was confirmed.

CONCLUSIONS

Diffusion-weighted MRI is the most sensitive technique with which to assess brain injury on day 3 of life in term newborns with neonatal encephalopathy, particularly for cortical injury and focal-multifocal lesions such as stroke and white matter injury. All 3 modalities identify the most serious patterns of brain injury similarly.

White matter injury in term newborns with neonatal encephalopathy

White matter injury (WMI) is the characteristic pattern of brain injury detected on magnetic resonance imaging in the premature newborn. Focal noncystic WMI is increasingly recognized in populations of term newborns. The aim of this study was to describe the occurrence of focal noncystic WMI in a cohort of 48 term newborns with encephalopathy studied with magnetic resonance imaging at 72 +/- 12 h of life, and to identify clinical risk factors for this pattern of injury. Eleven newborns (23%; 95% CI 11-35) were found to have WMI (four minimal, three moderate, and four severe). In 10 of the 11 newborns, the WMI was associated with restricted diffusion on apparent diffusion coefficient maps. An increasing severity of WMI was associated with lower gestational age at birth (p = 0.05), but not lower birth weight. Newborns with WMI had milder encephalopathy and fewer clinical seizures relative to other newborns in the cohort. Other brain injuries were seen in three of the 11 newborns: basal nuclei predominant pattern of injury in one and cortical strokes in two. These findings suggest that WMI in the term newborn is acquired near birth and that the state of brain maturation is an important determinant of this pattern of brain injury.

Brain cooling for preterm infants

There is strong evidence that prolonged, moderate cerebral hypothermia initiated within a few hours after severe hypoxia-ischemia and continued until resolution of the acute phase of delayed cell death can reduce neuronal loss and improve behavioral recovery in term infants and adults after cardiac arrest. This review examines the evidence that mild to moderate hypothermia is protective after hypoxia-ischemia in models of preterm brain injury and evaluates the potential risks. Induced hypothermia likely has potential to significantly reduce disability. Cautious, systematic trials are essential before hypothermia can be used in these vulnerable infants.

Preventing brain injury in newborns with congenital heart disease: brain imaging and innovative trial designs

BACKGROUND AND PURPOSE

Newborns with congenital heart disease are at high risk for brain injury and adverse neurodevelopmental outcomes. MRI enables the objective determination of the severity of brain injury in critically ill newborns with congenital heart disease. We will rationalize the use of MRI as a surrogate for neurodevelopmental outcome and describe novel randomization techniques that can be used in trials in this population.

METHODS

This article describes the evidence for the use of MRI and the link with neurodevelopmental outcome established in newborns. We also discuss the use of adaptive randomization techniques for future clinical trials in newborns with congenital heart disease. These strategies will be highlighted using an example.

RESULTS

Brain injuries occur with high frequency in newborns with congenital heart disease. It is not until school age that the full extent of neurological sequelae becomes apparent and the rapid pace of innovation in neonatal cardiac surgery prevents timely evaluation of changes in care. MRI provides a timely, safe, and reliable outcome measure and has been extensively studied in newborns with other conditions in which the link between brain injury and neurodevelopmental outcome has been established. Clinical trials using MRI as an outcome measure as well as adaptive randomization can improve the efficiency of such trials.

CONCLUSIONS

Clinical trials of brain protection are urgently needed in newborns with congenital heart disease given the unacceptable frequency of brain injury in this population; MRI provides an early surrogate marker of long-term neurodevelopmental outcome and adaptive randomization can be used to improve the efficiency of these clinical trials.

Prenatal head growth and white matter injury in hypoplastic left heart syndrome

Children with hypoplastic left heart syndrome (HLHS) have an increased prevalence of central nervous system (CNS) abnormalities. The extent to which this problem is due to CNS maldevelopment, prenatal ischemia, postnatal chronic cyanosis and/or multiple exposures to cardiopulmonary bypass is unknown. To better understand the etiology of CNS abnormalities in HLHS, we evaluated 68 neonates with HLHS; in 28 cases, both fetal ultrasound and echocardiogram data were available to assess head size, head growth and aortic valve anatomy (atresia or stenosis). In addition, we evaluated neuropathology in 11 electively aborted HLHS fetuses. The mean head circumference percentile in HLHS neonates was significantly smaller than HLHS fetuses (22 +/- 2% versus 40 +/- 4%, p < 0.001). A significant decrease in head growth, defined as a 50% reduction in head circumference percentile, was observed in half (14/28) of HLHS fetuses and nearly a quarter (6/28) were already growth restricted (<or=10%) at the time of initial evaluation. Brains from HLHS fetuses demonstrated chronic diffuse white matter injury of varying severity. These patterns of prenatal head growth and brain histopathology identify a spectrum of abnormal CNS development and/or injury in HLHS fetuses.

Magnetic resonance imaging and developmental outcome following preterm birth: review of current evidence

Preterm birth is associated with an increased risk of developmental difficulties. Magnetic resonance imaging (MRI) is increasingly being used to identify damage to the brain following preterm birth. It is hoped this information will aid prognostication and identify neonates who would benefit from early therapeutic intervention. Cystic periventricular white matter damage has traditionally been associated with abnormal motor developmental and cerebral palsy, but its presence on MRI does not preclude normal cognitive development. This has led to increasing interest in the identification of diffuse periventricular white matter damage with conventional and sophisticated MRI. However, the correlation between these appearances and developmental outcome remains unclear. Measurements of the size, volumes, and growth rates of many regions of the brain, such as the corpus callosum, ventricular system, cortex, deep grey matter, and cerebellum, are all also altered following preterm birth, but there is insufficient evidence to use this data in the clinical setting. This article is a review of the current evidence on MRI and developmental outcome, suggesting possible indications for the use of MRI following preterm birth.

Patterns of cerebral white matter damage and cognitive impairment in adolescents born very preterm

There is increasing evidence about the presence of white matter damage in subjects with a history of premature birth, even in those classified as good outcome because of an apparently normal development. Although intellectual performance is within normal limits in premature children it is significantly decreased compared to paired controls. The purpose of this study was to investigate the relationship between a lower performance intelligence quotient and white matter damage in preterm adolescents. The sample comprised 44 adolescents (mean age+/-S.D.: 14.4+/-1.6 years) born before 32 weeks of gestational age and 43 term-born adolescents (14.5+/-2.1 years). Individual voxel-based morphometry analyses demonstrated that 35/44 (80%) preterm subjects had white matter abnormalities. The centrum semiovale and the posterior periventricular regions were the most frequently affected areas. Correlation analysis showed that in preterms the performance intelligence quotient correlated with the whole-brain white matter volume (r=0.32; P=0.036) but not with grey matter volume. Complementary analysis showed that low scores in the Digit Symbol subtest, a measure of processing speed, in the preterm group correlated with reductions in white matter concentration. These results suggest that white matter damage is highly common and that it persists until adolescence. Hence, diffuse white matter loss may be responsible for performance intelligence quotient and processing speed decrements in subjects with very preterm birth.

Recurrent postnatal infections are associated with progressive white matter injury in premature infants

OBJECTIVE

Our objective was to identify clinical predictors of progressive white matter injury.

METHODS

We evaluated 133 infants of <34 weeks of gestation at birth from 2 university hospitals. Infants underwent MRI twice, initially when in stable condition for transport and again at term-equivalent age or before transfer or discharge. Two neuroradiologists who were blinded to the clinical course graded MRI white matter injury severity by using a validated scale. Potential risk factors were extracted from medical charts.

RESULTS

Twelve neonates (9.0%) had progressive white matter injury. In the unadjusted analysis of 10 newborns without Candida meningoencephalitis, recurrent culture-positive postnatal infection and chronic lung disease were associated with progressive white matter injury. Exposure to multiple episodes of culture-positive infection significantly increased the risk of progressive white matter injury. Of the 11 neonates with >1 infection, 36.4% (4 infants) had progressive injury, compared with 5.0% (6 infants) of those with <or=1 infection. Of the 35 infants with chronic lung disease, 17.1% (6 infants) had progressive injury, compared with 4.3% (4 infants) of those without chronic lung disease. After adjustment for gestational age at birth, the association between infection and white matter injury persisted, whereas chronic lung disease was no longer a statistically significant risk factor.

CONCLUSIONS

Recurrent postnatal infection is an important risk factor for progressive white matter injury in premature infants. This is consistent with emerging evidence that white matter injury is attributable to oligodendrocyte precursor susceptibility to inflammation, hypoxia, and ischemia.

Maturation-dependent sensitivity of oligodendrocyte lineage cells to apoptosis: implications for normal development and disease

Apoptosis plays a crucial role in brain development by ensuring that only appropriately growing, migrating, and synapse-forming neurons and their associated glial cells survive. This process involves an intimate relationship between cell-cell interactions and developmental cues and is further impacted by environmental stress during neurogenesis and disease. Oligodendrocytes (OLs), the major myelin-forming cells in the central nervous system, largely form after this wave of neurogenesis but also show a selective vulnerability to cell death stimuli depending on their stage of development. This can affect not only embryonic and early postnatal brain formation but also the response to demyelinating pathologies. In the present review, we discuss the stage-specific sensitivity of OL lineage cells to damage-induced death and how this might impact myelin survival and regeneration during injury or disease.

Cerebral blood flow heterogeneity in preterm sheep: lack of physiologic support for vascular boundary zones in fetal cerebral white matter

Periventricular white matter (PVWM) injury is the leading cause of neurologic disability in survivors of prematurity. To address the role of ischemia in PVWM and cerebral cortical injury, we hypothesized that immaturity of spatially distal vascular 'end zones' or 'border zones' predisposes PVWM to greater decreases in cerebral blood flow (CBF) than more proximal structures. We quantified regional CBF with fluorescently labeled microspheres in 0.65 gestation fetal sheep in histopathologically defined three-dimensional regions by post hoc digital dissection and coregistration algorithms. Basal flow in PVWM was significantly lower than in gyral white matter and cortex, but was equivalent in superficial, middle, and deep PVWM. Absolute and relative CBF (expressed as percentage of basal) did not differ significantly during ischemia or reperfusion between PVWM, gyral white matter, or cortex. Moreover, CBF during ischemia-reperfusion was equivalent in three adjacent PVWM levels and was not consistent with the magnitude of severity of PVWM injury, defined by TUNEL (terminal deoxynucleotidyltransferase-mediated dUPT nick end labeling) staining. However, the magnitude of ischemia was predicted by the severity of discrete cortical lesions. Hence, unlike cerebral cortex, unique CBF disturbances did not account for the distribution of PVWM injury. Previously defined cellular maturational factors, thus, appear to have a greater influence on PVWM vulnerability to ischemic injury than the presence of immature vascular boundary zones.

Prematurely born children demonstrate white matter microstructural differences at 12 years of age, relative to term control subjects: an investigation of group and gender effects

OBJECTIVE

The goal was to use diffusion tensor imaging to test the hypothesis that prematurely born children demonstrate long-term, white matter, microstructural differences, relative to term control subjects.

METHODS

Twenty-nine preterm subjects (birth weight: 600-1250 g) without neonatal brain injury and 22 matched, term, control subjects were evaluated at 12 years of age with MRI studies, including diffusion tensor imaging and volumetric imaging; voxel-based morphometric strategies were used to corroborate regional diffusion tensor imaging results. Subjects also underwent neurodevelopmental assessments.

RESULTS

Neurodevelopmental assessments showed significant differences in full-scale, verbal, and performance IQ and Developmental Test of Visual Motor Integration scores between the preterm and term control subjects. Diffusion tensor imaging studies demonstrated widespread decreases in fractional anisotropy (a measure of fiber tract organization) in the preterm children, compared with the control subjects. Regions included both intrahemispheric association fibers subserving language skills, namely, the right inferior frontooccipital fasciculus and anterior portions of the uncinate fasciculi bilaterally, and the deep white matter regions to which they project, as well as the splenium of the corpus callosum. These changes in fractional anisotropy occurred in subjects with significant differences in frontal, temporal, parietal, and deep white matter volumes. Fractional anisotropy values in the left anterior uncinate correlated with verbal IQ, full-scale IQ, and Peabody Picture Vocabulary Test-Revised scores for preterm male subjects. In addition, preterm male subjects were found to have the lowest values for fractional anisotropy in the right anterior uncinate fasciculus, and fractional anisotropy values in that region correlated with both verbal IQ and Peabody Picture Vocabulary Test-Revised scores for the preterm groups; these findings were supported by changes identified with voxel-based morphometric analyses.

CONCLUSIONS

Compared with term control subjects, prematurely born children with no neonatal ultrasound evidence of white matter injury manifest changes in neural connectivity at 12 years of age.

Neuroimaging and neurodevelopmental outcomes in preterm infants

Imaging of the preterm infant brain has advanced dramatically beyond the earliest era of transillumination. Computed tomography (CT), a crucial innovation during the early 1970s, allowed noninvasive visualization of intracerebral lesions, particularly hemorrhage. The capability to document brain injury in the preterm infant led to better clarification of links to developmental outcomes. With the development of cranial ultrasound (CUS), and more recently, magnetic resonance imaging (MRI), CT is used rarely for imaging the brain of preterm infants. Despite extensive experience with neonatal neuroimaging, significant questions still remain. Substantial controversies exist pertaining to when and how neuroimaging should be performed and how images should be interpreted.

White-matter injury is associated with impaired gaze in premature infants

Periventricular leukomalacia is a risk factor for visual impairment in children born prematurely. The impact of diffuse white-matter injury, as detected on magnetic resonance imaging, on early visual function is unknown. We developed two 5-point visual-gaze scores to analyze the association between this clinical assessment and white-matter injury in 93 premature neonates <34 weeks of gestational age at birth. Older postmenstrual age was associated with higher values of the two gaze scores. Infants with moderate or severe white-matter injury had lower scores than their peers without white-matter injury (0.41 points, 95% confidence interval of 0.13-0.69 for visual fixation score; and 0.70 points, 95% confidence interval of 0.30-1.10 for conjugate score, P < 0.005). Using the results from both scales, a score of >or=9 in an infant examined at >or=36 weeks postmenstrual age predicted normal white matter on magnetic resonance examination, with a sensitivity of 84% and a specificity of 100%. These preliminary findings suggest that white-matter injury affects visual function even before term equivalent postmenstrual age.

Abnormal brain development in newborns with congenital heart disease

BACKGROUND

Congenital heart disease in newborns is associated with global impairment in development. We characterized brain metabolism and microstructure, as measures of brain maturation, in newborns with congenital heart disease before they underwent heart surgery.

METHODS

We studied 41 term newborns with congenital heart disease--29 who had transposition of the great arteries and 12 who had single-ventricle physiology--with the use of magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and diffusion tensor imaging (DTI) before cardiac surgery. We calculated the ratio of N-acetylaspartate to choline (which increases with brain maturation), the ratio of lactate to choline (which decreases with maturation), average diffusivity (which decreases with maturation), and fractional anisotropy of white-matter tracts (which increases with maturation). We compared these findings with those in 16 control newborns of a similar gestational age.

RESULTS

As compared with control newborns, those with congenital heart disease had a decrease of 10% in the ratio of N-acetylaspartate to choline (P=0.003), an increase of 28% in the ratio of lactate to choline (P=0.08), an increase of 4% in average diffusivity (P<0.001), and a decrease of 12% in white-matter fractional anisotropy (P<0.001). Preoperative brain injury, as seen on MRI, was not significantly associated with findings on MRS or DTI. White-matter injury was observed in 13 newborns with congenital heart disease (32%) and in no control newborns.

CONCLUSIONS

Term newborns with congenital heart disease have widespread brain abnormalities before they undergo cardiac surgery. The imaging findings in such newborns are similar to those in premature newborns and may reflect abnormal brain development in utero.

Neurology of congenital heart disease: insight from brain imaging

Understanding of the specific pathophysiology of acquired brain injury in infants with CHD will help optimise treatment and brain protection strategies

Serial diffusion tensor imaging detects white matter changes that correlate with motor outcome in premature infants

The objective of the study was to assess predictive value of serial diffusion tensor MRI (DTI) for the white matter injury and neurodevelopmental outcome in a cohort of premature infants. Twenty-four infants less than 32 weeks' gestation were stratified to a control group (n = 11), mild brain injury with grades 1-2 of intraventricular hemorrhage (n = 6) and severe brain injury with grades 3-4 intraventricular hemorrhage (n = 4). Serial DTI studies were performed at around 30 and 36 weeks' gestation. Fractional anisotropy (FA) and apparent diffusion coefficient were calculated. Twelve infants were followed up for developmental outcome. Developmental testing was performed with the Bayley Scales of Infant Development to obtain psychomotor index (Performance Developmental Index). Apparent diffusion coefficient was higher in the severe injury group at the second MRI in the central and occipital white matter, and corona radiata; FA was lower in optic radiation compared to controls. Performance Developmental Index score correlated with FA on the scan taken at the 30th week and inversely with the change of FA between scans in internal capsule and occipital white matter. A low value of FA at 30 weeks and a higher change of FA predicted less favorable motor outcome at 2 years and suggests that early subtle white matter injury can be detected in premature infants even without obvious signs of injury.

Outcome after intrapartum hypoxic ischaemia at term

We consider the range of childhood disabilities that have been attributed to perinatal hypoxic ischaemia at term and review the strength of evidence for each. The strongest evidence is for a causal link between acute profound hypoxic ischaemia and dyskinetic tetraplegic cerebral palsy (CP). Hemiplegic CP is not usually due to a perinatal hypoxic ischaemic insult at term; an important cause is focal cerebral infarction or 'stroke'. Characteristically, diplegic CP is seen in ex-preterm children with periventricular leukomalacia. Ataxic CP is unlikely to be due to perinatal asphyxia. Recent careful follow-up studies have shown that childhood survivors of perinatal hypoxic ischaemia are at risk for cognitive deficits even in the absence of functional motor disorders. There is no evidence that, in isolation, either attention deficit hyperactivity disorder or autism is caused by hypoxic ischaemia. As effective neuroprotective therapies are introduced, notably cooling, it is possible that the prevalence of CP may be reduced.

Magnetic resonance imaging regional T1 abnormalities at term accurately predict motor outcome in preterm infants

OBJECTIVE

The aim of this study was to assess whether periventricular leukomalacia findings are sufficiently sensitive for predicting the severity of motor prognosis by conventional MRI in the near term.

METHODS

Preterm infants with T1 hyperintensity or cysts in the periventricular regions on term MRI were selected, and their gross motor functions were evaluated at the age of 3 to 5 years. Sixty-two infants had findings of T1 hyperintensity or cysts, and except for infants with these findings, none were diagnosed later as periventricular leukomalacia.

RESULTS

All 37 patients with cerebral palsy had periventricular lesions with T1 hyperintensity or cysts in the corona radiata above the posterior limb of the internal capsule on coronal sections. Small T1 hyperintensity lesions were seen on coronal slices and were often difficult to detect on axial slices. All of the 17 infants with T1 hyperintensity findings sparing the corona radiata above the posterior limb of the internal capsule showed normal motor development, irrespective of findings of ventriculomegaly. There was a tendency for the presence of widespread lesions in corona radiata above the posterior limb of the internal capsule to be correlated with the severity of motor handicap.

CONCLUSIONS

Lesions in the corona radiata above the posterior limb of the internal capsule on a coronal view by term MRI were useful for predicting motor prognosis in preterm infants with periventricular leukomalacia.

Brain abnormalities in extremely low gestational age infants: a Swedish population based MRI study

AIMS

Brain abnormalities are common in preterm infants and can be reliably detected by magnetic resonance (MR) imaging at term equivalent age. The aim of the present study was to acquire population based data on brain abnormalities in extremely low gestational age (ELGA) infants from the Stockholm region and to correlate the MR findings to perinatal data, in order to identify risk factors.

METHODS

All infants with gestational age <27 weeks, born in the Stockholm region between January 2004 and August 2005, were scanned on a 1.5 T MR system at term equivalent age. Images were analysed using a previously established scoring system for grey and white matter abnormalities.

RESULTS

No or only mild white matter abnormalities were observed in 82% and moderate to severe white matter abnormalities in 18% of infants. The Clinical Risk Index for Babies (CRIB II) score, use of inotropes, the presence of high-grade intraventricular haemorrhages and posthaemorrhagic ventricular dilatation were associated with white matter abnormalities.

CONCLUSION

The incidence of moderate to severe white matter abnormalities in a population-based cohort of ELGA infants from the Stockholm region was 18%. To examine the clinical relevance of these promising results, neurodevelopmental follow up at 30 month corrected age, is ongoing.

Patent ductus arteriosus and its treatment as risk factors for neonatal and neurodevelopmental morbidity

OBJECTIVES

The purpose of this work was to determine whether the reported association between neonatal morbidities and a patent ductus arteriosus is because of the left-to-right patent ductus arteriosus shunt itself, the therapies used to treat it, or the immaturity of the infants who are likely to develop a patent ductus arteriosus.

METHODS

A total of 446 infants (<28 weeks' gestation) were treated with the same patent ductus arteriosus care-oriented protocol, and logistic regression analysis was used to examine the effects of several patent ductus arteriosus-related variables (presence of a symptomatic patent ductus arteriosus, the number of indomethacin doses used, the ductus response to indomethacin, and the use of surgical ligation) on the incidence of retinopathy of prematurity, necrotizing enterocolitis, chronic lung disease, death, and neurodevelopmental impairment.

RESULTS

Most of the predictive effects that the presence of a patent ductus arteriosus and its treatment had on neonatal morbidity could be accounted for by the infants' immature gestation. Use of surgical ligation, however, was significantly associated with the development of chronic lung disease and was independent of immature gestation, other patent ductus arteriosus-related variables, or other perinatal and neonatal risk factors known to be associated with chronic lung disease.

CONCLUSIONS

These findings add to the growing uncertainty about the benefits and risks of surgical ligation during the neonatal period.

Maturation-dependent vulnerability of perinatal white matter in premature birth

Survivors of premature birth have a predilection for perinatal brain injury, especially to periventricular cerebral white matter. Periventricular white matter injury (PWMI) is now the most common cause of brain injury in preterm infants and the leading cause of chronic neurological morbidity. The spectrum of chronic PWMI includes focal cystic necrotic lesions (periventricular leukomalacia) and diffuse myelination disturbances. Recent neuroimaging studies support that the incidence of periventricular leukomalacia is declining, whereas focal or diffuse noncystic injury is emerging as the predominant lesion. In a significant number of infants, PWMI appears to be initiated by perturbations in cerebral blood flow that reflect anatomic and physiological immaturity of the vasculature. Ischemic cerebral white matter is susceptible to pronounced free radical-mediated injury that particularly targets immature stages of the oligodendrocyte lineage. Emerging experimental data supports that pronounced ischemia in the periventricular white matter is necessary but not sufficient to generate the initial injury that leads to PWMI. The developmental predilection for PWMI to occur during prematurity appears to be related to both the timing of appearance and regional distribution of susceptible oligodendrocyte progenitors. Injury to oligodendrocyte progenitors may contribute to the pathogenesis of PWMI by disrupting the maturation of myelin-forming oligodendrocytes. There has been substantial recent progress in the understanding of the cellular and molecular pathogenesis of PWMI. The oligodendrocyte progenitor is a key target for preventive strategies to reduce ischemic cerebral white matter injury in premature infants.

Magnetic resonance imaging of the neonatal brain

Neonatal magnetic resonance (MR) imaging is rapidly becoming the preferred modality for the evaluation of central nervous system disorders in the newborn. Recent literature supports the value of this imaging technique in diagnosing ischemic, hemorrhagic and infectious disease processes in the premature and full-term neonatal brain. Recent data in premature newborns with neurological injury also suggest a role for MR imaging in determining long-term neurodevelopmental outcomes. This review article provides a framework and overview on neonatal MR imaging techniques and examines the literature or radiological disease patterns and prognostic implications in common neurological disorders.

Advances in magnetic resonance neuroimaging techniques in the evaluation of neonatal encephalopathy

Magnetic resonance (MR) imaging has become an essential tool in the evaluation of neonatal encephalopathy. Magnetic resonance-compatible neonatal incubators allow sick neonates to be transported to the MR scanner, and neonatal head coils can improve signal-to-noise ratio, critical for advanced MR imaging techniques. Refinement of conventional imaging techniques include the use of PROPELLER techniques for motion correction. Magnetic resonance spectroscopic imaging and diffusion tensor imaging provide quantitative assessment of both brain development and brain injury in the newborn with respect to metabolite abnormalities and hypoxic-ischemic injury. Knowledge of normal developmental changes in MR spectroscopy metabolite concentration and diffusion tensor metrics is essential to interpret pathological cases. Perfusion MR and functional MR can provide additional physiological information. Both MR spectroscopy and diffusion tensor imaging can provide additional information in the differential of neonatal encephalopathy, including perinatal white matter injury, hypoxic-ischemic brain injury, metabolic disease, infection, and birth injury.

Temporal and Anatomic Risk Profile of Brain Injury With Neonatal Repair of Congenital Heart Defects

BACKGROUND AND PURPOSE

Brain injury is common in newborns with congenital heart disease (CHD) requiring neonatal surgery. The purpose of this study is to define the risk factors for preoperative and postoperative brain injuries and their association with functional cardiac anatomic groups.

METHODS

Sixty-two neonates with CHD were studied with preoperative MRI, and 53 received postoperative scans. Clinical and therapeutic characteristics were compared in newborns with and without newly acquired brain injuries. A subset of 16 consecutive patients was monitored with intraoperative cerebral near-infrared spectroscopy.

RESULTS

Brain injury was observed in 56% of patients. Preoperative brain injury, seen in 39%, was most commonly stroke and was associated with balloon atrial septostomy (P=0.002). Postoperative brain injury, seen in 35%, was most commonly white matter injury and was particularly common in neonates with single-ventricle physiology and aortic arch obstruction (P=0.001). Risk factors associated with acquired postoperative brain injury included cardiopulmonary bypass (CPB) with regional cerebral perfusion (P=0.01) and lower intraoperative cerebral hemoglobin oxygen saturation during the myocardial ischemic period of CPB (P=0.008). In a multivariable model, new postoperative white matter injury was specifically associated with low mean blood pressure during the first postoperative day (P=0.04).

CONCLUSIONS

Specific modifiable risk factors can be identified for preoperative and postoperative white matter injury and stroke associated with neonatal surgery for CHD. The high incidence of postoperative injury observed despite new methodologies of CPB indicates the need for ongoing evaluation to optimize neurological outcome.

Indomethacin prophylaxis for preterm infants: the impact of 2 multicentered randomized controlled trials on clinical practice

OBJECTIVES

Two multicenter randomized controlled trials (RCTs) in premature infants (Ment et al, 1994 and TIPP, 2001) found beneficial effects of indomethacin prophylaxis on the incidences of patent ductus arteriosus (PDA), PDA ligation, and severe intracranial hemorrhage (ICH). The Ment trial recommended the use of indomethacin prophylaxis. The TIPP trial failed to find a benefit in its primary outcome (improved survival/neurodevelopmental outcome); this negative result may have discouraged indomethacin prophylaxis use.

STUDY DESIGN

We used the National Institute of Child Health and Development's Neonatal Network Registry to determine the association between the 2 trials and the use of indomethacin prophylaxis. We also statistically assessed the assumptions that led to the TIPP trial's negative results.

RESULTS

Use of indomethacin prophylaxis among network clinicians increased after publication of the Ment trial and decreased after the TIPP trial. Analysis of the TIPP trial showed that the primary outcome's anticipated effect size (> or = 20%) was too large; a smaller effect size (< 3%) would have been more appropriate based on the incidence of ICH in their population and its association with neurodevelopmental outcome.

CONCLUSIONS

Two multicenter RCTs were associated with changes in indomethacin prophylaxis. After the Ment trial, the use of indomethacin prophylaxis increased. After the TIPP trial, which reported negative results based on an excessively large anticipated effect size, its use decreased.

Comparative prognostic utilities of early quantitative magnetic resonance imaging spin-spin relaxometry and proton magnetic resonance spectroscopy in neonatal encephalopathy

OBJECTIVE

We sought to compare the prognostic utilities of early MRI spin-spin relaxometry and proton magnetic resonance spectroscopy in neonatal encephalopathy.

METHODS

Twenty-one term infants with neonatal encephalopathy were studied at a mean age of 3.1 days (range: 1-5). Basal ganglia, thalamic and frontal, parietal, and occipital white matter spin-spin relaxation times were determined from images with echo times of 25 and 200 milliseconds. Metabolite ratios were determined from an 8-mL thalamic-region magnetic resonance spectroscopy voxel (1H point-resolved spectroscopy; echo time 270 milliseconds). Outcomes were assigned at age 1 year as follows: (1) normal, (2) moderate (neuromotor signs or Griffiths developmental quotient of 75-84), (3) severe (functional neuromotor deficit or developmental quotient <75 or died). Predictive efficacies for differentiation between normal and adverse (combined moderate and severe) outcomes were compared by receiver operating characteristic curve analysis and logistic regression.

RESULTS

Thalamic and basal ganglia spin-spin relaxation times correlated positively with outcome and predicted adversity. Although thalamic and basal ganglia spin-spin relaxation times were prognostic of adversity, magnetic resonance spectroscopy metabolite ratios were better predictors, and, of these, lactate/N-acetylaspartate was most accurate.

CONCLUSIONS

Deep gray matter spin-spin relaxation time was increased in the first few days after birth in infants with an adverse outcome. Proton magnetic resonance spectroscopy was more prognostic than spin-spin relaxation time, with lactate/N-acetylaspartate the best measure. Nevertheless, both techniques were useful for early prognosis, and the potential superior spatial resolution of spin-spin relaxometry may define better the precise anatomic pattern of injury in the early days after birth.

Cerebral outcomes in a preterm baboon model of early versus delayed nasal continuous positive airway pressure

BACKGROUND

The survival of prematurely born infants has greatly increased in recent decades because of advances in neonatal intensive care, which have included the advent of ventilatory therapies. However, there is limited knowledge as to the impact of these therapies on the developing brain. The purpose of this work was to evaluate the influence of randomized respiratory therapy with either early continuous positive airway pressure or delayed continuous positive airway pressure preceded by positive pressure ventilation on the extent of brain injury and altered development in a prematurely delivered primate model.

METHODS

Fetal baboons were delivered at 125 days of gestation (term: approximately 185 days of gestation) by cesarean section. Animals were maintained for 28 days postdelivery with either: early continuous positive airway pressure (commencing at 24 hours; n = 6) or delayed continuous positive airway pressure (positive pressure ventilation for 5 days followed by nCPAP; n = 5). Gestational controls (n = 4) were delivered at 153 days of gestation. At the completion of the study, animals were killed, the brains were assessed histologically for growth and development, and evidence of cerebral injury and indices for both parameters were formulated.

RESULTS

Brain and body weights were reduced in all of the nasal continuous positive airway pressure animals compared with controls; however, the brain/body weight ratio was increased in early continuous positive airway pressure animals. Within both nasal continuous positive airway pressure groups compared with controls, there was increased gliosis in the subcortical and deep white matter and cortex and a persistence of radial glia. Early continuous positive airway pressure was associated with less cerebral injury than delayed continuous positive airway pressure therapy. Neuropathologies were not observed in controls.

CONCLUSIONS

Premature delivery, in the absence of potentiating factors, such as hypoxia or infection, is associated with a decrease in brain growth and the presence of subtle brain injury, which seems to be modified by respiratory therapies with early continuous positive airway pressure being associated with less overall cerebral injury.

Hyperoxic exposure leads to nitrative stress and ensuing microvascular degeneration and diminished brain mass and function in the immature subject

BACKGROUND AND PURPOSE

Neonates that survive very preterm birth have a high prevalence of cognitive impairment in later life. A common factor detected in premature infants is their postnatal exposure to high oxygen tension relative to that in utero. Hyperoxia is known to elicit injury to premature lung and retina. Because data on the exposure of the brain to hyperoxia are limited, we studied the effects of high oxygen on this tissue.

METHODS

Rat pups were exposed from birth until day 6 to 21% or 80% O(2). Cerebral vascular density was quantified by lectin immunohistochemistry. Immunoblots for several proteins were performed on brain extracts. We assessed cerebral functional deficits by visual evoked potentials.

RESULTS

Exposure of pups to hyperoxia leads to cerebral microvascular degeneration, diminished brain mass, and cerebral functional deficits. These effects are preceded by an upregulation of endothelial nitric oxide synthase (eNOS) in cerebral capillaries and a downregulation of Cu/Zn superoxide dismutase (SOD). The imbalance in nitric oxide (NO) production and antioxidant defenses favors the formation of nitrating agents in the microvessels revealed by increased nitrotyrosine (3-nt) immunoreactivity and decreased expression of NF-kappaB and the dependent vascular endothelial growth factor receptor 2. NOS inhibitors and eNOS deletion as well as an SOD mimetic (CuDIPS) restore vascular endothelial growth factor receptor-2 levels and nearly abolish the vasoobliteration. NOS inhibitors and SOD mimetic also prevent O(2)-induced diminished brain mass and functional deficit.

CONCLUSIONS

Data identify NO and nitrating agents as major mediators of cerebral microvascular damage, ensuing impaired brain development and function in immature subjects exposed to hyperoxia.

Maternal infection and white matter toxicity

Studies examining maternal infection as a risk factor for neurological disorders in the offspring have suggested that altered maternal immune status during pregnancy can be considered as an adverse event in prenatal development. Infection occurring in the mother during the gestational period has been implicated in multiple neurological effects. The current manuscript will consider the issue of immune/inflammatory conditions during prenatal development where adverse outcomes have been linked to maternal systemic infection. The discussions will focus primary on white matter and oligodendrocytes as they have been identified as target processes. This white matter damage occurs in very early preterm infants and in various other human diseases currently being examined for a linkage to maternal or early developmental immune status. The intent is to draw attention to the impact of altered immune status during pregnancy on the offspring for the consideration of such contributing factors to the general assessment of developmental neurotoxicology.

Neonatal MRI to predict neurodevelopmental outcomes in preterm infants

BACKGROUND

Very preterm infants are at high risk for adverse neurodevelopmental outcomes. Magnetic resonance imaging (MRI) has been proposed as a means of predicting neurodevelopmental outcomes in this population.

METHODS

We studied 167 very preterm infants (gestational age at birth, 30 weeks or less) to assess the associations between qualitatively defined white-matter and gray-matter abnormalities on MRI at term equivalent (gestational age of 40 weeks) and the risks of severe cognitive delay, severe psychomotor delay, cerebral palsy, and neurosensory (hearing or visual) impairment at 2 years of age (corrected for prematurity).

RESULTS

At two years of age, 17 percent of infants had severe cognitive delay, 10 percent had severe psychomotor delay, 10 percent had cerebral palsy, and 11 percent had neurosensory impairment. Moderate-to-severe cerebral white-matter abnormalities present in 21 percent of infants at term equivalent were predictive of the following adverse outcomes at two years of age: cognitive delay (odds ratio, 3.6; 95 percent confidence interval, 1.5 to 8.7), motor delay (odds ratio, 10.3; 95 percent confidence interval, 3.5 to 30.8), cerebral palsy (odds ratio, 9.6; 95 percent confidence interval, 3.2 to 28.3), and neurosensory impairment (odds ratio, 4.2; 95 percent confidence interval, 1.6 to 11.3). Gray-matter abnormalities (present in 49 percent of infants) were also associated, but less strongly, with cognitive delay, motor delay, and cerebral palsy. Moderate-to-severe white-matter abnormalities on MRI were significant predictors of severe motor delay and cerebral palsy after adjustment for other measures during the neonatal period, including findings on cranial ultrasonography.

CONCLUSIONS

Abnormal findings on MRI at term equivalent in very preterm infants strongly predict adverse neurodevelopmental outcomes at two years of age. These findings suggest a role for MRI at term equivalent in risk stratification for these infants.

Natural history of brain lesions in extremely preterm infants studied with serial magnetic resonance imaging from birth and neurodevelopmental assessment

OBJECTIVES

The aim was to survey the range of cerebral injury and abnormalities of cerebral development in infants born between 23 and 30 weeks' gestation using serial MRI scans of the brain from birth, and to correlate those findings with neurodevelopmental outcome after 18 months corrected age.

METHODS

Between January 1997 and November 2000, consecutive infants born at < 30 weeks' gestational age underwent serial MRI brain scans from birth until term-equivalent age. Infants were monitored after 18 months of age, corrected for prematurity, with the Griffiths Mental Development Scales and neurologic assessment.

RESULTS

A total of 327 MRI scans were obtained from 119 surviving infants born at 23 to 30 weeks of gestation. Four infants had major destructive brain lesions, and tissue loss was seen at term for the 2 survivors. Fifty-one infants had early hemorrhage; 50% of infants with term scans after intraventricular hemorrhage had ventricular dilation. Twenty-six infants had punctate white matter lesions on early scans; these persisted for 33% of infants assessed at term. Early scans showed cerebellar hemorrhagic lesions for 8 infants and basal ganglia abnormalities for 17. At term, 53% of infants without previous hemorrhage had ventricular dilation and 80% of infants had diffuse excessive high signal intensity within the white matter on T2-weighted scans. Complete follow-up data were available for 66% of infants. Adverse outcomes were associated with major destructive lesions, diffuse excessive high signal intensity within the white matter, cerebellar hemorrhage, and ventricular dilation after intraventricular hemorrhage but not with punctate white matter lesions, hemorrhage, or ventricular dilation without intraventricular hemorrhage.

CONCLUSIONS

Diffuse white matter abnormalities and post-hemorrhagic ventricular dilation are common at term and seem to correlate with reduced developmental quotients. Early lesions, except for cerebellar hemorrhage and major destructive lesions, do not show clear relationships with outcomes.

Historical perspectives on the etiology of cerebral palsy

This essay presents the early history on the evolution of concepts about the etiology of cerebral palsy, especially the contributions of the early pioneers. Insight into how they derived their hypotheses, including the errors they made, can help one understand the complex processes of deciphering etiologic associations.

Prolonged indomethacin exposure is associated with decreased white matter injury detected with magnetic resonance imaging in premature newborns at 24 to 28 weeks' gestation at birth

OBJECTIVES

Newborns delivered before 28 weeks' gestation commonly have white matter lesions on MRI that are associated with adverse neurodevelopmental outcomes. Our objective was to determine the risk factors for MRI-detectable white matter injury in infants delivered before 28 weeks' gestation who were treated with prophylactic indomethacin.

METHODS

This was a prospective cohort study conducted at the intensive care nursery at University of California San Francisco Children's Hospital. Patients included 57 premature newborns between 24 and 27 (+6 days) weeks' gestation at birth (October 1998 to October 2004). We identified perinatal and neonatal risk factors associated with moderate-severe "white matter injuries" (T1 signal abnormalities >2 mm or >3 areas of T1 abnormality) and moderate-severe "brain abnormality" (moderate-severe white matter injuries, any degree of ventriculomegaly, or severe intraventricular hemorrhage) on MRI. Infants were studied with MRI at 31.1 weeks' postmenstrual age (median).

RESULTS

Moderate-severe white matter injuries were detected in 12 (21%) of 53 preterm newborns, and 20 (35%) of 57 had moderate-severe brain abnormality. Prolonged indomethacin exposure was the only risk factor independently associated with a lower risk of white matter injury or brain abnormality, even when adjusting for the presence of a hemodynamically significant PDA, gestational age at birth, prenatal betamethasone, systemic infection, and days of mechanical ventilation.

CONCLUSIONS

In this observational study, a longer duration of indomethacin exposure was associated with less white matter injury in infants delivered before 28 weeks' gestation. A randomized trial of prolonged indomethacin treatment is needed to determine whether indomethacin can decrease white matter injury and neurodevelopmental abnormalities.