Brain injury in the premature infant: overview of clinical aspects, neuropathology, and pathogenesis

Quantitative analysis of the corpus callosum in children with cerebral palsy and developmental delay: correlation with cerebral white matter volume

BACKGROUND

The direct quantitative correlation between thickness of the corpus callosum and volume of cerebral white matter in children with cerebral palsy and developmental delay has not been demonstrated.

OBJECTIVE

This study was conducted to quantitatively correlate the thickness of the corpus callosum with the volume of cerebral white matter in children with cerebral palsy and developmental delay.

MATERIAL AND METHODS

A clinical database of 70 children with cerebral palsy and developmental delay was established with children between the ages of 1 and 5 years. These children also demonstrated abnormal periventricular T2 hyperintensities associated with and without ventriculomegaly. Mid-sagittal T1-weighted images were used to measure the thickness (genu, mid-body, and splenium) and length of the corpus callosum. Volumes of interest were digitized based on gray-scale densities to define the hemispheric cerebral white matter on axial T2-weighted and FLAIR images. The thickness of the mid-body of the corpus callosum was correlated with cerebral white matter volume. Subgroup analysis was also performed to examine the relationship of this correlation with both gestational age and neuromotor outcome. Statistical analysis was performed using analysis of variance and Pearson correlation coefficients.

RESULTS

There was a positive correlation between the thickness of the mid-body of the corpus callosum and the volume of cerebral white matter across all children studied (R=0.665, P=0.0001). This correlation was not dependent on gestational age. The thickness of the mid-body of the corpus callosum was decreased in the spastic diplegia group compared to the two other groups (hypotonia and developmental delay only; P<0.0001). Within each neuromotor subgroup, there was a positive correlation between thickness of the mid-body of the corpus callosum and volume of the cerebral white matter.

CONCLUSION

The thickness of the mid-body of the corpus callosum positively correlates with volume of cerebral white matter in children with cerebral palsy and developmental delay, regardless of gestational age or neuromotor outcome. Assessment of the thickness of the corpus callosum might help in estimating the extent of the loss of volume of cerebral white matter in children with a broad spectrum of periventricular white matter injury.

Plasminogen Activators Contribute to Impairment of Hypercapnic and Hypotensive Cerebrovasodilation After Cerebral Hypoxia/Ischemia in the Newborn Pig

Background and Purpose— Babies are frequently exposed to hypoxia and ischemia during the perinatal period as a result of stroke or problems with delivery or respiratory management post delivery. The only U.S. Food and Drug Administration-approved treatment for acute stroke is the administration of tPA. Nonetheless, basic science studies indicate that tPA exhibits both beneficial and deleterious effects on central nervous system function. Cerebral hypoxia/ischemia (H/I) impairs dilation to hypercapnia and hypotension in the newborn pig. We investigated the role of exogenous and endogenous plasminogen activators (PA) in piglet hypercapnic and hypotensive dilator impairment after H/I.

Methods— Responses to dilator stimuli were measured in chloralose-anesthetized piglets equipped with a closed cranial window before and after hypoxia (P o 2 35 mm Hg) and subsequent global cerebral ischemia. Data (n=6) were analyzed by repeated-measures analysis of variance.

Results— Hypercapnic (P co 2 75 mm Hg) and hypotensive (mean arterial blood pressure decreased by 45%) pial artery dilation (PAD) was blunted after H/I and reversed to vasoconstriction in animals pretreated with tPA or uPA (10 −7 mol/L; 26±2, 11±1, and −4±1% for hypercapnia before, after H/I, and after H/I with tPA). In animals pretreated with EEIIMD (10 −7 mol/L), a peptide that binds uPA and tPA but does not affect proteolysis or soluble uPA receptor (suPAR, 10 −7 mol/L), which binds but does not affect the proteolytic activity of uPA. PAD induced by hypercapnia and hypotension was attenuated to a lesser extent (25±2 and 17±1% for hypercapnic PAD before and after H/I in EEIIMD-pretreated animals and 21±1 and 18±2% in suPAR-pretreated animals).

Conclusions— These data show that exogenous PA administration potentiates the impairment of hypercapnic and hypotensive PAD that occurs after H/I. Inhibition of endogenous PA may ameliorate the impairment of PAD induced by hypercapnia and hypotension PAD that develops after hypoxic central nervous system injury of diverse etiologies.

Object working memory deficits predicted by early brain injury and development in the preterm infant

Children born preterm and of very low birth weight are at increased risk of learning difficulties and educational under-achievement. However, little is known about the specific neuropsychological problems facing these children or their neurological basis. Using prospective longitudinal data from a regional cohort of 92 preterm and 103 full-term children, this study examined relations between term MRI measures of cerebral injury and structural brain development and children's subsequent performance on an object working memory task at the age of 2 years. Results revealed clear between-group differences, with preterm children having greater difficulty encoding new information in working memory than term control children. Within the preterm group, task performance at the age of 2 years was related to both qualitative MRI measures of white matter (WM) injury and quantitative measures of total and regional brain volumes assessed at term equivalent. Bilateral reductions in total tissue volumes (%region) of the following cerebral regions were specifically related to subsequent working memory performance: dorsolateral prefrontal cortex, sensorimotor, parietooccipital and premotor. Associations between total cerebral tissue volumes at term (adjusted and unadjusted for intracranial volume) persisted even after the effects of WM injury were taken into account. This suggests that early disturbance in cerebral development may have an independent adverse impact on later working memory function in the preterm infant. These findings add to our understanding of the neuropathological pathways associated with later executive dysfunction in the very preterm infant.

Are maternal hypertension and small-for-gestational age risk factors for severe intraventricular hemorrhage and cystic periventricular leukomalacia? Results of the EPIPAGE cohort study

OBJECTIVE

The purpose of this study was to examine the relationships between different causes of preterm delivery (eg, maternal hypertension, small-for-gestational age [SGA], other) and cerebral damage (eg, cystic periventricular leukomalacia [c-PVL], grade III intraventricular hemorrhage [IVH], and intra-parenchymal hemorrhage [IPH]).

STUDY DESIGN

This study included 1902 very preterm singletons who were transferred to neonatal intensive care units in 9 French regions. We used logistic regression models to compare the risk of cerebral injury associated with maternal hypertension, SGA, and all other causes of preterm delivery.

RESULTS

We found that the risk of c-PVL and grade III IVH was higher in infants born after preterm premature rupture of membranes (PPROM) with short latency or idiopathic preterm labor than in infants born to hypertensive mothers. We show that SGA and antepartum maternal hemorrhage significantly increase the risk of IPH.

CONCLUSION

Our results show that infants born to hypertensive mothers have a lower risk of cerebral injuries than infants born following idiopathic preterm labor and PPROM because they are less exposed to prenatal infection.

Age and cerebral circulation

Cerebral blood flow, and its control, vary as a function of age. This review focuses on the perinatal period and compares/contrasts this age period to that of the juvenile/adult. Additionally, this review describes mechanisms important in the control of the cerebral circulation as a function of age during physiologic and pathologic conditions. Two topics of pathophysiology are considered: cerebral hypoxia ischemia, often seen in perinates due to problems with delivery or respiratory management post delivery, and traumatic brain injury, described as the shaken impact syndrome, an example of child abuse. Clinically, it is important to understand the pathophysiology of the cerebral circulation in order to optimize mechanistically appropriate therapeutic modalities.

Intraventricular hemorrhage in the premature neonate

Intraventricular hemorrhage in the premature neonate has been and continues to be a cause of morbidity and mortality in NICUs around the globe. Much information is available concerning the etiology and preventative and treatment strategies to reduce the incidence of IVH in this patient population. As neonatal caregivers are struggling to care for and protect infants who are surviving despite extreme prematurity, this survival is complicated by the infant's cerebral vasculature, which is very susceptible to hemorrhage; by respiratory problems that require the use of lifesaving, but potentially harmful, ventilation interventions; and by the infant's compromised ability to self-regulate vascular responses to stress. The preventative treatments being explored and proposed may come with debilitating and potentially lethal sequelae. Research continues, however. New recommendations are being proffered, and perhaps, in the near future, the incidence of IVH and its associated morbidity and mortality will decline dramatically.

Significant head cooling can be achieved while maintaining normothermia in the newborn piglet

BACKGROUND

Hypothermia has been shown to be neuroprotective in animal models of hypoxia-ischaemia. It is currently being evaluated as a potentially therapeutic option in the management of neonatal hypoxic-ischaemic encephalopathy. However, significant hypothermia has adverse systemic effects. It has also recently been found that the stress of being cold can abolish the neuroprotective effects of hypothermia. It is hypothesised that selective head cooling (SHC) while maintaining normal core temperature would enable local hypothermic neuroprotection while limiting the stress and side effects of hypothermia.

OBJECTIVE

To determine whether it is possible to induce moderate cerebral hypothermia in the deep brain of the piglet while maintaining the body at normothermia (39 degrees C).

METHODS

Six piglets (<48 hours old) were anaesthetised, and temperature probes inserted into the brain. Temperature was measured at different depths from the brain surface (21 mm (T(deep brain)) to 7 mm (T(superficial brain))). After a 45 minute global hypoxic-ischaemic insult, each piglet was head cooled for seven hours using a cap circulated with cold water (median 8.9 degrees C (interquartile range 7.5-14)) wrapped around the head. Radiant overhead heating was used to warm the body during cooling.

RESULTS

During SHC it was possible to cool the brain while maintaining a normal core temperature. The mean (SD) T(deep brain) during the seven hour cooling period was 31.1 (4.9) degrees C while T(rectal) remained stable at 38.8 (0.4) degrees C. The mean T(rectal)-T(deep brain) difference throughout the cooling period was 9.8 (6.1) degrees C. The mean T(skin) required was 40.8 (1.1) degrees C. There was no evidence of skin damage secondary to these skin temperatures. During cooling only one piglet shivered.

CONCLUSIONS

It is possible to maintain systemic normothermia in piglets while significantly cooling the deeper structures of the brain. This method of cooling may further limit the side effects associated with systemic hypothermia and be feasible for premature infants.

Fine structural correlates of the choroid plexus of the lateral cerebral ventricle of the human fetal brain

The germinal matrix neuroepithelium and the choroidal fissure of the fetal choroid plexus commonly possess microvessels that are often poorly developed. There may be a reduction of type IV collagen that surrounds these fragile microvessels. During the first and second trimester of neural development, these microvessels are friable and can undergo intraventricular hemorrhage under a number of circumstances. Early subtle changes in the integrity of germinal matrix epithelium are not easily visualized by ultrasound. The current investigation employing scanning electron microscopy clearly defines subtle hemorrhagic events and tearing of the germinal matrix neuroepithelium in the brains of human fetuses. A 23-week-old fetus survived for 11 days but died from other causes. The choroid plexus of this fetus was compared with the choroid plexus and germinal matrix epithelium of a 22-week-old fetus that was the product of an elective termination due to severe anhydramnios of unknown origin and a 19-week-old male fetus from an elective termination. All tissues were autopsy material not requiring institutional review board approval.

Antenatal steroids may reduce adverse neurological outcome following chorioamnionitis: neurodevelopmental outcome and chorioamnionitis in premature infants

OBJECTIVE

To examine the effect of antenatal steroid exposure and in utero inflammation on the development of severe intraventricular haemorrhage, periventricular leukomalacia and long-term neurological outcome in infants less than 30 completed weeks gestation.

METHOD

Infants less than 30 completed weeks gestation from January 1996 to July 2001 were identified from a prospectively managed database. Placental pathology was reviewed for the presence or absence of chorioamnionitis and funisitis. Infants were divided into three groups depending on the degree of exposure to fetal inflammation (no inflammation, chorioamnionitis only and chorioamnionitis and funisitis). Data relating to gestational age, birthweight, sex, antenatal steroid exposure, surfactant treatment, days of positive pressure ventilation and days of oxygen requirement were collected. Cerebral ultrasound studies were examined for evidence of intraventricular or intraparenchymal echodensity and periventricular leukomalacia. Long-term neurological outcome was assessed by neurological examination for cerebral palsy and by Griffiths Mental Developmental Assessment for general developmental quotient.

RESULTS

Two hundred and twenty infants were identified. The mean gestational age was 27.7 weeks and the mean birthweight 1092 g. Seventy-two per cent of mothers had received a complete course of antenatal steroids. The risk of Grade III intraventricular haemorrhage or intraparenchymal echodensity was associated with exposure to in utero inflammation if a complete course of antenatal steroids had not been received (P = 0.002). This association did not exist if a complete course of antenatal steroids was given (P = 0.62). Fourteen infants had cerebral palsy (7%). The presence of cerebral palsy was also associated with in utero inflammation in the absence of complete antenatal steroid cover (P = 0.03) and not in the presence of complete cover (P = 0.59). The mean general developmental quotient on Griffiths Mental Developmental Assessment at 12 months or 3 years was not affected by exposure to in utero inflammation regardless of antenatal steroid exposure.

CONCLUSION

Risk of intraventricular haemorrhage or intraparenchymal echodensity and cerebral palsy was associated with in utero inflammation in the absence of a complete course of antenatal steroids. A complete course of antenatal steroids appeared to extinguish any association between in utero inflammation and adverse neurological outcome.

Learning disabilities in children with very low birthweight: prevalence, neuropsychological correlates, and educational interventions

This study examined achievement, neuropsychological, and intervention outcomes at a mean age of 11 years in children with very low birthweight (VLBW, <1500 g) compared with a term-born control group. To assess the prevalence and correlates of specific learning disabilities (LD), the sample was limited to children without neurosensory disorders who had at least low average IQ. Participants included 31 children with <750 g birthweight, 41 with 750-1499 g birthweight, and 52 controls. The <750 g group obtained lower scores in math, IQ, and perceptual-organizational skills than the term-born group. The < 750 g group also had higher rates of past and present LD than the controls. Despite these differences, the groups did not differ significantly in rates of special education or tutorial/remedial assistance. These findings suggest that children with extremely low birthweight without gross physical or intellectual impairments are at higher risk for LD and cognitive deficiencies than their term-born peers and that further efforts are needed to improve identification and treatment of these learning problems.

White matter injury in the immature brain: role of interleukin-18

Inflammation is likely to be important in the pathophysiology of white matter damage in the immature brain. In order to investigate the involvement of interleukin (IL)-18, we subjected 9-day-old IL-18-deficient and wild-type (WT) mice to hypoxia-ischemia (HI) (unilateral carotid ligation and exposure to 10% oxygen) and white matter injury was evaluated after 3 days by immunostaining for myelin basic protein (MBP) and neurofilament (NF). The immunoreactivity of MBP was significantly higher by 92, 49 and 21%, respectively, in subcortical white matter, striatum and thalamus in IL-18-deficient mice versus WT mice following HI. Similarly, there was a more pronounced immunoreactivity of NF by 78% in the subcortical white matter in IL-18 KO versus WT mice. IL-18 was expressed by astrocytes and microglia, whereas the IL-18 receptor was mainly found in astrocytes localized in and around the subventricular white matter. Taken together, these results indicate that release of IL-18 may play an important role in the development of white matter injury in the neonatal brain.

Long-term neuropsychological outcomes of very low birth weight: associations with early risks for periventricular brain insults

Few follow-up studies of children with very low birth weight (VLBW, <1,500 g) have examined neuropsychological sequelae at later ages or neonatal risks as predictors of these outcomes. The present study assessed cognitive skills at mean age 16 years in 48 participants with <750 g birth weight, 47 with 750-1,499 g birth weight, and 52 term-born controls. Our major objectives were to delineate the long-term cognitive consequences of VLBW, and to determine if risks for periventricular brain insults accounted for variations in outcomes. Analysis revealed poorer outcomes for the <750 g group than for term-born controls on nearly all measures, with specific impairments in visual-motor skills, spatial memory, and executive function. Predictors of outcome for participants with VLBW included lower birth weight, lower weight for gestational age, and a longer period of oxygen requirement for chronic lung disease. The longer-term consequences of VLBW are consistent with expectations based on early brain pathology and suggest limitations to functional plasticity.

Les troubles du développement des enfants grands prématurés mesurés à l’âge scolaire

Advances in perinatal care have lead to the survival of an increasing number of children born very premature. The purpose of this review is to discuss findings in the literature regarding long term developmental outcome of infants born prematurely especially for studies with children at least 5 years old, born in the 80's or after, in a context of care with increased use of antenatal corticoids, in utero transfer, and surfactant therapy. Developmental sequelae, which are seen in children older than those presenting severe deficiencies, concerns a greater number of very premature children. They have poorer outcomes than term children or normal birth weight controls for cognitive-neuropsychological skills, school performances and behavior. Long term follow up of these children shows that consequences are still present for adolescents or young adults. There is a gradient of developmental sequelae in children that is inversely related to decreasing gestational age or birth weight. Developmental sequelae are related to neonatal medical complications and social risks factors. Research should be conducted in order to better understand etiology and neuropathological basis of sequelae, and the long term developmental implication of being born very premature and the type of care or intervention which could improve their development. An early and regular follow up by a team specialized in child development should be proposed in order to detect developmental sequelae and propose early intervention.

Executive functioning in school-aged children who were born very preterm or with extremely low birth weight in the 1990s

OBJECTIVE

To determine the frequency, nature, and severity of executive dysfunction (EDF) at 8 years of age in extremely low birth weight (ELBW)/very preterm infants who were born in the 1990s, compared with normal birth weight (NBW) control subjects.

METHODS

A geographically determined cohort study was conducted in Victoria, Australia. The ELBW/very preterm cohort comprised 298 consecutive survivors at 2 years of age who had gestational ages <28 completed weeks or birth weights <1000 g and were born during 1991-1992. The NBW cohort comprised 262 randomly selected children of birth weight >2499 g matched on date of birth, gender, ethnicity, and health insurance status. The participation rate was 92% (275 of 298) for the ELBW/very preterm cohort and 85% (223 of 262) for the NBW cohort. Cognitive and behavioral measures of executive functioning were administered.

RESULTS

The ELBW/very preterm cohort exhibited significant EDF compared with their NBW peers in all areas assessed. The cognitive assessment revealed global impairment rather than deficits in specific executive domains. The ELBW/very preterm children also displayed more behavioral problems indicative of EDF than the NBW children. Severe impairments were exhibited in only a small minority of ELBW/very preterm children. No statistical conclusions were altered after adjustment for sociodemographic variables or when children with substantial neurosensory impairment were excluded.

CONCLUSIONS

School-aged children who were born in the 1990s and were very preterm or had ELBW are at greater risk for developing EDF and require ongoing neuropsychological review throughout middle childhood.

Postnatal changes in cerebral oxygen extraction in the preterm infant are associated with intraventricular hemorrhage and hemorrhagic parenchymal infarction but not periventricular leukomalacia

Fluctuations in cerebral hemodynamics have been implicated in the pathogenesis of acquired brain damage in babies born prematurely. This study examined the changes in cerebral fractional oxygen extraction (FOE) over the first 3 d after birth in 25 very-low-birth-weight preterm infants. Twelve infants had no major cerebral injury and 13 had acquired brain injury; cystic periventricular leukomalacia (PVL) was present in 4 and intraventricular hemorrhage (IVH) in 9, of whom 2 also had hemorrhagic parenchymal infarction (HPI). Normal values (median, 5(th)-95(th) centiles) for cerebral FOE in very-low-birth-weight infants with no cerebral injury were 0.38 (0.23-0.53) on d 1, 0.31 (0.18-0.45) on d 2, and 0.28 (0.17-0.38) on d 3. Infants who developed cystic PVL had no significant change in cerebral FOE during the first 3 d after birth. By contrast, cerebral FOE fluctuated in infants with IVH over the 3 d of measurement, decreasing from d 1 to d 2 (p = 0.03) and increasing from d 2 to d 3 (p = 0.02). The highest cerebral FOE values were seen in the two infants with HPI. The different patterns of change in cerebral FOE with HPI and cystic PVL provide additional evidence that the pathogenesis of these two conditions is different. Because high cerebral FOE is likely to be a consequence of low cerebral oxygen delivery, probably because of low cerebral blood flow, our results indicate that fluctuations in cerebral blood flow may occur when there is IVH or HPI.

Longitudinal outcomes of very low birth weight: neuropsychological findings

To investigate the effects of very low birth weight (VLBW, &1500 g) on the development of neuropsychological skills, we assessed 67 children with birth weight <750 g, 64 with birth weight 750-1499 g, and 67 term-born controls. Growth modeling of raw scores from mean ages 7-14 years revealed persistent VLBW sequelae. Even when adjusting for IQ, the <750 g group scored more poorly than the term-born group on measures of language processing, verbal list learning, and perceptual-motor and organizational abilities. This group also made slower age-related progress than the control group on tests of perceptual-motor and executive functions. Environmental factors moderated group differences in change on other cognitive measures. These results revealed further evidence for slower skill development in both VLBW groups relative to controls, as well as"catch-up" growth in the 750-1499 g group on some measures. The findings suggest age-related changes in the cognitive sequelae of VLBW that depend on the skill assessed, the degree of VLBW, and environmental factors.

Value of neurosonography in predicting subsequent cognitive and motor development in extremely low birth weight neonates

OBJECTIVE

To compare the results of neurosonography (NSG) with subsequent neurodevelopmental testing in extremely low birth weight (ELBW; < or =1000 g) neonates.

STUDY DESIGN

NSG at hospital discharge was available in 164 neonates and Bayley Scores of Infant Development (BSID II) evaluations (MDI and PDI) were performed in 158 of these infants at 18 to 22 months. Neurosonographic studies obtained prior to the discharge study also were evaluated. Neurosonograms were interpreted by pediatric radiologists, and BSID II examinations were performed by certified examiners masked to the results of the neurosonographic studies.

RESULTS

A normal sonographic study at discharge was observed in 44% (14/32) of neonates with MDI <70 and 29% (7/24) with PDI <70. Furthermore, the sonographic study at discharge was normal in 59% (36/61) of neonates with MDI 70 to 84 and 56% (31/55) with PDI 70 to 84. Conversely, approximately 30 to 40% of those with an abnormality noted on neurosonogram at discharge, or at any time during hospitalization, had MDI and/or PDI scores > or =85. The association between abnormal NSG at discharge and low BSID II results was stronger for the PDI exam compared with the MDI exam.

CONCLUSION

These results emphasize the limitations of NSG in predicting subsequent neurodevelopmental outcome in ELBW neonates. The primary role for NSG in ELBW neonates may be in the diagnosis and management of acute problems, such as intraventricular hemorrhage and posthemorrhagic hydrocephalus, and not as a tool to predict subsequent outcome.

Long-term follow-up study of West syndrome: Differences of outcome among symptomatic etiologies

OBJECTIVES

To evaluate the outcome of West syndrome and to elucidate the differences in the outcome related to the timing of brain injury.

STUDY DESIGN

Medical records of 60 patients who were followed regularly for more than seven years were reviewed. The following clinical features were assessed: onset, seizure evolution, electroencephalography and intelligence. Those variables were compared among five groups: cryptogenic, prenatal, preterm, term, and postnatal groups.

RESULTS

The onset ages of the postnatal group were later than those of the others (P<.05). The relapse after adrenocorticotropic hormone therapy of the preterm group was the earliest among the groups (P<.05). Regarding encelphalography, the ratio of patients with focal discharges was higher in the postnatal group than in the prenatal group (P<.05). The ratios of patients in whom focal epilepsy developed were higher in the term and postnatal group than in the cryptogenic and prenatal group (P<.05). The term group showed similar characteristics to those of the postnatal group. Seven of the 60 had normal intelligence, including three girls with tuberous sclerosis.

CONCLUSION

The diverse outcomes of West syndrome depending on etiology seemed to be related to the timing of brain injury and brain development.

Magnetic resonance imaging of preterm brain injury

Magnetic resonance imaging (MRI) has proved to be a valuable tool for monitoring development and pathology in the preterm brain. This imaging modality is useful for assessing numerous pathologies including periventricular leukomalacia, intraventricular haemorrhage/germinal layer haemorrhage, and periventricular haemorrhagic infarction, and can help to predict outcome in these infants. MRI has also allowed the detection of posterior fossa lesions, which are not easily seen with ultrasound. Additionally, and perhaps most relevant, quantitative MR studies have shown differences between the normal appearing preterm brain at term equivalent age and term born infants, confirming that the brain develops differently in the ex utero environment. Further studies using quantifiable MR techniques will improve our understanding of the effects of the ex utero environment, including aspects of neonatal intensive care on the developing brain.

Increased platelet-activating factor-induced periventricular brain microvascular constriction associated with immaturity

Oxidant stress contributes to the pathogenesis of hypoxic-ischemic encephalopathies. Platelet-activating factor (PAF) is generated during oxidant stress. We studied the vasomotor mode of actions of PAF on periventricular (PV) microvessels of fetal ( approximately 75% of term), newborn (1-3 days), and adult pigs. PAF constricted PV microvessels from fetal (29.27 +/- 2.6%) and newborn (22.14 +/- 3.2%) pigs but was ineffective in adults (<2.5%). Specific [(3)H]PAF binding was greater in fetus and newborn than in adults; a concordant developmental PAF-induced inositol phosphate formation was observed. PAF-induced vasoconstriction was abrogated by thromboxane A(2) (TXA(2)) synthase and receptor inhibitors, calcium channel blockers, and by removal of endothelium; vasoconstriction to TXA(2) mimetic U-46619 did not differ with age. Immunoreactive TXA(2) synthase expression and PAF-evoked TXA(2) formation revealed a fetus> newborn>adult profile. Thus the greater PAF-induced PV microvascular constriction in younger subjects seems attributable to greater PAF receptor density and mostly secondary to TXA(2) formation from endothelium. The resulting decrease in blood flow may contribute to the increased vulnerability of the PV brain regions to oxidant stress-induced injury in immature subjects.

Selective neuromicrovascular endothelial cell death by 8-Iso-prostaglandin F2alpha: possible role in ischemic brain injury

BACKGROUND AND PURPOSE

Free radical-induced peroxidation is an important factor in the genesis of hypoxic-ischemic encephalopathy, including that of the preterm infant. Isoprostanes are major peroxidation products. Since microvascular dysfunction seems to contribute to ischemic encephalopathies, we studied the cytotoxicity of 8-iso-prostaglandin F2alpha (PGF2alpha) on cerebral microvascular cells.

METHODS

Microvascular endothelial, astroglial, and smooth muscle cells from newborn brain were cultured. The cytotoxicity of 8-iso-PGF2alpha on these cells was determined by MTT assays and lactate dehydrogenase (LDH) release, propidium iodide incorporation, and DNA fragmentation (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling [TUNEL]). In addition, effects of intraventricular injections of 8-iso-PGF2alpha and possible involvement of thromboxane in 8-iso-PGF2alpha-induced cytotoxicity were determined.

RESULTS

8-Iso-PGF2alpha induced time- and concentration-dependent endothelial cell death (EC50=0.1 nmol/L) but exerted little effect on smooth muscle and astroglial cells; endothelial cell death seemed mostly of oncotic nature (propidium iodide incorporation and LDH release). Cell death was associated with increased endothelial thromboxane A2 (TXA2) formation and was prevented by TXA2 synthase inhibitors (CGS12970 and U63557A); TXA2 mimetics U46619 and I-BOP also caused endothelial cell death. Intraventricular injection of 8-iso-PGF2alpha induced periventricular damage, which was attenuated by CGS12970 pretreatment.

CONCLUSIONS

These data disclose a novel action of 8-iso-PGF2alpha involving TXA2 in oxidant stress-induced cerebral microvascular injury and brain damage.

White matter injury following systemic endotoxemia or asphyxia in the fetal sheep

White matter injury is the most frequently observed brain lesion in preterm infants. The etiology remains unclear, however, both cerebral hypoperfusion and intrauterine infections have been suggested as risk factors. We compared the neuropathological outcome, including the effect on oligodendrocytes, astrocytes, and microglia, following either systemic asphyxia or endotoxemia in fetal sheep at midgestation. Fetal sheep were subjected to either 25 minutes of umbilical cord occlusion or systemic endotoxemia by administration of Escherichia coli lipopolysaccharide (LPS O111:B4, 100 ng/kg, IV). Periventricular white matter lesions were observed in 2 of 6 asphyxiated fetuses, whereas the remaining animals showed diffuse injury throughout the subcortical white matter and neuronal necrosis in subcortical regions, including the striatum and hippocampus. LPS-treatment resulted in focal inflammatory infiltrates and cystic lesions in periventricular white matter in 2 of 5 animals, but with no neuron specific injury. Both experimental paradigms resulted in microglia activation in the white matter, damaged astrocytes, and loss of oligodendrocytes. These results show that the white matter at midgestation is sensitive to injury following both systemic asphyxia and endotoxemia. Asphyxia induced lesions in both white and subcortical grey matter in association with microglia activation, and endotoxemia resulted in selective white matter damage and inflammation.

Role of Nociceptin/Orphanin FQ in the physiologic and pathologic control of the cerebral circulation

Nociceptin/orphanin FQ is a newly described member of the opioid family. Previous minireviews in this series have described the contribution of important factors, including opioids, in the regulation of the cerebral circulation during physiologic and pathologic conditions. The present review extends these initial comments to an opioid whose vascular actions have only very recently been appreciated. In particular, this review discusses the contribution of nociceptin/orphanin FQ to impaired cerebral hemodynamics after cerebral hypoxia/ischemia and traumatic brain injury.

Advances in postnatal neuroimaging: relevance to pathogenesis and treatment of brain injury

The human brain is susceptible to a wide variety of insults. The permanent residua of these abnormalities are represented in dysfunction of one or more areas of neurodevelopment. A full understanding of normal brain development, mechanisms of brain injury, and consequences for subsequent brain development is required to determine which infants are at risk for neurodevelopmental handicap, and to monitor the effects of new treatments and management regimens designed to prevent these disabilities. Advanced magnetic resonance techniques, such as quantitative morphometric magnetic resonance techniques, diffusion-weighted magnetic resonance techniques, and magnetic resonance spectroscopy applied to the study of early human brain development have given us a better understanding of the pathophysiologic mechanisms of brain injury and its effects on subsequent brain development. Magnetic resonance imaging has provided an invaluable tool for the study of the fetal and newborn brain in vivo.

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.

Models of white matter injury: comparison of infectious, hypoxic-ischemic, and excitotoxic insults

White matter damage (WMD) in preterm neonates is strongly associated with adverse outcome. The etiology of white matter injury is not known but clinical data suggest that ischemia-reperfusion and/or infection-inflammation are important factors. Furthermore, antenatal infection seems to be an important risk factor for brain injury in term infants. In order to explore the pathophysiological mechanisms of WMD and to better understand how infectious agents may affect the vulnerability of the immature brain to injury, numerous novel animal models have been developed over the past decade. WMD can be induced by antenatal or postnatal administration of microbes (E. coli or Gardnerella vaginalis), virus (border disease virus) or bacterial products (lipopolysaccharide, LPS). Alternatively, various hypoperfusion paradigms or administration of excitatory amino acid receptor agonists (excitotoxicity models) can be used. Irrespective of which insult is utilized, the maturational age of the CNS and choice of species seem critical. Generally, lesions with similarity to human WMD, with respect to distribution and morphological characteristics, are easier to induce in gyrencephalic species (rabbits, dogs, cats and sheep) than in rodents. Recently, however, models have been developed in rats (PND 1-7), using either bilateral carotid occlusion or combined hypoxia-ischemia, that produce predominantly white matter lesions. LPS is the infectious agent most often used to produce WMD in immature dogs, cats, or fetal sheep. The mechanism whereby LPS induces brain injury is not completely understood but involves activation of toll-like receptor 4 on immune cells with initiation of a generalized inflammatory response resulting in systemic hypoglycemia, perturbation of coagulation, cerebral hypoperfusion, and activation of inflammatory cells in the CNS. LPS and umbilical cord occlusion both produce WMD with quite similar distribution in 65% gestational sheep. The morphological appearance is different, however, with a more pronounced infiltration of inflammatory cells into the brain and focal microglia/macrophage ("inflammatory WMD") in response to LPS compared to hypoperfusion evoking a more diffuse microglial response usually devoid of cellular infiltrates ("ischemic WMD"). Furthermore, low doses of LPS that by themselves have no adverse effects in 7-day-old rats (maturation corresponding to the near term human fetus), dramatically increase brain injury to a subsequent hypoxic-ischemic challenge, implicating that bacterial products can sensitize the immature CNS. Contrary to this finding, other bacterial agents like lipoteichoic acid were recently shown to induce tolerance of the immature brain suggesting that the innate immune system may respond differently to various ligands, which needs to be further explored.

Public health issues related to infection in pregnancy and cerebral palsy

Cerebral palsy is the most common neuromotor developmental disability of childhood, affecting as many as 8,000 to 12,000 children born in the U.S. each year (corresponding to a prevalence rate of between 2 and 3 per 1000 children). Recent improvements in neonatal care have not resulted in a decline in the overall prevalence of cerebral palsy and, in fact, greater numbers of very preterm/very low birth weight infants are surviving with cerebral palsy and other developmental problems. Infection in pregnancy may be an important cause of the disorder. In preterm infants, there appears to be about a 2-fold increased risk for cerebral palsy from chorioamnionitis, and in term infants the estimated increased risk is about 4-fold. Provisionally, chorioamnionitis might account for 12% of spastic cerebral palsy in term infants and 28% of cerebral palsy in preterm infants. Studies of biochemical markers of fetal inflammation typically associated with infection also suggest that an inflammatory response may be an important independent etiologic factor. If a substantial proportion of cerebral palsy is attributable to acute amnionitis infection and/or neonatal sepsis, cerebral palsy should have decreased in the United States after administration of intrapartum antibiotics became widespread in response to publication of public health consensus guidelines for Group B streptococcus in 1996. However, failure to detect declines could have a number of explanations and these explanations illustrate the many public health challenges related to intrauterine infection and cerebral palsy. Given the gaps in our current knowledge about intrauterine infection and cerebral palsy, public health recommendations for timely and specific prevention activities are limited at this time.

NOC/oFQ and NMDA contribute to piglet hypoxic ischemic hypotensive cerebrovasodilation impairment

Previous studies have observed that hypotensive pial artery dilation was blunted after hypoxia-ischemia. In unrelated studies, the opioid nociceptin/orphanin FQ (NOC/oFQ) was observed to contribute to hypoxic ischemic impairment of N-methyl-D-aspartate (NMDA)-induced pial dilation. This study determined the contribution of NOC/oFQ and NMDA to hypoxic ischemic hypotensive cerebrovasodilation impairment in newborn pigs equipped with a closed cranial window. Global cerebral ischemia was produced via elevated intracranial pressure. Hypoxia decreased PO(2) to 33 +/- 3 mm Hg. Topical NOC/oFQ (10(-10) M), the cerebrospinal fluid concentration after hypoxia-ischemia, had no effect on pial artery diameter by itself but attenuated hypotension (mean arterial blood pressure decrease of 44 +/- 2%) -induced pial artery dilation (35 +/- 2% versus 22 +/- 3%). Hypotensive pial artery dilation was blunted by hypoxia-ischemia, but such dilation was partially protected by pretreatment with the putative NOC/oFQ receptor antagonist, [F/G] NOC/oFQ (1-13) NH(2) (10(-6) M; 29 +/- 2%, sham control; 7 +/- 2%, hypoxia-ischemia; and 13 +/- 2%, hypoxia-ischemia and [F/G] NOC/oFQ (1-13) NH(2)). Coadministration of the NMDA antagonist MK801 (10(-5) M) with NOC/oFQ(10(-10) M) partially prevented hypotensive pial dilation impairment. Similarly, pretreatment with MK801 partially protected hypoxic ischemia impairment of hypotensive pial dilation (35 +/- 2%, sham control; 7 +/- 1%, hypoxia-ischemia; 22 +/- 2%, hypoxia-ischemia + MK801). These data show that NOC/oFQ and NMDA contribute to hypoxic ischemic hypotensive cerebrovasodilation impairment. These data suggest that NOC/oFQ modulation of NMDA vascular activity also contributes to such hypotensive impairment.

Selective vulnerability of late oligodendrocyte progenitors to hypoxia-ischemia

In the premature infant, hypoxic-ischemic damage to the cerebral white matter [periventricular leukomalacia (PVL)] is a common and leading cause of brain injury that often results in chronic neurologic disability from cerebral palsy. The cellular basis for the propensity of white matter injury to occur in the developing brain and the greater resistance of the adult white matter to similar injury remains unknown. By using a neonatal rat model of hypoxic-ischemic injury, we found that the mechanism of perinatal white matter injury involved maturation-dependent vulnerability in the oligodendroctye (OL) lineage. The timing of appearance of late OL progenitors was the major developmental factor that accounted for the susceptibility of the neonatal white matter to injury. Late OL progenitors were the major OL lineage stage killed by apoptosis, whereas early OL progenitors and more mature OLs were highly resistant. The density of pyknotic late OL progenitors was significantly increased in the ischemic hemisphere (67 +/- 31 cells/mm2) versus the control hemisphere (2.2 +/- 0.4 cells/mm2; mean +/- SEM; p = 0.05), which resulted in the death of 72 +/- 6% of this OL stage. Surviving late OL progenitors displayed a reactive response in which an increase in cell density was accompanied by accelerated maturation to a P27/kip1-positive oligodendrocyte. Because we showed recently that late OL progenitors populate human cerebral white matter during the high risk period for PVL (Back et al., 2001), maturation-dependent vulnerability of OL progenitors to hypoxia-ischemia may underlie the selective vulnerability to PVL of the white matter in the premature infant.

Hypoxic-ischemic oligodendroglial injury in neonatal rat brain

Neonatal periventricular white matter injury is a major contributor to chronic neurologic dysfunction. In a neonatal rat stroke model, myelin basic protein (MBP) immunostaining reveals acute periventricular white matter injury. Yet, the extent to which myelin proteins can recover after neonatal hypoxic-ischemic injury is unknown. We developed a quantitative method to correlate the severity of the hypoxic-ischemic insult with the magnitude of loss of MBP immunostaining. Seven-day-old (P7) rats underwent right carotid ligation, followed by exposure to 8% oxygen for 1, 1.5, 2, or 2.5 h. On both P12 and P21, white matter integrity was evaluated by densitometric analysis of MBP immunostaining, and the amount of tissue injury was evaluated by morphometric measurements of cerebral hemisphere areas. The most severe hypoxic-ischemic insults (2.5 h) elicited marked reductions in MBP immunostaining ipsilaterally on both P12 and P21. In contrast, in mildly lesioned animals (1.5 h), MBP immunostaining was reduced ipsilaterally on P12, but 2 wk after lesioning, on P21, there was a substantial restoration of MBP immunostaining. The restoration in MBP immunostaining could reflect either functional recovery of injured oligodendroglia or proliferation and maturation of oligodendroglial precursors. Our data demonstrate that quantitative measurement of MBP immunostaining provides a sensitive indicator of acute oligodendroglial injury. Most importantly, we show that in this neonatal rodent stroke model, restoration of myelin proteins occurs after moderate, but not after more severe, cerebral hypoxia-ischemia.

Oxidative stress in preterm rat brain is due to mitochondrial dysfunction

Prematurity-mediated cerebral damage has been associated with oxidative stress. The aim of the present work was to study the possible role played by free oxygen radicals generated by mitochondrial respiratory function in cerebral injury in preterm neonates. Our results show that whereas total glutathione concentrations are similar in term and preterm neonates, the GSH/GSSG ratio decreases sharply in preterm neonates immediately after birth. This effect is not due to a lack of enzymes involved in GSH regeneration, such as glutathione reductase and glucose-6-phosphate dehydrogenase, but to a significant increase in free-radical generation in preterm rat brain as shown by the increase in lipoperoxidation. Because the mitochondrion is the main source of free radicals in the cell, mitochondrial respiratory function was studied in the brain of preterm neonates. Our results show that prematurity prevented the postnatal increases in complex II-III activity and ATP concentrations that occur in term neonates at 5 min after delivery. All these effects were counteracted by the oxygen supply, suggesting that the inhibition of mitochondrial function is caused by restricted oxygen availability. Consequently, cerebral damage associated with prematurity may be mediated by mitochondrial free-radical generation as a consequence of hypoxia undergone by preterm neonates at birth.

Indices of hemodynamic and respiratory functions in premature infants at risk for the development of cerebral white matter injury

OBJECTIVE

To examine potential differences in clinical risk factors, including indices of hemodynamic and respiratory functions, of premature infants developing periventricular hemorrhagic infarction (PHI) or periventricular leukomalacia (PVL).

STUDY DESIGN

Indices of hemodynamic stability and respiratory function were measured prospectively during the first week of life in a cohort of 100 premature infants with respiratory distress. Maternal history was retrospectively reviewed. These data were correlated with cranial ultrasonography using one-way ANOVA, Bonferroni multiple comparisons, and Wilcoxon rank sum tests. Longitudinal analysis was performed using Generalized Estimating Equations.

RESULTS

Fifty-two infants with normal cranial ultrasound studies were compared to 12 with PHI and 9 with PVL. Infants developing PHI had significantly lower birth weights, lower Apgar scores, were more often male and multiple gestations, and required more vasopressor support than infants with normal ultrasound studies. Infants with PHI had significantly worse indices of respiratory function than either normal infants or those with PVL. PVL was significantly associated with maternal chorioamnionitis, whereas PHI was not.

CONCLUSION

These data suggest that there are important differences in the pathogenesis of PHI and PVL. A clear understanding of these differences is required before future preventive strategies can be formulated.

Decreased activity and oxygen desaturation in prone ventilated preterm infants during the first postnatal week

OBJECTIVE

To compare the effects of supine and prone positions on oxygen saturation (SpO(2)), desaturation episodes (SpO(2) < 90% and >or= 20 seconds), and motor activity in ventilated preterm infants during their first postnatal week.

DESIGN

With use of a crossover design, we randomly assigned infants to a supine/prone or prone/supine position sequence. Infants were placed in each position for 2 hours. A stabilization period of 10 minutes before observation of each position was allowed. During the protocol, care procedures were kept minimal and ventilator settings remained unchanged.

SETTING

Neonatal intensive care units at 2 tertiary care centers in Taiwan.

SAMPLE

The sample consisted of 28 infants receiving mechanical ventilation who were 25 to 36 weeks' gestation, without known congenital abnormalities, within 7 postnatal days of birth, and were not receiving sedation.

RESULTS

When prone, infants had higher SpO(2), fewer episodes of oxygen desaturation, and less motor activity than when supine. No significant differences in duration of SpO(2) less than 90%, 85%, and 80% were found between the 2 positions. Seventy-four percent of desaturation episodes were associated with vigorous motor activity and crying.

CONCLUSION

The prone position results in less motor activity and may stabilize oxygenation for ventilated preterm infants. This may conserve energy and decrease complications of hypoxia for sick preterm infants.

Volumetric brain differences in children with periventricular T2-signal hyperintensities: a grouping by gestational age at birth

OBJECTIVE

The purpose of this study was to compare both the volumes of the lateral ventricles and the cerebral white matter with gestational age at birth of children with periventricular white matter (PVWM) T2-signal hyperintensities on MR images. The spectrum of neuromotor abnormalities associated with these hyperintensities was also determined.

MATERIALS AND METHODS

We retrospectively reviewed the MR images of 70 patients who were between the ages of 1 and 5 years and whose images showed PVWM T2-signal hyperintensities. The patients were divided into premature (n = 35 children) and term (n = 35) groups depending on their gestational age at birth. Volumetric analysis was performed on four standardized axial sections using T2-weighted images. Volumes of interest were digitized on the basis of gray-scale densities of signal intensities to define the hemispheric cerebral white matter and lateral ventricles. Age-adjusted comparisons of volumetric measurements between the premature and term groups were performed using analysis of covariance.

RESULTS

The volume of the cerebral white matter was smaller in the premature group (54 +/- 2 cm(3)) than in the term group (79 +/- 3 cm(3), p < 0.0001). The volume of the lateral ventricles was greater among the patients in the premature group (30 +/- 2 cm(3)) than among those in the term group (13 +/- 1 cm(3), p < 0.0001). Fifty percent of all the premature children had spastic diplegia or quadriplegia. Thirty-two percent of all the term children had hypotonia. There were patients in both groups whose PVWM T2-signal hyperintensities did not correlate with any neuromotor abnormalities but were associated with seizures or developmental delays.

CONCLUSION

The differences in volumetric measurements of cerebral white matter and lateral ventricles in children with PVWM T2-signal hyperintensities are related to their gestational age at birth. Several neurologic motor abnormalities are found in children with such hyperintensities.

Cerebral palsy births in eastern Denmark, 1987--90: implications for neonatal care

The Cerebral Palsy Register in eastern Denmark has collected cases using a uniform data sampling procedure since birth year 1979. We have investigated changes in the rate of cerebral palsy, related to gestational age, mortality and perinatal risk factors in children born 1983--90. The total cerebral palsy birth prevalence decreased from 3.0 in the birth year period 1983--86 to 2.4 per 1000 live births (P < 0.01) in 1987--90, owing to a decrease among all preterm infants (29--19 per 1000, P < 0.001). The perinatal and early neonatal mortality in preterm infants was unchanged from 1983--86 to 1987--90. The rate of cerebral palsy in term infants was 1.5 per 1000 in all birth-year periods from 1979--90. Among the cerebral palsy infants, the proportion of very preterm babies treated with mechanical ventilation in the neonatal period decreased from 95% in 1983--86 to 61% in 1987--90 (P < 0.001), while the group treated with CPAP among the moderately preterm babies increased from 61% to 78% (P < 0.05). The significant decline in cerebral palsy rate in preterm infants born 1987--90 may be due to a change in treatment at the neonatal intensive care units using less mechanical ventilation, a hypothesis which needs further investigation.

Late oligodendrocyte progenitors coincide with the developmental window of vulnerability for human perinatal white matter injury

Hypoxic-ischemic injury to the periventricular cerebral white matter [periventricular leukomalacia (PVL)] results in cerebral palsy and is the leading cause of brain injury in premature infants. The principal feature of PVL is a chronic disturbance of myelination and suggests that oligodendrocyte (OL) lineage progression is disrupted by ischemic injury. We determined the OL lineage stages at risk for injury during the developmental window of vulnerability for PVL (23-32 weeks, postconceptional age). In 26 normal control autopsy human brains, OL lineage progression was defined in parietal white matter, a region of predilection for PVL. Three successive OL stages, the late OL progenitor, the immature OL, and the mature OL, were characterized between 18 and 41 weeks with anti-NG2 proteoglycan, O4, O1, and anti-myelin basic protein (anti-MBP) antibodies. NG2+O4+ late OL progenitors were the predominant stage throughout the latter half of gestation. Between 18 and 27 weeks, O4+O1+ immature OLs were a minor population (9.9 +/- 2.1% of total OLs; n = 9). Between 28 and 41 weeks, an increase in immature OLs to 30.9 +/- 2.1% of total OLs (n = 9) was accompanied by a progressive increase in MBP+ myelin sheaths that were restricted to the periventricular white matter. The developmental window of high risk for PVL thus precedes the onset of myelination and identifies the late OL progenitor as the major potential target. Moreover, the decline in incidence of PVL at approximately 32 weeks coincides with the onset of myelination in the periventricular white matter and suggests that the risk for PVL is related to the presence of late OL progenitors in the periventricular white matter.

Intraventricular haemorrhage and posthaemorrhagic hydrocephalus: pathogenesis, prevention and future interventions

Intraventricular haemorrhage (IVH) is still a major complication of preterm birth with serious disability resulting. The fragile blood vessels in the germinal matrix below the ventricular lining and the instability of blood flow to this highly vascular area are the main mechanisms behind IVH. There is good evidence that corticosteroid therapy before preterm delivery reduces mortality and IVH substantially with a trend towards a reduction in disability. There is good evidence that postnatal indomethacin reduces IVH but no evidence that mortality or disability is reduced. There is evidence that stabilizing cerebral blood flow with pancuronium in infants with respiratory distress reduces IVH in the minority of infants with marked fluctuations. There is limited evidence that postnatal vitamin E and ethamsylate reduce IVH but insufficient evidence of reduced mortality or disability. Hydrocephalus following IVH results initially from multiple small blood clots throughout the CSF channels impeding circulation and re-absorption. Transforming growth factor beta is released into the CSF and there is mounting evidence that this cytokine stimulates the laying down of extracellular matrix proteins such as laminin and fibronectin which produce permanent obstruction to the CSF pathways. Interventions such as early lumbar punctures, diuretic drugs to reduce CSF production and intraventricular fibrinolytic therapy have been tested and, not only fail to prevent shunt dependence, death or disability, but have significant adverse effects. Surgical interventions such as subcutaneous reservoir and external drain have not been subject to controlled trial. Ventriculoperitoneal shunt is not feasible in the early phase after IVH but, despite the problems with blockages and infections, remains the only option for infants with excessive head expansion over periods of weeks. New treatment approaches aimed at preventing hydrocephalus are needed.

Cerebral hemodynamics after exogenous surfactant administration for respiratory distress syndrome in piglet model

OBJECTIVE

The rapid improvement of lung function after exogenous surfactant treatment for respiratory distress syndrome (RDS) can affect the functions of several other systems, which includes cerebral blood flow volume (CBF). To evaluate the change in CBF after treatment with exogenous surfactant, we measured CBF in a newborn piglet model with RDS.

METHOD

After the lung lavage with normal saline, ten animals under mechanical ventilation were administered either 120 mg/kg surfactant-TA (Surfacten) or air placebo. Heart rate, blood pressure, dynamic lung compliance (Cdyn), PaO2, PaCO2, and CBF were recorded before and every 15 min after surfactant treatment up to 120 min.

RESULTS

Cdyn was improved significantly at 45 min and later after treatment; that of the control group remained unchanged. PaO2 increased and PaCO2 decreased significantly after surfactant treatment in both groups. However, the improvement was significantly less in the control group. CBF significantly decreased by about 30% in the control group, and by about 50% in the treated group at 120 min, with a significant difference between groups. Almost 70% of the changes in CBF were attributable to changes in PaCO2 by multivariate regression analysis.

CONCLUSIONS

Treatment with exogenous surfactant improves lung compliance, and has little effect on CBF itself. The drop in levels of PaCO2 after treatment, however, had a strong relationship with decreases in CBF.

School-age consequences of birth weight less than 750 g: a review and update

Recent advances in perinatal care have led to the survival of increasing numbers of children born at the lower limits of viability. Children with very low birth weight (LBW; less than 1,500 g, 3 lb 5 oz) have been studied extensively. Findings document poorer outcomes relative to normal birth weight term-born controls in neurologic and health status, cognitive-neuropsychological skills, school performance, academic achievement, and behavior. This report reviews current knowledge regarding LBW children, with special emphasis on outcomes for children with birth weight less than 750 g (1 lb 10 oz). Results from an ongoing longitudinal study suggest a gradient of sequelae, with poorer outcomes in less than 750 g birth weight children compared to both 750 g to 1,499 g birth weight children and term-born controls. Children with less than 750 g birth weight fail to catch up with their peers over time and may even be at risk for age-related increases in sequelae. Outcomes are highly variable but related to neonatal medical complications of prematurity and social risk factors. Further research is needed to understand the etiology and neuropathological basis of sequelae, the long-term developmental implications of LBW, and treatment needs.

Impaired cerebral cortical gray matter growth after treatment with dexamethasone for neonatal chronic lung disease

OBJECTIVE

The specific aim of this study was to quantify at term the influence of postnatal systemic dexamethasone treatment for neonatal chronic lung disease on subsequent brain growth and development in premature infants without evidence of severe intraventricular hemorrhage or white matter injury.

METHODS

Eighteen premature (23 to 31 weeks) infants, 7 treated with dexamethasone and 11 not treated, were studied at term, ie, 38 to 41 postconceptional weeks, by an advanced quantitative volumetric 3-dimensional magnetic resonance imaging (MRI) technique to quantify cerebral tissue volumes. Fourteen healthy term infants also were studied for comparison. A sequence of image processing algorithms was used to segment each of the MRI slices into the following separate tissue classes: cerebral cortical gray matter, basal ganglia/thalami, unmyelinated white matter, myelinated white matter, and cerebrospinal fluid, all classified based on magnetic resonance signal intensity and anatomic location. A final summing of voxels for each tissue class was performed to compute absolute volumes in milliliters.

RESULTS

Cerebral cortical gray matter volume in premature infants treated with dexamethasone was reduced 35% when compared with gray matter volume in premature infants not treated with dexamethasone (mean +/- standard deviation, 130.3 +/- 54.0 vs 200.6 +/- 35.1 mL, respectively). Subcortical gray matter volumes (basal ganglia and thalami) and myelinated and unmyelinated white matter volumes were not significantly different among the treated and untreated groups. However, premature infants treated with dexamethasone exhibited a reduction (30%) in total cerebral tissue volume compared with total cerebral tissue volume in both the premature infants not treated with dexamethasone and the control term infants (312.7 +/- 43.7 vs 448.2 +/- 50.2 and 471.6 +/- 36.4 mL respectively). This latter finding relates primarily to the decrease in cerebral cortical gray matter volume.

CONCLUSIONS

The data suggest an impairment in brain growth, principally affecting cerebral cortical gray matter, secondary to systemic dexamethasone therapy. Although the premature infants who received dexamethasone were smaller with more severe respiratory disease, these findings are consistent with growing evidence of a potential deleterious effect of dexamethasone on neonatal brain and subsequent neurodevelopmental outcome. This apparent deleterious effect should be taken into consideration by clinicians when weighing the potential risks and benefits of this therapy for low birth weight infants with neonatal chronic lung disease.

Prediction of outcome at school age in neonatal intensive care unit graduates using neonatal neurologic tools

Prediction of outcome for neonatal intensive care unit graduates is clinically useful to counsel families effectively and target those who may benefit from early interventions. Evoked potentials have proven prognostic value of neurologic outcomes in early childhood; however, their long-term predictive validity remains to be determined. The objective of this prospective study was to determine the long-term predictive value of three neonatal neurologic assessments: brainstem auditory evoked potentials, somatosensory evoked potentials, and the Einstein Neonatal Neurobehavioral Assessment Scale. Seventy-eight high-risk newborns and 28 healthy controls were recruited and were assessed in the newborn period using these tests. At 8 to 9 years of age, 42 subjects and 13 controls were re-evaluated for developmental progress using a range of psychologic, sensorimotor, and neurologic measures. Findings indicated that the somatosensory evoked potential was most accurate at predicting outcome at school age, with high specificity (83-100%) across all domains tested and good sensitivity (80-100%) for intellectual performance and sensorimotor abilities. The brainstem auditory evoked potential was limited by false-negatives, whereas the neonatal neurobehavioral assessment yielded many false-positives. This study provides new evidence that associations between neonatal somatosensory evoked potentials and developmental sequelae continue to be significant at school age.

Augmented vasoconstriction and thromboxane formation by 15-F(2t)-isoprostane (8-iso-prostaglandin F(2alpha)) in immature pig periventricular brain microvessels

BACKGROUND AND PURPOSE

Oxidant stress, especially in the premature, plays a major role in the pathogenesis of hypoxic-ischemic encephalopathies mostly manifested in the periventricular region. We studied the vasomotor mode of actions of the peroxidation product 15-F(2t)-isoprostane (15-F(2t)-IsoP) (8-iso-prostaglandin F(2alpha)) on periventricular region during development.

METHODS

Effects of 15-F(2t)-IsoP on periventricular microvessels of fetal, newborn, and juvenile pigs were studied by video imaging and digital analysis techniques. Thromboxane formation and intracellular Ca(2+) were measured by radioimmunoassay and by using the fluorescent indicator fura 2-AM.

RESULTS

15-F(2t)-IsoP-mediated constriction of periventricular microvessels decreased as a function of age such that in the fetus it was approximately 2.5-fold greater than in juvenile pigs. 15-F(2t)-IsoP evoked more thromboxane formation in the fetus than in the newborn, which was greater than that in the juvenile periventricular region; this was associated with immunoreactive thromboxane A(2) (TXA(2)) synthase expression in the fetus that was greater than that in newborn pigs, which was greater than that in juvenile pigs. 15-F(2t)-IsoP-induced vasoconstriction was markedly inhibited by TXA(2) synthase and receptor blockers (CGS12970 and L670596). Vasoconstrictor effects of the TXA(2) mimetic U46619 on fetal, neonatal, and juvenile periventricular microvessels did not differ. 15-F(2t)-IsoP increased TXA(2) synthesis by activating Ca(2+) influx through non-voltage-gated channels in endothelial cells (SK&F96365 sensitive) and N-type voltage-gated channels (omega-conotoxin sensitive) in astrocytes; smooth muscle cells were not responsive to 15-F(2t)-IsoP but generated Ca(2+) transients to U46619 via L-type voltage-sensitive channels.

CONCLUSIONS

15-F(2t)-IsoP causes periventricular brain region vasoconstriction in the fetus that is greater than that in the newborn, which in turn is greater than that in the juvenile due to greater TXA(2) formation generated through distinct stimulatory pathways, including from endothelial and astroglial cells. The resulting hemodynamic compromise may contribute to the increased vulnerability of the periventricular brain areas to oxidant stress-induced injury in immature subjects.

Human oligodendroglial development: relationship to periventricular leukomalacia

Periventricular leukomalacia in the premature infant is a lesion of cerebral white matter with its greatest period of risk when white matter is immature, that is, when oligodendrocyte precursors are proliferating and differentiating, and before myelin sheaths are actively synthesized. Although the pathogenesis of perinatal cerebral white matter damage involves multiple factors, the correlation of the timing of the lesion with dominance of oligodendrocyte precursors in cerebral white matter suggests that intrinsic factors related to oligodendrocyte precursors are critical. Ischemia and infection have both been implicated as causes of perinatal white matter damage. Major mechanisms underlying oligodendrocyte injury in ischemia include glutamate toxicity, free-radical injury, and cytokine damage mediated by macrophages accompanying ischemia-induced inflammation. Factors related to a vulnerability of immature oligodendrocytes to ischemia potentially include a developmental lack of antioxidant enzymes to mediate oxidative stress. Cytokine-mediated injury to oligodendrocytes is also potentially important. A complete understanding of the role of immature white matter in the pathogenesis of periventricular leukomalacia is essential for developing strategies to prevent it.