[Periventricular leukomalacia. I. Histological and pathophysiological aspects]

Clinical Spectrum of Ocular and Visual Dysfunction in Children with Periventricular Leukomalacia: A Need for an Interdisciplinary Approach

The study aimed to evaluate the ocular motility and visual and optic disc abnormalities in children diagnosed with periventricular leukomalacia (PVL). A retrospective analysis was performed on 51 consecutive children who had ophthalmic symptoms and were diagnosed with PVL by using magnetic resonance imaging. The patients were assessed for visual function, strabismus, cycloplegic refraction, fundus examination, and if appropriate, spectral-domain optical coherence tomography and visual field testing were applied. The primary outcome measures were the prevalence and visual and ocular motility dysfunctions. Mean age was 5.72 ± 2.6 years (range = 1–12), median birth weight was 2,740 g (range = 1,240–3,460), and median gestational age was 34 weeks (range = 28–38). In total, 21 patients (39.6%) had neurological deficit, 11 (21.5%) had intellectual disability, and 19 (37.2%) had no neurological symptom. In the spherical equivalent refractive error and cylinder power analysis, 10 patients had ≥3.0 D myopia, 15 had ≥3.0 D hyperopia, and eight had ≥2.50 D astigmatism. Thirteen (25.4%) children had a best-corrected visual acuity between 20/40 and 20/20 for Snellen card, while 9 (17.6%) had strabismic amblyopia and 6 (11.7%) had anisometropic amblyopia. Manifest strabismus was present in 35 patients (68.6%); of whom 12 had esotropia (23.5%), 16 had exotropia (31.3%) and 6 had vertical deviation (11.7%). Manifest or latent nystagmus was detected in 14 patients (27.4%). In 28 patients (54.9%), there was optic nerve abnormality. Two patients had hypoplastic disc, 14 had optic disc pallor, 7 had large cupping, and 5 had total optic atrophy. Six subjects underwent reliable visual field (VF) examinations, and all six had abnormal VFs, with inferior fields being most affected. Ocular motility disorders, optic nerve abnormalities, VF defects, and low visual acuity are common findings in this cohort of PVL patients and maybe the only presenting signs of the disease. The recognition of the visual disabilities and implementation of early rehabilitation may have a significant benefit in these children.

Critical Congenital Heart Diseases in Preterm Neonates: Is Early Cardiac Surgery Quite Reasonable?

Prematurity is a recognized risk factor for morbidity and mortality following cardiac surgery. Postoperative and long-term outcomes after cardiac surgery performed in the preterm period are poorly described. The aim of this study was to analyze a population of preterm neonates operated on for critical congenital heart disease (CHD) before 37 weeks of gestational age (wGA) with special attention given to early and late mortality and morbidity. Between 2000 and 2013, 28 preterm neonates (median gestational age (GA) 34.3 weeks) underwent cardiopulmonary bypass (CPB) surgery for critical CHD before 37 wGA; records were retrospectively reviewed. All patients except three with single ventricle physiology had a single-stage anatomic repair. Overall mortality was 43 % (95 % CI 25-62). Risk factors for death were birth weight (p = 0.032) and weight at surgery (p = 0.037), independently of GA, preoperative status, CPB and aortic clamp time. Seven patients, including those with univentricular hearts, died during the postoperative period, and five in the first year after surgery. Median follow-up was 5.9 years (range 1 month-12.8 years). Kaplan-Meier survival rate was 75 % (95 % CI 59-91) at 1 month, and 57 % (95 % CI 39-75) at 1 and 5 years. Eight patients required reoperations after a delay of 2.8 ± 1.3 months; eight had bronchopulmonary dysplasia. At the end of follow-up, nine patients were asymptomatic. One-stage biventricular repair for critical CHD on preterm neonates was feasible. Mortality remained high but acceptable, mainly confined to the first postoperative year and related to small weight. Despite reoperations, long-term clinical status was good in most survivors. Further long-term prospective investigations are necessary to evaluate neurodevelopmental outcomes.

Neonatal MRI in preterm infants with periventricular leukomalacia and mild disability

BACKGROUND

The aim of the present study was to describe the neonatal magnetic resonance imaging (MRI) findings of preterm infants with periventricular leukomalacia and mild neurological disability.

METHODS

MRI findings at term equivalent were retrospectively investigated in eight preterm infants with mild disability and periventricular leukomalacia diagnosed on MRI in infancy.

RESULTS

Linear, spotted, or macular areas of hyperintensity on T1-weighted imaging and hypointensity on T2-weighted imaging were identified in all subjects in the white matter lateral to the body of the lateral ventricle. No cystic lesions were seen. These findings were more widespread and more clearly visualized on T2-weighted imaging than T1-weighted imaging.

CONCLUSIONS

Linear, spotted, or macular lesions that are hyperintense on T1-weighted imaging and hypointense on T2-weighted imaging are possibly compatible with periventricular leukomalacia.

Coupled oxygenation oscillation measured by NIRS and intermittent cerebral activation on EEG in premature infants

Electroencephalography of premature neonates shows a physiological discontinuity of electrical activity during quiet sleep. Near infrared spectroscopy (NIRS) shows spontaneous oscillations of hemoglobin oxygenation and volume. Similar oscillations are visible in term neonates and adults, with NIRS and other functional imaging techniques (fMRI, Doppler, etc.), but are generally thought to result from vasomotion and to be a physiological artifact of limited interest. The origin and possible relationship to neuronal activity of the baseline changes in the NIRS signal have not been established. We carried out simultaneous EEG-NIRS recordings on six healthy premature neonates and four premature neonates presenting neurological distress, to determine whether changes in the concentration of cerebral oxy- and deoxy- and total hemoglobin were related to the occurrence of spontaneous bursts of cerebral electric activity. Bursts of electroencephalographic activity in neonates during quiet sleep were found to be coupled to a transient stereotyped hemodynamic response involving a decrease in oxy-hemoglobin concentration, sometimes beginning a few seconds before the onset of electroencephalographic activity, followed by an increase, and then a return to baseline. This pattern could be either part of the baseline oscillations or superimposed changes to this baseline, influencing its shape and phase. The temporal patterns of NIRS parameters present an unique configuration, and tend to be different between our healthy and pathological subjects. Studies of physiological activities and of the effects of intrinsic regulation on the NIRS signal should increase our understanding of these patterns and EEG-NIRS studies should facilitate the integration of NIRS into the set of clinical tools used in neurology.

Patterns of excitotoxin-induced brain lesions in the newborn rabbit: a neuropathological and MRI correlation

There is pressing need to employ new advances in structural MR brain imaging to better diagnose brain damage in newborn infants. Timely application of such technology will enable improved therapeutic interventions. Diffusion-weighted sequences are a sensitive marker of very early neuronal injury, the spatial pattern of which provides critical information regarding the underlying pathophysiology. We have modified our murine model of excitotoxic neonatal brain injury to the rabbit, an animal whose brain is larger and where the neuroanatomic organization of the subcortical white matter more closely resembles that of the human. Utilizing this rabbit model, we undertook an MRI/histopathologic correlation. We found that as with the mouse, there is a spatiotemporal selectivity to the pattern of brain injury, and that the period from postnatal day (P) 7 to P9 in rabbits corresponds to the time of maximum vulnerability of the brain to excitotoxic white matter damage, which neuropathologically simulates periventricular leukomalacia (PVL). We additionally noted that diffusion-weighted imaging provided the most sensitive means of detecting such lesions and that this method was sensitive to structural maturational changes accompanying the normal cortical ontogeny. Taken together, our findings suggest that this rabbit model of perinatal excitotoxic brain injury will be a valuable addition to experimental approaches to further our understanding of perinatal brain damage, that diffusion-weighted imaging will be an invaluable adjunct to the diagnosis of such injury, and that therapeutic strategies aimed at interrupting the evolution of PVL should include targeting the pathophysiologic cascade induced by excitotoxic neonatal brain injury.

Prenatal Risk Factors for Cerebral Palsy in Very Preterm Singletons and Twins

OBJECTIVE

To identify the main prenatal risk factors for cerebral palsy in very preterm singletons and twins.

METHODS

The data were from the Epipage study, which included all very preterm children (< 33 weeks) born in 1997 in 9 regions of France. The analysis included 1,954 children for whom a medical questionnaire was completed at the age of 2 years (83% of the surviving children). The risk factors studied were pregnancy complications and specific factors in twins (type of placenta and death of cotwin). Logistic regression analysis was carried out for singletons and generalized estimating equation models used for twins.

RESULTS

The proportion of cerebral palsy was 8% in singletons and 9% in twins. For singletons, spontaneous preterm labor (adjusted odds ratio [OR] 3.4, 95% confidence interval [CI] 1.7-6.7), preterm premature rupture of membranes (PPROM) with short latency (adjusted OR 4.9, 95% CI 2.0-11.8), and prolonged PPROM (adjusted OR 2.7, 95% CI 1.4-5.3) were associated with a higher risk of cerebral palsy than was hypertension. No such link was found between these pregnancy complications and cerebral palsy in twins. For twins, a monochorionic placenta (OR 1.9, 95% CI 1.0-3.6) increased the risk of cerebral palsy, but the OR became nonsignificant after adjustment (OR 1.7, 95% CI 0.8-3.4).

CONCLUSION

In very preterm singletons, spontaneous preterm labor and PPROM increased the risk of cerebral palsy compared with hypertension.

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.

Expression of induced nitric oxide synthase in amoeboid microglia in postnatal rats following an exposure to hypoxia

The present study showed the expression of induced nitric oxide synthase (iNOS) immunoreactivity in amoeboid microglia following an exposure to transient hypoxia in postnatal rats. iNOS immunoreactivity was expressed mainly in the amoeboid microglia in corpus callosum and subependymal regions of the ventricles within 3 h after hypoxia. The expression declined after 5 h, and became undetectable after 15 h and in longer surviving rats. The immunoreactivity of these cells with OX-42, which is a marker for microglia cells and detects complement type three receptors (CR3), was comparable in the rats exposed to hypoxia and the control rats. Immunoglobulin G (IgG) immunoreactivity was observed in the amoeboid microglia up to 3 h after hypoxia but it was undetectable in longer surviving rats and in the control rats. The iNOS expression in the amoeboid mircoglial cells may be related to the host defense and maintenance of structural integrity of the highly vulnerable periventricular white matter after hypoxia. The immunostaining of amoeboid microglial cells with IgG following hypoxia indicates leakage of plasma immunoglobulin from the blood vessels and its removal by the amoeboid microglial cells.

Hypothyroxinemia of prematurity and the risk of cerebral white matter damage

OBJECTIVE

Infants with hypothyroxinemia of prematurity (HOP) are at increased risk for neurodevelopmental dysfunction. Infants born near the end of the middle trimester are also at increased risk for an echolucency (EL) in the cerebral white matter, which reflects white matter damage and is the cranial ultrasound abnormality that best predicts neurodevelopmental dysfunction. We postulated that some of the increased risk of neurodevelopmental problems associated with HOP reflects an increased risk of EL.

STUDY DESIGN

We studied 1414 infants weighing 500 to 1500 g who were born at 4 medical centers between 1991 and 1993. The infants had thyroxine blood levels measured during the first weeks of life, at least 1 of 3 cranial ultrasound scans performed at specified postnatal intervals, and their own and their mother's hospital charts reviewed. Infants were classified by whether or not their first thyroxine level placed them in the lowest quartile among all infants in this sample (ie, <67.8 nmol/L, our definition of HOP, equivalent to <5.3 micrograms/dL).

RESULTS

After adjusting for such potential confounders as low gestational age and measures of illness severity, infants with HOP had twice the risk of EL as their peers with higher thyroxine levels.

CONCLUSION

Our findings are consistent with the hypothesis that a "normal" blood thyroxine level protects infants born near the end of the middle trimester against the risk of cerebral white matter damage.

[Prenatal inhibition of intestinal vasoactive peptide and cerebral excitatory lesions in the newborn mouse]

The glutamatergic agent ibotenate induces cortical plate and white matter lesions in the newborn mouse, mimicking brain lesions of the human neonate. In this model, co-treatment with ibotenate and a vasoactive intestinal peptide antagonist (VA) aggravates the excitotoxic lesions, suggesting a protective role of endogenous VIP. On the other hand, prenatal injection of VA is followed by a dramatic depletion of astrocytes in the neocortex. Since astrocytes produce numerous neuronotrophic agents, we studied the consequences of a decreased astrocytic density by prenatal VIP blockade on the excitotoxic brain lesions in newborn mice. Pregnant females were pre-treated with VA during the last 2 days of gestation and ibotenate was intracerebrally injected on postnatal day (P) 2 or P5. When compared to controls, pups pre-treated with VA and injected with ibotenate at P2 displayed a significant reduction of the white matter lesion size while cortical plate lesion was not affected. This protective effect disappeared when ibotenate was injected at P5. White matter protection by VA pre-treatment did not seem to be linked to the decreased astrocytic density since, i) this astrocytic paucity concerns only superficial cortical layers and does not affect white matter, ii) protective effects are only observed at P2 while astrocytic density reduction is observed at P2 and P5. This white matter protection could be secondary to an up-regulation of VIP receptors: an increased density of VIP receptors, which was described in other developmental models following VA treatment, could increase the efficacy of the endogenous VIP after an excitotoxic insult.