Magnetic resonance imaging of preterm brain injury

Cerebral white matter and neurodevelopment of preterm infants after coagulase-negative staphylococcal sepsis

OBJECTIVE

Coagulase-negative staphylococci are the most common pathogens causing late-onset sepsis in the neonatal intensive care unit. Neonatal sepsis can be associated with cerebral white matter damage in preterm infants. Neurodevelopment has been shown to be correlated with apparent diffusion coefficients, fractional anisotropy, and axial and radial diffusivities of the white matter.

DESIGN

Prospective cohort study.

SETTING

Twenty-eight-bed neonatal intensive care unit at a tertiary care children's hospital.

PATIENTS

Seventy preterm infants (gestational age <32 wks), 28 with coagulase-negative staphylococcal sepsis (group 1) and 42 without sepsis (group 2).

INTERVENTION

The values of apparent diffusion coefficients, fractional anisotropy, and axial and radial diffusivity of three white matter regions (parietal, frontal, and occipital), estimated with diffusion-tensor magnetic resonance imaging with a 3.0-T magnetic resonance imaging system, were obtained at term-equivalent age. Neurodevelopmental outcome assessments were performed at 15 months (Griffiths Mental Developmental Scales) and 24 months (Bayley Scales of Infant and Toddler Development, Third Edition) corrected age.

MEASUREMENTS AND MAIN RESULTS

Values of apparent diffusion coefficients, fractional anisotropy, and axial and radial diffusivity of the left and right white matter regions were equal in all patients. There was no significant difference in apparent diffusion coefficient values (mean of total: 1.593 ± 0.090 × 10mm(-3)/sec(2) and 1.601 ± 0.117 × 10mm(-3)/sec(2), respectively, p = .684), fractional anisotropy values (mean of total: 0.19 ± 0.04 and 0.19 ± 0.03, respectively, p = .350), radial diffusivity (mean of total: 1.420 ± 0.09 × 10mm(-3)/sec(2)and 1.425 ± 0.12 × 10mm(-3)/sec(2), respectively, p = .719), and axial diffusivity (mean of total: 1.940 ± 0.12 × 10mm(-3)/sec(2) and 1.954 ± 0.13 × 10mm(-3)/sec(2), respectively, p = .590) in the three combined regions between the two groups. No significant differences were found in neurodevelopmental outcome at 24 months.

CONCLUSIONS

No association was found between coagulase-negative staphylococcal sepsis in preterm infants and cerebral white matter damage as determined by values of apparent diffusion coefficients, fractional anisotropy, and radial and axial diffusivity at term-equivalent age, and no adverse effect was seen on early neurodevelopmental outcome.

Automated detection of white matter signal abnormality using T2 relaxometry: application to brain segmentation on term MRI in very preterm infants

Hyperintense white matter signal abnormalities, also called diffuse excessive high signal intensity (DEHSI), are observed in up to 80% of very preterm infants on T2-weighted MRI scans at term-equivalent age. DEHSI may represent a developmental stage or diffuse microstructural white matter abnormalities. Automated quantitative assessment of DEHSI severity may help resolve this debate and improve neonatal brain tissue segmentation. For T2-weighted sequence without fluid attenuation, the signal intensity distribution of DEHSI greatly overlaps with that of cerebrospinal fluid (CSF) making its detection difficult. Furthermore, signal intensities of T2-weighted images are susceptible to magnetic field inhomogeneity. Increased signal intensities caused by field inhomogeneity may be confused with DEHSI. To overcome these challenges, we propose an algorithm to detect DEHSI using T2 relaxometry, whose reflection of the rapid changes in free water content provides improved distinction between CSF and DEHSI over that of conventional T2-weighted imaging. Moreover, the parametric transverse relaxation time T2 is invulnerable to magnetic field inhomogeneity. We conducted computer simulations to select an optimal detection parameter and to validate the proposed method. We also demonstrated that brain tissue segmentation is further enhanced by incorporating DEHSI detection for both simulated preterm infant brain images and in vivo in very preterm infants imaged at term-equivalent age.

Differences in amplitude among electrode locations on amplitude-integrated electroencephalograms in preterm infants

INTRODUCTION

To assess differences in amplitude among electrode locations on amplitude-integrated electroencephalograms (aEEGs) in preterm infants and change therein between preterm age and term-equivalent age (TEA), we investigated aEEGs in preterm infants at both 30-32 wk post-conceptional age (PCA) and TEA.

METHODS

The median values of upper- and lower-margin amplitudes were quantitatively calculated every 5 min (Med-UMA5 and Med-LMA5, respectively), and peak, median, and bottom values were extracted at each location for the trans-frontal, trans-central, trans-occipital, fronto-central, and centro-occipital electrodes.

RESULTS

In 38 clinically stable preterm infants studied, most measurement items showed significant differences among the electrode locations at both preterm age and TEA. At 30-32 wk PCA, the bottom of Med-LMA5 was significantly higher for the trans-frontal electrodes than for the trans-central electrodes. In contrast, all measurements for Med-LMA5 were significantly lower for the trans-frontal electrodes than for the trans-central electrodes.

DISCUSSION

Amplitudes on aEEGs were significantly different among the electrode locations in preterm infants, and locational differences in amplitude changed between preterm age and TEA. It is necessary to understand the differences in amplitudes among the electrode locations on aEEGs in infants to appropriately evaluate them.

MR Imaging of the Newborn: a technical perspective

This article discusses neonatal magnetic resonance (MR) imaging and reviews equipment and procedures for MR-related transport, sedation, monitoring, and scanning. MR is gaining importance in the diagnosis and clinical management of critically ill, and often very low birth weight infants, so research is ongoing to make transport and examination safer and imaging more successful. Efforts are focused on integration of dedicated neonate MR scanners in neonatal intensive care units, improvements in incubator technology and handling, and more efficient use of scan/sedation time by choosing dedicated neonate coil arrays that improve the signal-to-noise-ratio and facilitate the choice of modern imaging techniques.

Safety of routine early MRI in preterm infants

BACKGROUND

Cerebral MRI performed on preterm infants at term-equivalent 30 weeks' gestational age (GA) is increasingly performed as part of standard clinical care.

OBJECTIVE

We evaluated safety of these early MRI procedures.

MATERIALS AND METHODS

We retrospectively collected data on patient safety of preterm infants who underwent early MRI scans. Data were collected at fixed times before and after the MRI scan. MRI procedures were carried out according to a comprehensive guideline.

RESULTS

A total of 52 infants underwent an MRI scan at 30 weeks' GA. Although no serious adverse events occurred and vital parameters remained stable during the procedure, minor adverse events were encountered in 26 infants (50%). The MRI was terminated in three infants (5.8%) because of respiratory instability. Increased respiratory support within 24 h after the MRI was necessary for 12 infants (23.1%) and was significantly associated with GA, birth weight and the mode of respiratory support. Hypothermia (core temperature < 36°C) occurred in nine infants (17.3%). Temperature dropped significantly after the MRI scan.

CONCLUSION

Minor adverse events after MRI procedures at 30 weeks GA were common and should not be underestimated. A dedicated and comprehensive guideline for MRI procedures in preterm infants is essential.

Altered microstructure of white matter except the corpus callosum is independent of prematurity

BACKGROUND

Diffusion tensor imaging (DTI) reflects the maturation of the brain microstructure. Although preterm infants are at significant risk for altered brain microstructure, it remains unclear whether this is affected by prematurity itself or other clinical factors.

OBJECTIVES

To investigate DTI parameters in preterm infants at a term-equivalent age (TEA) compared with healthy term infants and to assess the associations between DTI parameters and clinical factors that may affect brain development.

METHODS

We studied 34 preterm infants without apparent brain lesions and 12 healthy term infants using tract-based spatial statistics. Region-of-interest analysis was performed in the posterior and anterior limbs of the internal capsule (PLIC and ALIC), corpus callosum (CC), optic radiation, and cerebral peduncle.

RESULTS

Preterm infants had significantly decreased fractional anisotropy (FA) in nearly the entire white matter (WM) compared with term infants (p < 0.01). Multiple regression analysis showed that FA in the PLIC, ALIC, optic radiation, and cerebral peduncle were positively associated with postmenstrual age (PMA) at imaging and that the apparent diffusion coefficient was negatively associated with PMA. Only FA in the CC was positively correlated with gestational age. Chronic lung disease (CLD) and postnatal infection were associated with decreased FA in the CC and PLIC, respectively.

CONCLUSIONS

Preterm infants at TEA showed an altered microstructure of the WM compared with healthy term infants. The altered microstructure of the measured WM except the CC was independent of the degree of prematurity. Chronic lung disease and postnatal infection are related to localized WM alterations.

Post mortem magnetic resonance imaging in the fetus, infant and child: a comparative study with conventional autopsy (MaRIAS Protocol)

Background

Minimally invasive autopsy by post mortem magnetic resonance (MR) imaging has been suggested as an alternative for conventional autopsy in view of the declining consented autopsy rates. However, large prospective studies rigorously evaluating the accuracy of such an approach are lacking. We intend to compare the accuracy of a minimally invasive autopsy approach using post mortem MR imaging with that of conventional autopsy in fetuses, newborns and children for detection of the major pathological abnormalities and/or determination of the cause of death.

Methods/Design

We recruited 400 consecutive fetuses, newborns and children referred for conventional autopsy to one of the two participating hospitals over a three-year period. We acquired whole body post mortem MR imaging using a 1.5 T MR scanner (Avanto, Siemens Medical Solutions, Enlargen, Germany) prior to autopsy. The total scan time varied between 90 to 120 minutes. Each MR image was reported by a team of four specialist radiologists (paediatric neuroradiology, paediatric cardiology, paediatric chest & abdominal imaging and musculoskeletal imaging), blinded to the autopsy data. Conventional autopsy was performed according to the guidelines set down by the Royal College of Pathologists (UK) by experienced paediatric or perinatal pathologists, blinded to the MR data. The MR and autopsy data were recorded using predefined categorical variables by an independent person.

Discussion

Using conventional post mortem as the gold standard comparator, the MR images will be assessed for accuracy of the anatomical morphology, associated lesions, clinical usefulness of information and determination of the cause of death. The sensitivities, specificities and predictive values of post mortem MR alone and MR imaging along with other minimally invasive post mortem investigations will be presented for the final diagnosis, broad diagnostic categories and for specific diagnosis of each system.

Clinical Trial Registration

NCT01417962

NIHR Portfolio Number: 6794

Neonatal intensive care practices harmful to the developing brain

There has been a marked increase in the survival of extremely low birth weight (ELBW) infants, but these babies have a long stay in the NICU. Strategies to decrease their neurodevelopmental impairment become very important. The maximum development of the brain occurs between 29-41 weeks. From the warm, dark, acquatic econiche, where the baby hears pleasant sounds like the mother's heart beat, the baby suddenly finds itself in the dry, cold, excessively bright, noisy, environment of the NICU. Noise, bright light, painful procedures, and ill-timed caregiving activities, adversely affect the infant's development. Excessive radiation from X-rays of babies on the ventilator and CT scans also affect the brain. Medications like steroids for chronic lung disease also cause damage to the brain. Aminoglycides and frusemide are known to cause hearing impairment. Hence a developmentally supportive, humanized care will go a long way in enhancing the developmental outcome of these babies.

Imaging of neonatal brain emergencies: multisequence MRI analysis of pathologic spectrum including diffusion and MR spectroscopy

The purpose of this pictorial essay is to review the normal neonatal brain MR anatomy and the MR imaging appearances of neonatal brain emergencies and discuss the advantages of individual MR imaging sequences and the clinical implications of utilizing MRI as a problem-solving modality in the neonatal intensive care unit. Here we briefly discuss the normal MR imaging anatomy and myelination pattern and normal MR spectroscopy findings in a neonate. The role of individual MR imaging sequences in evaluating various neonatal abnormalities is being emphasized. For example, the utility of diffusion-weighted imaging for the diagnosis of profound hypoxic-ischemic injury and other forms of hypoxic-ischemic encephalopathies and MR spectroscopy in the diagnosis of metabolic encephalopathies and genetic disorders including aminoacidurias is being presented.

Neuro-developmental outcome at 18 months in premature infants with diffuse excessive high signal intensity on MR imaging of the brain

BACKGROUND

Diffuse excessive high signal intensity (DEHSI) may represent damage to the white matter in preterm infants, but may be best studied alongside quantitative markers. Limited published data exists on its neuro-developmental implications.

OBJECTIVE

The purpose of this study was to assess whether preterm children with DEHSI at term-corrected age have abnormal neuro-developmental outcome.

MATERIALS AND METHODS

This was a prospective observational study of 67 preterm infants with MRI of the brain around term-equivalent age, including diffusion-weighted imaging (DWI). Images were reported as being normal, overtly abnormal or to show DEHSI. A single observer placed six regions of interest in the periventricular white matter and calculated the apparent diffusion coefficients (ADC). DEHSI was defined as (1) high signal on T2-weighted images alone, (2) high signal with raised ADC values or (3) raised ADC values independent of visual appearances. The neuro-development was assessed around 18 months' corrected age using the Bayley Scales of Infant and Toddler Development (3rd Edition). Standard t tests compared outcome scores between imaging groups.

RESULTS

No statistically significant difference in neuro-developmental outcome scores was seen between participants with normal MRI and DEHSI, regardless of which definition was used.

CONCLUSION

Preterm children with DEHSI have similar neuro-developmental outcome to those with normal brain MRI, even if the definition includes objective markers alongside visual appearances.

Deep medullary vein involvement in neonates with brain damage: an MR imaging study

BACKGROUND AND PURPOSE

Different and specific MR imaging patterns of lesions involving WM are widely defined in neonatal encephalopathy. The aim of this study was to describe a novel MR imaging pattern of damage characterized by the abnormal prominence of DMVs in premature and full-term neonates.

MATERIALS AND METHODS

Twenty-one (11 premature and 10 full-term) neonates with MR imaging evidence of linear radially oriented fan-shaped lesions in the periventricular WM and without dural venous thrombosis were enrolled in this retrospective study. A total of 37 MR imaging examinations were performed at ages ranging from day 0 to 24 months.

RESULTS

According to the appearance of linear anomalies on T2-weighted images, we identified 2 main patterns: T2 hypointense lesions without WM cavitations and T2 hypointense lesions associated with linear cysts. The first pattern was found in 17 examinations performed between 0 and 44 days of life; the second pattern was found in another 14 examinations performed between 6 days and 4 months of life. Five examinations performed between 9 and 24 months of life showed a reduction in volume and hyperintense signal intensity of the periventricular WM on T2-weighted and FLAIR images.

CONCLUSIONS

Subtle linear WM lesions with the same anatomic distribution of DMVs may be evident in premature and full-term neonates without signs of major venous thrombosis, both in the acute and subacute phases. Their appearance and evolution suggest that transient DMV engorgement/thrombosis may be responsible for WM damage that can lead to a PVL-like pattern.

Optimized T1- and T2-weighted volumetric brain imaging as a diagnostic tool in very preterm neonates

BACKGROUND

T1- and T2-W MR sequences used for obtaining diagnostic information and morphometric measurements in the neonatal brain are frequently acquired using different imaging protocols. Optimizing one protocol for obtaining both kinds of information is valuable.

OBJECTIVE

To determine whether high-resolution T1- and T2-W volumetric sequences optimized for preterm brain imaging could provide both diagnostic and morphometric value.

MATERIALS AND METHODS

Thirty preterm neonates born between 24 and 32 weeks' gestational age were scanned during the first 2 weeks after birth. T1- and T2-W high-resolution sequences were optimized in terms of signal-to-noise ratio, contrast-to-noise ratio and scan time and compared to conventional spin-echo-based sequences.

RESULTS

No differences were found between conventional and high-resolution T1-W sequences for diagnostic confidence, image quality and motion artifacts. A preference for conventional over high-resolution T2-W sequences for image quality was observed. High-resolution T1 images provided better delineation of thalamic myelination and the superior temporal sulcus. No differences were found for detection of myelination and sulcation using conventional and high-resolution T2-W images.

CONCLUSION

High-resolution T1- and T2-W volumetric sequences can be used in clinical MRI in the very preterm brain to provide both diagnostic and morphometric information.

The effect of gestational age on developmental outcomes: a longitudinal study in the first 2 years of life

BACKGROUND

Extremely low and very low gestational age (ELGA and VLGA) constitutes a risk factor for development even in absence of cerebral damage, as an immature central nervous system is exposed to invasive and inadequate stimulation. We tested the hypothesis that GA impacts developmental outcomes and trajectories of preterms without major cerebral damage in the first 2 years of life, expecting poorer developmental outcomes and higher rate of impairment with the decreasing of GA. We also evaluated whether GA, together with developmental outcomes in the first year of life, was related to developmental outcomes at 24 months.

METHODS

Eighty-eight infants, divided into three GA groups (ELGA: ≤28 weeks; VLGA: 29-32 weeks; full term: >37 weeks) were assessed longitudinally at 6, 12, 18 and 24 months using the Griffiths Mental Development Scales.

RESULTS

Use of a repeated measure multivariate analysis of variance resulted in several significant findings. GA was associated with the developmental quotient (DQ) scores (P= 0.006); and locomotor (P < 0.001), eye and hand co-ordination (P= 0.016) and performance (P= 0.040) sub-scale quotient (SQ) scores; age of evaluation was also associated with DQ scores (P= 0.002), and locomotor (P < 0.001) and performance (P < 0.001) SQ scores. In particular, ELGAs exhibited lower DQ and SQ scores compared with the VLGA and full-term groups; some ELGAs showed mild, moderate or severe cognitive impairments, while few VLGAs mild impairments. Linear regression analysis showed that GA (P= 0.034) and 12-month developmental outcome (P < 0.001) were related to 24-month developmental outcome.

CONCLUSIONS

Different developmental trajectories emerged in relation to GA, with poorer developmental outcomes and higher rates of impairment in ELGAs and few mild impairments in VLGAs. The relevance of taking into account both GA and repeated assessments in the first 2 years of life was shown.

Development of laminar organization of the fetal cerebrum at 3.0T and 7.0T: a postmortem MRI study

INTRODUCTION

The purpose of this study is to show the condition of laminar organization on 3.0T and 7.0T postmortem magnetic resonance imaging (MRI) and analyze developmental changes.

METHODS

Heads of 131 fetal specimens of 14-40 weeks gestational age (GA) were scanned by 3.0T MRI. Eleven fetal specimens of 14-27 weeks GA were scanned by 7.0T MRI. Clear images were chosen for analysis.

RESULTS

On T₁-weighted 3.0T MRI, layers could be visualized at 14 weeks GA and appeared clearer after 18 weeks GA. On 7.0T MRI, four zones could be recognized at 14 weeks GA. During 15-22 weeks GA, when laminar organization appeared typical, seven layers including the periventricular zone and external capsule fibers could be differentiated, which corresponded to seven zones in histological stained sections. At 23-28 weeks GA, laminar organization appeared less typical, and borderlines among them appeared obscured. After 30 weeks GA, it disappeared and turned into mature-like structures. The developing lamination appeared the most distinguishable at the parieto-occipital part of brain and peripheral regions of the hippocampus. The migrating thalamocortical afferents were probably delineated as a high signal layer located at the lower, middle, and upper part of the subplate zone at 16-28 weeks GA on T₁-weighted 3.0T MRI.

CONCLUSIONS

T₁-weighted 3.0T MRI and T₂-weighted 7.0T MRI can well demonstrate the laminar organization. Development of the lamination follows a specific spatio-temporal regularity, and postmortem MRI of the parieto-occipital part of brain obtained with 3.0T or 7.0T is an effective way to show developmental changes.

Young adults born preterm with very low birth weight demonstrate widespread white matter alterations on brain DTI

Preterm birth with very low birth weight (VLBW, ≤1500 g) is connected to reduced white matter (WM) integrity in childhood and adolescence. These changes in WM are correlated to motor, sensory and neuropsychological impairments. CNS myelination continues into the early twenties, but the consequences of this for WM integrity in VLBWs have not been explored. DTI and tract based spatial statistics (TBSS) was carried out to test for voxelwise differences in fractional anisotropy (FA), eigenvalues and mean diffusivity (MD) between a preterm VLBW group (n=49) and a control group born at term (n=59) at 18-22 years of age. TBSS was also used to explore the relationship between perinatal clinical data and general cognitive ability (total IQ), respectively, and the DTI metrics (FA and MD), with gender and age as a confounder. In the VLBW group several major WM tracts particularly in the posterior region had significantly reduced FA caused by an increase in the two lowest eigenvalues. MD was significantly increased in the VLBWs in 50% of the same regions as the FA changes, but encompassing also more peripheral WM. In the VLBW group, FA was found to correlate positively with birth weight and negatively with number of days in intensive care and on mechanical ventilator, particularly in the corpus callosum. FA was found to correlate positively with total IQ in the young preterm adults. In the controls there was no correlation between FA and total IQ. Our results indicate that the neurologic sequelae of preterm birth with VLBW are a lifelong condition inducing structural and functional impairments also in adulthood in VLBW survivors. The greatest risk of having reduced WM integrity in adulthood was found in the most immature VLBW neonates requiring mechanical ventilation and long-term intensive care.

Tractography of developing white matter of the internal capsule and corpus callosum in very preterm infants

OBJECTIVES

To investigate in preterm infants associations between Diffusion Tensor Imaging (DTI) parameters of the posterior limb of the internal capsule (PLIC) and corpus callosum (CC) and age, white matter (WM) injury and clinical factors.

METHODS

In 84 preterm infants DTI was performed between 40-62 weeks postmenstrual age on 3 T MR. Fractional anisotropy (FA), apparent diffusion coefficient (ADC) values and fibre lengths through the PLIC and the genu and splenium were determined. WM injury was categorised as normal/mildly, moderately and severely abnormal. Associations between DTI parameters and age, WM injury and clinical factors were analysed.

RESULTS

A positive association existed between FA and age at imaging for fibres through the PLIC (r = 0.48 p < 0.001) and splenium (r = 0.24 p < 0.01). A negative association existed between ADC and age at imaging for fibres through the PLIC (r = -0.65 p < 0.001), splenium (r = -0.35 p < 0.001) and genu (r = -0.53 p < 0.001). No association was found between DTI parameters and gestational age, degree of WM injury or categorical clinical factors.

CONCLUSIONS

These results indicate that in our cohort of very preterm infants, at this young age, the development of the PLIC and CC is ongoing and independent of the degree of prematurity or WM injury.

Appearances of diffuse excessive high signal intensity (DEHSI) on MR imaging following preterm birth

BACKGROUND

Diffuse damage to the periventricular white matter has recently been suggested to be a cause of the cognitive deficits seen following preterm birth. It is unclear whether this form of injury can be visualised on MR imaging, but one group has described diffuse excessive high signal intensity (DEHSI) as a possible form of diffuse white matter injury. This finding is dependent on window imaging and the subjective assessment of the reviewer, but little data have been published on the degree of subjectivity on its appearance among raters.

OBJECTIVE

To assess the subjectivity of DEHSI on conventional and ultrafast T2-weighted MR imaging following preterm birth.

MATERIALS AND METHODS

An observational study of 40 preterm infants who had MR imaging of the brain around term-equivalent age, including conventional fast spin-echo (FSE) and ultrafast single-shot fast spin-echo (SSFSE) T2-weighted sequences in the axial plane. Images were anonymised and scored twice by four observers for the presence of DEHSI. Inter- and intra-observer agreement were calculated.

RESULTS

Sixty-five percent of conventional and 100% of the ultrafast images were of diagnostic quality. DEHSI was noted in between 0% and 69.2% of conventional images and 27.5-90% of the ultrafast images. Inter- and intra-observer agreement ranged from none to moderate.

CONCLUSION

The visual appearances of DEHSI on conventional FSE and ultrafast SSFSE T2-W images are highly subjective, limiting its clinical application.

Diffusion-weighted imaging of cerebral white matter and the cerebellum following preterm birth

AIM

The aim of this study was to determine if apparent diffusion coefficients (ADCs) generated with diffusion-weighted imaging of cerebral white matter and the cerebellum are affected by white matter damage.

METHOD

Seventy-two preterm infants (32 males, 40 females; mean gestational age at birth 30.3 wks, SD 3.0 wks; mean birthweight 1458g, SD 534g) underwent magnetic resonance imaging of the brain around term-equivalent age and were categorized into three groups: normal, overt abnormality, and diffuse excessive high signal intensity (DEHSI). ADC values were calculated from cerebral white matter, cerebellar hemispheres, and cerebellar midline, and were compared between groups. Regression analysis identified clinical parameters correlated with ADC values.

RESULTS

Imaging was normal in 27 infants, and revealed overt abnormalities in 14 and DEHSI in 31. ADC values did not differ between groups. ADC values from cerebral white matter were negatively correlated with the number of episodes of postnatal sepsis (p=0.002). ADC values from cerebellar hemispheres (p=0.007) and cerebellar midline (p=0.036) correlated with gestational age at birth.

INTERPRETATION

ADC values from white matter are not altered in preterm infants with DEHSI but are negatively correlated with the number of episodes of postnatal sepsis. ADC values in the cerebellum are not altered by white matter damage, but are affected by preterm birth itself.

Brain lesions in preterm infants: initial diagnosis and follow-up

Children surviving premature birth present with a wide spectrum of motor, sensory and cognitive disabilities, ranging from slight motor deficits, school difficulties and behavioural problems to cerebral palsy and mental retardation. The anatomic and functional substrate of these problems can be investigated using a variety of imaging techniques. Cranial US coupled with colour Doppler is a well-established method for the initial diagnosis of intraventricular haemorrhage, parenchymal haemorrhagic infarct and periventricular leukomalacia. MRI is useful for the follow-up study of brain maturation. Conventional T1- and T2-weighted sequences, magnetization transfer and diffusion tensor imaging coupled with sophisticated tools of tissue segmentation and analysis at a voxel level offer substantial anatomic and functional information on pathological conditions that define the prognosis of preterm infants.

Neuroimaging in very preterm infants

Cranial ultrasonography (cUS) and MRI are the preferred modalities used to image the neonatal brain. Both have their specific contributions and advantages. A neuroimaging study, including sequential cUS and single MRI, was performed in a cohort of very preterm infants (gestational age <32 weeks). The major aims were: to study brain imaging findings and to assess the incidences of brain abnormalities and the relationship between brain abnormalities and perinatal clinical parameters; to compare cUS and MRI findings; to describe imaging findings of the thalami and basal ganglia; and to study the reliability of cUS for detection of (diffuse) white matter injury. Patients & methods: Very preterm infants, born during a 1.5-year period, were eligible if there were no exclusion criteria (i.e., metabolic and genetic disorders, or infections and/or congenital malformations of the CNS). Sequential cUS was performed from admission until discharge and on the day of the MRI following a standardized protocol. MRI (3 Tesla) was performed around or shortly after term equivalent age (TEA). Results: A total of 133 infants were included. The mean number of cUS scans per infant was 8.3 (range: 2–23). MRI was performed in 113 infants at a mean postmenstrual age of 44.7 weeks (range: 40.0–55.9). During admission we found periventricular echodensities and intraventricular hemorrhage in 80 and 30% of infants, respectively – both significantly associated with male gender. The incidence of lenticulo striate vasculopathy (LSV) was 19%. Around TEA, ventricular dilatation and widening of extracerebral spaces were frequent findings. In addition, MRI showed punctate white matter lesions and diffuse excessive high-signal intensity. MRI detected subtle white matter lesions more effectively, whereas cUS was better for the detection of LSV, calcifications and germinolytic and plexus cysts. Diffuse, subtle echogenicity of the basal ganglia and thalami was observed in the majority of infants with normal MRI findings in this area. Focal deep gray matter lesions were only rarely encountered. Conclusions: In very preterm infants, frequent, sequential cUS is an excellent tool to image and follow the brain throughout the neonatal period and detects some lesions and transient changes more effectively than MRI. Single MRI provides invaluable and detailed additional information on the growth and development of, and injury to, the brain. Sequential cUS throughout the neonatal period and a single MRI around TEA are therefore warranted. Bilateral, diffuse and subtle echogenicity in the deep gray matter on cUS probably reflects (normal) maturational processes in the immature brain. With the exception of LSV, focal lesions in the deep gray matter are rare and need to be distinguished from benign phenomena in the deep gray matter. Sequential high-quality cUS during the neonatal period predicts severe white matter injury, but is less predictive of mild-to-moderate white matter injury around TEA.

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.

Early motor repertoire is related to level of self-mobility in children with cerebral palsy at school age

AIM

To determine the predictive value of the early motor repertoire for the level of self-mobility in children with cerebral palsy (CP) at school age.

METHOD

Video recordings were made at 11 to 17 weeks post-term of 37 preterm infants (20 males, 17 females) who later developed CP. The early motor repertoire was assessed by obtaining a motor optimality score. At 6 to 12 years, children were classified according to the Gross Motor Function Classification System (GMFCS).

RESULTS

Of 37 children (mean gestational age 29.1wks, SD 1.9; mean birthweight 1273g, SD 324), nine had unilateral and 28 had bilateral spastic CP. Twelve children were in GMFCS level I, three level II, 10 level III, four level IV, and eight level V. The absence of the age-adequate motor repertoire, a cramped motor repertoire, an abnormal kicking pattern, and a non-flat supine posture were associated with lower levels of self-mobility (chi(2) for trend test, p<0.05). Predictive for a low level of self-mobility was a cramped motor repertoire/non-flat supine posture (positive predictive values [PPV] 100%, negative predictive values [NPV] 54%). Predictive for a high level of self-mobility was a non-cramped repertoire/flat supine posture (PPV 80%, NPV 74%).

INTERPRETATION

Several aspects of the motor repertoire at 11 to 17 weeks post-term predicted the degree of functional limitations in children with CP at school age.

Reconsidering the impact of preterm birth on language outcome

BACKGROUND

Since preterm birth is associated with a constellation of pre-, peri- and post-natal risk factors, we hypothesised that prematurity may continue to impact the development of linguistic abilities even up to the end of the preschool years and beyond, giving rise to an atypical developmental trajectory. The study tested this hypothesis at six years of age, investigating whether language is affected by preterm birth and how different linguistic abilities are interrelated.

METHOD

Seventy monolingual Italian preterms and 34 age-matched controls were recruited. Linguistic abilities (vocabulary, grammar, and phonological awareness) as well as general cognitive developmental levels were measured.

RESULTS

No general cognitive delay emerged, but less developed abilities in vocabulary, grammar, and phonological awareness were found in preterms compared to fullterms. Moreover, the relations among the different linguistic competences differed across groups.

CONCLUSIONS

Our study shows that even without brain damage, preterm birth continues to affect linguistic development up to the end of the preschool years, and probably beyond, highlighting a continuity between pre- and peri-natal life and subsequent development, and pointing to an atypical developmental trajectory in this population compared to fullterms (different rates of development, different strategies employed, and differences in the relationships among linguistic abilities).

Sensory and motor deficits in children with cerebral palsy born preterm correlate with diffusion tensor imaging abnormalities in thalamocortical pathways

AIM

Cerebral palsy (CP) is frequently linked to white matter injury in children born preterm. Diffusion tensor imaging (DTI) is a powerful technique providing precise identification of white matter microstructure. We investigated the relationship between DTI-observed thalamocortical (posterior thalamic radiation) injury, motor (corticospinal tract) injury, and sensorimotor function.

METHOD

Twenty-eight children born preterm (16 males, 12 females; mean age 5y 10mo, SD 2y 6mo, range 16mo-13y; mean gestational age at birth 28wks, SD 2.7wks, range 23-34wks) were included in this case-control study. Twenty-one children had spastic diplegia, four had spastic quadriplegia, two had hemiplegia, and one had ataxic/hypotonic CP; 15 of the participants walked independently. Normative comparison data were obtained from 35 healthy age-matched children born at term (19 males, 16 females; mean age 5y 9mo, SD 4y 4mo, range 15mo-15y). Two-dimensional DTI color maps were created to evaluate 26 central white matter tracts, which were graded by a neuroradiologist masked to clinical status. Quantitative measures of touch, proprioception, strength (dynamometer), and spasticity (modified Ashworth scale) were obtained from a subset of participants.

RESULTS

All 28 participants with CP had periventricular white-matter injury on magnetic resonance imaging. Using DTI color maps, there was more severe injury in the posterior thalamic radiation pathways than in the descending corticospinal tracts. Posterior thalamic radiation injury correlated with reduced contralateral touch threshold, proprioception, and motor severity, whereas corticospinal tract injury did not correlate with motor or sensory outcome measures.

INTERPRETATION

These findings extend previous research demonstrating that CP in preterm children reflects disruption of thalamocortical connections as well as descending corticospinal pathways.

Segmentation of white matter flaring areas in ultrasound images of very-low-birth-weight preterm infants

In this article, we present an interactive algorithm segmenting white brain matter, visible as hyperechoic flaring areas in ultrasound (US) images of preterm infants with periventricular leukomalacia (PVL). The algorithm combines both the textural properties of pathological brain tissue and mathematical morphology operations. An initial flaring area estimate is derived from a multifeature multiclassifier tissue texture classifier. This area is refined based on the structural properties of the choroid plexus, a brain feature known to have characteristics similar to flaring. Subsequently, a combination of a morphological closing, gradient and opening by reconstruction operation determines the final flaring area boundaries. Experimental results are compared with a gold standard constructed from manual flaring area delineations of 12 medical experts. In addition, we compared our algorithm to an existing active contour method. The results show our technique agrees to the gold standard with statistical significance and outperforms the existing method in accuracy. Finally, using the flaring area as a criterion we improve the sensitivity of PVL detection up to 98% as compared with the state of the art.

Visuospatial skills, ocular alignment, and magnetic resonance imaging findings in very low birth weight adolescents

PURPOSE

To describe ocular alignment and stereoacuity in adolescents with very low birth weight (VLBW) in comparison with a matched control group and to investigate associations with white matter damage of immaturity (WMDI) and visuospatial skills in the VLBW group.

METHODS

Fifty-nine 15-year-old VLBW subjects and 55 age- and sex-matched controls with normal birth weight underwent examination, including measurement of ocular alignment using cover test and Maddox rod and cycloplegic refraction. Stereoacuity was assessed with the TNO test, best-corrected visual acuity with a Konstantin Moutakis letter chart, and visuospatial skills with the performance tests, defined as performance intelligence quotient (IQ), in the Wechsler Intelligence Scale for Children (WISC-III). All VLBW subjects underwent magnetic resonance imaging of the brain.

RESULTS

Ocular misalignment was significantly more common in the VLBW group than in the control group (22% compared with 4%; p = 0.004). Exophoria, subnormal stereoacuity, and subnormal performance IQ were significantly more common in the VLBW group than in the control group (p = 0.006, p = 0.011, and p = 0.015, respectively). Ocular misalignment was associated with WMDI (p = 0.035) and subnormal performance IQ (p = 0.020). Of the VLBW subjects with ocular misalignment, 69% had WMDI and/or subnormal performance IQ.

CONCLUSIONS

The VLBW adolescents had more visuospatial problems, lower stereoacuity, and more ocular misalignment than the control subjects. Ocular misalignment was associated with visuospatial deficiencies and/or WMDI in the VLBW group and was a better predictor for visuospatial deficits than WMDI.

Magnetic resonance imaging of the brain in newborn infants: practical aspects

Magnetic Resonance Imaging is becoming more widely available and increasingly important for imaging the neonatal brain. In newborn infants it poses challenges regarding patient preparation, safety, optimal timing, and sequence optimization. These issues are addressed in this paper and indications for performing neonatal Magnetic Resonance Imaging are presented.

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.

Susceptibility weighted imaging: a new tool in magnetic resonance imaging of stroke

Susceptibility weighted imaging (SWI) is a magnetic resonance (MR) technique that is exquisitely sensitive to paramagnetic substances, such as deoxygenated blood, blood products, iron, and calcium. This sequence allows detection of haemorrhage as early as 6h and can reliably detect acute intracerebral parenchymal, as well as subarachnoid haemorrhage. It detects early haemorrhagic transformation within an infarct and provides insight into the cerebral haemodynamics following stroke. It helps in the diagnosis of cerebral venous thrombosis. It also has applications in the work-up of stroke patients. The sequence helps in detecting microbleeds in various conditions, such as vasculitis, cerebral autosomal dominant arteriopathy, subacute infarcts and leucoencephalopathy (CADASIL), amyloid angiopathy, and Binswanger's disease. The sequence also aids in the diagnosis of vascular malformations and perinatal cerebrovascular injuries. This review briefly illustrates the utility of this MR technique in various aspects of stroke diagnosis and management.

Abnormal cerebral MRI findings and neuroimpairments in very low birth weight (VLBW) adolescents

BACKGROUND

High prevalence of abnormal cerebral MRI findings as well as major and minor motor, perceptual and cognitive impairments has been reported in very low birth weight (VLBW) children.

AIM

To investigate whether cerebral MRI pathology relates to different types of neuroimpairments in adolescents with VLBW.

METHODS

At age 15, 55 adolescents with birth weight < or = 1500 g (VLBW) were examined. Motor function was evaluated by Movement Assessment Battery for Children (ABC) and the Grooved Pegboard (GP) test, cognitive function by Wechsler Intelligence Scales, and visuo-motor and visual perceptual function by The Developmental Test of Visual-Motor Integration (VMI) with the supplementary tests of Visual Perception (VP), and Motor Coordination (MC). Executive functions were assessed by Wisconsin Card Sorting Test (WCST) and the Stroop test. Cerebral MRI was assessed semi-quantitatively for ventricular, white and grey matter pathology.

RESULTS

There was a rather weak relationship between MRI pathology and neuroimpairments. Poor performance on the WCST was related with ventricular dilatation (VD), white matter reduction and corpus callosum thinning. There was a correlation between results on the VMI test and the Movement ABC test and MRI pathology, but the correlation became much weaker when children with cerebral palsy were excluded. There was no relationship between MRI findings and estimated intelligence quotient (IQ) scores. Normal MRI predicted normal or near normal neuropsychological functioning.

CONCLUSION

Cerebral MRI pathology suggestive of perinatal white matter injury was related to disadvantages in performances on executive functions, to a lesser degree to motor and visual perceptual problems, but not to cognitive impairments in VLBW adolescents.

Diffusion tensor imaging in children with periventricular leukomalacia: variability of injuries to white matter tracts

BACKGROUND AND PURPOSE

Conventional MR imaging shows evidence of brain injury and/or maldevelopment in 70%-90% of children with cerebral palsy (CP), though its capability to identify specific white matter tract injury is limited. The great variability of white matter lesions in CP already demonstrated by postmortem studies is thought to be one of the reasons why response to treatment is so variable. Our hypothesis is that diffusion tensor imaging (DTI) is a suitable technique to provide in vivo characterization of specific white matter tract lesions in children with CP associated with periventricular leukomalacia (PVL).

MATERIALS AND METHODS

In this study, 24 children with CP associated with PVL and 35 healthy controls were evaluated with DTI. Criteria for identification of 26 white matter tracts on the basis of 2D DTI color-coded maps were established, and a qualitative scoring system, based on visual inspection of the tracts in comparison with age-matched controls, was used to grade the severity of abnormalities. An ordinal grading system (0=normal, 1=abnormal, 2=severely abnormal or absent) was used to score each white matter tract.

RESULTS

There was marked variability in white matter injury pattern in patients with PVL, with the most frequent injury to the retrolenticular part of the internal capsule, posterior thalamic radiation, superior corona radiata, and commissural fibers.

CONCLUSION

DTI is a suitable technique for in vivo assessment of specific white matter lesions in patients with PVL and, thus, a potentially valuable diagnostic tool. The tract-specific evaluation revealed a family of tracts that are highly susceptible in PVL, important information that can potentially be used to tailor treatment options in the future.

Stem cell therapies for perinatal brain injuries

This chapter reviews four groups of paediatric brain injury. The pathophysiology of these injuries is discussed to establish which cells are damaged and therefore which cells represent targets for cell replacement. Next, we review potential sources of cellular replacements, including embryonic stem cells, fetal and neonatal neural stem cells and a variety of mesenchymal stem cells. The advantages and disadvantages of each source are discussed. We review published studies to illustrate where stem cell therapies have been evaluated for therapeutic gain and discuss the hurdles that will need to be overcome to achieve therapeutic benefit. Overall, we conclude that children with paediatric brain injuries or inherited genetic disorders that affect the brain are worthy candidates for stem cell therapeutics.

Are early grammatical and phonological working memory abilities affected by preterm birth?

There have been few investigations of the effects of very immature preterm birth on specific linguistic competencies and phonological working memory at preschool age. Study 1 aimed to investigate early grammatical abilities in very immature healthy preterms, taking into account their cognitive development and biological and social factors. The linguistic and cognitive differences found between preterms and fullterms led to investigate in Study 2 the role of phonological working memory on preterms' grammatical development. Very immature preterm birth resulted to affect grammatical, cognitive and phonological working memory abilities until 3.5 years leading to persisting difficulties in comparison with fullterms, albeit not severe deficits. Tight relations between phonological working memory and grammar were found both in preterms and fullterms, that highlights the reciprocal support of these abilities in development. A partial compensatory effect by the maternal level of education on preterms' grammatical and cognitive abilities was also found.

LEARNING OUTCOMES

The reader will become familiar with the relations between grammatical and phonological working memory abilities in typical and preterm 3.5-year-old children.

Aspects IRM de l’encéphalopathie anoxo-ischémique du nouveau-né à terme et du prémature

These past few years have seen an increasing role of MRI in the investigation of neonatal cerebral anoxic-ischemic pathology. This is due not only to greater precision in diagnosing lesion extension, but also to earlier detection of lesions with the diffusion of weighted imagery. The aim of this iconographic review is to illustrate the main MRI aspects of anoxic-ischemic encephalopathy in a pedagogical way. After a brief physiopathology reminder, the different cerebral lesions are studied in a first chapter on the premature newborn pathology and a second chapter on full-term newborn pathology.

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.

Urinary S100B protein concentrations are increased in intrauterine growth-retarded newborns

BACKGROUND

Intrauterine growth retardation is one of the major causes of perinatal mortality and morbidity. To date, there are no reliable methods to detect brain damage in these patients.

METHODS

We conducted a case-control study in tertiary NICUs from December 2001 to December 2003 with 42 intrauterine growth retardation infants and 84 controls. Routine laboratory variables, neurologic outcome at 7-day follow-up, ultrasound imaging, and urine concentrations of S100B protein were determined at 5 time points. Urine S100B levels were measured by an immunoluminometric assay at first urination, 24, 48, and 72 hours, and 7 days after birth. Routine laboratory parameters and neurologic patterns were assessed at the same time as urine sampling.

RESULTS

S100B protein was significantly higher at all of the monitoring time points in urine taken from intrauterine growth retardation newborns than in control infants. When intrauterine growth retardation infants were corrected for the presence of abnormal (group A) or normal (group B) neurologic examination 7 days after birth, S100B was significantly higher at all of the predetermined monitoring time points in group A infants than in group B or controls. At a cutoff of 7.37 multiples of median at first urination, S100B achieved a sensitivity of 95% and a specificity of 99.1% as a single marker for predicting an adverse neurologic outcome. Twenty of 126 patients had neurologic abnormalities, making an overall prevalence of the disease in our population of 15.9% (pretest probability). With respect to the performance of S100B in predicting brain damage, its positive and negative predictive values were 91.0% and 99.0%, respectively.

CONCLUSIONS

Increased urine S100B protein levels in intrauterine growth retardation newborns in the first week after birth suggest the presence of brain damage reasonably because of intrauterine hypoxia. Longitudinal S100B protein measurements soon after birth are a useful tool to identify which intrauterine growth retardation infants are at risk of possible neurologic sequelae.

Magnetic resonance imaging in preterm infants

MR imaging of the premature infant poses a number of challenges with regard to safety, sequence optimization and recognition of the normal appearances of the developing brain. In this paper we discuss these challenges, and review the common intracerebral abnormalities associated with premature birth. Although the outcome for very-low-birth-weight babies has improved over the last decade, there remains a significant risk of subsequent development of neurological disability. The relationship between MRI abnormalities and long-term outcome is considered.

In vitro MRI of brain development

In this review, we demonstrate the developmental appearance, structural features, and reorganization of transient cerebral zones and structures in the human fetal brain using a correlative histological and MRI analysis. The analysis of postmortem aldehyde-fixed specimens (age range: 10 postovulatory weeks to term) revealed that, at 10 postovulatory weeks, the cerebral wall already has a trilaminar appearance and consists of: (1) a ventricular zone of high cell-packing density; (2) an intermediate zone; (3) the cortical plate (in a stage of primary consolidation) with high MRI signal intensity. The anlage of the hippocampus is present as a prominent bulging in the thin limbic telencephalon. The early fetal telencephalon impar also contains the first commissural fibers and fornix bundles in the septal area. The ganglionic eminence is clearly visible as an expanded continuation of the proliferative ventricular zone. The basal ganglia showed an initial aggregation of cells. The most massive fiber system is in the hemispheric stalk, which is in continuity with thalamocortical fibers. During the mid-fetal period (15-22 postovulatory weeks), the typical fetal lamination pattern develops and the cerebral wall consists of the following zones: (a) a marginal zone (visible on MRI exclusively in the hippocampus); (b) the cortical plate with high cell-packing density and high MRI signal intensity; (c) the subplate zone, which is the most prominent zone rich in extracellular matrix and with a very low MRI signal intensity; (d) the intermediate zone (fetal "white matter"); (e) the subventricular zone; (f) the periventricular fiber-rich zone; (g) the ventricular zone. The ganglionic eminence is still a very prominent structure with an intense proliferative activity. During the next period (22-26 postovulatory weeks), there is the developmental peak of transient MRI features, caused by the high content of hydrophyllic extracellular matrix in the subplate zone and the accumulation of waiting afferent axons. The period between 27 and 30 postovulatory weeks is characterized by gradual blurring of the laminar structure in parallel with the formation of cerebral convolutions. In near-term preterm infants, T2-weighted MR images showed better contrast resolution than T1-weighted images. We conclude that transient fetal zones and subcortical structures display characteristic MRI features due to the high content of extracellular matrix in the subplate zone, higher MRI signal intensity of zones with high cell-packing intensity, and the presence of growing fibers.

Periventricular leukomalacia: overview and recent findings

Periventricular leukomalacia (PVL), the main substrate for cerebral palsy, is characterized by diffuse injury of deep cerebral white matter, accompanied in its most severe form by focal necrosis. The classic neuropathology of PVL has given rise to several hypotheses about the pathogenesis, largely relating to hypoxia-ischemia and reperfusion in the sick premature infant. These include free radical injury, cytokine toxicity (especially given the epidemiologic association of PVL with maternofetal infection), and excitotoxicity. Among the recent findings directly in human postmortem tissue is that immunocytochemical markers of lipid peroxidation (hydroxy-nonenal and malondialdehyde) and protein nitration (nitrotyrosine) are significantly increased in PVL. Premyelinating oligodendrocytes, which predominate in periventricular regions during the window of vulnerability to PVL (24 to 34 postconceptional weeks), are the targets of this free radical injury, and suffer cell death. Susceptibility can be attributed, at least in part, to a relative deficiency of superoxide dismutases in the preterm white matter, including premyelinating oligodendrocytes. Several cytokines, including interferon-gamma (known to be directly toxic to immature oligodendroglia in vitro), as well as tumor necrosis factor-alpha and interleukins 2 and 6, have been demonstrated in PVL. Microglia, which express toll-like receptors to bacterial products such as lipopolysaccharide, are increased in PVL white matter and may contribute to the injury. Preliminary work suggests a role for glutamate receptors and glutamate transporters in PVL, as has been seen in experimental animals. These findings pave the way for eventual therapeutic or preventive strategies for PVL.

Cerebral MRI findings in very-low-birth-weight and small-for-gestational-age children at 15 years of age

BACKGROUND

A high prevalence of abnormal cerebral MRI findings has been reported in low-birth-weight children.

OBJECTIVE

To compare MRI findings in very-low-birth-weight (VLBW) and term small-for-gestational-age (SGA) children with controls in early adolescence.

MATERIALS AND METHODS

Cerebral MRI was used to examine 55 VLBW, 54 SGA and 66 controls at 15 years of age. The MR images were qualitatively assessed, and size of ventricles, white-matter and grey-matter abnormalities were reported.

RESULTS

The VLBW teenagers had a higher prevalence of various MRI abnormalities than SGA children and controls. Dilation of the ventricular system, especially of the occipital horns, was found in 82% of the VLBW group, in 19% of the SGA group and in 21% of controls. White-matter reduction was found in 53% of the VLBW, in 6% of the SGA and in 2% of controls. Corpus callosum thinning was found in 47% of the VLBW, in 2% of the SGA and in 6% of controls. Periventricular gliosis was found in 29% of the VLBW, in 4% of the SGA and in 8% of controls.

CONCLUSIONS

Cerebral MRI pathology in white matter is a common finding in VLBW teenagers. The findings may indicate minor perinatal PVL with resulting loss of white-matter tissue and ventricular dilation.