Understanding brain injury and neurodevelopmental disabilities in the preterm infant: the evolving role of advanced magnetic resonance imaging

Anatomical characterization of athetotic and spastic cerebral palsy using an atlas-based analysis

PURPOSE

To analyze diffusion tensor imaging (DTI) in two types of cerebral palsy (CP): the athetotic-type and the spastic-type, using an atlas-based anatomical analysis of the entire brain, and to investigate whether these images have unique anatomical characteristics that can support functional diagnoses.

MATERIALS AND METHODS

We retrospectively analyzed the DTI of seven children with athetotic-type, 11 children with spastic-type, and 20 healthy control children, all age-matched. The severity of motor dysfunction was evaluated with the Gross Motor Function Classification System (GMFCS). The images were normalized using a linear transformation, followed by large deformation diffeomorphic metric mapping. For 205 parcellated brain areas, the volume, fractional anisotropy, and mean diffusivity were measured. Principal component analysis (PCA) was performed for the Z-scores of these parameters.

RESULTS

The GMFCS scores in athetotic-type were significantly higher than those in spastic-type (P < 0.001). PCA extracted anatomical components that comprised the two types of CP, as well as the severity of motor dysfunction. In the athetotic group, the abnormalities were more severe than in the spastic group. In the spastic group, significant changes were concentrated in the lateral ventricle and periventricular structures.

CONCLUSION

Our results quantitatively delineated anatomical characteristics that reflected the functional findings in two types of CP.

Tractography of white-matter tracts in very preterm infants: a 2-year follow-up study

AIM

The aim of this study was to determine whether tractography of white-matter tracts can independently predict neurodevelopmental outcome in very preterm infants.

METHOD

Out of 84 very preterm infants admitted to a neonatal intensive care unit, 64 (41 males, 23 females; median gestational age 29.1 weeks [range 25.6-31.9]; birthweight 1163 g [range 585-1960]) underwent follow-up at 2 years. Diffusion tensor imaging (DTI) values obtained around term were associated with a neurological examination and mental and psychomotor developmental index scores at 2 years based on the Bayley Scales of Infant Development (version 3). Univariate and logistic regression analyses tested for associations between DTI values and follow-up parameters. Cut-off values predicting motor delay and cerebral palsy (CP) were determined for fractional anisotropy, apparent diffusion coefficient (ADC), and fibre lengths.

RESULTS

Infants with psychomotor delay and CP had significantly lower fractional anisotropy values (p=0.002, p=0.04 respectively) and shorter fibre lengths (p=0.02, p=0.02 respectively) of the posterior limb of the internal capsule. Infants with psychomotor delay also had significantly higher ADC values (p=0.03) and shorter fibre lengths (p=0.002) of the callosal splenium. Fractional anisotropy values of the posterior limb of the internal capsule independently predicted motor delay and CP, with sensitivity between 80 and 100% and specificity between 66 and 69%. ADC values of the splenium independently predicted motor delay with sensitivity of 100% and specificity of 65%.

INTERPRETATION

Diffusion tensor imaging tractography at term-equivalent age independently predicts psychomotor delay at 2 years of age in preterm infants.

Assessing postural asymmetry with a podoscope in infants with Central Coordination Disturbance

The aim of this study was to digitally evaluate the incidence and severity of postural asymmetry in infants with Central Coordination Disturbance (CCD) by using a computer-aided podoscope (PodoBaby) from CQ Elektronik System. A sample of 120 infants aged from 3 months (± 1 week) to 6 months (± 1 week) took part in the study, of which 60 were diagnosed with CCD by a neurologist using Vojta's method and the remaining half healthy, non-afflicted infants. The relationships between Vojta's method, as a subjective clinical diagnostic tool for assessing the functional performance of infants with CCD, and the postural asymmetry results recorded with the podoscope, were also defined. Each infant was placed on the podoscope and photographed underneath in two positions: first lying on their back and then on their stomach. A symmetry index was used to calculate body asymmetry, i.e., the percent difference of abnormal body posture by favoring one side of the body to the other. The results confirmed that postural asymmetry assessed by the PodoBaby was in line with the earlier clinical diagnosis using Vojta's method. Statistically significant differences in postural asymmetry were also found between the healthy infants and infants with CCD. In addition, significant relationships were demonstrated in the magnitude and direction of asymmetry in the stomach and back positions.

Sedation and analgesia in mechanically ventilated preterm neonates: continue standard of care or experiment?

Attention to comfort and pain control are essential components of neonatal intensive care. Preterm neonates are uniquely susceptible to pain and agitation, and these exposures have a negative impact on brain development. In preterm neonates, chronic pain and agitation are common adverse effects of mechanical ventilation, and opiates or benzodiazepines are the pharmacologic agents most often used for treatment. Questions remain regarding the efficacy, safety, and neurodevelopmental impact of these therapies. Both preclinical and clinical data suggest troubling adverse drug reactions and the potential for adverse longterm neurodevelopmental impact. The negative impacts of standard pharmacologic agents suggest that alternative agents should be investigated. Dexmedetomidine is a promising alternative therapy that requires further interprofessional and multidisciplinary research in this population.

White matter and cortical injury in hypoxic-ischemic encephalopathy: antecedent factors and 2-year outcome

OBJECTIVE

To examine the spectrum of isolated white matter (WM)/cortical injury and its relation to outcomes in infants with hypoxic-ischemic encephalopathy (HIE) and normal appearing basal ganglia and thalami.

STUDY DESIGN

From 1992-2007, 84 term infants with HIE and normal basal ganglia and thalami on neonatal magnetic resonance imaging were studied; WM/cortical lesions were classified by site and severity. Neurodevelopmental outcomes and head growth were documented at a median age of 2 years.

RESULTS

The WM was normal or mildly abnormal in 33.5%, moderate in 40.5%, and severely abnormal in 26% of infants. Cortical involvement was not seen or was only mild in 75.5%, moderate in 13%, and severe in 12% of infants. WM and cortical injury severity were highly correlated (Spearman ρ = 0.74; P < .001). Infants with severe WM injury had more severe neonatal courses and a higher incidence of hypoglycemia. No infant died. Five infants (6%) developed cerebral palsy but all could walk independently. Cognitive, visual, language, behavioral, and seizure problems were highly prevalent and correlated significantly with the severity of WM injury and poor postnatal head growth.

CONCLUSION

Infants with HIE and selective WM/cortical injury have a low prevalence of cerebral palsy but have a wide range of other problems, which occur more often with severe WM/cortical lesions.

Reduced corticomotor excitability and motor skills development in children born preterm

The mechanisms underlying the altered neurodevelopment commonly experienced by children born preterm, but without brain lesions, remain unknown. While individuals born the earliest are at most risk, late preterm children also experience significant motor, cognitive and behavioural dysfunction from school age, and reduced income and educational attainment in adulthood. We used transcranial magnetic stimulation and functional assessments to examine corticomotor development in 151 children without cerebral palsy, aged 10-13 years and born after gestations of 25-41 completed weeks. We hypothesized that motor cortex and corticospinal development are altered in preterm children, which underpins at least some of their motor dysfunction. We report for the first time that every week of reduced gestation is associated with a reduction in corticomotor excitability that remains evident in late childhood. This reduced excitability was associated with poorer motor skill development, particularly manual dexterity. However, child adiposity, sex and socio-economic factors regarding the child's home environment soon after birth were also powerful influences on development of motor skills. Preterm birth was also associated with reduced left hemisphere lateralization, but without increasing the likelihood of being left handed per se. These corticomotor findings have implications for normal motor development, but also raise questions regarding possible longer term consequences of preterm birth on motor function.

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.

The instrumented fetal sheep as a model of cerebral white matter injury in the premature infant

Despite advances in neonatal intensive care, survivors of premature birth remain highly susceptible to unique patterns of developmental brain injury that manifest as cerebral palsy and cognitive-learning disabilities. The developing brain is particularly susceptible to cerebral white matter injury related to hypoxia-ischemia. Cerebral white matter development in fetal sheep shares many anatomical and physiological similarities with humans. Thus, the fetal sheep has provided unique experimental access to the complex pathophysiological processes that contribute to injury to the human brain during successive periods in development. Recent refinements have resulted in models that replicate major features of acute and chronic human cerebral injury and have provided access to complex clinically relevant studies of cerebral blood flow and neuroimaging that are not feasible in smaller laboratory animals. Here, we focus on emerging insights and methodologies from studies in fetal sheep that have begun to define cellular and vascular factors that contribute to white matter injury. Recent advances include spatially defined measurements of cerebral blood flow in utero, the definition of cellular maturational factors that define the topography of injury and the application of high-field magnetic resonance imaging to define novel neuroimaging signatures for specific types of chronic white matter injury. Despite the higher costs and technical challenges of instrumented preterm fetal sheep models, they provide powerful access to clinically relevant studies that provide a more integrated analysis of the spectrum of insults that appear to contribute to cerebral injury in human preterm infants.

Quantitative fiber tracking in the corpus callosum and internal capsule reveals microstructural abnormalities in preterm infants at term-equivalent age

BACKGROUND AND PURPOSE

Signal-intensity abnormalities in the PLIC and thinning of the CC are often seen in preterm infants and associated with poor outcome. DTI is able to detect subtle abnormalities. We used FT to select bundles of interest (CC and PLIC) to acquire additional information on the WMI.

MATERIALS AND METHODS

One hundred twenty preterm infants born at <31 weeks' gestation with 3T DTI at TEA entered this prospective study. Quantitative information (ie, volume, length, anisotropy, and MD) was obtained from fiber bundles passing through the PLIC and CC. A general linear model was used to assess the effects of factor (sex) and variables (GA, BW, HC, PMA, and WMI) on FT-segmented parameters.

RESULTS

Seventy-two CC and 85 PLIC fiber bundles were assessed. For the CC, increasing WMI and decreasing FA (P = .038), bundle volume (P < .001), and length (P = .001) were observed, whereas MD increased (P = .001). For PLIC, MD increased with increasing WMI (P = .002). Higher anisotropy and larger bundle length were observed in the left PLIC compared with the right (P = .003, P = .018).

CONCLUSIONS

We have shown that in the CC bundle, anisotropy was decreased and diffusivity was increased in infants with high WMI scores. A relation of PLIC with WMI was also shown but was less pronounced. Brain maturation is affected more if birth was more premature.

Fiber tracking at term displays gender differences regarding cognitive and motor outcome at 2 years of age in preterm infants

White matter microstructural changes can be detected with diffusion tensor imaging. It was hypothesized that diffusion parameters in the posterior limb of the internal capsule (PLIC) and corpus callosum (CC) bundles in preterm infants at term equivalent age (TEA) were associated with neurodevelopment at 2 y corrected age. In 67 preterm infants, fiber tracking was performed at TEA for the CC and both PLIC bundles. Volume, length, fractional anisotropy (FA), mean diffusivity, axial diffusivity, and radial diffusivity were determined for the three bundles. These parameters were assessed in relation to outcome on the Bayley Scales of Infant and Toddler Development III. In girls, volume and length of the CC bundle and right PLIC bundle volume were associated with cognition. In boys, volume, FA, mean and radial diffusivity, and length of the left PLIC were associated with fine motor scores. Correction for GA, birth weight, intraventricular hemorrhage, white matter injury, and maternal education did not change the results. Fiber tracking parameters in the PLIC and CC bundles in preterm infants at TEA revealed different associations with neurodevelopment between boys and girls. This study suggested that fiber tracking is a useful method to predict neurodevelopment in preterm infants.

Histopathological correlates of magnetic resonance imaging-defined chronic perinatal white matter injury

OBJECTIVE

Although magnetic resonance imaging (MRI) is the optimal imaging modality to define cerebral white-matter injury (WMI) in preterm survivors, the histopathological features of MRI-defined chronic lesions are poorly defined. We hypothesized that chronic WMI is related to a combination of delayed oligodendrocyte (OL) lineage cell death and arrested maturation of preoligodendrocytes (preOLs). We determined whether ex vivo MRI can distinguish distinct microglial and astroglial responses related to WMI progression and arrested preOL differentiation.

METHODS

We employed a preterm fetal sheep model of global cerebral ischemia in which acute WMI results in selective preOL degeneration. We developed novel algorithms to register histopathologically-defined lesions with contrast-weighted and diffusion-weighted high-field ex vivo MRI data.

RESULTS

Despite mild delayed preOL degeneration, preOL density recovered to control levels by 7 days after ischemia and was ~2 fold greater at 14 days. However, premyelinating OLs were significantly diminished at 7 and 14 days. WMI evolved to mostly gliotic lesions where arrested preOL differentiation was directly proportional to the magnitude of astrogliosis. A reduction in cerebral WM volume was accompanied by four classes of MRI-defined lesions. Each lesion type displayed unique astroglial and microglial responses that corresponded to distinct forms of necrotic or non-necrotic injury. High-field MRI defined 2 novel hypointense signal abnormalities on T(2) -weighted images that coincided with microscopic necrosis or identified astrogliosis with high sensitivity and specificity.

INTERPRETATION

These studies support the potential of high-field MRI for early identification of microscopic necrosis and gliosis with preOL maturation arrest, a common form of WMI in preterm survivors.

Ultrasound detection of white matter injury in very preterm neonates: practical implications

AIM

Diffuse white matter injury is not well detected by cranial ultrasonography (CUS). The aim of this study was twofold: (1) to assess in very preterm neonates the predictive values of individual CUS abnormalities for white matter injury on MRI and neurological outcome; (2) to develop a strategy optimizing CUS detection of white matter injury.

METHOD

Very preterm neonates (n=67; 44 males, 23 females) underwent serial CUS and single MRI. Predictive values of CUS findings for a white matter classification on MRI, individual MRI findings, and neurological outcome at 2 years corrected age were calculated. The effects of timing and frequency of CUS were evaluated.

RESULTS

Periventricular echodensities (PVEs) predicted abnormal white matter on MRI, but absence of PVEs did not predict absence of white matter changes. Peri- and intraventricular haemorrhage (P/IVH) was highly predictive of abnormal white matter on MRI. Frequency and timing of CUS did not influence predictive values. P/IVH and abnormal ventricular size/shape were reasonably predictive of unfavourable outcome, whereas absence of CUS abnormalities predicted a favorable outcome.

INTERPRETATION

(1) If PVEs are present, there is a significant chance of abnormal white matter on MRI. (2) Increasing frequency of CUS does not increase its diagnostic performance for white matter injury. (3) P/IVH is highly predictive of abnormal white matter on MRI and reasonably predictive of unfavourable outcome. (4) Absence of PVEs and P/IVH on CUS does not guarantee normal white matter, but predicts a favourable outcome.

Need for quality control for aEEG monitoring of the preterm infant: a 2-year experience

AIM

To establish and apply a questionnaire for the evaluation of amplitude-integrated electroencephalogram (aEEG) with respect to practicability and feasibility in the NICU, to reveal strategies for improvements in daily use and to investigate the level of staff know-how with regard to performance and evaluation of bedside aEEG for the purpose of quality control.

METHODS

Amplitude-integrated electroencephalogram was routinely applied in preterm infants below 32 weeks of gestational age for a period of 2 years. Practicability, feasibility and the level of know-how with regard to aEEG were assessed using a multiple-choice questionnaire.

RESULTS

Major problems in the use of aEEG in preterm infants were identified as time needed for placement and frequent readjustment of electrodes. Quality control showed the following problems: seizure activity was correctly diagnosed in 60.0%, discontinuous (DC) background in 45.5% and burst suppression (BS) in 41.8% of patients. Overall, BS and DC were the patterns most frequently interpreted incorrectly.

CONCLUSION

Amplitude-integrated electroencephalogram is frequently used in neonatology. In preterm infants with several challenges, repeated theoretical and practical trainings as well as quality control are needed in order for aEEG to become a routinely used monitoring instrument in daily preterm care.

Magnetic resonance imaging studies without sedation in the neonatal intensive care unit: safe and efficient

Use of magnetic resonance imaging (MRI) in the neonatal intensive care unit has been increasing over the past several years because of improved MRI technology and increased clinical awareness of the prognostic and diagnostic information available. Historically, the use of sedation has been the standard for achieving quality imaging without motion artifact, but it exposed the patient to risks associated with sedation medications. In an effort to obtain MRI studies with elimination of risks associated with sedation, a quality improvement project was initiated. Implementing a standardized approach utilizing a vacuum immobilizer has led to successful neonatal MRI completion without the need for sedation in 94% of study attempts. Acceptable or excellent image quality was achieved in more than 97% of attempts. Time away from the neonatal intensive care unit significantly decreased with this approach, with the mean duration of time away decreasing from 60 to 48 minutes (P < .0001). Obtaining MRI studies without sedation can be successfully implemented in a neonatal intensive care unit, nearly eliminating patient risks associated with sedation while improving utilization of hospital resources and maintaining adequate quality imaging.