The postmigrational development of polymicrogyria documented by magnetic resonance imaging from 31 weeks' postconceptional age

An ode to fetal, infant, and toddler neuroimaging: Chronicling early clinical to research applications with MRI, and an introduction to an academic society connecting the field

Fetal, infant, and toddler neuroimaging is commonly thought of as a development of modern times (last two decades). Yet, this field mobilized shortly after the discovery and implementation of MRI technology. Here, we provide a review of the parallel advancements in the fields of fetal, infant, and toddler neuroimaging, noting the shifts from clinical to research use, and the ongoing challenges in this fast-growing field. We chronicle the pioneering science of fetal, infant, and toddler neuroimaging, highlighting the early studies that set the stage for modern advances in imaging during this developmental period, and the large-scale multi-site efforts which ultimately led to the explosion of interest in the field today. Lastly, we consider the growing pains of the community and the need for an academic society that bridges expertise in developmental neuroscience, clinical science, as well as computational and biomedical engineering, to ensure special consideration of the vulnerable mother-offspring dyad (especially during pregnancy), data quality, and image processing tools that are created, rather than adapted, for the young brain.

Multicystic encephalomalacia: An autopsy report of 4 cases

Multicystic encephalomalacia is varying sized cystic lesions in the brain encountered in developing fetuses or infants. These cysts start at the periventricular area and may extend onto the cortex. The cause of the formation of these cystic lesions is secondary to an ischemic or hypoxic insult, which leads to liquefactive necrosis and subsequent formation of gliotic cyst walls having an admixture of microglia. We discuss four autopsy cases that had multicystic encephalomalacia to highlight the scenarios in which these lesions are encountered.

Cortical structural abnormalities in very preterm children at 7 years of age

We analyzed long-lasting alterations in brain morphometry associated with preterm birth using volumetric and surface-based analyses applied to children at age 7 years. Comparison of 24 children born very preterm (VPT) to 24 healthy term-born children revealed reductions in total cortical gray matter volume, white matter volume, cortical surface area and gyrification index. Regional cortical shape abnormalities in VPT children included the following: shallower anterior superior temporal sulci, smaller relative surface area in the inferior sensori-motor cortex and posterior superior temporal cortex, larger relative surface area and a cingulate sulcus that was shorter or more interrupted in medial frontoparietal cortex. These findings indicate a complex pattern of regional vulnerabilities in brain development that may contribute to the diverse and long-lasting neurobehavioral consequences that can occur after very premature birth.

The role of neuroimaging in predicting neurodevelopmental outcomes of preterm neonates

Magnetic resonance imaging (MRI) is a safe and high-resolution neuroimaging modality that is increasingly used in the neonatal population to assess brain injury and its consequences on brain development. It is superior to cranial ultrasound for the definition of patterns of both white and gray matter maturation and injury and therefore has the potential to provide prognostic information on the neurodevelopmental outcomes of the preterm population. Furthermore, the development of sophisticated MRI strategies, including diffusion tensor imaging, resting state functional connectivity, and magnetic resonance spectroscopy, may increase the prognostic value, helping to guide parental counseling and allocate early intervention services.

Multimodality evaluation of the pediatric brain: DTI and its competitors

The development of the human brain, from the fetal period until childhood, happens in a series of intertwined neurogenetical and histogenetical events that are influenced by environment. Neuronal proliferation and migration, cell aggregation, axonal ingrowth and outgrowth, dendritic arborisation, synaptic pruning and myelinisation contribute to the 'plasticity of the developing brain'. These events taken together contribute to the establishment of adult-like neuroarchitecture required for normal brain function. With the advances in technology today, mostly due to the development of non-invasive neuroimaging tools, it is possible to analyze these structural events not only in anatomical space but also longitudinally in time. In this review we have highlighted current 'state of the art' neuroimaging tools. Development of the new MRI acquisition sequences (DTI, CHARMED and phase imaging) provides valuable insight into the changes of the microstructural environment of the cortex and white matter. Development of MRI imaging tools dedicated for analysis of the acquired images (i) TBSS and ROI fiber tractography, (ii) new tissue segmentation techniques and (iii) morphometric analysis of the cortical mantle (cortical thickness and convolutions) allows the researchers to map the longitudinal changes in the macrostructure of the developing brain that go hand-in-hand with the acquisition of cognitive skills during childhood. Finally, the latest and the newest technologies, like connectom analysis and resting state fMRI connectivity analysis, today, for the first time provide the opportunity to study the developing brain through the prism of maturation of the systems and networks beyond individual anatomical areas. Combining these methods in the future and modeling the hierarchical organization of the brain might ultimately help to understand the mechanisms underlying complex brain structure function relationships of normal development and of developmental disorders.

Malformations of cortical development: diagnostic accuracy of fetal MR imaging

PURPOSE

To determine the diagnostic accuracy of fetal magnetic resonance (MR) imaging for malformations of cortical development by using postnatal MR imaging as reference standard.

MATERIALS AND METHODS

Eighty-one patients who had undergone fetal and postnatal MR imaging of the brain were identified in this institutional review board-approved, HIPAA-compliant study. Images were retrospectively reviewed in consensus by two pediatric neuroradiologists who were blinded to clinical information. Sensitivity and specificity were calculated according to retrospective review of the images and clinical reports for fetal MR images. The Fisher exact test was used to compare results for fetuses imaged before and after 24 gestational weeks and for image review versus clinical reports for fetal MR images.

RESULTS

Median gestational age at fetal MR imaging was 25.0 weeks (range, 19.71-38.14 weeks). Postnatal MR imaging depicted 13 cases of polymicrogyria, three cases of schizencephaly, and 15 cases of periventricular nodular heterotopia. Sensitivity and specificity of fetal MR imaging were 85% and 100%, respectively, for polymicrogyria; 100% each for schizencephaly; and 73% and 92%, respectively, for heterotopia. When heterotopia was seen in two planes, specificity was 100% and sensitivity was 67%. Sensitivity for heterotopia decreased to 44% for fetuses younger than 24 weeks. According to reports for fetal MR images, prospective sensitivity and specificity, respectively, were 85% and 99% for polymicrogyria, 100% and 99% for schizencephaly, and 40% and 91% for heterotopia.

CONCLUSION

Fetal MR imaging had the highest sensitivity for polymicrogyria and schizencephaly. Specificity was 100% for all cortical malformations when the abnormality was seen in two planes. Sensitivity for heterotopia was lower for fetuses younger than 24 weeks. Knowledge of the gestational age is important, especially for counseling patients about heterotopia.

Cortical development in the fetus and the newborn: advanced MR techniques

Brain function is tightly linked to the development of the cortex. Until recently, assessing the human cortical development and folding was not possible in vivo. It is magnetic resonance imaging and new post-processing image analysis tools that have improved the understanding of cortical development. The combination of conventional magnetic resonance imaging and diffusion tensor imaging has further allowed depiction of the relationship of changes in intracortical layering and cortical folding. Being able to follow these early developmental processes has elucidated changes in early brain development due to changed environmental conditions in fetal life such as twinning and fetal growth restriction and postnatal conditions such as prematurity. This review further illustrates new data on brain structural asymmetries linked to the emergence of early language functions.

Clinical and imaging heterogeneity of polymicrogyria: a study of 328 patients

Polymicrogyria is one of the most common malformations of cortical development and is associated with a variety of clinical sequelae including epilepsy, intellectual disability, motor dysfunction and speech disturbance. It has heterogeneous clinical manifestations and imaging patterns, yet large cohort data defining the clinical and imaging spectrum and the relative frequencies of each subtype are lacking. The aims of this study were to determine the types and relative frequencies of different polymicrogyria patterns, define the spectrum of their clinical and imaging features and assess for clinical/imaging correlations. We studied the imaging features of 328 patients referred from six centres, with detailed clinical data available for 183 patients. The ascertainment base was wide, including referral from paediatricians, geneticists and neurologists. The main patterns of polymicrogyria were perisylvian (61%), generalized (13%), frontal (5%) and parasagittal parieto-occipital (3%), and in 11% there was associated periventricular grey matter heterotopia. Each of the above patterns was further divided into subtypes based on distinguishing imaging characteristics. The remaining 7% were comprised of a number of rare patterns, many not described previously. The most common clinical sequelae were epileptic seizures (78%), global developmental delay (70%), spasticity (51%) and microcephaly (50%). Many patients presented with neurological or developmental abnormalities prior to the onset of epilepsy. Patients with more extensive patterns of polymicrogyria presented at an earlier age and with more severe sequelae than those with restricted or unilateral forms. The median age at presentation for the entire cohort was 4 months with 38% presenting in either the antenatal or neonatal periods. There were no significant differences between the prevalence of epilepsy for each polymicrogyria pattern, however patients with generalized and bilateral forms had a lower age at seizure onset. There was significant skewing towards males with a ratio of 3:2. This study expands our understanding of the spectrum of clinical and imaging features of polymicrogyria. Progression from describing imaging patterns to defining anatomoclinical syndromes will improve the accuracy of prognostic counselling and will aid identification of the aetiologies of polymicrogyria, including genetic causes.

Imaging biomarkers of outcome in the developing preterm brain

The neurodevelopmental disabilities of those who were born prematurely have been well described, yet the underlying alterations in brain development that lead to these changes remain poorly understood. Processes that are vulnerable to injury in the developing brain include maturation of oligodendrocyte precursors and genetically programmed changes in cortical connectivity; recent data have indicated that diffuse injury of the white matter accompanied by neuronal and axonal disruption is common in prematurely born infants. Recent advances in MRI include diffusion tensor imaging and sophisticated image analysis tools, such as functional connectivity, voxel-based morphometry, and mathematical morphology-based cortical folding strategies. These advanced techniques have shown that white matter structure is dependent on gestational age and have started to provide important information about the dynamic interactions between development, injury, and functional recovery in the preterm brain. Identification of early biomarkers for outcome could enable physicians and scientists to develop targeted pharmacological and behavioural therapies to restore functional connectivity.

Cerebral blood flow and metabolism in the developing fetus

The inaccessibility of the human fetal brain to studies of perfusion and metabolism has impeded progress in the understanding of the normal and abnormal systems of oxygen substrate supply and demand. Consequently, current understanding is based on studies in fetal animals or in the premature infant (ex utero fetus), neither of which is ideal. Despite promising developments in fetal magnetic resonance imaging (MRI) and Doppler ultrasound, major advances in fetal neurodiagnostics will be required before rational and truly informed brainoriented care of the fetus becomes feasible.

Mapping the early cortical folding process in the preterm newborn brain

In the developing human brain, the cortical sulci formation is a complex process starting from 14 weeks of gestation onward. The potential influence of underlying mechanisms (genetic, epigenetic, mechanical or environmental) is still poorly understood, because reliable quantification in vivo of the early folding is lacking. In this study, we investigate the sulcal emergence noninvasively in 35 preterm newborns, by applying dedicated postprocessing tools to magnetic resonance images acquired shortly after birth over a developmental period critical for the human cortex maturation (26-36 weeks of age). Through the original three-dimensional reconstruction of the interface between developing cortex and white matter and correlation with volumetric measurements, we document early sulcation in vivo, and quantify changes with age, gender, and the presence of small white matter lesions. We observe a trend towards lower cortical surface, smaller cortex, and white matter volumes, but equivalent sulcation in females compared with males. By precisely mapping the sulci, we highlight interindividual variability in time appearance and interhemispherical asymmetries, with a larger right superior temporal sulcus than the left. Thus, such an approach, included in a longitudinal follow-up, may provide early indicators on the structural basis of cortical functional specialization and abnormalities induced by genetic and environmental factors.

The neuropathology of acquired pre- and perinatal brain injuries

Acquired pre- and perinatal brain injuries comprise a significant proportion of perinatal neuropathology. They are associated with placental abnormalities, maternal factors, multiple gestations, and preterm labor, as well as with the later development of cerebral palsy and developmental delay. The patterns of perinatal brain injury depend on the etiology (often hypoxic-ischemic) and the timing relative to the development of the fetal nervous system, since the vulnerabilities of gray and white matter differ across postconceptional age and by neuroanatomic site. Nevertheless, characteristic features allow determination of the approximate age and cause of each pattern of injury in the perinatal brain.

Postnatal onset cortical dysplasia associated with infarction of white matter

On MRI at 35 weeks of a boy born at 25 weeks, focal disorganization of the cortex was observed near a frontal venous infarct developed in the first week. Disruption of the final steps of cell migration, injury to the subplate and/or disruption of corticospinal axons are possible mechanisms behind it. Preterms with white matter lesions at or below 25 weeks postconceptional age should be scrutinized for cortical dysplasia.

Neonatal seizure classification: a fetal perspective concerning childhood epilepsy

Neonatal seizures are markers for time-specific etiologies during antepartum, intrapartum and neonatal time periods. Seizures with or without encephalopathic signs can represent a continuum of maternal, placental, fetal and neonatal risk factors and disease states. A multi-dimensional classification scheme for neonatal seizures is suggested that will help strategize specific therapeutic interventions to optimize neurologic outcome and anticipate later neurological morbidities including epilepsy risk. This scheme combines "epileptic" and "non-epileptic" seizure descriptions which capture time-specific and brain region-specific mechanisms for seizures. Synchronized video electroencephalographic monitoring provides the most accurate start and endpoints for cortically generated seizures. However, subcortical sites of injury may also initiate abnormal clinical signs with or without the subsequent expression of electrographic seizures. Co-registration of digital neuroimaging techniques such as magnetic resonance imaging with computational electroencephalographic datasets will provide more precise structure-function correlates for neonatal seizures that address both cortical and subcortical sites of injury. Finally, more precise definitions of neonatal status epilepticus need to be established because of the long-term harmful effects on brain development by prolonged seizures expressed as epilepsy and cognitive-behavioral deficits. With this expanded classification scheme for neonatal seizures, novel pharmacologic and surgical strategies can be designed for disease-specific rescue, repair, and regeneration strategies of damaged brain tissue that occur during fetal and neonatal periods, and are later expressed during infancy and childhood. Clinical neuroscientists must strive to develop a classification scheme that bridges bench to bedside concepts of developmental neural plasticity research, recognizing both negative and positive consequences of brain remodeling and repair of the child and adolescent brain. Developmental neural plasticity also extends into adulthood when brain remodeling mechanisms further contribute to epileptogenesis and continues to impair quality of life.

MRI of fetal acquired brain lesions

Acquired fetal brain damage is suspected in cases of destruction of previously normally formed tissue, the primary cause of which is hypoxia. Fetal brain damage may occur as a consequence of acute or chronic maternal diseases, with acute diseases causing impairment of oxygen delivery to the fetal brain, and chronic diseases interfering with normal, placental development. Infections, metabolic diseases, feto-fetal transfusion syndrome, toxic agents, mechanical traumatic events, iatrogenic accidents, and space-occupying lesions may also qualify as pathologic conditions that initiate intrauterine brain damage. MR manifestations of acute fetal brain injury (such as hemorrhage or acute ischemic lesions) can easily be recognized, as they are hardly different from postnatal lesions. The availability of diffusion-weighted sequences enhances the sensitivity in recognizing acute ischemic lesions. Recent hemorrhages are usually readily depicted on T2 (*) sequences, where they display hypointense signals. Chronic fetal brain injury may be characterized by nonspecific changes that must be attributable to the presence of an acquired cerebral pathology. The workup in suspected acquired fetal brain injury also includes the assessment of extra-CNS organs that may be affected by an underlying pathology. Finally, the placenta, as the organ that mediates oxygen delivery from the maternal circulation to the fetus, must be examined on MR images.

The value of autopsy in determining the cause of failure to respond to resuscitation at birth

Autopsy is invaluable in identifying the causes of severe depression and very low Apgar score after birth and in assessing contributory conditions. Brain scans are increasingly used in the care of neonates who fail to respond to resuscitation at birth but their interpretation depends on the information gained from sound neuropathological studies. Asphyxia, both acute intrapartum asphyxia and chronic asphyxia, is an important cause of low Apgar scores. The gestational age and the nature of the asphyxial insult both have a profound influence on the ultimate pattern of injury. Asphyxia in the preterm brain tends to damage preferentially the white matter but some white matter damage is also seen in many infants who have an hypoxia-ischaemic insult at term though the predominant site of injury is to the central grey matter. The nature of the cellular damage and reactive change seen at autopsy is described. There is an association between low Apgar scores and intrauterine exposure to infection and maternal pyrexia. Detailed autopsy examination should include the search for infection. The placenta, cord and membranes should be examined in view of the mounting evidence of the association between intrauterine infection of the placenta and fetal membranes and prenatal brain damage. Additionally, the presence of placental thrombosis and infarction should be sought in relation to focal and global injury in the full term infant. Acquired prepartum lesions rarely cause the infant to present with a low Apgar score. The exception to this is severe damage to the brainstem and basal ganglia. Traumatic injury to the brain is now much less common than in previous decades. Subdural haemorrhage occurs more frequently than intraventricular or subarachnoid haemorrhage. Instrumental and assisted deliveries are associated with an increased incidence of subdural haemorrhage though these rarely cause significant long term damage. Careful autopsy, particularly of the neck and paravertebral tissues, spinal cord, brainstem and nerve roots is important where trauma is suspected. Tearing of nerve roots or fibre bundles in the spinal cord is readily demonstrated under the microscope using immunocytochemistry to beta-amyloid precursor protein. Disorders of the spinal cord, peripheral nerve and muscle as well as some metabolic diseases may cause a baby to be both floppy and weak. Metabolic disease, including peroxisomal disorders, non-ketotic hyperglycinaemia, lipid and glycogen storage disorders and mitochondrial diseases may cause profound hypotonia and respiratory failure at birth or shortly afterwards.

Prenatal ultrasound detection of bilateral focal polymicrogyria

OBJECTIVES

Prenatal diagnosis by ultrasound of fetal polymicrogyria has been reported only once.

METHODS

We describe an additional case of polymicrogyria in a fetus from a monozygotic twin pair, probably the consequence of twin-to-twin transfusion syndrome.

RESULTS

On ultrasound, there were bilateral cortical hyperechogenic spots, and prenatal magnetic resonance imaging demonstrated the typical features of bilateral focal polymicrogyria.

CONCLUSION

Polymicrogyria can be considered in the differential diagnosis of hyperechogenic brain lesions on fetal ultrasound. We also confirm the risk of brain damage in monochorionic twins pregnancies and the likely hypoxic-ischemic etiology of polymicrogyria.

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

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

Preserved visual function in a case of occipitoparietal microgyria

A 20-year-old man with bilateral parasagittal occipitoparietal polymicrogyria and epilepsy, from whom normal functional magnetic resonance imaging and electroencephalogram responses to visual stimuli were obtained, was found to have no visual perceptual deficits. This suggests that microgyric cortex can perform normal visual functions, despite its gross structural abnormalities.