Neuroimaging in disorders of cortical development

MRI of Malformations of Cortical Development- A Comprehensive Review

MCDs (malformations of cortical development) are structural anomalies that disrupt the normal process of the cortical development. These include microcephaly with simplified gyral pattern/microlissencephaly, hemimegalencephaly, focal cortical dysplasia, lissencephaly, heterotopia, polymicrogyria and schizencephaly. They can present with intractable epilepsy, developmental delay, neurological deficits or cognitive impairment. Though the definitive diagnosis of MCD depends on histopathology, the pathological tissue is rarely available hence diagnosis begins with neuroimaging. This article shall briefly review the embryology followed by specific MRI imaging features of MCD in an attempt to simplify the process of diagnosing these disorders with clinical and genetic correlation.A table has been included to highlight the embryological, clinical and genetic findings associated with various MCDs.

A journey through formation and malformations of the neo-cortex

PURPOSE

Malformations of cortical development (MCD) are a heterogeneous group of disorders characterized by abnormal structure of the cerebral cortex. MCDs are an important cause of development delay and intractable epilepsy in children. In this review, we explore the embryological stages of development of neo-cortex, the imageology of various malformations which may occur during the journey of this development, the recent advances in imaging techniques used for diagnosing these malformations, and finally a simplified radiological approach to malformations of cortical development.

REVIEW

We discuss the classification of MCD according to the embryologic stage of cerebral cortex at which the abnormality occurred and the unique imaging features of various malformations, including microcephaly, hemimegalencephaly, lissencephaly, focal cortical dysplasia, heterotopias, polymicrogyria, schizencephaly, and neonatal CMV infection. Also, a rare variant of hemimegalencephaly, namely posterior quadrantic dysplasia, is illustrated; the diagnosis of which is crucial for neurosurgeons to decide management. The technological advancement in the imaging of MCD has taken a leap in the recent years. Imaging now also plays an enormous role in mapping of the abnormalities, delineation of proper surgical boundaries, and quantifying risks of visual, language, and sensorimotor dysfunction. With the introduction of various motor-sparing surgeries and disconnection procedures, proper identification and delineation of these malformations have gained utmost significance.

CONCLUSION

Knowledge of the wide imaging spectrum of MCD, familiarity with recent advances in imaging and an optimal radiological approach is essential for the general radiologist to accurately diagnose and prognosticate MCD as well as provide the best surgical approach to the operating surgeon.

Effect of gabapentin on fetal rat brain and its amelioration by ginger

Intrauterine exposure to antiepileptic drugs (AEDs) is associated with neurodevelopmental alterations causing postnatal behavioral and cognitive alterations. These disorders are associated with the interference of these AEDs with the developing cerebral cortex and hippocampal neurons. Therefore, it is crucial to identify the drugs that should be avoided during pregnancy in order to prevent AED mediated developmental alterations. The present study was conducted to investigate the effects of prenatal exposure to the antiepileptic drug gabapentin (GBP) on the rat fetal brain during the organogenesis phase and to examine the potential ameliorative effect of ginger (Zingiber officinale). Consequently, the current study addressed the developmental neural changes on the histological, immuno-histochemical and ultrastructural levels. The brain of fetuses from the GBP group showed a highly significant decrease in their weight. Histologically, the cerebral cortex and hippocampus regions of fetuses maternally injected with GBP showed layer disorganization, vacuolated neuropil and massive cell degeneration. The expression of Caspase 3 was significantly increased in the brain of GBP fetuses, unlike the expression of Bcl-2 which was significantly decreased. On the ultrastructure level, the neurons showed pyknotic and chromatolytic nuclei. The cytoplasm was rarefied with swollen organelles. Co-administration of ginger evidently ameliorated most of these effects. In conclusion, GBP administration during pregnancy could possibly affect the developing fetal brain and ginger may have ameliorating effect against the induced GBP neurotoxicity and should be taken in parallel.

Imaging the term neonatal brain

Brain imaging is important for the diagnosis and management of sick term neonates. Although ultrasound and computed tomography may provide some information, magnetic resonance imaging is now the brain imaging modality of choice because it is the most sensitive technique for detecting and quantifying brain abnormalities and does not expose infants to radiation. This statement describes the principles, roles and limitations of these three imaging modalities and makes recommendations for appropriate use in term neonates. The primary focus is the brain of term infants with neonatal encephalopathy, many of whom are diagnosed with hypoxic-ischemic encephalopathy.

Maternal carbamazepine alters fetal neuroendocrine-cytokines axis

This study detected the impact of maternal carbamazepine (CBZ) on the fetal neuroendocrine-cytokines axis. 25 or 50mg/kg of CBZ was intraperitoneally administrated to pregnant albino rats from the gestation day (GD) 1 to 20. Both administrations of CBZ caused a hypothyroidism in dams and fetuses whereas the decreases in serum thyroxine (T4) and triiodothyronine (T3) and increases in serum thyrotropin (TSH) levels were highly significant (LSD; P <0.01) at GD 20 compared to untreated control dams. Also, both administrations had undesirable impacts on the maternofetal body weight, litter weight, survival of dams and fetuses, and their food consumption in comparison to the corresponding control. These administrations also elicited a reduction in fetal serum growth hormone (GH), interferon-γ (IFNγ), interleukins (IL-2 & 4) and prostaglandin E2 (PGE2) levels. Also, the elevation in fetal serum tumor necrosis factor-alpha (TNFα), transforming growth factor-beta (TGFβ), and interleukins (IL-1β & 17) levels was observed at embryonic day (ED) 20. Moreover, there were a cellular fragmentation, distortion, hyperemia, oedema and vacuolation in the fetal cerebellar cortex due to both maternal administrations. These developmental changes were dose-dependent. These novel results suggest that CBZ may act as a developmental immunoneuroendocrine disruptor.

Sulcus-based MR analysis of focal cortical dysplasia located in the central region

Objective

Focal cortical dysplasias (FCDs) are mainly located in the frontal region, with a particular tropism for the central sulcus. Up to 30% of lesions are undetected (magnetic resonance [MR]-negative FCD patients) or belatedly diagnosed by visual analysis of MR images. We propose an automated sulcus-based method to analyze abnormal sulcal patterns associated with central FCD, taking into account the normal interindividual sulcal variability.

Methods

We retrospectively studied 29 right-handed patients with FCD in the central region (including 12 MR negative histologically-confirmed cases) and 29 right-handed controls. The analysis of sulcal abnormalities from T1-weighted MR imaging (MRI) was performed using a graph-based representation of the cortical folds and an automated sulci recognition system, providing a new quantitative criterion to describe sulcal patterns, termed sulcus energy.

Results

Group analysis showed that the central sulcus in the hemisphere ipsilateral to the FCD exhibited an abnormal sulcal pattern compared with controls (p = 0.032). FCDs were associated with abnormal patterns of the central sulci compared with controls (p = 0.006), a result that remained significant when MR-negative and MR-positive patients were considered separately, while the effects of sex, age and MR-field were not significant. At the individual level, sulcus energy alone failed to detect the FCD lesion. We found, however, a significant association between maximum z-scores and the site of FCD (p = 0.0046) which remained significant in MR-negative (p = 0.024) but not in MR-positive patients (p = 0.058). The maximum z-score pointed to an FCD sulcus in four MR-negative and five MR-positive patients.

Conclusions

We identified abnormal sulcal patterns in patients with FCD of the central region compared with healthy controls. The abnormal sulcal patterns ipsilateral to the FCD and the link between sulcus energy and the FCD location strengthen the interest of sulcal abnormalities in FCD patients.

Brain development in infants born preterm: looking beyond injury

Infants born very preterm are high risk for acquired brain injury and disturbances in brain maturation. Although survival rates for preterm infants have increased in the last decades owing to improved neonatal intensive care, motor disabilities including cerebral palsy persist, and impairments in cognitive, language, social, and executive functions have not decreased. Evidence from neuroimaging studies exploring brain structure, function, and metabolism has indicated abnormalities in the brain development trajectory of very preterm-born infants that persist through to adulthood. In this chapter, we review neuroimaging approaches for the identification of brain injury in the preterm neonate. Advances in medical imaging and availability of specialized equipment necessary to scan infants have facilitated the feasibility of conducting longitudinal studies to provide greater understanding of early brain injury and atypical brain development and their effects on neurodevelopmental outcome. Improved understanding of the risk factors for acquired brain injury and associated factors that affect brain development in this population is setting the stage for improving the brain health of children born preterm.

High frequency oscillations in intracranial EEGs mark epileptogenicity rather than lesion type

High frequency oscillations (HFOs) called ripples (80-250 Hz) and fast ripples (FR, 250-500 Hz) can be recorded from intracerebral EEG macroelectrodes in patients with intractable epilepsy. HFOs occur predominantly in the seizure onset zone (SOZ) but their relationship to the underlying pathology is unknown. It was the aim of this study to investigate whether HFOs are specific to the SOZ or result from pathologically changed tissue, whether or not it is epileptogenic. Patients with different lesion types, namely mesial temporal atrophy (MTA), focal cortical dysplasia (FCD) and nodular heterotopias (NH) were investigated. Intracranial EEG was recorded from depth macroelectrodes with a sampling rate of 2000 Hz. Ripples (80-250 Hz) and Fast Ripples (250-500 Hz) were visually marked in 12 patients: five with MTA, four with FCD and three with NH. Rates of events were statistically compared in channels in four areas: lesional SOZ, non-lesional SOZ, lesional non-SOZ and non-lesional non-SOZ. HFO rates were clearly more linked to the SOZ than to the lesion. They were highest in areas in which lesion and SOZ overlap, but in patients with a SOZ outside the lesion, such as in NHs, HFO rates were clearly higher in the non-lesional SOZ than in the inactive lesions. No specific HFO pattern could be identified for the different lesion types. The findings suggest that HFOs represent a marker for SOZ areas independent of the underlying pathology and that pathologic tissue changes alone do not lead to high rates of HFOs.

Disorders of cortical formation: MR imaging features

The purpose of this article was to review the embryologic stages of the cerebral cortex, illustrate the classification of disorders of cortical formation, and finally describe the main MR imaging features of these disorders. Disorders of cortical formation are classified according to the embryologic stage of the cerebral cortex at which the abnormality occurred. MR imaging shows diminished cortical thickness and sulcation in microcephaly, enlarged dysplastic cortex in hemimegalencephaly, and ipsilateral focal cortical thickening with radial hyperintense bands in focal cortical dysplasia. MR imaging detects smooth brain in classic lissencephaly, the nodular cortex with cobblestone cortex with congenital muscular dystrophy, and the ectopic position of the gray matter with heterotopias. MR imaging can detect polymicrogyria and related syndromes as well as the types of schizencephaly. We concluded that MR imaging is essential to demonstrate the morphology, distribution, and extent of different disorders of cortical formation as well as the associated anomalies and related syndromes.

Neuroimaging in pediatric epilepsy: a multimodality approach

Pediatric patients with intractable epilepsy represent a challenging clinical population. However, recent advances in neuroimaging with a multimodality imaging approach that combines fluorine 18 fluorodeoxyglucose positron emission tomography, magnetoencephalography, diffusion tensor imaging, and magnetic source imaging with conventional magnetic resonance imaging continue to improve diagnosis and treatment in affected patients. These advances are increasing the understanding of the underlying disease process and improving the ability to noninvasively detect epileptogenic foci that in the past went undetected and whose accurate localization is crucial for a good outcome following surgical resection.

Small focal cortical dysplasia lesions are located at the bottom of a deep sulcus

Focal cortical dysplasia (FCD) is often characterized by minor structural changes that may go unrecognized by standard radiological analysis. Visual assessment of morphological characteristics of FCD and sulci harbouring them is difficult due to the complexity of brain convolutions. Our purpose was to elucidate and quantify the spatial relationship between FCD lesions and brain sulci using automated sulcal extraction and morphometry. We studied 43 consecutive FCD patients using high-resolution MRI. Lesions were classified into small and large using qualitative (detection on initial clinical assessment of conventional MRI) and quantitative (volume) criteria. Sulci were identified and labelled automatically using an algorithm based on a congregation of neural networks. Segmented FCD lesions and sulci were then simultaneously visualized in 3D. We measured mean and maximum depth of sulci related to each FCD and of the corresponding sulci in 21 healthy controls. In addition, we calculated sulcal depth within the FCD neighbourhood. Twenty-one (21/43 = 49%) patients had small FCD lesions (volume range: 128-3093 mm(3)). Among them, 17 (81%) had been overlooked during initial radiological evaluation and were subsequently identified using image processing. Eighteen (18/21 = 86%) small FCD lesions were located at the bottom of a sulcus. Two others were related to the walls of two sulci and one was located at the crown of a gyrus. Mean and maximum depth of sulci related to the FCD was higher than that of the corresponding sulci in controls (P < 0.008). Sulcal depth within lesional neighbourhood had larger mean depth than that of the entire sulcus (P < 0.0002). Evidence that small FCD lesions are preferentially located at the bottom of an abnormally deep sulcus may be used to direct the search for developmental abnormalities, particularly in patients in whom large-scale MRI features are only mildly abnormal or absent.

Disorders of cortical formation: MR imaging features

The purpose of this article was to review the embryologic stages of the cerebral cortex, illustrate the classification of disorders of cortical formation, and finally describe the main MR imaging features of these disorders. Disorders of cortical formation are classified according to the embryologic stage of the cerebral cortex at which the abnormality occurred. MR imaging shows diminished cortical thickness and sulcation in microcephaly, enlarged dysplastic cortex in hemimegalencephaly, and ipsilateral focal cortical thickening with radial hyperintense bands in focal cortical dysplasia. MR imaging detects smooth brain in classic lissencephaly, the nodular cortex with cobblestone cortex with congenital muscular dystrophy, and the ectopic position of the gray matter with heterotopias. MR imaging can detect polymicrogyria and related syndromes as well as the types of schizencephaly. We concluded that MR imaging is essential to demonstrate the morphology, distribution, and extent of different disorders of cortical formation as well as the associated anomalies and related syndromes.

Pathophysiologic characteristics of balloon cells in cortical dysplasia

OBJECTS

Balloon cells are histopathological hallmarks of cortical malformations, i.e., focal cortical dysplasia (FCD) of the Taylor type or the cortical tubers of tuberous sclerosis, and they are believed to be the epileptogenic substrate and cause therapeutic drug resistant epilepsy in man. This study was carried out to investigate the developmental histogenesis and epileptogenesis of balloon cells in FCD.

MATERIALS AND METHODS

We used an immunohistochemical approach to examine the expressions of primitive neuroepithelial cell antigens (CD34, nestin, and vimentin), ionotrophic glutamate receptor subunits (NR1, NR2A/B, GluR1, GluR2, GluR3, GluR4, and GluR5/6/7), and P-glycoprotein in balloon cells from FCD and normal cerebral cortex epileptogenic lesions.

CONCLUSION

Balloon cells presented in clusters or as scattered cells throughout FCD lesions involving the gray and white matter. We found the balloon cells to be classifiable into three subtypes based on glial fibrillary acidic protein (GFAP) and neurofilament protein (NF-L) immunohistochemistry, i.e., as neuronal, astrocytic, and uncommitted. Immunopositivity for nestin, CD34, and vimentin in balloon cells of FCD suggests that they may be derived from the abnormal development and differentiation of neural stem cells. Moreover, it appears that epileptogenesis in cortical dysplasia is partly caused by the upregulations of some glutamate receptor subunit proteins (NR1, NR2A/B, GluR1, and GluR3) in balloon cells and dysplastic neurons. We speculate that the presence of the drug resistance protein P-glycoprotein in balloon cells might explain medically refractory epilepsy in FCD.

Electrocorticography discharge patterns in patients with a cavernous hemangioma and pharmacoresistent epilepsy

OBJECT

Neurodevelopmental lesions (NDLs) such as glioneuronal tumors and cortical dysplasia produce characteristic electrocorticography (ECoG) discharge patterns. Because cavernomas, another congenital abnormality, are also associated with pharmacoresistant epilepsy, the authors wondered whether they exhibit discharge patterns similar to those occurring in NDLs.

METHODS

Intraoperative ECoG recordings from 19 patients with cavernomas and 54 with NDLs were reviewed for continuous spikes, bursts, or recruiting discharges and to determine whether these patterns were spatially coincident with the lesion. Relative densities of microglia and the intensity of Fe3+ staining in surgical samples were evaluated. Seizure outcome was assessed 1 year after surgery.

RESULTS

The mean ages at seizure onset and surgery were higher in patients in the cavernoma group than in the NDL group (22.5 and 36.4 years compared with 10.0 and 25.2 years, respectively). Neocortical discharge patterns occurred equally in patients with either cavernomas (53%) or NDLs (41%). In the mesiotemporal area coincident bursts occurred more often in patients with cavernomas than patients with NDLs (55% compared with 10%, respectively). Coincident continuous spiking was associated with a longer duration of epilepsy in patients with cavernomas (23.5 years compared with 11.4 years for those without coincident continuous spiking) and with a lower age at seizure onset in those with NDLs (4.1 years compared with 11.8 years for those without coincident continuous spiking). In the cavernoma group the absence of coincident bursts was associated with high microglia density. There were no associations between the intensity of Fe3+ staining and discharge patterns, although the discharge patterns were associated with a worse outcome in patients with NDLs.

CONCLUSIONS

In patients with NDLs, continuous spiking patterns may be markers of a widespread epileptogenic zone due to an early insult to the developing brain; in patients with cavernomas, such patterns may indicate secondary epileptogenesis. Microglia may inhibit discharge patterns in patients with cavernomas.

Structural magnetic resonance imaging in epilepsy

Because of its sensitivity and high tissue contrast, magnetic resonance imaging (MRI) is the technique of choice for structural imaging in epilepsy. In this review the effect of using optimised scanning protocols and the use of high field MR systems on detection sensitivity is discussed. Also, the clinical relevance of adequate imaging in patients with focal epilepsy is highlighted. The most frequently encountered MRI findings in epilepsy are reported and their imaging characteristics depicted. Imaging focus will be on the diagnosis of hippocampal sclerosis and malformations of cortical development, two major causes of medically intractable focal epilepsy.

Fetal Exposure to GABA-Acting Antiepileptic Drugs Generates Hippocampal and Cortical Dysplasias

PURPOSE

The management of epilepsy during pregnancy entails a number of concerns. While seizures may affect adversely maternal and fetal outcome, antiepileptic drugs (AEDs) may increase the incidence of congenital abnormalities and possibly affect postnatal cognitive development in the offspring. Experimental animal studies can aid in assessing teratogenic features associated with individual AEDs and/or with seizures, and to identify the mechanisms involved. The purpose of this study was to investigate the consequences of prenatal exposure to (a) different AEDs and (b) maternal seizures on brain maturational processes in rats.

METHODS

Pregnant rats received from embryonic days 14 to 19 intraperitoneal injections of carbamazepine (20 mg/kg/day), vigabatrin (200 mgkg/day), and valproate (100 mg/kg/day) at doses not widely different from those used clinically. Pups exposed to AEDs in utero were analyzed postnatally. Animals born to "kindled" pregnant animals that had experienced one generalized convulsive seizure per day during the same gestational period were analyzed in parallel.

RESULTS

Prenatal exposure to vigabatrin and valproate, which act on GABA signaling, induced hippocampal and cortical dysplasias, which were likely to result from a neuronal migration defect and neuronal death. By contrast, offspring of rats exposed to carbamazepine (which at the dose used produced low plasma concentrations) or to generalized convulsive seizures showed no clear-cut evidence of dysplasias.

CONCLUSIONS

We suggest that AEDs that increase the extracellular concentration of GABA might induce severe neuronal migration disorders. Drugs acting through other molecular targets would also perturb cortical maturation. The potential clinical relevance of these results should be a subject of future research.

Neuroimaging of the child with developmental delay

Developmental delay (DD) affects approximately 1% to 3% of all children in the United States. This diagnosis significantly impedes quality of life and full participation in the life of the family, school, and community. In this setting, the clinician's ability to detect, diagnose, and possibly treat the cause for DD in a timely manner depends on a multimodality approach to neuroimaging and a robust understanding of the various imaging algorithms aimed at determining the etiology of disease, structural and/or anatomic defects, functional activity, metabolic profiles, and genetic characteristics. Taken separately and in combination, these features are effectively depicted and analyzed using an array of brain imaging modalities: ultrasound, computed tomography, nuclear medicine, magnetic resonance (MR) spectroscopy, and a growing mix of sophisticated MR imaging (MRI) techniques, including diffusion-weighted imaging, diffusion tensor imaging, perfusion MRI, and functional MRI. Thus, equipped with these advanced imaging capabilities, pediatric neurologists and neuroradiologists are now positioned to diagnose with greater accuracy and speed; this, in turn, results in more effective treatment plans and improved patient outcomes as measured by progress in reaching developmental milestones and in ameliorating secondary conditions such as seizures, poor motor control, incontinence, and impulsivity. The purpose of this article is to present the numerous causes of pediatric DD, describe their respective neuroimaging findings, discuss various neuroimaging approaches for elucidating etiology, and offer specific guidelines for optimizing imaging results in the setting of multimodality imaging capabilities.

Histometric changes and cell death in the thalamus after neonatal neocortical injury in the rat

Freezing injury to the developing cortical plate results in a neocortical malformation resembling four-layered microgyria. Previous work has demonstrated that following freezing injury to the somatosensory cortex, males (but not females) have more small and fewer large cells in the medial geniculate nucleus. In the first experiment, we examined the effects of induced microgyria to the somatosensory cortex on neuronal numbers, neuronal size, and nuclear volume of three sensory nuclei: ventrobasal complex, dorsal lateral geniculate nucleus, and medial geniculate nucleus. We found that there was a decrease in neuronal number and nuclear volume in ventrobasal complex of microgyric rats when compared with shams, whereas there were no differences in these variables in the dorsal lateral geniculate nucleus or medial geniculate nucleus. We also found that there were more small and fewer large neurons in both ventrobasal complex and medial geniculate nucleus. In experiment 2, we attempted to determine the role of cell death in the thalamus on these histometric measures. We found that cell death peaked within 24 h of the freezing injury and was concentrated mostly in ventrobasal complex. In addition, there was evidence of greater cell death in males at this age. Taken together, these results support the notion that males are more severely affected by early injury to the cerebral cortex than females.