Can early postnatal closed head injury induce cortical dysplasia

CNS autoimmune response in the MAM/pilocarpine rat model of epileptogenic cortical malformation

The development of seizures in epilepsy syndromes associated with malformations of cortical development (MCDs) has traditionally been attributed to intrinsic cortical alterations resulting from abnormal network excitability. However, recent analyses at single-cell resolution of human brain samples from MCD patients have indicated the possible involvement of adaptive immunity in the pathogenesis of these disorders. By exploiting the MethylAzoxyMethanol (MAM)/pilocarpine (MP) rat model of drug-resistant epilepsy associated with MCD, we show here that the occurrence of status epilepticus and subsequent spontaneous recurrent seizures in the malformed, but not in the normal brain, are associated with the outbreak of a destructive autoimmune response with encephalitis-like features, involving components of both cell-mediated and humoral immune responses. The MP brain is characterized by blood-brain barrier dysfunction, marked and persisting CD8+ T cell invasion of the brain parenchyma, meningeal B cell accumulation, and complement-dependent cytotoxicity mediated by antineuronal antibodies. Furthermore, the therapeutic treatment of MP rats with the immunomodulatory drug fingolimod promotes both antiepileptogenic and neuroprotective effects. Collectively, these data show that the MP rat could serve as a translational model of epileptogenic cortical malformations associated with a central nervous system autoimmune response. This work indicates that a preexisting brain maldevelopment predisposes to a secondary autoimmune response, which acts as a precipitating factor for epilepsy and suggests immune intervention as a therapeutic option to be further explored in epileptic syndromes associated with MCDs.

Rapamycin Cannot Reduce Seizure Susceptibility in Infantile Rats with Malformations of Cortical Development Lacking mTORC1 Activation

The mechanistic target of the rapamycin (mTOR) pathway is involved in cortical development. However, the efficacy of mTOR inhibitors in malformations of cortical dysplasia (MCD) outside of the tuberous sclerosis complex is unknown. We selected the MCD rat model with prenatal MAM exposure to test the efficacy of mTOR inhibitors in MCDs. We explored the early cortical changes of mTOR pathway protein expression in rats aged P15. We also monitored the early treatment effect of the mTOR inhibitor, rapamycin, on N-methyl-D-aspartate (NMDA)-induced spasms at P15 and their behavior in the juvenile stage. In vivo MR spectroscopy was performed after rapamycin treatment and compared with vehicle controls. There was no difference in mTORC1 pathway protein expression between MAM-exposed MCD rats and controls at P15, and prolonged treatment of rapamycin had no impact on NMDA-induced spasms despite poor weight gain. Prenatal MAM-exposed juvenile rats treated with rapamycin showed increased social approaching and freezing behavior during habituation. MR spectroscopy showed altered neurometabolites, including Gln, Glu+Gln, Tau, and Cr. Despite behavioral changes and in vivo neurometabolic alteration with early prolonged rapamycin treatment, rapamycin had no effect on spasms susceptibility in prenatal MAM-exposed infantile rats with MCD without mTORC1 activation. For MAM-exposed MCD rats without mTORC1 activation, treatment options outside of mTOR pathway inhibitors should be explored.

Neurodevelopmental Findings and Epilepsy in Malformations of Cortical Development

Aim:

The purpose of this study is to classify the malformations of cortical development in children according to the embryological formation, localization, and neurodevelopmental findings. Seizure/epilepsy and electrophysiological findings have also been compared.

Material and Methods:

Seventy-five children (age: 1 month-16.5 years; 56% male) followed with the diagnosis of malformation of cortical development, in Marmara University Pendik Research and Educational Hospital Department of Pediatric Neurology, were included in the study. Their epilepsy characteristics, electroencephalogram (EEG) findings, and prognosis were reported. Neurodevelopmental characteristics were evaluated by the Bayley Scales of Infant and Toddler Development (Bayley-III) for the ages of 0-42 months (n = 30); the Denver Developmental Screening Test-II (DDST-II) for ages 42 months-6 years (n = 11); and the Wechsler Intelligence Scales for Children (WISC-R), used for children 6 years and older (n = 34).

Results:

The patients were classified as 44% premigrational (14.6% microcephaly, 24% tuberous sclerosis, 2.7% focal cortical dysplasia, 1.3% hemimegalencephaly, and 1.3% diffuse cortical dysgenesis); 17.3% migrational (14.6% lissencephaly, 2.7% heterotopia); and 38.6% postmigrational (14.6% schizencephaly, 24% polymicrogyria) developmentally. According to involved area, the classification was 34.7% hemispheric/multilobar, 33.3% diffuse, and 32% focal. Seventy-five percent of the patients had a history of epilepsy, and 92% were resistant to treatment. The seizures started before the age of 12 months in diffuse malformations, and epileptic encephalopathy was more common in microcephaly with a rate of 80% and lissencephaly with a rate of 54.5% in the first EEGs. Ninety-five percent of patients had at least one level of neurodevelopmental delay detected by DDST/Bayley-III; this was more common in patients with accompanying epilepsy (P < .05). As seen more commonly in patients with diffuse pathologies and intractable frequent seizures, mental retardation was detected by WISC-R in 64.5% of patients (P < .05).

Conclusion:

In cases with cortical developmental malformation, epilepsy/EEG features and neurodevelopmental prognosis can be predicted depending on the developmental process and type and extent of involvement. Patients should be followed up closely with EEG.

Neuropathology of Surgically Managed Epilepsy Specimens

Epilepsy is characterized as recurrent seizures, and it is one of the most prevalent disorders of the human nervous system. A large and diverse profile of different syndromes and conditions can cause perturbations in neural networks that are associated with epilepsy. Advances in neuroimaging and electrophysiological monitoring have enhanced our ability to localize the neuropathological lesions that alter the neural networks giving rise to epilepsy, whereas advances in surgical management have resulted in excellent seizure control in many patients following resections. Histopathologic study using a variety of special stains, molecular analysis, and functional studies of these resected tissues has facilitated the neuropathological characterization of these lesions. Here, we review the neuropathology of common structural lesions that cause epilepsy and are amenable to neurosurgical resection, such as hippocampal sclerosis, focal cortical dysplasia, and its associated principal lesions, including long-term epilepsy-associated tumors, as well as other malformations of cortical development and Rasmussen encephalitis.

Inter-ictal EEG patterns in malformations of cortical development and epilepsy

OBJECTIVES

Malformations of cortical Development (MCDs) are associated with refractory epilepsy. We evaluated scalp inter-ictal EEG patterns in various types of MCD, and its association with clinical features and seizure control.

PATIENTS AND METHODS

Retrospective analysis of demographic, clinical, inter-ictal EEG and seizure outcome data of 665 patients with epilepsy and MCD with at least two years follow up was performed.

RESULTS

Average age of study population was 15.95 ± 10.79 years with 291(43.8 %) women. Multiregional spikes were more common in children (22.7 % vs 8.5; p < 0.001), if age of onset of epilepsy was <2 years (21.8 % vs 11.4 %; p = 0.001) and polymicrogyria (12.1 % vs 37.3 %; p < 0.001). Generalized epileptiform discharges were more frequent in patients with developmental delay (24.7 % vs 12.6 %; p < 0.001); and were associated with lissencephaly(14.0 % vs 59.3 %; p < 0.001) and heterotopias(14.5 % vs 34.9 %;p = 0.002). Regional spikes were more common if age of onset of epilepsy is >2 years (26.2 % vs 38.4 %; p = 0.003), and also in FCD (17.1 % vs 42.6 %; p < 0.001). At latest follow-up, 151(22.7 %) patients were seizure free; 401(60.7 %) had refractory epilepsy and the rest had remissions with relapse. No association was found between inter-ictal EEG patterns and seizure control.

CONCLUSION

In patients with MCD, generalized epileptiform discharges were associated with developmental delay, lissencephaly and heterotopias. Regional spikes were frequent in FCD while multiregional spikes in children and polymicrogyria. Inter-ictal EEG patterns did not influence seizure outcome.

Surgical outcomes and prognostic factors of drug-resistant epilepsy secondary to encephalomalacia

OBJECTIVE

To evaluate long-term outcomes and prognostic factors in patients who underwent surgical resection for drug-resistant epilepsy secondary to encephalomalacia.

METHODS

A total of 143 patients with drug-resistant epilepsy who underwent surgical resection with a follow-up of at least 5 years were included. Seizure outcomes were evaluated based on the International League Against Epilepsy classification. Univariate analysis and a multivariate logistic regression model in a backward fashion were used to identify the potential predictors of seizure outcomes.

RESULTS

Three months after surgery, 102 of 143 (71.3%) patients had achieved favorable seizure outcomes. Five years after surgery, 107 of 143 (74.8%) patients had achieved favorable seizure outcomes. Changes in the postoperative seizure status were observed in 22 of 143 (15.4%) patients during follow-up, but the difference in the seizure-free rate between 3 months and 5 years after surgery was not significant. Univariate and multivariate analyses revealed that only a monthly seizure frequency of >30 seizures (odds ratio = 3.42, 95% confidence interval = 1.19-9.76) and bilateral ictal onset rhythms (odds ratio = 4.46, 95% confidence interval = 1.61-12.39) were independent predictors of unfavorable seizure outcomes.

SIGNIFICANCE

Surgical resection is an effective treatment for patients with drug-resistant epilepsy secondary to encephalomalacia. Knowledge of the predictors of seizure outcomes may help during preoperative counseling and selection of optimal candidates for epilepsy surgery among patients with drug-resistant epilepsy secondary to encephalomalacia.

Prevalence of neuropsychiatric symptoms associated with malformations of cortical development

PURPOSE

Malformations of cortical development (MCD) are structural abnormality of the cortex or brain parenchyma with diverse clinical manifestations. Little is known about the association of psychiatric and behavioral problems in MCD. We aimed to determine prevalence and risk factors of neuropsychiatric symptoms in a cohort of adult patients with MCD.

METHODS

We conducted a retrospective medical records review of 86 adult patients followed at the epilepsy clinic of the Montreal Neurological Hospital. Information on diagnosis of medical and psychiatric disorders, family history, intellectual disability, and psychiatric symptoms was obtained from their medical records.

RESULTS

The cohort (n = 86) had a mean age of 39 ± 14.07 (range: 18-74) years. The three most common MCD subtypes were focal cortical dysplasia (47.7%), periventricular nodular heterotopia (29.1%), and polymicrogyria (16.3%). Overall, prevalence of formally diagnosed psychiatric disorders and psychiatric symptoms were respectively 15.1% and 31.4%. The most frequently described symptoms were anxiety-related (59.3%), followed by irritability (40.7%) and agitation (37.0%). Patients with family psychiatric history (OR: 8.168, 95% CI: 1.44-46.48) and intellectual disability (OR: 5.824, 95% CI: 1.30-26.10) were significantly more likely to have psychiatric symptoms than those without. The prevalence of psychiatric symptoms did not defer between major groups of MCD.

CONCLUSIONS

Neuropsychiatric symptoms are commonly associated with MCD, but psychiatric disorders may be underrecognized given that only half of the patients with psychiatric symptoms were referred for a specialized consultation. The presence of intellectual disability and family psychiatric history may help identify and predict risk of psychiatric manifestations in MCD.

Malformations of Cerebral Cortex Development: Molecules and Mechanisms

Malformations of cortical development encompass heterogeneous groups of structural brain anomalies associated with complex neurodevelopmental disorders and diverse genetic and nongenetic etiologies. Recent progress in understanding the genetic basis of brain malformations has been driven by extraordinary advances in DNA sequencing technologies. For example, somatic mosaic mutations that activate mammalian target of rapamycin signaling in cortical progenitor cells during development are now recognized as the cause of hemimegalencephaly and some types of focal cortical dysplasia. In addition, research on brain development has begun to reveal the cellular and molecular bases of cortical gyrification and axon pathway formation, providing better understanding of disorders involving these processes. New neuroimaging techniques with improved resolution have enhanced our ability to characterize subtle malformations, such as those associated with intellectual disability and autism. In this review, we broadly discuss cortical malformations and focus on several for which genetic etiologies have elucidated pathogenesis.

Classification and pathological characteristics of the cortical dysplasias

BACKGROUND

Focal cortical dysplasias (FCD) are a well-recognized cause of medically intractable epilepsy. They are defined as malformations of cortical development and are marked by abnormalities of cortical layering and neuronal differentiation and maturation. A number of classification approaches have been devised over the last four decades, indicating controversies surrounding issues of recognition, definition, and philosophical approach. More recent attempts have attempted to correlate morphologic phenotype with clinical or developmental parameters in order to provide a clinical relevance.

DISCUSSION

This short review provides an overview of the issues which account for the varied historical approaches to FCD classification and descriptions of gross pathologic findings associated with FCD and an overview of two more recently developed and widely used schema, the Palmini et al. (Neurology 62: S2-8, 2004) and the International League Against Epilepsy (ILAE) classifications Blumcke et al. Epilepsia 52: 158-174, 2011. The pathologic features of these two approaches will be reviewed and compared, including discussion of their limitations.

Focal malformations of cortical development: a most relevant etiology of epilepsy in children

Malformations of cortical development (MCD) are now well established as a most prevalent and relevant etiology of medically refractory epilepsies in children and adolescents. Focal cortical dysplasia (FCD) and hemimegalencephalies (HMG) occupy a special status because their focality (or in the case of HMG, their unihemispheric distibution) makes them amenable to surgical treatment to attempt seizure control. Since interictal epileptiform discharges and frequent seizures can lead to abnormal development because of brain plasticity during early childhood, the aim of surgical treatment is not only seizure control but also the redirection of development toward more physiological paths. In this review, we propose an "imaging-semiological organization" including (1) patients whose dysplastic lesion surrounds the fronto-rolandic cortex with increased signal and a transmantle sign, (2) multilobar hemispheric lesions, predominating in the anterior or posterior quadrants with large areas of abnormal gyration, increased cortical thickness, and gray-white blurring, (3) anterior temporal dysplasias usually featuring volume reduction combined with blurring of the underlying white matter in the temporal pole, and (4) a very relevant group of patients with refractory seizures, normal or roughly normal intellect, and normal MRI, later shown to harbor microscopic "nidus" of dysplastic cells. Classification takes into account the cortical disorganization, the presence of aberrant cellular elements, and the association with other lesion types.

Development and dysgenesis of the cerebral cortex: malformations of cortical development

The cerebral cortex develops in several stages from a pseudostratified epithelium at 5 weeks to an essentially complete cortex at 47 weeks. Cortical connectivity starts with thalamocortical connections in the 3rd trimester only and continues until well after birth. Vascularity adapts to proliferation and connectivity. Malformations of cortical development are classified into disorders of specification, proliferation/apoptosis, migration, and organization. However, all processes are intermingled, as for example a dysplastic cell may migrate incompletely and not connect appropriately. However, this classification is convenient for didactic purposes as long as the complex interactions between the different processes are kept in mind.

The clinicopathologic spectrum of focal cortical dysplasias: a consensus classification proposed by an ad hoc Task Force of the ILAE Diagnostic Methods Commission

PURPOSE

  Focal cortical dysplasias (FCD) are localized regions of malformed cerebral cortex and are very frequently associated with epilepsy in both children and adults. A broad spectrum of histopathology has been included in the diagnosis of FCD. An ILAE task force proposes an international consensus classification system to better characterize specific clinicopathological FCD entities.

METHODS

Thirty-two Task Force members have reevaluated available data on electroclinical presentation, imaging, neuropathological examination of surgical specimens as well as postsurgical outcome.

KEY FINDINGS

The ILAE Task Force proposes a three-tiered classification system. FCD Type I refers to isolated lesions, which present either as radial (FCD Type Ia) or tangential (FCD Type Ib) dyslamination of the neocortex, microscopically identified in one or multiple lobes. FCD Type II is an isolated lesion characterized by cortical dyslamination and dysmorphic neurons without (Type IIa) or with balloon cells (Type IIb). Hence, the major change since a prior classification represents the introduction of FCD Type III, which occurs in combination with hippocampal sclerosis (FCD Type IIIa), or with epilepsy-associated tumors (FCD Type IIIb). FCD Type IIIc is found adjacent to vascular malformations, whereas FCD Type IIId can be diagnosed in association with epileptogenic lesions acquired in early life (i.e., traumatic injury, ischemic injury or encephalitis).

SIGNIFICANCE

This three-tiered classification system will be an important basis to evaluate imaging, electroclinical features, and postsurgical seizure control as well as to explore underlying molecular pathomechanisms in FCD.

The clinicopathologic spectrum of focal cortical dysplasias: a consensus classification proposed by an ad hoc Task Force of the ILAE Diagnostic Methods Commission

PURPOSE

  Focal cortical dysplasias (FCD) are localized regions of malformed cerebral cortex and are very frequently associated with epilepsy in both children and adults. A broad spectrum of histopathology has been included in the diagnosis of FCD. An ILAE task force proposes an international consensus classification system to better characterize specific clinicopathological FCD entities.

METHODS

Thirty-two Task Force members have reevaluated available data on electroclinical presentation, imaging, neuropathological examination of surgical specimens as well as postsurgical outcome.

KEY FINDINGS

The ILAE Task Force proposes a three-tiered classification system. FCD Type I refers to isolated lesions, which present either as radial (FCD Type Ia) or tangential (FCD Type Ib) dyslamination of the neocortex, microscopically identified in one or multiple lobes. FCD Type II is an isolated lesion characterized by cortical dyslamination and dysmorphic neurons without (Type IIa) or with balloon cells (Type IIb). Hence, the major change since a prior classification represents the introduction of FCD Type III, which occurs in combination with hippocampal sclerosis (FCD Type IIIa), or with epilepsy-associated tumors (FCD Type IIIb). FCD Type IIIc is found adjacent to vascular malformations, whereas FCD Type IIId can be diagnosed in association with epileptogenic lesions acquired in early life (i.e., traumatic injury, ischemic injury or encephalitis).

SIGNIFICANCE

This three-tiered classification system will be an important basis to evaluate imaging, electroclinical features, and postsurgical seizure control as well as to explore underlying molecular pathomechanisms in FCD.

Malformations of cortical development

BACKGROUND

Malformations of cortical development (MCD) are increasingly recognized as an important cause of epilepsy and developmental delay. MCD encompass a wide spectrum of disorders with various underlying genetic etiologies and clinical manifestations. High resolution imaging has dramatically improved our recognition of MCD.

REVIEW SUMMARY

This review will provide a brief overview of the stages of normal cortical development, including neuronal proliferation, neuroblast migration, and neuronal organization. Disruptions at various stages lead to characteristic MCD. Disorders of neurogenesis give rise to microcephaly (small brain) or macrocephaly (large brain). Disorders of early neuroblast migration give rise to periventricular heterotopia (neurons located along the ventricles), whereas abnormalities later in migration lead to lissencephaly (smooth brain) or subcortical band heterotopia (smooth brain with a band of heterotopic neurons under the cortex). Abnormal neuronal migration arrest give rise to over migration of neurons in cobblestone lissencephaly. Lastly, disorders of neuronal organization cause polymicrogyria (abnormally small gyri and sulci). This review will also discuss the known genetic mutations and potential mechanisms that contribute to these syndromes.

CONCLUSION

Identification of various gene mutations has not only given us greater insight into some of the pathophysiologic basis of MCD, but also an understanding of the processes involved in normal cortical development.

Focal cortical dysplasia with calcification: a case report

CASE REPORT

Focal cortical dysplasia (FCD) with calcification is rare. We presented a 13-year-old epileptic patient with FCD and calcification in the left frontal lobe. At age 24, the FCD lesion and the surrounding epileptogenic cortex and underlying subcortex were removed after chronic subdural electrode recording. Histological examination showed that the calcified lesion was not independent of the FCD lesion but located in the subcortical area of the FCD lesion. A neoplastic nature was ruled out for the lesion.

DISCUSSION

The pathophysiological mechanism involved in the coexistence of FCD and calcification is discussed.

An investigation of the expression of G1-phase cell cycle proteins in focal cortical dysplasia type IIB

Balloon cells (BCs) are the pathologic hallmark of focal cortical dysplasia type IIB, a common cause of pharmacoresistent epilepsy. Expression of markers of cell immaturity and of the proliferation marker minichromosome maintenance protein 2 (mcm2) have been previously shown in BCs, suggesting that these cells might represent a pool of less-differentiated cells licensed for replication. An alternative explanation is that these cells are the remnants of early cortical plate cells that have failed to differentiate or to be eliminated during development and are arrested in the cell cycle, a hypothesis that this study aims to explore. Using immunohistochemical methods and semiquantitative analysis in 19 cases of focal cortical dysplasia (ages 1-81 years), we studied the expression of cell cycle proteins important either in regulating progression through the G1 phase or inducing cell arrest and promoting premature senescence. Only a small fraction of BCs expressed geminin, suggesting that few BCs enter the S phase or complete the cell cycle. Variable expression of nonphosphorylated retinoblastoma protein (Rb), cdk4, and p53 was noted in BCs. Cyclin E, D1, cdk2, phosphorylated Rb (795 and 807/811), and checkpoint 2 expression levels were low in BCs. These findings suggest early rather than late G1 arrest. Cell senescence could be induced by an undefined cerebral insult during development or alternatively represent a physiologic replicative senescence. These findings also suggest that dysregulation of cell cycle pathways may occur in focal cortical dysplasia, which opens further areas for exploration as potential new treatment avenues.

The neuropathology of autism

Autism is a brain disorder characterized by abnormalities in how a person relates and communicates to others. Both post-mortem and neuroimaging studies indicate the presence of increased brain volume and, in some cases, an altered gray/white matter ratio. Contrary to established gross findings there is no recognized microscopic pathology to autism. Early studies provided multiple leads none of which have been validated. Clinicopathological associations have been difficult to sustain when considering possible variables such as use of medications, seizures, mental retardation and agonal/pre-agonal conditions. Research findings suggest widespread cortical abnormalities, lack of a vascular component and an intact blood-brain barrier. Many of the previously mentioned findings can be explained in terms of a mini-columnopathy. The significance of future controlled studies should be judged based on their explanatory powers; that is, how well do they relate to brain growth abnormalities and/or provide useful clinicopathological correlates.

Pathophysiological mechanisms of focal cortical dysplasia: a critical review of human tissue studies and animal models

Cortical dysplasia (CD, also known as malformations of cortical development) are the pathological substrates in a large percentage of patients with pharmacoresistant epilepsy who may be amenable to surgical treatment. Therefore, research on the mechanisms of dysplastic lesion formation and epileptogenicity is of paramount importance for the prevention, detection, and treatment of CD-induced epilepsy. The purpose of this review is to discuss and critically evaluate the current state and results of human tissue experimentation (focusing on reported results of studies done on neocortical dysplastic tissue resected from patients with pharmacoresistant epilepsy), and to discuss some of the concerns related to research that uses surgically resected epileptic human tissue. The use of better animal models of CD as a tool toward the better understanding of the mechanisms of pathogenesis, epileptogenesis, and epileptogenicity of dysplastic lesions will be reviewed from the perspective of their usefulness in a model of translational research that should ultimately result in better diagnostic and therapeutic techniques of CD.

Pediatric posttraumatic seizures: epidemiology, putative mechanisms of epileptogenesis and promising investigational progress

Posttraumatic seizures and epilepsy are common in children experiencing traumatic brain injury and portend worse functional outcome. Unfortunately, the pathogenesis of pediatric posttraumatic seizures and epilepsy remains poorly understood, and no efficacious preventive therapy for post-traumatic epilepsy has been identified. This article reviews the epidemiology of pediatric posttraumatic seizures, discusses prominent putative mechanisms of posttraumatic epileptogenesis and highlights recent promising progress in experimental investigations of posttraumatic seizures and epilepsy.

Imaging surgical epilepsy in children

INTRODUCTION

Epilepsy surgery rests heavily upon magnetic resonance imaging (MRI). Technical developments have brought significantly improved efficacy of MR imaging in detecting and assessing surgical epileptogenic lesions, while more clinical experience has brought better definition of the pathological groups.

DISCUSSION

MRI is fairly efficient in identifying developmental, epilepsy-associated tumors such as ganglioglioma (with its variants gangliocytoma and desmoplastic infantile ganglioglioma), the complex, simple and nonspecific forms of dysembryoplastic neuroepithelial tumor, and the rare pleomorphic xanthoastrocytoma. The efficacy of MR imaging is not as good for the diagnosis of focal cortical dysplasia (FCD), as it does not necessarily correlate with histopathological FCD subtypes and does not show the real extent of the dysplasia which may even be missed in a high percentage of cases. Further developments with better, multichannel coils, higher magnetic fields, specific sequences, and different approaches (such as diffusion tensor imaging) for depicting the structural abnormalities may hopefully improve this efficacy. A general review of the MR features of the diverse pathologies concerned with epilepsy surgery in the pediatric context is provided with illustrative images.

Dystrophic neuritic processes in epileptic cortex

Cortical dysplasia is a frequent finding in cortical resections from children with refractory epilepsy. Diagnostic criteria and a classification scheme for cortical dysplasia has been proposed, though the relationship between specific cortical dysplasia features and their causal relationship with epilepsy is poorly understood. We reviewed 28 surgical resections from children and identified a common and easily recognized feature of cortical dysplasia: maloriented, misshapen and occasionally coarse neurofilament stained process forming a dystrophic neuritic background. The dystrophic neuritic background was associated with other features of cortical dysplasia in all 28 patients with cortical dysplasia, 26 with refractory epilepsy and 2 patients with other neurologic diagnoses. In seven children with refractory epilepsy due to other pathologic diagnosis such as vascular or glial lesions, the dystrophic neuritic background was only found in one patient with a ganglioglioma and other features suggestive of an associated cortical dysplasia. Our data indicate that a dystrophic neuritic background is a common and relatively specific neuropathologic finding in cortical dysplasia.

Embryonic and early postnatal abnormalities contributing to the development of hippocampal malformations in a rodent model of dysplasia

While there are many recent examples of single gene deletions that lead to defects in cortical development, most human cases of cortical disorganization can be attributed to a combination of environmental and genetic factors. Elucidating the cellular or developmental basis of teratogenic exposures in experimental animals is an important approach to understanding how environmental insults at particular developmental junctures can lead to complex brain malformations. Rats with prenatal exposure to methylazoxymethanol (MAM) reproduce many anatomical features seen in epilepsy patients. Previous studies have shown that heterotopic clusters of neocortically derived neurons exhibit hyperexcitable firing activity and may be a source of heightened seizure susceptibility; however, the events that lead to the formation of these abnormal cell clusters is unclear. Here we used a panel of molecular markers and birthdating studies to show that in MAM-exposed rats the abnormal cell clusters (heterotopia) first appear postnatally in the hippocampus (P1-2) and that their appearance is preceded by a distinct sequence of perturbations in neocortical development: 1) disruption of the radial glial scaffolding with premature astroglial differentiation, and 2) thickening of the marginal zone with redistribution of Cajal-Retzius neurons to deeper layers. These initial events are followed by disruption of the cortical plate and appearance of subventricular zone nodules. Finally, we observed the erosion of neocortical subventricular zone nodules into the hippocampus around parturition followed by migration of nodules to hippocampus. We conclude that prenatal MAM exposure disrupts critical developmental processes and prenatal neocortical structures, ultimately resulting in neocortical disorganization and hippocampal malformations.

Neurodevelopmental disorders as a cause of seizures: neuropathologic, genetic, and mechanistic considerations

This review will consider patterns of developmental neuropathologic abnormalities-malformations of cortical development (MCD)--encountered in infants (often with infantile spasms), children, and adults with intractable epilepsy. Treatment of epilepsy associated with some MCD, such as focal cortical dysplasia and tubers of tuberous sclerosis, may include cortical resection performed to remove the "dysplastic" region of cortex. In extreme situations (eg, hemimegalencephaly), hemispherectomy may be carried out on selected patients. Neuropathologic (including immunohistochemical) findings within these lesions will be considered. Other conditions that cause intractable epilepsy and often mental retardation, yet are not necessarily amenable to surgical treatment (eg, lissencephaly, periventricular nodular heterotopia, double cortex syndrome) will be discussed. Over the past 10 years there has been an explosion of information on the genetics of MCD. The genes responsible for many MCD (eg, TSC1, TSC2, LIS-1, DCX, FLN1) have been cloned and permit important mechanistic studies to be carried out with the purpose of understanding how mutations within these genes result in abnormal cortical cytoarchitecture and anomalous neuroglial differentiation. Finally, novel techniques allowing for analysis of patterns of gene expression within single cells, including neurons, is likely to provide answers to the most vexing and important question about these lesions: Why are they epileptogenic?

Cortical neuronal densities and lamination in focal cortical dysplasia

Focal cortical dysplasia (FCD) is considered to represent a malformation due to abnormal cortical development (MCD) and is an important cause of focal epilepsy. The histopathological features include abnormal laminar architecture, the presence of hypertrophic and dysmorphic neurones in FCD type IIA and additional balloon cells in FCD type IIB. The events causing these sporadic lesions are unknown, but abnormal progenitor cell proliferation occurring late in corticogenesis has been proposed. FCD-like lesions have, however, also been described following a cerebral injury early in life. We carried out a stereological assessment on 15 cases of FCD on NeuN- and Nissl-stained sections from patients with a wide age range, and identified a significant reduction in the neuronal density in all cases in the region of dysplasia compared to the adjacent unaffected cortex (mean neuronal densities 19.2x10(3)/mm3 in the region of dysplasia; 42.8x10(3)/mm3 in the adjacent cortex). Relative differences in neuronal density and size in FCD cases between the superficial (layer I and II) and deep cortical laminae (layer V and VI) were similar to that observed in other pathologies including mild MCD, temporal neocortex adjacent to hippocampal sclerosis as well as in a non-epilepsy surgical control group. The lower overall neuronal densities observed in FCD may reflect neuropil expansion, a local failure of neuronal migration, proliferation or secondary neuronal loss. The preservation of relative differences in neuronal densities between cortical layers and laminar patterns of neurofilament staining in FCD would support the view that the temporal sequence of lamination is not affected.

Long-term outcome after epilepsy surgery for focal cortical dysplasia

OBJECT

Reports of outcomes for surgical treatment of cortical dysplasia associated with epilepsy are conflicting due to the inclusion of patients with a wide range of malformations of cortical development. The authors report their experience and the long-term outcome for a subgroup of patients with the histopathological diagnosis of focal cortical dysplasia of Taylor.

METHODS

The records of 22 patients with focal cortical dysplasia of Taylor (15 with the balloon-cell type and seven with the nonballoon-cell type) were reviewed. There were 11 female and 11 male patients whose mean age was 26 +/- 17.6 years (mean +/- standard deviation [SD]) at surgery. The details of their epilepsy evaluation and resection were analyzed. Extent of resection was preoperatively planned using information obtained from long-term intracranial monitoring (15 patients) and/or more definitively determined by histopathologically proven clear margins during resection when feasible (12 patients). The mean duration of follow up was 6.3 +/- 5.1 years (mean +/- SD, range 0.5-15.6 years). Risk factors for epilepsy were trauma (seven patients) or meningoencephalitis (one patient); 14 patients (64%) had no obvious risk factors. The mean age at seizure onset was 9.2 years and the mean duration of their epilepsy was 16.1 +/- 9 years. In two patients there were no adverse findings on magnetic resonance (MR) imaging. In 15 patients (68%), the epileptogenic zone identified on long-term intracranial monitoring extended beyond the abnormality observed on MR images. Focal resection (lesion plus margins) was performed in 14 patients (64%), whereas eight (36%) underwent partial/tailored lobectomy. Two patients underwent multiple subpial transections in addition to partial lesionectomy because their lesions involved the sensorimotor cortex. In these two, functional MR imaging confirmed a normal functional anatomy despite the presence of the cortical dysplasia. Eleven (92%) of 12 patients who underwent resection guided by histopathologically proven clear margins and three (43%) of seven patients who underwent histopathologically proven subtotal resection have remained seizure free. Evidence of clear margins was significantly associated with an improved seizure outcome (p = 0.003). Postoperatively, expected deficits included nondisabling visual field defects, which occurred in three patients (14%), and transient sensorimotor deficits, which appeared in five (23%). Two patients had meningitis, which was successfully treated with antibiotics. Overall, 16 patients (73%) are either seizure free (13 patients), have rare nondisabling partial seizures (one patient), or had one seizure after their medication was changed (two patients). Thirteen patients (59%) have discontinued anticonvulsant medications or are being maintained on monotherapy. Of five patients (23%), two have had rare disabling seizures or significant reduction in their seizure frequency (three patients). One patient's seizures have remained the same.

CONCLUSIONS

Focal cortical dysplasias are a distinct subgroup of malformations of cortical development and have a favorable outcome after resection. The epileptogenic zone often extends beyond the abnormality found on neuroimaging. Resection of the epileptogenic zone guided by histopathologically proven clear margins is associated with an improved seizure outcome.

Malformations of cortical development: molecular pathogenesis and experimental strategies

Malformations of cortical development (MCD) are developmental brain lesions characterized by abnormal formation of the cerebral cortex and a high clinical association with epilepsy in infants, children, and adults. Despite multiple anti-epileptic drugs (AEDs), treatment of epilepsy associated with MCD may require cortical resection performed to remove the cytoarchitecturally abnormal region of cortex. Single genes responsible for distinct MCD including lissencephaly, subcortical band heterotopia, and tuberous sclerosis, have been identified and permit important mechanistic insights into how gene mutations result in abnormal cortical cytoarchitecture. The pathogenesis of MCD such as focal cortical dysplasia, hemimegalencephaly, and polymicrogyria, remains unknown. A variety of new techniques including cDNA array analysis now allow for analysis of gene expression within MCD.

Reelin' in Genes for Cortical Dysplasia

Malformations of cortical development are a broad family of disorders that are characterized by abnormal cytoarchitecture of the cerebral cortex and a high association with epilepsy. In recent years positional cloning strategies have been implemented to identify several distinct gene mutations that are responsible for developmental brain malformations. The defined functional roles of proteins encoded by these genes have provided pivotal insights into the cellular mechanisms of brain development. Identification of these genes provides important clinical information used in genetic counseling for patients and their families.

Subtle Microscopic Abnormalities in Hippocampal Sclerosis Do Not Predict Clinical Features of Temporal Lobe Epilepsy

PURPOSE

Subtle microdysplastic features are found in some patients with hippocampal sclerosis (HS) and refractory temporal lobe epilepsy. The significance of these findings is unknown. We investigated their frequency, relation to the pattern of HS, and clinical associations.

METHODS

One-hundred forty patients with histologically confirmed HS (mean age at operation, 35 years; 85 women) were analyzed. The presence of HS and subtle structural abnormalities (SSAs) in the mesial temporal lobe and in the lateral neocortical tissue was assessed in detail. Antecedents, seizure characteristics, two verbal memory tests, and outcome in HS patients with and without SSAs were determined.

RESULTS

SSAs were found in 60 (43%) of the 140 HS patients, being mesial only in 32 of the 60 cases, and lateral only in nine cases; the remaining 19 cases had both mesial and lateral abnormalities. The frequency of SSA was not related to the pattern of HS or other tested variables. Prolonged febrile convulsions were present in 26 (44%) patients with SSAs, and in 26 (34%) patients (not significant) without SSAs. The outcome after surgery did not differ between patients with SSAs (incidence rate ratio for seizure recurrence, 0.9; 95% confidence interval, 0.5-1.6) compared with patients without SSAs (reference ratio, 1).

CONCLUSIONS

Forty-three percent of HS patients have SSAs in their lobectomy specimens. The presence of SSAs does not predict clinical characteristics, such as presence of prolonged febrile convulsions, postsurgical outcome, or neuropsychological performance, nor does it correlate with the histologic pattern of HS.

Aetiology of epilepsy in surgically treated patients in China

The aim of this retrospective, multicenter clinical study was to evaluate the aetiology of epilepsy in surgically treated patients in China. The detailed clinical records of all intractable partial epilepsy (IPE) were reviewed in five tertiary referral centres from June 1991 to June 2000. 1650 patients (927 males, 723 females) were recruited. 41.4% had aetiological factors, including the histories of major brain trauma (20.9%), febrile seizure (6.5%), meningitis (5.4%), encephalitis (5.0%), prenatal distress (2.1%), birth trauma (0.8%) and family history of seizure (0.7%). The pathological lesions were divided into eight groups according to the nature of the lesion: scar (19.2%), vascular malformations (VM) (17.7%), hippocampal sclerosis (HS) (16.2%), tumours (15.0%), gliosis (12.1%), neuronal migration disorders (NMDs) (7.4%), intracranial infection (4.5%), and other lesions (7.9%). In conclusion, effective management of these aetiological factors and pathological lesions may be essential to deal with IPE. Scar, HS, VM, NMDs are the most likely consequences of antecedent morbid events.

Classification issues in malformations caused by abnormalities of cortical development

Malformations caused by abnormalities of cortical development (MCDs) as a group are now widely recognized as a key cause of medically refractory epilepsies, often leading to a consideration of surgical treatment. A practical classification scheme including histopathologic, imaging, and, if possible, clinical-electrographic features of the various different types of MCDs, will be important to the delineation of surgical strategies and anticipation of medical and surgical prognoses. A proposal of such a scheme with emphasis on the focal cortical dysplasias is given in the hopes that it will reopen the debate on the best way to classify these disorders.

Operative results without invasive monitoring in patients with frontal lobe epileptogenic lesions

PURPOSE

To further explore the still controversial issues regarding whether all or most candidates for epilepsy surgery should be investigated preoperatively with invasive long-term video-EEG monitoring techniques (ILTVE).

METHODS

We studied five patients with intractable seizures since early childhood using the same protocol: clinical evaluation, magnetic resonance imaging (MRI) with fluid-attenuated inversion recovery (FLAIR) sequences, long-term video-EEG (LTVE) monitoring with scalp electroencephalogram (EEG), interictal single photon emission computed tomography (SPECT), positron emission tomography (PET), and neuropsychological testing. The patients' seizures had clinical features suggesting a frontal lobe (FL) origin. MRI scans revealed focal cortical dysplasia (CD) in four patients and a probable gliotic lesion in the fifth. The findings in both PET and SPECT images were congruent with those of the MRI. Scalp LTVE failed to localize the ictal onset, although the data exhibited features suggestive of both CDs and FL seizures. On the basis of these results, surgery was performed with intraoperative corticography, and the cortical area exhibiting the greatest degree of spiking was ablated.

RESULTS

Histopathologic study of four of the resected specimens confirmed the presence of CD, whereas in the fifth, there were features consistent with a remote encephaloclastic lesion. There were no postoperative deficits. Seizures in three of the patients were completely controlled at 2-3.5 years of follow-up; a fourth patient is still having a few seizures, which have required reinstitution of pharmacotherapy, and the fifth has obtained > or =70% control. All patients have had significant improvement in psychosocial measures. For comparison, five patients with generally similar clinical and neuroradiologic features to the previous group underwent preoperative ILTVE monitoring. The surgical outcomes between the two groups have not differed significantly.

CONCLUSIONS

We conclude that patients with FL epilepsies may be able to undergo successful surgery without preoperative ILTVE monitoring, provided there is high concordance between neuroimaging tests (MRI, SPECT, PET) and the seizure phenotypes, even when routine EEGs and scalp LVTE fail to localize ictal onset unambiguously. The surgical outcomes of these patients generally paralleled those of the other subjects who also had FL epilepsy but who were operated on only after standard ILTVE monitoring.

Electrophysiological and morphological characterization of neurons within neocortical ectopias

Focal developmental abnormalities in neocortex, including ectopic collections of neurons in layer I (ectopias), have been associated with behavioral and neurological deficits. In this study, we used infrared differential interference contrast microscopy and whole cell patch-clamp to complete the first characterization of neurons within and surrounding neocortical ectopias. Current-clamp recordings revealed that neurons within ectopias display multiple types of action potential firing patterns, and biocytin labeling indicated that approximately 20% of the cells in neocortical ectopias can be classified as nonpyramidal cells and the rest as atypically oriented pyramidal cells. All cells had spontaneous excitatory (glutamatergic) and inhibitory (GABAergic) postsynaptic currents. Exhibitory postsynaptic currents consisted of both N-methyl-D-aspartate (NMDA) receptor-mediated and AMPA/kainate (A/K) receptor-mediated currents. The NMDA receptor-mediated component had decay time constants of 15.35 +/- 2.2 (SE) ms, while the A/K component had faster decay kinetics of 7.6 +/- 1.7 ms at -20 mV. GABA(A) receptor-mediated synaptic currents in ectopic cells reversed at potentials near the Cl- equilibrium potential and had decay kinetics of 16.65 +/- 1.3 ms at 0 mV. Furthermore we show that cells within ectopias receive direct excitatory and inhibitory input from adjacent normatopic cortex and can display a form of epileptiform activity.