Prenatal events and genetic factors in epileptic patients with neuronal migration disorders

Malformation of cortical development with abnormal cortex: early ultrasound diagnosis between 14 and 24 weeks of gestation

OBJECTIVE

To describe neurosonographic findings diagnostic or highly suggestive of the presence of malformations of cortical development involving the cortex that may be identified before 24 weeks of gestation.

METHODS

This was a retrospective single-center study of fetuses referred for neurosonography, during 2012-2019, with an abnormal cortical or sulcation pattern diagnosed early in the mid trimester. Stored files were analyzed for demographic data, abnormal brain findings, non-central nervous system abnormalities, final diagnosis and postnatal outcome.

RESULTS

The study cohort included 20 fetuses, with a mean gestational age at diagnosis of 18.7 (range, 14.4-23.6) weeks, in 11 of which the diagnosis was made before 20 weeks of gestation. Reasons for referral were: midline anomaly (n = 7), ventriculomegaly (n = 4), infratentorial findings (n = 3), suspected malformation of cortical development (n = 3), 'abnormal brain' (n = 2) and skeletal dysplasia (n = 1). On neurosonography, both the sulcation pattern and the cortical layer were abnormal in four cases, only the sulcation pattern was considered abnormal in seven and only the cortical layer was abnormal in nine. Nineteen fetuses presented with associated central nervous system anomalies and six also had non-central nervous system malformations. One case was recurrent. Eighteen parents opted for termination of pregnancy, including one selective termination in a twin pregnancy, and two fetuses were liveborn.

CONCLUSIONS

Familiarity with fetal brain anatomy and its early sonographic landmarks allowed early diagnosis of malformations involving cortical development. These patients are likely to represent the most severe cases and all had associated malformations. The presence of an abnormal cortical layer and/or abnormal overdeveloped sulci appear to be early signs of malformation of cortical development. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Evaluation of different ulegyria patterns with magnetic resonance imaging

Ulegyria is a parenchymal sequel of hypoxic ischemic encephalopathy causing mushroom-like appearance in gyri. Aim of the present study was to evaluate clinico-radiological findings of patients who applied with different clinical features, predominantly epilepsy, and who were found to have ulegyria formations in MRI examinations. The study included a total of 30 patients (12 female and 18 male) who applied with different types of seizures in February 2011-August 2016 period and had brain MRI examinations using 1.5T MRI scanner. Mushroom-shaped gyri accompanied by gliosis and atrophy in subcortical white matter were considered ulegyria. Locations, MRI features and accompanying pathologies of ulegyria formations were studied. Age of the patients ranged from 4 to 62 (mean 26.0 ± 13.8). Both cerebral lobes were involved in 18 patients. In terms of involved area, symmetrical or asymmetrical involvements were observed in occipital lobes in 26 patients, parietal lobes in 19, frontal lobes in 12 and temporal lobes in 4. The most common involvement type was bilateral occipital and bilateral parieto-occipital lobe involvements with five patients each. Lesions were symmetrical in 11 patients. Six patients had cingulate gyrus atrophy. Nineteen patients had different levels of symmetrical or asymmetrical ventricular dilatation. Cranial asymmetry was observed in six patients with unilateral involvement and in one patient with generalized involvement. Although ulegyria predominantly involves parasagittal watershed areas in MRI examinations of patients applying with epilepsy, clinical manifestations and appearance of lesions could vary depending upon the size of involved area and level of injury.

A distinct clinicopathological variant of focal cortical dysplasia IIId characterized by loss of layer 4 in the occipital lobe in 12 children with remote hypoxic-ischemic injury

OBJECTIVE

In 2011, the International League Against Epilepsy (ILAE) proposed a consensus classification system of focal cortical dysplasia (FCD) to distinguish clinicopathological subtypes, for example, "isolated" FCD type Ia-c and IIa-b, versus "associated" FCD type IIIa-d. The histopathological differentiation of FCD type I and III variants remains, however, a challenging issue in everyday practice. We present a unique histopathological pattern in patients with difficult-to-diagnose FCD, which highlights this dilemma, but also helps to refine the current ILAE classification scheme of FCD.

METHODS

We present a retrospective series of 11 male and one female patient with early onset pharmacoresistant epilepsy of the posterior quadrant (mean age at seizure onset = 4.6 years). All surgical specimens were reviewed. Clinical histories were retrieved and extracted from archival patient files.

RESULTS

Microscopic inspection revealed abnormalities in cortical architecture with complete loss of layer 4 in all surgical samples of the occipital lobe, as confirmed by semiquantitative measurements (p < 0.01). Clinical history reported early transient hypoxic condition in nine patients (75%). Magnetic resonance imaging (MRI) revealed abnormal signals in the occipital lobe in all patients, and signal changes suggestive of subcortical encephalomalacia were found in seven patients. Surgical treatment achieved favorable seizure control (Engel class I and II) in seven patients with an available follow-up period of 6.1 years.

SIGNIFICANCE

Prominent disorganization of cortical layering and lack of any other microscopically visible principle lesion in the surgical specimen would result in this neuropathological pattern hitherto being classified as FCD ILAE type Ib. However, perinatal hypoxia with distinctive MRI changes suggested primarily a hypoxemic lesion and acquired pathomechanism of neuronal cell loss in the occipital lobe of our patient series. We propose, therefore, classifying this distinctive clinicopathological pattern as a separate variant of FCD ILAE type IIId.

Seasonality of birth in patients with temporal lobe epilepsy

OBJECTIVES

We investigated the seasonal pattern in births of patients with temporal lobe epilepsy and mesial temporal sclerosis. We hypothesized that the seasonal pattern in births of these patients is different from that in the general population.

MATERIALS AND METHODS

In this retrospective study, all patients who were evaluated for epilepsy surgery at Jefferson Comprehensive Epilepsy Center, Thomas Jefferson, Philadelphia, USA, between 1986 and 2014 and had a diagnosis of mesial temporal sclerosis (made by definite imaging findings of atrophy and/or sclerosis) were included. The seasonality in births of patients was compared with the seasonal pattern in the live births of the general population from Pennsylvania State.

RESULTS

Two hundred and eighty-two patients (146 females and 136 males) were studied. The seasonality pattern in birth of patients was not statistically different from that in the general population.

CONCLUSIONS

The observed contradictory findings among various studies indicate the need for further studies to elucidate whether season of birth brings the possibility of acquiring various epilepsy syndromes in the future. To investigate any possible association between season of birth and epilepsy, we suggest avoid pooling all patients with epilepsy together.

Malformations of cortical development and neocortical focus

Developmental neocortical malformations resulting from abnormal neurogenesis, disturbances in programmed cell death, or neuronal migration disorders may cause a long-term hyperexcitability. Early generated Cajal-Retzius and subplate neurons play important roles in transient cortical circuits, and structural/functional disorders in early cortical development may induce persistent network disturbances and epileptic disorders. In particular, depolarizing GABAergic responses are important for the regulation of neurodevelopmental events, like neurogenesis or migration, while pathophysiological alterations in chloride homeostasis may cause epileptic activity. Although modern imaging techniques may provide an estimate of the structural lesion, the site and extent of the cortical malformation may not correlate with the epileptogenic zone. The neocortical focus may be surrounded by widespread molecular, structural, and functional disturbances, which are difficult to recognize with imaging technologies. However, modern imaging and electrophysiological techniques enable focused hypotheses of the neocortical epileptogenic zone, thus allowing more specific epilepsy surgery. Focal cortical malformation can be successfully removed with minimal rim, close to or even within eloquent cortex with a promising risk-benefit ratio.

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.

Low-grade focal cortical dysplasia is associated with prenatal and perinatal brain injury

PURPOSE

Prenatal and perinatal adverse events are reported to have a pathogenetic role in focal cortical dysplasia (FCD). However, no data are available regarding the prevalence and significance of this association. A cohort of children with significant prenatal and perinatal brain injury and histologically proven mild malformations of cortical development (mMCD) or FCD was analyzed.

METHODS

We retrospectively evaluated a surgical series of 200 patients with histologically confirmed mMCD/FCD. Combined historical and radiologic inclusion criteria were used to identify patients with prenatal and perinatal risk factors. Electroclinical, imaging, neuropsychological, surgical, histopathologic, and seizure outcome data were reviewed.

RESULTS

Prenatal and perinatal insults including severe prematurity, asphyxia, bleeding, hydrocephalus, and stroke occurred in 12.5% of children with mMCD/FCD (n = 25). Their epilepsy was characterized by early seizure onset, high seizure frequency, and absence of seizure control. Patients with significant prenatal and perinatal risk factors had more abnormal neurologic findings, lower intelligence quotient (IQ) scores, and slower background EEG activity than mMCD/FCD subjects without prenatal or perinatal brain injury. MRI evidence of cortical malformations was identified in 74% of patients. Most patients underwent large multilobar resections or hemispherectomies; 54% were seizure-free 2 years after surgery. Histologically "milder" forms of cortical malformations (mMCD and FCD type I) were observed most commonly in our series.

CONCLUSIONS

Surgically remediable low-grade cortical malformations may occur in children with significant prenatally and perinatally acquired encephalopathies and play an important role in the pathogenesis of their epilepsy. Presurgical detection of dysplastic cortex has important practical consequences for surgical planning.

Different features of histopathological subtypes of pediatric focal cortical dysplasia

OBJECTIVE

Focal cortical dysplasia (FCD) is the most frequent pathological finding in pediatric epilepsy surgery patients. Several histopathological types of FCD are distinguished. The aim of the study was to define distinctive features of FCD subtypes.

METHODS

We retrospectively reviewed clinical, electroencephalographic, magnetic resonance imaging, neuropsychological, and surgical variables, and seizure outcome data in 200 children. Cortical malformations were histopathologically confirmed in all patients, including mild malformation of cortical development type II (mMCD) in 36, FCD type Ia in 55, FCD type Ib in 39, FCD type IIa in 35, and FCD type IIb in 35 subjects.

RESULTS

Perinatal risk factors were more frequent in mMCD/FCD type I than FCD type II. Children with FCD type IIb had more localized ictal electroencephalographic patterns and magnetic resonance imaging changes. Increased cortical thickness, abnormal gyral/sulcal patterns, gray/white matter junction blurring, and gray matter signal abnormality in fluid-attenuated inversion recovery and T2-weighted sequences occurred more often in FCD type II, were infrequent in FCD type I, and rare in mMCD. Lobar hypoplasia/atrophy was common in FCD type I. Hippocampal sclerosis was most frequent in FCD type I. Neuropsychological testing demonstrated no significant differences between the groups. There was a trend toward better surgical outcomes in FCD type II compared with FCD type I patients.

INTERPRETATION

Different histopathological types of mMCD/FCD have distinct clinical and imaging characteristics. The ability to predict the subtype before surgery could influence surgical planning. Invasive electroencephalographic study should be considered when mMCD/FCD type I is expected based on noninvasive tests.

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.

Pathology of cortical development and neuropsychiatric disorders

Epilepsy is a well-documented consequence of about 150 rare genetic syndromes and malformations of the central nervous system. These syndromes are generally associated with fairly gross defects within the central nervous system and they were thought to be responsible for a small minority of cases. However, improved methods of neuropathological investigations and extensive magnetic resonance imaging studies have revealed a range of disturbances in cortical cytoarchitecture in patients with epileptic seizures previously considered as idiopathic (up to 70% of epilepsy). Structural abnormalities have also been demonstrated in the brain in schizophrenia. These consist of disturbed cortical cytoarchitecture (best described in the temporal lobe) and a diffuse loss of grey matter. The absence of the pathological stigma characteristic of degenerative processes indicates that these structural changes are the result of an abnormal pattern of brain development. The relationship between the type and location of developmental abnormality and the subsequent clinical syndrome (e.g. generalized or localized epilepsy) and the effects of aberrant cortical development on the functional integrity of the adult brain require definition.

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.

Prenatal diagnosis of malformations of cortical development by dedicated neurosonography

OBJECTIVE

Malformations of cortical development (MCD) are rarely diagnosed in utero. We describe and compare the ultrasonographic and pathology findings in a cohort of fetuses with MCD.

METHODS

Fetuses with MCD were identified among all fetuses evaluated for suspected brain anomalies at the Fetal Neurology Clinic, and the ultrasonographic findings were compared with the results of the pathology examination.

RESULTS

We suspected the presence of MCD by ultrasonography in 23 fetuses. The mean gestational age at the time of ultrasound diagnosis was 26.2 (range, 18-40) weeks. The ultrasonographic findings leading to the diagnosis of MCD were abnormally overdeveloped gyri and sulci for gestational age (n = 7), delay in sulcation (n = 5), abnormally thin cortex (n = 5) abnormally wide and broad sulci (n = 3), bulging into the lateral ventricle (n = 1), cortical cleft (n = 1), and multiple intraparenchymal echogenic nodules (n = 1). All fetuses had associated central nervous system (CNS) and/or non-CNS anomalies. Pathology examination (performed in 17 fetuses) confirmed MCD in 16.

CONCLUSIONS

Cortical malformations can be diagnosed in utero by ultrasonography based on the presence of specific deviations from the normal pattern of development. The identified cases may represent the more severe forms in the MCD spectrum. The pathology findings do not always conform to the current classification systems of MCD but help in differentiating between possible genetic and acquired etiologies and in some cases provide a definitive syndromic diagnosis.

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.

Prognostic Factors in Neocortical Epilepsy Surgery: Multivariate Analysis

PURPOSE

Defining prognostic factors for neocortical epilepsy surgery is important for the identification of ideal candidates and for predicting the prognosis of individual patients. We use multivariate analysis to identify favorable prognostic factors for neocortical epilepsy surgery.

METHODS

One hundred ninety-three neocortical epilepsy patients, including 91 without focal lesions on MRI, were included. Sixty-one had frontal lobe epilepsy (FLE), 80 had neocortical temporal lobe epilepsy (nTLE), 21 had parietal lobe epilepsy (PLE), and 22 had occipital lobe epilepsy (OLE). The primary outcome variable was patient status >or=2 years after surgery (i.e., seizure free or not). Clinical characteristics and the recent presurgical diagnostic modalities were considered as probable prognostic factors. Univariate and standard multiple logistic regression analyses were used to identify favorable prognostic factors.

RESULTS

The seizure-free rate was 57.5%. By univariate analysis, a focal lesion on MRI, localized ictal onset on surface EEG, epilepsies other than FLE, localized hypometabolism on fluorodeoxyglucose-positron emission tomography (FDG-PET), and pathologies other than cortical dysplasia were significantly associated with a seizure-free outcome (p<0.05). Multivariate analysis revealed that a focal lesion on MRI (p=0.003), correct localization by FDG-PET (p=0.007), and localized ictal onset on EEG (p=0.01) were independent predictors of a good outcome.

CONCLUSIONS

The presence of a focal lesion on MRI, correct localized hypometabolism on FDG-PET, or localized ictal rhythms on EEG were identified as predictors of a seizure-free outcome. Our results suggest that these findings allow the selection of better candidates for neocortical epilepsy surgery.

Surgical outcome and predictive factors in adult patients with intractable epilepsy and focal cortical dysplasia

OBJECTIVES

To determine the surgical outcome and prognostic factors in adult patients with intractable epilepsy and focal cortical dysplasia (FCD).

MATERIALS AND METHODS

We retrospectively studied the operative outcome in 21 consecutive adult patients with FCD who underwent surgical treatment for intractable partial epilepsy.

RESULTS

The mean age at surgery was 32.7 years (range, 18-58 years). The median post-operative follow-up was 2.5 years. The FCD was extratemporal in 11 patients, involved the temporal lobe in 10 patients, and was multilobar in eight patients. Eleven patients (52%) were rendered seizure-free, four patients (19%) had >95% reduction in seizures, and two patients (10%) had an 80-94% reduction in seizures. A seizure-free outcome was associated with shorter duration of epilepsy (P = 0.02).

CONCLUSION

Adult patients with FCD may be candidates for surgical treatment of intractable partial epilepsy. Most individuals have neocortical, extrahippocampal seizures and approximately 50% of patients are rendered seizure-free.

Similarities and differences between the Wnt and reelin pathways in the forming brain

One of the key features in development is the reutilization of successful signaling pathways. Here, we emphasize the involvement of the Wnt pathway, one of the five kinds of signal transduction pathway predominating early embryonic development of all animals, in regulating the formation of brain structure. We discuss the interrelationships between the Wnt and reelin pathways in the regulation of cortical layering. We summarize data emphasizing key molecules, which, when mutated, result in abnormal brain development. This integrated view, which is based on conservation of pathways, reveals the relative position of participants in the pathway, points to control mechanisms, and allows raising testable working hypotheses. Nevertheless, although signaling pathways are highly conserved from flies to humans, the overall morphology is not. We propose that future studies directed at understanding of diversification will provide fruitful insights on mammalian brain formation.

Pilocarpine-induced seizure susceptibility in rats following prenatal methylazoxymethanol treatment

Several rodent models of cortical malformation are available for the study of cellular mechanisms associated with early-onset epilepsy, but few are associated with spontaneous seizures. We examined the effect of pilocarpine on the spontaneous seizure development and excitability of the CA1 pyramidal cells of rats after prenatal treatment with methylazoxymethanol (MAM). Pilocarpine induced status epilepticus (SE) onset latency was greater for normal rats than for MAM-treated rats. After several days of normal behavior following pilocarpine treatment, the duration of spontaneous seizures were greater in MAM-pilocarpine rats than in normal-pilocarpine rats. Compared with the normal rats, electrical stimulation of afferent fibers resulted in more robust population responses in the CA1 region in all groups. At interstimulus intervals of 30 and 70 ms, the MAM-pilocarpine rats displayed a decrease in paired pulse inhibition versus the conventional MAM rats. A loss of somatostatin- and parvalbumin-immunoreactive neurons was apparent in the normal-pilocarpine rats, MAM-pilocarpine rats, and conventional MAM rats. These results indicate that pilocarpine induces spontaneous seizures and hyperexcitability in MAM-pilocarpine rats.

Seasonality of birth in epilepsy: a Southern Hemisphere study

A consistent pattern has emerged from research in Northern Hemisphere populations indicating differences in the seasonality of birth between patients with epilepsy and the general population. This is the first study using similar methodology to look at Southern Hemisphere data. The population studied is composed of patients discharged from Australian hospitals with a diagnosis of epilepsy, in the period 1998-1999. The results show a significantly higher incidence of epilepsy in the patients born during the Australian winter and summer and a deficit of patients born during the spring and fall. This pattern is consistent with the Northern Hemisphere findings. This study provides further evidence of the existence of a seasonal aetiological agent(s) for epilepsy acting in the perinatal period.

Electro-clinical and imaging characteristics of focal cortical dysplasia: Correlation with pathological subtypes

INTRODUCTION

Focal cortical dysplasia (CD) is a common cause of pharmaco-resistant epilepsy. CD is due to abnormalities in neuronal migration, proliferation, and/or differentiation that result in four distinct pathological subtypes: 1A, 1B, 2A, and 2B. In order to provide clinical correlation to these pathological subtypes, we reviewed the electro-clinical and imaging characteristics and surgical outcomes of the four pathological subtypes of CD.

METHODS

We retrospectively reviewed patient data from epilepsy surgeries at the Cleveland Clinic Foundation between 1990 and 2002. Only those patients with the definite pathological diagnosis of isolated cortical dysplasia were included in the study (n = 145).

RESULTS

Pathological subtypes 2A and 2B were predominantly frontal in location, and had a more severe epilepsy syndrome with lower intelligence quotient scores than subtypes 1A and 1B. Patients with subtype 1A FCD had less severe, later onset epilepsy that was predominantly located in the temporal lobe. Risk factors for epilepsy included febrile seizures for type 1A, head trauma for types 1A and 1B, and perinatal adverse events for type 2B. Type 2B demonstrated significantly more FLAIR signal abnormalities than the other groups. Sixty-three percent of patients overall had an Engel I outcome at 6 months follow-up. The best outcomes were in the 2B subtype, and in those who did not require an invasive EEG evaluation.

CONCLUSIONS

Clinically important differences exist between the pathological subtypes of CD, which may assist in their management, and provide further insight into their underlying pathophysiology.

Occipital lobe epilepsy secondary to ulegyria

OBJECTIVE

To analyse clinical and therapeutic aspects of epilepsy secondary to ulegyria in adults.

PATIENTS

Out of 1,020 consecutive patients studied at a tertiary care epilepsy centre, eight cases of ulegyria were identified. All patients had comprehensive clinical evaluation, neuropsychological testing, interictal EEG, and brain magnetic resonance imaging (MRI). In addition, five patients had video-EEG monitoring. Ulegyria was confirmed by histological analysis in two patients who had successful epilepsy surgery.

RESULTS

All patients had a history of perinatal asphyxia. In four of them there was psychomotor developmental delay. Mean age at onset of seizures was 5.8 years (range first week to 21 years). Brain MRI demonstrated predominant involvement of occipito-parietal cortical and subcortical areas. This posterior distribution of lesions was also supported by the presence of auras with occipital and parietal semiology in six patients, and signs of visuospatial dysfunction in five. Four patients had medically refractory epilepsy and two of them had significant improvement with surgical treatment.

CONCLUSIONS

In this group of adult epileptic patients with ulegyria brain MRI, ictal semiology, and neurological examination are consistent with occipital lobe epilepsy. Most patients have severe epilepsy, but in some of them epilepsy can be controlled with antiepileptic drugs, while in others surgical treatment can be effective. Brain MRI criteria of ulegyria are well established, and in two cases it was possible to confirm their diagnosis with histological analysis.

Polymicrogyria in glycogenosis type III: an incidental finding?

The purpose of the present report is to document a 20-year-old woman with glycogenosis type III who presented a malformation of cortical development, in this case a polymicrogyria over bilateral perisylvian regions. Association of a malformation of cortical development in this type of glycogenosis has not been previously reported. The existence of previous cases of glycogenosis associated with malformations of cortical development led us to believe that glycogen storage during pregnancy may act as a harmful prenatal event. On the other hand, the presence of a lesion associated with severe neurologic deficits in one patient with a milder form of glycogenosis is in disagreement with the idea that there is a strong correlation between the severity of the central nervous system lesion and that of the disease.

Cortical dysplasia and epilepsy: animal models

Cortical dysplasia syndromes--those conditions of abnormal brain structure/organization that arise during aberrant brain development--frequently involve epileptic seizures. Neuropathological and neuroradiological analyses have provided descriptions and categorizations based on gross anatomical and cellular histological features (e.g., lissencephaly, heterotopia, giant cells), as well as on the developmental mechanisms likely to be involved in the abnormality (e.g., cell proliferation, migration). Recently, the genes responsible for several cortical dysplastic conditions have been identified and the underlying molecular processes investigated. However, it is still unclear how the various structural abnormalities associated with cortical dysplasia are related to (i.e., "cause") chronic seizures. To elucidate these relationships, a number of animal models of cortical dysplasia have been developed in rats and mice. Some models are based on laboratory manipulations that injure the brain (e.g., freeze, undercut, irradiation, teratogen exposure) of immature animals; others are based on spontaneous genetic mutations or on gene manipulations (knockouts/transgenics) that give rise to abnormal cortical structures. Such models of cortical dysplasia provide a means by which investigators can not only study the developmental mechanisms that give rise to these brain lesions, but also examine the cause-effect relationships between structural abnormalities and epileptogenesis.

Experimentally-induced microencephaly: effects on cortical neurons

Genetic and epigenetic factors may alter the normal development of cerebral cortex, producing laminar and cellular abnormalities and heterotopiae, major causes of juvenile, drug-resistant epilepsy. Experimentally-induced migration disorders provide interesting insights in the mechanisms of the determination of neuronal phenotype and connectivity, of congenital cortical dysgenesis and the pathophysiology of associated neurological disorders, such as epilepsy. We investigated the effects of E14 administration of methylazoxymethanol acetate (MAM), which induces microencephaly by ablating dividing cells. Brains from newborn and adult rats were reacted for NADPH-d and CO histochemistry. Moreover, callosally-projecting neurons were retrogradely labeled with DiI at P9 or with BDA in adults. MAM-treated rats displayed a remarkable reduction in cortical thickness, mainly due to reduction in layer IV and in supragranular layers. Heterotopic nodules appeared in the supragranular layers and in the hippocampus. CO-positive barrels in somatosensory cortex were almost absent. The distribution of NADPH-d-positive neurons was regular, but they were rare in heterotopic nodules. Callosally-projecting neurons displayed abnormal orientation of the apical dendrite and increase in the basal dendritic length. Alterations in the dendritic arborization of pyramidal neurons may be one of the substrates for the increased sensitivity to drugs which induce epileptic seizures in these animals.

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.

Brain development and generation of brain pathologies

The timing of brain development is genetically programmed and can be profoundly altered by a number of abnormal genes that control proliferation, differentiation, migration, synapse formation, and elimination of cells and synapses. With advances in genetic techniques both the gene and gene product responsible for brain malformation are being identified which will permit a better understanding of the pathophysiology of brain malformations. In addition to genetic abnormalities, brain development can be influenced by a variety of acquired disorders. The type of brain abnormality is highly dependent on the stage of brain development during which the insult occurs. While our understanding of experience- or activity-dependent processes on brain development is limited, it is now clear that this activity can significantly alter the timing of a number of maturational events including receptor maturation and neurogenesis. The future challenge will be both to understand the biological basis of these processes and to use this information to enhance brain development.

Cognitive outcome of children with epilepsy and malformations of cortical development

OBJECTIVE

To assess intellectual functioning (IQ) in 54 children and adolescents with intractable epilepsy who later underwent cortical resection due to unilateral malformations of cortical development acquired in utero.

METHODS

Lesion type was classified into circumscribed mass lesions and diffuse cortical dysplasia based on histopathologic analysis of surgical tissue. Cortical dysplastic lesions were further graded as mild, moderate, or severe according to specific microscopic features. Laterality of lesion was determined through neurologic examination and electrophysiologic and neuroradiologic procedures. Classification of lesion type was corroborated by its significant relationship with other disease-related variables known to be related to clinical severity (age at seizure onset, age at resection, and extent of lesion).

RESULTS

Analyses of covariance revealed that circumscribed lesions had a less deleterious effect on nonverbal IQ than did diffuse cortical dysplasia, after controlling for age at seizure onset and extent of lesion. This effect was also found on verbal IQ measures, but only in subjects with right-sided lesions. Subjects with left-sided lesions performed significantly more poorly on verbal IQ measures than those with right-sided lesions. Additionally, younger age at onset and greater extent of lesion were associated with poorer cognitive outcome.

CONCLUSIONS

Cortical dysplasia and early left hemisphere lesions have a significantly worse impact on cognitive functioning than circumscribed lesions or right hemisphere developmental lesions in children with epilepsy.

Characterization of heterotopic cell clusters in the hippocampus of rats exposed to methylazoxymethanol in utero

Cortical disorganization represents one of the major clinical findings in many children with medically intractable epilepsy. To study the relationship between seizure propensity and abnormal cortical structure, we have begun to characterize an animal model exhibiting aberrant neuronal clusters (heterotopia) and disruption of cortical lamination. In this model, exposing rats in utero to the DNA methylating agent methylazoxymethanol acetate (MAM; embryonic day 15) disrupts the sequence of normal brain development. In MAM-exposed rats, cells in hippocampal heterotopia exhibit neuronal morphology and do not stain with immunohistochemical markers for glia. In hippocampal slices from MAM-exposed animals, extracellular field recordings within heterotopia suggest that these dysplastic cell clusters make synaptic connections locally (i.e. within the CA1 hippocampal subregion) and also make aberrant synaptic contact with neocortical cells. Slice perfusion with bicuculline or 4-aminopyridine leads to epileptiform activity in dysplastic cell clusters that can occur independent of input from CA3. Taken together, our findings suggest that neurons within regions of abnormal hippocampal organization are capable of independent epileptiform activity generation, and can project abnormal discharge to a broad area of neocortex, as well as hippocampus.

Disorders of cortical development

It is only a decade since the realization (facilitated by magnetic resonance imaging) in early 1990s that disorders of cortical development occupy an important place in the aetiologic categorization of epilepsy. Since then research has demonstrated the intrinsic epileptogenicity of disorders of cortical development, their genetic bases and their functional properties. Some of the key points of this most exciting medical and scientific enterprise are reviewed here, with an emphasis in the advances seen within the past 2 years.

Can early postnatal closed head injury induce cortical dysplasia

PURPOSE

Increased availability of surgically resected epileptogenic tissues reveals often unsuspected cortical dysplasia (CD). There is some controversy about the ontogenic stages in which these occur. Although most take place during neuroblast proliferation and migration, there is some evidence for some CD occurring during postmigrational intrinsic cortical organization. It has been shown that various kinds of focal cortical manipulations in rats, if performed within 3-4 postnatal days, lead to the genesis of various cortical malformations including a four-layered microgyrus or an unlayered CD. It is not known whether such events also might occur in the human brain.

METHODS

Two children sustained minor head trauma within 4 postnatal days and later developed intractable epilepsy, which was relieved by surgery. Neuropathologic analysis of the resected tissues revealed an unsuspected microdysplastic cortex immediately adjacent to a focal, modest meningeal fibrosis, presumably secondary to the old closed head trauma.

RESULTS

The main histologic features were a disorganized, unlayered cortex; abnormal clusters of neurons, often with complex, randomly oriented proximal dendritic patterns with absent apical orientation; the presence of a number of heterotopic small and large neurons in the white matter; absence of inflammatory infiltrates, of hemosiderine, of reactive gliosis, or of an excessive number of blood vessels. The morphologic features in these surgical specimens suggest that these focal malformations occur because of a regional disorder of postmigrational intrinsic cortical remodeling.

CONCLUSIONS

The clinical histories and the pathologic findings lend some support to the hypothesis that minor morbid events occuring in the immediate postnatal period may lead to microdysplasia in the human similar to those induced in rat pups. The animal model could be helpful to clarify the genesis of some cases of CD and of the epileptogenicity often manifesting later in life.

Cortical malformations and epilepsy: new insights from animal models

In the last decade, the recognition of the high frequency of cortical malformations among patients with epilepsy especially children, has led to a renewed interest in the study of the pathophysiology of cortical development. This field has also been spurred by the recent development of several experimental genetic and non-genetic, primarily rodent, models of cortical malformations. Epileptiform activity in these animals can appear as spontaneous seizure activity in vivo, in vitro hyperexcitability, or reduced seizure susceptibility in vitro and in vivo. In the neonatal freeze lesion model, that mimics human microgyria, hyperexcitability is caused by a reorganization of the network in the borders of the malformation. In the prenatal methylazoxymethanol model, that causes a diffuse cortical malformation, hyperexcitability is associated with alteration of firing properties of discrete neuronal subpopulations together with the formation of bridges between normally unconnected structures. In agreement with clinical evidence, these experimental data suggest that cortical malformations can both form epileptogenic foci and alter brain development in a manner that causes a diffuse hyperexcitability of the cortical network.

Taylor's cortical dysplasia: a confocal and ultrastructural immunohistochemical study

In the present report we describe the neuropathological characteristics of tissue surgically resected from three patients affected by intractable epilepsy secondary to cortical dysplasia. Common features, suggestive of a focal cortical dysplasia of Taylor, were observed in all specimens. Immunocytochemical procedures were performed using neuronal and glial markers and the sections were observed at light traditional and confocal microscopes. This part of the investigation pointed out: 1. cortical laminar disruption; 2. very large neurons displaying a pyramidal or round shape; 3. ballooned cells; 4. decrease of calcium binding proteins immunoreactivity; 5. abnormal nets of parvalbumin- and glutamic acid decarboxylase-positive puncta around giant neurons but not around ballooned cells. Ultrastructural investigation on the same material provided evidence of a high concentration of neurofilaments in giant neurons and of glial intermediate filaments in ballooned cells. In addition, immunolabeled GABAergic terminals clustered around giant neurons were not found to establish synapses on their cell bodies. The present data, derived from a limited sample of patients but showing very consistent features, suggest that in Taylor's type of cortical dysplasia a disturbance of migratory events could be paralleled by a disruption of cell differentiation and maturation and by an impairment of synaptogenesis. This latter mechanism seemed to affect especially the inhibitory elements, and could account for the hyperexcitability of this tissue and thus for the high epileptogenicity of Taylor's dysplasia.

Metabolic changes in neuronal migration disorders: evaluation by combined MRI and proton MR spectroscopy

PURPOSE

To assess the role of 1H-magnetic resonance spectroscopy (MRS) in detecting biochemical abnormalities in neuronal migration disorders (NMDs).

METHODS

We performed 1H-MRS studies on 17 brain NMD areas [five polymicrogyria, eight subcortical heterotopia, and four cortical dysplasia on magnetic resonance imaging (MRI)]. The study group consisted of 15 patients, all but one affected by partial epileptic seizures. Spectra were acquired from volumes of interest localized on NMDs and contralateral sides and compared with those obtained on gray and white matter of 18 neurologic controls.

RESULTS

NMD lesions were characterized by lower N-acetylaspartate to creatine (NAA/Cr) and choline to Cr (Cho/Cr) ratios than those of the white (p = 0.002 and p = 0.004) and gray matter (p = 0.03 and p = 0.06) of neurologic controls. In addition, the normal-appearing contralateral sides to the NMD lesions showed a significant decrease of Cho/Cr ratio when compared with those of white (p = 0.003) and gray matter (p = 0.05) of neurologic controls. No relation was found between NAA/Cr decrease, EEG abnormalities, and NMD sides, or between NAA/Cr ratios, duration of epilepsy, and frequency of seizures. Lactate signal was detected in the spectra of four patients who had an epileptic seizure a short time before MR examination.

CONCLUSIONS

NAA/Cr decrease may be related more to structural and functional alteration of the NMD sides than to epileptic activity in these lesions. Low Cho/Cr may be related to a more extensive diffuse hypomyelination than suggested by the MRI findings. An activation of anerobic glycolysis during and after seizures could account for the presence of lactate. These data confirm that H-MRS is an advanced technique that may provide useful biochemical information in vivo on neurobiologic processes underlying NMDs.

Decreased seizure threshold and more rapid rate of kindling in rats with cortical malformation induced by prenatal treatment with methylazoxymethanol

In humans, cortical malformations are highly epileptogenic. In rats, prenatal treatment with methylazoxymethanol (MAM) cause a diffuse cortical malformation that is yet not associated with seizures. We performed rapid hippocampal kindling in MAM and control rats. We show that MAM rats present (i) a lower initial afterdischarge threshold; (ii) a more rapid progression to generalized seizures. We conclude that MAM rats may serve as models for human epileptogenic cortical malformations.

In utero irradiation of rats as a model of human cerebrocortical dysgenesis: a review

Certain developmental abnormalities of the cerebral cortex are closely associated with epilepsy in humans. Exposure of fetal rats to external gamma-irradiation produces diffuse cortical dysplasia and neuronal heterotopia. These abnormalities are the result of radiation-induced cell death coupled with continued cortical development in an altered cellular environment. In vivo electroencephalography studies in these animals have revealed an increased propensity for electrographic seizures in the presence of the sedating agents, acepromazine and xylazine. In vitro neocortical slices containing dysplastic cortex demonstrate enhanced excitability, as compared to control neocortex, when inhibition that is mediated by the A-type gamma-amino butyric acid receptor is blocked with bicuculline methiodide. In utero irradiation of rats produces structural changes that mimic some aspects of cerebral dysgenesis in humans and results in physiologic changes that increase the animals' propensity for seizures. Similarities and differences between the animal model and the human syndromes are discussed.

Immunocytochemical investigation on dysplastic human tissue from epileptic patients

In this report we describe three patients with developmental cortical abnormalities (generally referred as cortical dysplasia), revealed by MRI and operated on for intractable epilepsy. Tissue, removed for strictly therapeutic reasons, was defined as the epileptogenic area by electroclinical data and stereo EEG (SEEG) recordings. Tissue samples were processed initially for histology, and selected sections were further processed for immunocytochemical investigation in order to determine whether the region of cortical dysplasia was co-extensive with the epileptogenic area. In two patients with nodular heterotopia, disorganized aggregates of neurons (as revealed by neuronal cytoskeletal markers) were found within the nodules. Both pyramidal and local circuit neurons were present in the nodules, but no reactive gliosis was present. When nodules reached the cortex, the cortical layers were disrupted. In the patient with localized cortical dysplasia, a complete disorganization of the cortical lamination was found, and numerous neurons were also present in the white matter. Disoriented pyramidal neurons weakly labelled with cytoskeletal neuronal markers were also present but no cytomegalic cells were found. One of the patients with nodular heterotopia underwent only partial resection of both the 'epileptogenic area' and of the lesion; this patient still presents with seizures. The other patient with nodular heterotopia is seizure-free after a complete lesionectomy and excision of the epileptogenic area. The third patient, with focal cortical dysplasia, had two surgeries; she became seizure-free only after the excision of the epileptogenic area detected by SEEG recording. The present data suggest that the dysplastic areas identified by MRI should not be considered as the only place of origin of the ictal discharges. From the neuropathological point of view, the focal cortical dysplasia can be considered as a pure form of migrational disorder. However, the presence of large aggregates of neurons interspersed within the white matter, in the subcortical nodular heterotopia, suggests that a defect of neuronal migration could be associated with an exuberant production of neuroblasts and/or a disruption of mechanisms for naturally occurring cell death.

A clinically recognizable neuronal migration disorder: congenital bilateral perisylvian syndrome. Case report with long-term clinical and EEG follow-up

Congenital bilateral perisylvian syndrome (CBPS) is a recently described, neuronal migration disorder, characterized by pseudobulbar palsy, epilepsy and mental retardation and bilateral perisylvian dysplasia. A 15-year-old boy was diagnosed with CBPS according to the typical clinical, and magnetic resonance imaging (MRI) features. The patient was suffering from atypical absence seizures, repeating daily in spite of antiepileptic drug therapy, since age 7 years. He had also experienced rare generalized tonic-clonic seizures and complex partial seizures. Neurological examination showed severe restriction of tongue movements, severe dysarthria, dysphagia, facial diplegia, mild pyramidal signs and moderate mental retardation. A computed tomographic (CT) scan demonstrated bilateral perisylvian enlargement. The diagnosis was corrected with MRI after six years. Frequent irregular generalized spike and wave abnormalities and focal sharp and slow waves over the posterior regions of both hemispheres were shown by electroencephalograms (EEG). The patient was treated with Na-Valproate, carbamazepine and lamotrigine but did now show any significant change in seizure frequency in the eight-year follow-up period. Intractable seizures, mental retardation and particularly congenital pseudobulbar palsy suggest this congenital entity. Those patients who exhibit these typically clinical features, must have MRI.

Function and organization in dysgenic cortex. Case report

Cerebral dysgenesis is a subject of interest because of its relationship to cerebral development and dysfunction and to epilepsy. The authors present a detailed study of a 16-year-old boy who underwent surgery for a severe seizure disorder. This patient had dysgenesis of the right hemisphere, which was composed of a giant central frontoparietal nodular gray matter heterotopia with overlying large islands of cortical dysplasia around a displaced central fissure. Exceptional insight into the function, biochemistry, electrophysiology, and histological structure of this lesion was obtained from neurological studies that revealed complementary information: magnetic resonance (MR) imaging, [18]fluoro-2-deoxy-D-glucose positron emission tomography (PET), functional PET scanning, proton MR spectroscopic (1H-MRS) imaging, intraoperative cortical mapping and electrocorticography, in vitro electrophysiology, and immunocytochemistry. These studies demonstrated compensatory cortical reorganization and showed that large areas of heterotopia and cortical dysplasia in the central area may retain normal motor and sensory function despite strikingly altered cytoarchitectonic organization and neuronal metabolism. Such lesions necessitate appropriate functional imaging studies prior to surgery and cortical mapping to avoid creating neurological deficits. Integrated studies, such as PET, 1H-MRS imaging, cortical mapping, immunocytochemistry, and electrophysiology may provide information on the function of developmental disorders of cerebral organization.

Season of birth: aetiological implications for epilepsy

In most cases of epilepsy it is not possible to reach an aetiological diagnosis. Recent research points to a pre-perinatal disruption of the neurodevelopment as being the cause of at least some of these epilepsies of unknown aetiology. The object of this study was to corroborate this hypothesis from an epidemiological perspective and identify the most likely candidates for causes of this damage. The approach used was an analysis of the seasonal pattern of births in a large sample of epileptic patients discharged from NHS hospitals in England and Wales. The results illustrated that the seasonality of the births in the epileptic sample was significantly different from that of the general population, with an excess of patients born in December and January and a deficit of those born in September. This "seasonality' was present only in the patients born before the late 1950s. These results are suggestive of the existence of an aetiological factor for epilepsy with a seasonal presence in the environment and which is epileptogenic when acting in the pre-perinatal period. Prenatal infections, obstetric complications and nutrititional deficiencies are amongst the hypotheses developed on the nature of this agent(s).

Characterization of neuronal migration disorders in neocortical structures: I. Expression of epileptiform activity in an animal model

Hypoxia, ischemia and other forms of brain injury during the pre- and perinatal period may cause neuronal migration disorders which results in irreversible structural modifications. In human neocortex, these malformations have been associated with severe mental retardation, motor dysfunction and the manifestation of therapy-resistant epilepsy. We were interested in analyzing the expression of epileptiform activity in an animal model of neocortical migration disorders. Newborn rats received a focal freeze lesion and were investigated anatomically and in vitro electrophysiologically after survival times of up to five months. Anatomic abnormalities included loss of normal cortical lamination (focal microgyrus) and presence of ectopic cell clusters in layer I and in the white matter (heterotopia). The functional in vitro analyses with eight extracellular recording electrodes revealed a prominent hyperexcitability of the disorganized neocortical network. Electrical stimulation of the afferents elicited epileptiform responses that propagated over > 4 mm in the horizontal direction. In untreated and sham-operated animals, this spread of evoked activity was restricted to 0.5-1 mm. Epileptiform responses were not significantly affected by APV but blocked by NBQX, indicating that AMPA receptors play a prominent role in the generation and propagation of this pathophysiological activity. Our data suggest that the experimentally induced migration disturbances cause long-term structural and/or functional modifications in the neocortical network which may form the basis for the expression of epileptiform activity.

The epidemiology of epilepsy. Past, present, and future

Much has been learned from epidemiologic studies about the frequency, causes, natural history, and prognosis of epilepsy and other seizure disorders. This knowledge has resulted in significant changes in the clinical management of individuals who have seizures and epilepsy. Recent changes in the known causal factors and diagnostic technologic advances, among other factors, will affect the epidemiology and prognosis of epilepsy. Continued epidemiologic monitoring of this common neurologic condition is necessary to ensure an accurate understanding of the current forms of the disorder.

Discordant occurrence of cerebral unilateral heterotopia and epilepsy in monozygotic twins

Cerebral developmental malformations are increasingly recognized as a cause of epilepsy. Magnetic resonance imaging (MRI) has advanced our understanding of these disorders and their relation to epilepsy. We report the occurrence of discordant unilateral heterotopia and epilepsy in monozygotic twins. The affected individual developed intractable focal seizures at age 16 years. Mild cognitive difficulties had been present in early life. Evaluation showed right hemisphere EEG epileptogenic abnormalities, and the MRI scan showed massive right hemisphere heterotopia. EEG and MRI examinations in the patient's twin brother were normal. These findings suggest that the development of some developmental brain malformations and epilepsy is strongly influenced by nongenetic factors such as an environmental insult.