Clinical spectrum of cortical dysplasia in childhood: diagnosis and treatment issues

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.

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.

Synthetic aperture magnetometry and excess kurtosis mapping of Magnetoencephalography (MEG) is predictive of epilepsy surgical outcome in a large pediatric cohort

OBJECTIVE

Resective surgery is the most effective treatment option for patients with refractory epilepsy; however identification of patients who will benefit from epilepsy surgery remains challenging. Synthetic aperture magnetometry and excess kurtosis mapping (SAM(g2)) of magnetoencephalography (MEG) is a non-invasive tool that warrants further examination in the pediatric epilepsy population. Here, we examined the utility of MEG with SAM(g2) to determine if MEG epileptiform foci correlates with surgical outcome and to develop a predictive model incorporating MEG information to best assess likelihood of seizure improvement/freedom from resective surgery.

METHODS

564 subjects who had MEG at the Children's Hospital of Philadelphia between 2010-2015 were screened. Clinical epilepsy history and prior electrographic records were extracted and reviewed and correlated with MEG findings. MEG assessments were made by both a neurologist and neuroradiologist. Predictive models were developed to assess the utility of MEG in determining Engel class at one year and five years after resective epilepsy surgery.

RESULTS

The number of MEG spike foci was highly associated with Engel class outcome at both one year and five years; however, using MEG data in isolation was not significantly predictive of 5 year surgical outcome. When combined with clinical factors; scalp EEG (single ictal onset zone), MRI (lesional or not), age and sex in a logistic regression model MEG foci was significant for Engel class outcome at both 1 year (p = 0.03) and 5 years (0.02). The percent correctly classified for Engel class at one year was 78.43% and the positive predictive value was 71.43.

SIGNIFICANCE

MEG using SAM(g2) analysis in an important non-invasive tool in the identification of those patients who will benefit most from surgery. Integrating MEG data analysis into pre-surgical evaluation can help to predict epilepsy outcome after resective surgery in the pediatric population if utilized with skilled interpretation.

The Sub-Regional Functional Organization of Neocortical Irritative Epileptic Networks in Pediatric Epilepsy

Between seizures, irritative network generates frequent brief synchronous activity, which manifests on the EEG as interictal epileptiform discharges (IEDs). Recent insights into the mechanism of IEDs at the microscopic level have demonstrated a high variance in the recruitment of neuronal populations generating IEDs and a high variability in the trajectories through which IEDs propagate across the brain. These phenomena represent one of the major constraints for precise characterization of network organization and for the utilization of IEDs during presurgical evaluations. We have developed a new approach to dissect human neocortical irritative networks and quantify their properties. We have demonstrated that irritative network has modular nature and it is composed of multiple independent sub-regions, each with specific IED propagation trajectories and differing in the extent of IED activity generated. The global activity of the irritative network is determined by long-term and circadian fluctuations in sub-region spatiotemporal properties. Also, the most active sub-region co-localizes with the seizure onset zone in 12/14 cases. This study demonstrates that principles of recruitment variability and propagation are conserved at the macroscopic level and that they determine irritative network properties in humans. Functional stratification of the irritative network increases the diagnostic yield of intracranial investigations with the potential to improve the outcomes of surgical treatment of neocortical epilepsy.

Cortical dysplasias, and corpus callosum and posterior fossa abnormalities: correlation of clinical findings with magnetic resonance imaging (MRI) characteristics

This study examined clinical findings and magnetic resonance imaging (MRI) characteristics in 114 patients with cortical dysplasia and corpus callosum and posterior fossa abnormalities to determine the clinical findings with the extent of the lesions on MRI. The age of patients was between 1 day and 15 years. Group 1 included 74 patients with corpus callosum abnormalities and/or cortical dysplasias and group 2 included 40 patients with posterior fossa abnormalities, which were isolated and/or associated with cortical dysplasia and/or corpus callosum abnormalities. Although associated congenital abnormality apart from central nervous system abnormalities, syndrome, or systemic disorder were more common in group 2 than group 1 patients (P < .05), we did not find a difference between the groups for psychomotor retardation and epilepsy (P > .05).

Neurological morbidity and the pertussis vaccine: An old story revisited

We describe 3 children with neurological disorders that developed in association with their receipt of the whole-cell pertussis vaccine. Newer studies supported the ability of the wP vaccine to adversely affect the CNS. The possibility that it worsened their clinical course in infancy by causing additional damage should not be disregarded.

Assessment and surgical outcomes for mild type I and severe type II cortical dysplasia: a critical review and the UCLA experience

Recent findings on the clinical, electroencephalography (EEG), neuroimaging, and surgical outcomes are reviewed comparing patients with Palmini type I (mild) and type II (severe) cortical dysplasia. Resources include peer-reviewed studies on surgically treated patients and a subanalysis of the 2004 International League Against Epilepsy (ILAE) Survey of Pediatric Epilepsy Surgery. These sources were supplemented with data from University of California, Los Angeles (UCLA). Cortical dysplasia is the most frequent histopathologic substrate in children, and the second most common etiology in adult epilepsy surgery patients. Cortical dysplasia patients present with seizures at an earlier age than other surgically treated etiologies, and 33-50% have nonlocalized scalp EEG and normal magnetic resonance imaging (MRI) scans. 2-((18)F)Fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) is positive in 75-90% of cases. After complete resection, 80% of patients are seizure free compared with 20% with incomplete resections. Compared with type I, patients with type II cortical dysplasia present at younger ages, have higher seizure frequencies, and are extratemporal. Type I dysplasia is found more often in adult patients in the temporal lobe and is often MRI negative. These findings identify characteristics of patients with mild and severe cortical dysplasia that define surgically treated epilepsy syndromes. The authors discuss future challenges to identifying and treating medically refractory epilepsy patients with cortical dysplasia.

Surgical treatment of intractable epilepsy associated with focal cortical dysplasia

Focal cortical dysplasias (FCDs) are congenital malformations of cortical development that are a frequent cause of refractory epilepsy in both children and adults. With advances in structural and functional neuroimaging, these lesions are increasingly being identified as a cause of intractable epilepsy in patients undergoing surgical management for intractable epilepsy. Comprehensive histological classification of FCDs with the establishment of uniform terminology and reproducible pathological features has aided in our understanding of FCDs as an epilepsy substrate. Complete resection of FCDs and the associated epileptogenic zone can result in a good surgical outcome in the majority of patients.

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.

The clinical spectrum of malformations of cortical development

BACKGROUND

Malformations of cortical development (MCD) usually manifest in childhood with epilepsy, developmental delay and focal neurological abnormalities.

OBJECTIVE

To evaluate the presentation and severity of epilepsy in the different types of MCD.

METHOD

We evaluated the first 100 consecutive patients with a neuroimaging diagnosis of MCD. They were identified among all the high resolution magnetic resonance imaging exams performed at our service between 1997 and 2001. The causes of referral were diverse, according to the routine of the neurology outpatient clinic. After magnetic resonance imaging diagnosis of the subtype of MCD a detailed clinical assessment was performed.

RESULTS

There were 55 females and 45 males, with ages ranging from five months to 71 years old (mean=15.2 years). Seventy-seven patients presented with epilepsy. Sixty-one had partial epileptic syndromes, 13 secondary generalized syndromes, and in three, the type of epileptic syndrome could not be established. Epilepsy was less frequent in patients with the MCD subtypes of polymicrogyria and schizencephaly (p<0.001). Patients with schizencephaly and polymicrogyria had their seizures more easily controlled by antiepileptic drugs (p<0.001).

CONCLUSION

That the frequency of epilepsy is lower and seizures are more easily controlled in the setting of polymicrogyria and schizencephaly. Patients with MCD frequently present with secondary generalized epilepsy early in childhood.

Surgical outcome and prognostic factors of pediatric epilepsy caused by cortical dysplasia

OBJECTS

We analyzed 30 patients with cortical dysplasia (CD) and epilepsy to evaluate the clinical characteristics and surgical outcome of both epilepsy control and neurocognition.

MATERIALS AND METHODS

The mean ages at seizure onset and at the time of the operation were 3.6 years (range, 1 month-12.6 years) and 10.3 years (range, 1.5-18.3 years), respectively. The mean follow-up period was 3.2 years (range, 1-5.3 years). (18)FDG-positron emission tomography was the most sensitive and magnetic resonance imaging was the most specific in localizing the lesion. Developmental/intellectual delay was predominant in the early-onset group (n=18, seizure onset <3 years), with intelligence tending to be normal in the late-onset group (n=12, seizure onset >or=3 years). Mild CD predominated in the late-onset epilepsy group and moderate or severe CD in the early-onset group (p=0.005). The surgical success rate of epilepsy control was 87%. A better outcome was obtained if the lesion was confined to the temporal lobe. School performance was favorable in 43%. The age at seizure onset and preoperative developmental/intellectual delay were the important prognostic factors in school performance as well as the epilepsy control. A total of 77% of patients had relatively good social adaptation. Successful epilepsy control and good school performance were affirmative conditions precedent to social adaptation.

CONCLUSIONS

Due to the favorable control of epilepsy and its effect on school performance and social adaptation, surgical treatment is strongly recommended for cortical dysplasia and intractable epilepsy.

Expression of neural stem cell surface marker CD133 in balloon cells of human focal cortical dysplasia

PURPOSE

Focal cortical dysplasia (CD) is characterized by the presence of dysmorphic neurons, laminar and columnar disorganization. A few patients with CD have balloon cells intermixed with dysmorphic neurons. The cellular characteristics of balloon cells remain unknown. This study was intended to determine further the cellular characteristics of balloon cells.

METHODS

Neocortical tissue resected from five patients with medically intractable focal epilepsy due to CD was studied. The presence of balloon cells (large opalescent cells with eccentric nuclei) was confirmed in all five patients by using cresylecht violet staining. Immunocytochemistry used antibodies against markers of pluripotential stem cells (CD133), multipotential progenitor cells (nestin), antiapoptotic gene products (Bcl-2), immature neurons (beta-tubulin 3, TUJ1), immature glia (vimentin), mature neurons (MAP2 and NeuN), and astrocytes (glial fibrillary acidic protein; GFAP).

RESULTS

Balloon cells (BCs) were found to be immunoreactive to Bcl-2 (46%), vimentin (41%), Nestin (28%), CD133 (28%), MAP2 (27%), GFAP (14%), and TUJ1 (10%). An extremely small number of BCs were immunopositive for NeuN. Confocal double labeling showed that balloon cells were dually immunopositive for CD133/nestin; CD133/GFAP; CD133/Bcl-2, and nestin/GFAP.

CONCLUSIONS

These results show that balloon cells are heterogeneous cell populations expressing cell-surface markers for pluripotential stem cells and proteins for multipotent progenitors, or immature neurons/glia. The presence of stem cell/progenitor markers in the balloon cells could be due to a persistent postnatal neurogenesis or early embryonic insult that resulted in arrest of proliferation/differentiation at their early stages. Additionally, the coexpression of Bcl-2 in CD133-positive balloon cells suggests that a resistance to programmed cell death may be involved in the pathogenesis of cortical dysplasia.

Three-dimensionally reconstructed magnetic source imaging and neuronavigation in pediatric epilepsy: technical note

OBJECTIVE

To determine the role of reconstructing three-dimensional magnetic source imaging (MSI) data on cortical resections for children undergoing epilepsy surgery using neuronavigation.

METHODS

Magnetoencephalographic recordings were analyzed in 16 children under 18 years of age with intractable epilepsy. The data were transferred to the neuronavigation workstation for intraoperative localization of MSI spike sources in selected patients. With the aid of neuronavigation, the MSI spike sources were resected. Intraoperative electrocorticography was then used to survey the surrounding field for residual epileptiform activity.

RESULTS

MSI spike sources were obtained in 13 of 16 patients. MSI spike sources localized the cortical and subcortical discharges before intraoperative electrocorticography in nine patients and before extraoperative subdural grid electroencephalographic monitoring in four patients. The localization of MSI spikes sources was characterized by clustered spike sources in 10 patients. By use of neuronavigation, the clustered spike sources were correlated to the interictal zone indicated by intraoperative electrocorticography in six patients and to the ictal onset zone shown on extraoperative subdural grid electroencephalography in three patients. Cortical excision of the spike cluster focus was then performed in these six patients. The technique used here to resect MSI spike source clusters that correlate with the ictal onset zone by invasive subdural grid monitoring is illustrated in one patient who underwent cortical resection for epilepsy surgery.

CONCLUSION

Three-dimensional reconstruction of MSI data linked to neuronavigation is a promising technique to facilitate resections around eloquent cortex in children with epilepsy.

Molecular pathogenesis of focal cortical dysplasia and hemimegalencephaly

My laboratory recently demonstrated that there is selective expression of phosphoribosomal S6 protein in balloon cells in focal cortical dysplasia and hemimegalencephaly but no expression of the upstream kinase, phospho-p70S6 kinase. Two proteins activated by phospho-p70S6 kinase, phospho-STAT3 and phospho-4EBP1, were not detected in balloon cells. Using complementary DNA arrays in hemimegalencephaly specimens, we found increased expression of cyclin D1 and c-myc messenger ribonucleic acids (RNAs). Expression of cyclin D1 and c-myc genes is transcriptionally activated by beta-catenin. Western analysis demonstrated increased levels of nonphosphorylated beta-catenin in hemimegalencephalic cortex. Reduced levels of Ser33, Ser37, and Thr41 phospho-beta-catenin, sites known to be phosphorylated by glycogen synthase kinase 3 and to be essential for beta-catenin inactivation, were detected in hemimegalencephaly. Enhanced transcription of cyclin D1 and c-myc messenger RNAs, increased transcriptionally active beta-catenin, and decreased Ser33/Ser37/Thr41 phospho-beta-catenin suggest activation of the Wnt-1/beta-catenin cascade in hemimegalencephaly, which can lead to aberrant cell proliferation and hemispheric enlargement during brain development. Enhanced activation of phospho-S6 and beta-catenin suggests two converging cell pathways that can be pivotal in the pathogenesis of focal cortical dysplasia and hemimegalencephaly.

Surgical treatment of epilepsy in children caused by focal cortical dysplasia

Focal cortical dysplasia (FCD) is a congenital disorder of neuronal migration that is increasingly recognized as a common cause of seizures in children, occurring in 20-30% of all surgically treated cases of epilepsy in the pediatric population. Advances in neuroimaging have contributed to recognition of FCD. We report 15 children (9 female, 6 male) with FCD and surgically treated intractable epilepsy. In 9 cases, a surgical strategy of anatomic (frameless stereotactic) grid placement and physiologic (electrocorticography) resection was employed. Postoperative MRI scans were obtained, the pathologic specimen was graded according to the Brannstrom system, and seizure outcome was defined using the Engel classification. There were no deaths and no permanent morbidity. After, on average, 4 years since treatment, 10 children are seizure free, 2 are 2A, 2 are 2B and 1 is 3A. Predictors of good outcome are an MRI-defined lesion and increased cortical disorganization (higher Brannstrom grade). Subtotal resection did not preclude a seizure-free outcome.

mTOR cascade activation distinguishes tubers from focal cortical dysplasia

Balloon cells (BCs) in focal cortical dysplasia (FCD) and giant cells (GCs) in tubers of the tuberous sclerosis complex (TSC) share phenotypic similarities. TSC1 or TSC2 gene mutations in TSC lead to mTOR pathway activation and p70S6kinase (phospho-S6K) and ribosomal S6 (phospho-S6) protein phosphorylation. Phospho-S6K, phospho-S6, and phospho-S6K-activated proteins phospho-STAT3 and phospho-4EBP1 were detected immunohistochemically in GCs, whereas only phospho-S6 was observed in BCs. Expression of four candidate gene families (cell signaling, cell adhesion, growth factor/receptor, and transcription factor mRNAs) was assayed in single, microdissected phospho-S6-immunolabeled BCs and GCs as a strategy to define whether BCs and GCs exhibit differential transcriptional profiles. Among 60 genes, differential expression of 24 mRNAs distinguished BCs from GCs and only 4 genes showed similar expression profiles between BCs and GCs. Tuberin mRNA levels were reduced in GCs from TSC patients with TSC2 gene mutations but were unchanged in BCs. Phospho-S6K, -S6, -STAT3, and -4EBP1 expression in GCs reflects loss of hamartin-tuberin-mediated mTOR pathway inhibition. Phospho-S6 expression alone in BCs does not support mTOR cascade activation in FCD. Differential gene expression profiles in BCs and GCs supports the hypothesis that these cell types derive by distinct pathogenic mechanisms.

Malformations of cortical development: burdens and insights from important causes of human epilepsy

Malformations of cortical development (MCD) are important causes of chronic epilepsy in human beings. A blanket term, MCD encompasses many varied developmental disorders with diverse clinical manifestations in patients that neurologists, paediatricians, and learning disability psychiatrists will encounter. Advances in imaging and genetics have led to a significant increase in our understanding of MCD, which has in turn enriched our knowledge of human epileptogenesis and normal brain development and function. In this review, I discuss some of the most common or enlightening MCD: focal cortical dysplasia, periventricular heterotopia, polymicrogyria, band heterotopia and lissencephaly, dysembryoplastic neuroepithelial tumours, and microdysgenesis. Clinical and imaging features, genetic aetiologies, treatments, and the insights that have resulted from MCD study are covered. The burden of epilepsy due to MCD is significant and there is still much to learn about MCD.

Agyria-pachygyria complex: MR findings and correlation with clinical features

The aim of this study was to determine the spectrum of clinical abnormalities in the agyria-pachygyria complex, to identify possible causes, and to correlate the clinical features with the extent of the lesions on magnetic resonance imaging. On the basis of the magnetic resonance imaging findings, 37 patients (22 males, 15 females; mean age 21.1 +/- 31.2 months) with agyria-pachygyria complex were separated into two groups: Group 1 (18 children) manifested generalized or bilateral gyral malformation, and Group 2 (19 children) manifested localized or unilateral gyral malformation. The ratio of generalized seizures in Group 1 was significantly higher, whereas partial seizures were more common in Group 2. Group 1 patients had seizures significantly more frequently than Group 2 patients. Diffuse electroencephalographic abnormalities were significantly more common in Group 1, as were the localized abnormalities in Group 2. Hemipareses were the most frequent neurologic deficit among Group 2 patients. Spastic quadriparesis and microcephaly were more common in Group 1. In conclusion, the extent of agyria-pachygyria complex varies widely and the clinical features are accordingly diverse. Patients with bilateral or generalized gyral anomalies have poor prognosis for outcome of epilepsy and neurologic disability. The recognition of these lesions with higher-resolution techniques of magnetic resonance imaging is important for planning proper treatment and genetic counseling.

Cortical dysplasia in extratemporal lobe intractable epilepsy: a study of 52 cases

Cortical dysplasias or malformations due to abnormalities of cortical development are a well-recognized cause of intractable seizures. This study retrospectively examines the clinicopathologic features of 52 cases of extratemporal cortical dysplasia (from 135 total resections performed over a 16-year period). The study consists of 52 patients (27 males; 25 females) who underwent extratemporal resection for epilepsy at a mean age of 15.1 years (range, 3 months to 44.1 years). Seizure duration before surgery ranged from 7 to 372 months (mean duration, 129 months). Patterns of cortical dysplasia observed included diffuse architectural disorganization (n=48), neuronal cytomegaly (n=32), increased number of molecular layer neurons (n=32), balloon cells (n=19), gray matter heterotopia (n=3), neuronal glial clustering (n=3), and pial glial neuronal tissue (n=2). Five patients had coexistent nodular hamartomas. Coexistent tumors were present in five patients; including three dysembryoplastic neuroepithelial tumors, one ganglioglioma, and one low-grade fibrillary astrocytoma. Two patients had tuberous sclerosis. Follow-up was available in 50 patients (mean follow-up, 29 months). Thirty-eight patients (73%) had complete resolution or significant decrease in seizure frequency, 13 patients (25%) had increased seizures or no change in seizures, and one patient died in the postoperative period. In conclusion, (1). cortical dysplasia was identified in 38.5% of extratemporal resections for epilepsy; (2). the common cortical dysplasia patterns observed included diffuse cortical disorganization, neuronal cytomegaly, and increased molecular layer neurons; (3). 10% of extratemporal cortical dysplasia was associated with tumors; (4). improved seizure control was obtained in approximately three fourths of patients after resection; and (5). seizures associated with balloon cell dysplasia were less successfully managed with surgery.

Focal cortical dysplasia and intractable epilepsy in adults: clinical, EEG, imaging, and surgical features

PURPOSE

The clinical features of focal cortical dysplasia (FCD) in adults are poorly understood. The purpose of this report is to describe the clinical, electrographic, and neuroimaging characteristics of adults with FCD undergoing surgical resection for intractable epilepsy.

METHODS

Case series of 55 patients, aged 17-57 years, with a histopathological diagnosis of FCD. Medical history, neurological examination, non-invasive video-EEG, neuroimaging, and surgical outcome data were analyzed retrospectively.

RESULTS

There were 36 patients with temporal, 19 with extra-temporal lobe resections. Mean age at surgery was 29 years. Mean age at epilepsy onset was 10 years. Dual pathology was seen in 56% of patients, with 68% of these having hippocampal sclerosis (HS). Epilepsy risk factors included febrile seizures (16%), head trauma (16%), CNS infections (11%), and perinatal stroke (4%). Interictal EEG showed regional epileptiform activity in 89% of patients. Only 24% were diagnosed with FCD pre-operatively. Of those with dual pathology, only 6% were suspected of having FCD pre-operatively. Of those patients with >12 months follow-up, surgical outcomes were as follows: 65% seizure-free, 19% significant improvement, 16% without significant improvement.

CONCLUSIONS

In this series of adult patients with intractable epilepsy and FCD, a significant number have other seizure risk factors, normal neurological examinations and neuroimaging, and regional EEG findings. Dual pathology was common in patients with FCD. FCD should be considered as an etiology of epilepsy even in patients whose evaluation suggests other mechanisms.

Metabolic properties of band heterotopia differ from those of other cortical dysplasias: a proton magnetic resonance spectroscopy study

PURPOSE

To assess the biochemical properties of band heterotopia in comparison with other cortical developmental malformations (CDMs) by using proton magnetic resonance spectroscopy (1H-MRS).

METHODS

We performed localized single-voxel 1H-MRS studies on 13 patients [five band heterotopia (BH), two focal cortical dysplasia (CD), two unilateral CD, one bilateral perisylvian dysplasia, three hemimegalencephaly]. CDMs other than BH were categorized as CD. Spectra were acquired from volumes of interest (VOIs) localized in the CD and in normal-appearing cortex on the contralateral side. In BH patients, the VOIs were the external cortex and the laminar heterotopia. For the BH study, spectra also were obtained from the cortex of age-matched normal volunteers.

RESULTS

The spectra of CD lesions were characterized by significantly lower ratios of N-acetyl aspartate to creatine (NAA/Cr) and by higher choline to Cr (Cho/Cr) ratios than in the contralateral remote cortex (p = 0.01 and 0.01, respectively). The NAA/Cr and Cho/Cr ratios of the external cortex of BH were not significantly different from those of normal volunteers. The NAA/Cr ratio of the laminar heterotopia was not significantly different from that of the external cortex (p = 0.12) or normal volunteers (p = 0.60), whereas Cho/Cr was significantly higher in laminar heterotopias than in the external cortex (p = 0.04) or controls (p = 0.03).

CONCLUSIONS

1H-MRS can distinguish between the metabolic properties of BH and CD.

Neuroimaging studies in the evaluation of developmental delay/mental retardation

The employment of neuroimaging studies in the evaluation of individuals with developmental delay/mental retardation (DD/MR) is still highly debated. The Consensus Conference of the American College of Medical Genetics has suggested that "neuroimaging appears to have an especially important role in patients with microcephaly or macrocephaly, seizures, loss of psychomotor skills and neurologic signs," whereas the value of neuroimaging investigations "in the normocephalic patient without focal neurological signs is unclear" [Curry et al., 1997]. However, recent literature reports show how the latest neuroimaging techniques (in vivo proton magnetic resonance spectroscopy [H-MRS]) may prove to be useful in the diagnostic process of those individuals with DD/MR and no neurological signs/symptoms. The use of these techniques can, in addition, help in monitoring treatment in distinct metabolic disorders. This review will focus on the usefulness of neuroimaging studies in some of the newer metabolic disorders. This paper will also cover those recognizable patterns of human malformation where neuroimaging findings seem to be relevant both toward diagnosis and management, and add to our understanding of the related behavior phenotype. The essential role of magnetic resonance imaging (MRI) on the progress in the diagnostic recognition of malformations of cerebral cortical development is stressed.

Characteristics of epilepsy in focal cortical dysplasia in infancy

To describe the poorly known characteristics of epilepsy during infancy in focal cortical dysplasia (FCD), one of the most frequent cause of infantile epilepsy. All 28 patients with FCD referred to two specialized centres were retrospectively studied regarding seizure characteristics, psychomotor evaluation, and response to medical and surgical treatment. All patients presented with early partial seizures. Semiology, but not the age of onset, depended on the topography of the dysplasia, with abnormal eye movements in all cases of posterior FCD. Eleven patients also developed infantile spasms (IS), mainly asymmetrical. IS were easily controlled with Vigabatrin or ACTH, but no partial seizures could be medically controlled except in one patient. All patients except one had abnormal neuropsychological findings. Fifteen patients had surgery, eight became seizure free, and seven were significantly improved regarding psychomotor development. Very early and refractory partial seizures, but easily controlled IS are the main characteristics of FCD in infancy. Only the focal ictal semiology may help differentiate the localization of FCD. Its intrinsic epileptogenicity could sustain this clinical pattern. Since the chances for medical control and normal neurodevelopment are poor, surgical treatment should be considered early in infants with FCD.

Complex central cortex in pediatric patients with malformations of cortical development

We investigated whether malformations of cortical development yield a complex central cortex by studying nine children with malformations of cortical development and seven without malformations who underwent epilepsy surgery following extraoperative subdural somatosensory evoked potential and electrical stimulation to identify the sensorimotor cortex. We analyzed superficial structures of the central cortex, latency, amplitude, and location of N20 and P25. Sensorimotor responses in malformations of cortical development extended across the central sulcus in 1 to 4 of 3 to 12 electrodes (mean 32%) compared with 1 to 6 of 4 to 15 electrodes (mean 12%) in cases without malformations with a statistical significance (P < .05). N20 amplitudes were lower in epileptic than nonepileptic cortices (three with and three without malformations of cortical development) (P < .05). The central vein coursed partially along the central sulcus in eight cases of malformations of cortical development and five cases without malformations. We conclude that the sensorimotor cortex in malformations of cortical development is more complex than in cases without malformations, reduced N20 amplitude is indicative of epileptic sensorimotor cortex, and superficial veins do not indicate the sensory and motor cortical boundary.

Pathologic characteristics of the cortical dysplasias

The gross and microscopic features of cortical dysplasia (malformations caused by abnormalities of cortical development) are reviewed and illustrated in this article. The pathologic associations of neurocutaneous disorders, neoplasms, and hippocampal sclerosis with cortical dysplasia also are discussed.

Surgery for hemispheric malformations of cortical development

The treatment of patients with hemispheric malformations of cortical development presents a challenging clinical problem that often requires surgical intervention. The development of a safe and effective treatment strategy for these patients requires an extensive work-up with a great deal of attention to a variety of multidisciplinary testing methods. In this article, the authors describe the presurgical evaluation of patients with hemispheric malformations of cortical development and epilepsy and review the surgical techniques currently available. They also detail some of the controversial issues regarding surgical treatment of these patients.

Preoperative clinical evaluation and noninvasive electroencephalogram in cortical dysplasia

The preoperative evaluation of patients with suspected cortical dysplasia involves detailed neurologic and neuropsychologic evaluations, electroencephalography, and comprehensive neuroimaging and functional studies. The goal is to identify a focal region of seizure onset and to assess for motor impairments, speech and language difficulties, or developmental delay. Although the electroencephalogram abnormalities in cortical dysplasia are nonspecific, they typically include unusual high-amplitude (slowing and focal) activity. The association of cortical dysplasia with cardiovascular, dermatologic, and other systemic disorders is discussed.

Role of functional magnetic resonance imaging in the evaluation of patients with malformations caused by cortical development

As functional MR imaging (fMRI) continues to offer unparalleled advantages in probing neural activity, diagnostic applications continue to flourish. The evaluation of malformations caused by abnormalities of cortical development is an area in which fMRI has an emerging role and potential to provide new insights into epileptogenesis through multimodal integration with electroencephalagraphy. The clinical impact, however, is just beginning to be felt as new data emerge.

Hippocampal heterotopia lack functional Kv4.2 potassium channels in the methylazoxymethanol model of cortical malformations and epilepsy

Human cortical malformations often result in severe forms of epilepsy. Although the morphological properties of cells within these malformations are well characterized, very little is known about the function of these cells. In rats, prenatal methylazoxymethanol (MAM) exposure produces distinct nodules of disorganized pyramidal-like neurons (e.g., nodular heterotopia) and loss of lamination in cortical and hippocampal structures. Hippocampal nodular heterotopias are prone to hyperexcitability and may contribute to the increased seizure susceptibility observed in these animals. Here we demonstrate that heterotopic pyramidal neurons in the hippocampus fail to express a potassium channel subunit corresponding to the fast, transient A-type current. In situ hybridization and immunohistochemical analysis revealed markedly reduced expression of Kv4.2 (A-type) channel subunits in heterotopic cell regions of the hippocampus of MAM-exposed rats. Patch-clamp recordings from visualized heterotopic neurons indicated a lack of fast, transient (I(A))-type potassium current and hyperexcitable firing. A-type currents were observed on normotopic pyramidal neurons in MAM-exposed rats and on interneurons, CA1 pyramidal neurons, and cortical layer V-VI pyramidal neurons in saline-treated control rats. Changes in A-current were not associated with an alteration in the function or expression of delayed, rectifier (Kv2.1) potassium channels on heterotopic cells. We conclude that heterotopic neurons lack functional A-type Kv4.2 potassium channels and that this abnormality could contribute to the increased excitability and decreased seizure thresholds associated with brain malformations in MAM-exposed rats.

Cortical malformations and epilepsy

Brain malformations, resulting from aberrant patterns of brain development, are highly correlated with childhood seizure syndromes, as well as with cognitive disabilities and other neurological disorders. The structural malformations, often referred to as cortical dysplasia, are extremely varied, reflecting diverse underlying processes and critical timing of the developmental aberration. Recent studies have revealed a genetic basis for many forms of dysplasia. Gene mutations responsible for such common forms of dysplasia as lissencephaly and tuberous sclerosis have been identified, and investigators are beginning to understand how these gene mutations interrupt and/or misdirect the normal developmental pattern. Laboratory investigations, using animal models of cortical dysplasia, are beginning to elucidate how these structural malformations give rise to epilepsy and other functional pathologies.

MRI spectrum of cortical malformations in tuberous sclerosis complex

The diagnostic and prognostic value of magnetic resonance imaging in the tuberous sclerosis complex has increasingly been recognized. In this paper, we review the presumed pathogenesis of the cerebral dysgenesis seen in this condition in the light of magnetic resonance imaging features of selected patients. In addition to typical findings related to tubers, we show and discuss varied cortical malformations (from simple localized cortical dysplasia to transmantle dysplasia and schizencephaly) similar to those seen in sporadic cerebral dysgenesis. These cases support the hypothesis that the tuberous sclerosis complex focally affects the radial glial-neuronal complex as a basic unit for brain development. Abnormal stem cells would create dysplastic glia and neurons that fail to differentiate, proliferate, migrate and form a normally organized cortex.

Epilepsy and Cortical Dysplasias

Focal cortical dysplasias (FCD) and diffuse cortical dysplasias (DCD) are a heterogeneous group of disorders defined by abnormal cerebral cortical cytoarchitecture that are associated with epilepsy. Patients with either DCD or FCD may suffer from a variety of epilepsy subtypes and these are often refractory to most anti-epileptic drugs (AEDs) despite polytherapy. The etiologies of cortical dysplasias (CD) are diverse, and include inherited genetic syndromes such as Miller-Dieker or X-linked lissencephaly, subcortical band heterotopia, and the tuberous sclerosis complex, as well as nongenetic exogenous insults such as hypoxic-ischemic injury, viral or other type of central nervous system infection, or traumatic injury. A large number of FCD cases are idiopathic and very small regions of FCD (microdysgenesis) are now being identified in resected epilepsy specimens. Recent data suggests that nearly 30% of epilepsy specimens evaluated histologically will contain regions of overt or microscopic CD. The mainstay of appropriate therapy for CD remains the standard AEDs or epilepsy surgery. In too few disorders, specific AEDs provide therapeutic advantage in the setting of individual forms of CD. The ketogenic diet may provide seizure control in a subpopulation of patients. In both DCD and FCD, surgical resection can be curative in the appropriately selected patients. Surgical approaches include focal neocortical resections, temporal lobectomy, or larger hemispheric resection procedures.

Defective neurogenesis in citron kinase knockout mice by altered cytokinesis and massive apoptosis

Citron-kinase (Citron-K) has been proposed by in vitro studies as a crucial effector of Rho in regulation of cytokinesis. To further investigate in vivo its biologic functions, we have inactivated Citron-K gene in mice by homologous recombination. Citron-K-/- mice grow at slower rates, are severely ataxic, and die before adulthood as a consequence of fatal seizures. Their brains display defective neurogenesis, with depletion of specific neuronal populations. These abnormalities arise during development of the central nervous system due to altered cytokinesis and massive apoptosis. Our results indicate that Citron-K is essential for cytokinesis in vivo but only in specific neuronal precursors. Moreover, they suggest a novel molecular mechanism for a subset of human malformative syndromes of the CNS.

Epilepsy surgery in children with developmental disabilities

Surgery for treatment of medically uncontrolled epilepsy in children is now widely accepted with reported outcomes similar to those in adults. Epilepsy is reported in 8.8% to 32% of children with mental retardation (MR) and in up to half of children with severe retardation. There has been concern that patients with low IQ will experience unsatisfactory outcomes from epilepsy surgery and not achieve good seizure control. It is appropriate to reassess the prior bias against resective epilepsy surgery in children with MR in view of the changing criteria for potential candidacy for epilepsy surgery in infants and young children. There are three prerequisites for epilepsy surgery: (1) the epilepsy must be medically intractable; (2) the surgery must be feasible, that is, the epileptogenic zone can identified and safely resected; and (3) there is high likelihood of a satisfactory outcome as regards both the epilepsy and the patient's functional status. Patients with MR may have diffuse cerebral dysfunction and diffuse or multifocal epileptogenic regions. Appropriate patient selection is made possible through use of current technology that allows identification of lesions or areas of cerebral dysgenesis, aiding in identification of localized areas of epileptogenesis. Results from various series of patients with MR who have undergone resective surgery for epilepsy have shown that with careful presurgical evaluations, outcomes are similar between patients with normal IQ scores and those with low scores. Surgical protocols specifically for patients with MR and intractable epilepsy are required, including careful definition of desired outcomes.

Epilepsy surgery in children, with special attention to focal cortical resections

Epilepsy surgery is an important alternative for children and adolescents with medically intractable epilepsy. Advances in imaging have allowed the visualization of epileptogenic regions, including cortical dysplasia. The presurgical evaluation will likely become less invasive as imaging technology improves. Long-term development is a critical outcome measure, in addition to seizure control. The long-term prognosis after epilepsy surgery may be related to factors other than seizure control, including the timing of the intervention and the cause of the epilepsy. It may be useful to independently analyze children based on cause, and further studies examining the long-term outcome should become feasible as surgical experience grows.

Consequences of epilepsy in the developing brain: implications for surgical management

The developing brain is highly susceptible to seizures, as demonstrated by both human and animal studies. Until recently, the brain has been considered to be relatively resistant to damage induced by seizures early in life. Accumulating evidence in animal models now suggests that early seizures can cause structural and physiologic changes in developing neural circuits that result in permanent alterations in the balance between neuronal excitation and inhibition, deficits in cognitive function, and increased susceptibility to additional seizures. The disruption of normal neuronal activity by seizures can affect multiple developmental processes, resulting in these long-lasting changes. These data should be considered in the clinical approach to children with intractable epilepsy and suggest that early intervention may avoid some of these long-term neurologic deficits.