Inhibitory networks in epilepsy-associated gangliogliomas and in the perilesional epileptic cortex

Structural changes in the neocortex as correlates of variations in EEG spectra and seizure susceptibility in rat brains with different degrees of dysplasia

Disturbances of the early stages of neurogenesis lead to irreversible changes in the structure of the mature brain and its functional impairment, including increased excitability, which may be the basis for drug‐resistant epilepsy. The range of possible clinical symptoms is as wide as the different stages of disturbed neurogenesis may be. In this study, we used a quadruple model of brain dysplasia by comparing structural and functional disorders in animals whose neurogenesis was disturbed with a single dose of 1 Gy of gamma rays at one of the four stages of neurogenesis, that is, on days 13, 15, 17, or 19 of prenatal development.

When reached adulthood, the prenatally irradiated rats received EEG teletransmitter implantation. Thereafter, pilocarpine was administered and significant differences in susceptibility to seizure behavioral symptoms were detected depending on the degree of brain dysplasia. Before, during, and after the seizures significant correlations were found between the density of parvalbumin‐immunopositive neurons located in the cerebral cortex and the intensity of behavioral seizure symptoms or increases in the power of particular EEG bands. Neurons expressing calretinin or NPY showed also dysplasia‐related increases without, however, correlations with parameters of seizure intensity. The results point to significant roles of parvalbumin‐expressing interneurons, and also to expression of NPY—an endogenous anticonvulsant and neuroprotectant reducing susceptibility to seizures and supporting neuronal survival.

Epileptogenesis and oncogenesis: An antineoplastic role for antiepileptic drugs in brain tumours?

The first description of epileptic seizures due to brain tumours occurred in 19th century. Nevertheless, after over one hundred years, scientific literature is still lacking on how epilepsy and its treatment can affect tumour burden, progression and clinical outcomes. In patients with brain tumours, epilepsy dramatically impacts their quality of life (QoL). Even antiepileptic therapy seems to affect tumor lesion development. Numerous studies suggest that certain actors involved in epileptogenesis (inflammatory changes, glutamate and its ionotropic and metabotropic receptors, GABA-A and its GABA-AR receptor, as well as certain ligand- and voltage-gated ion channel) may also contribute to tumorigenesis. Although some antiepileptic drugs (AEDs) are known operating on such mechanisms underlying epilepsy and tumor development, few preclinical and clinical studies have tried to investigate them as targets of pharmacological tools acting to control both phenomena. The primary aim of this review is to summarize known determinants and pathophysiological mechanisms of seizures, as well as of cell growth and spread, in patients with brain tumors. Therefore, a special focus will be provided on the anticancer effects of commonly prescribed AEDs (including levetiracetam, valproic acid, oxcarbazepine and others), with an overview of both preclinical and clinical data. Potential clinical applications of this finding are discussed.

Lateral orbitofrontal dysfunction in the Sapap3 knockout mouse model of obsessive–compulsive disorder

BACKGROUND

Obsessive–compulsive disorder (OCD) is a common psychiatric disorder that affects about 2% of the population, but the underlying neuropathophysiology of OCD is not well understood. Although increasing lines of evidence implicate dysfunction of the orbitofrontal cortex (OFC) in OCD, a detailed understanding of the functional alterations in different neuronal types in the OFC is still elusive.

METHODS

We investigated detailed activity pattern changes in putative pyramidal neurons and interneurons, as well as local field potential oscillations, in the lateral OFC underlying OCD-relevant phenotypes. We applied in vivo multichannel recording in an awake OCD mouse model that carried a deletion of the Sapap3 gene, and in wildtype littermates.

RESULTS

Compared with wildtype mice, the lateral OFC of Sapap3 knockout mice exhibited network dysfunction, demonstrated by decreased power of local field potential oscillations. The activity of inhibitory and excitatory neurons in the lateral OFC showed distinct perturbations in Sapap3 knockout mice: putative interneurons exhibited increased activity; putative pyramidal neurons exhibited enhanced bursting activity; and both putative pyramidal neurons and interneurons exhibited enhanced discharge variability and altered synchronization.

LIMITATIONS

To exclude motor activity confounders, this study examined functional alterations in lateral OFC neurons only when the mice were stationary.

CONCLUSION

We provide, to our knowledge, the first direct in vivo electrophysiological evidence of detailed functional alterations in different neuronal types in the lateral OFC of an OCD mouse model. These findings may help in understanding the underlying neuropathophysiology and circuitry mechanisms for phenotypes relevant to OCD, and may help generate and refine hypotheses about potential biomarkers for further investigation.

Discrimination of epileptogenic lesions and perilesional white matter using diffusion tensor magnetic resonance imaging

The aim of this study was to evaluate whether ganglioglioma (GGL), dysembryoplastic neuroepithelial tumour (DNET) and FCD (focal cortical dysplasia) are distinguishable through diffusion tensor imaging. Additionally, it was investigated whether the diffusion measures differed in the perilesional (pNAWM) and in the contralateral normal appearing white matter (cNAWM). Six GGLs, eight DNETs and seven FCDs were included in this study. Quantitative diffusion measures, that is, axial, radial and mean diffusivity and fractional anisotropy, were determined in the lesion identified on isotropic T2 or FLAIR-weighted images and in pNAWM and cNAWM, respectively. DNET differed from FCD in mean diffusivity, and GGL from FCD in radial diffusivity. Both types of glioneuronal tumours were different from pNAWM in fractional anisotropy and radial diffusivity. For identifying the tumour edges, threshold values for tumour-free tissue were investigated with receiver operating characteristic analyses: tumour could be separated from pNAWM at a threshold ≤ 0.32 (fractional anisotropy) or ≥ 0.56 (radial diffusivity) *10-3 mm2/s (area under the curve 0.995 and 0.990 respectively). While diffusion parameters of FCDs differed from cNAWM (radial diffusivity (*10-3 mm/s2): 0.74 ± 0.19 vs. 0.43 ± 0.05; corrected p-value < 0.001), the pNAWM could not be differentiated from the FCD.

BRAF somatic mutation contributes to intrinsic epileptogenicity in pediatric brain tumors

Pediatric brain tumors are highly associated with epileptic seizures¹. However, their epileptogenic mechanisms remain unclear. Here, we show that the oncogenic BRAF somatic mutation p.Val600Glu (V600E) in developing neurons underlies intrinsic epileptogenicity in ganglioglioma, one of the leading causes of intractable epilepsy². To do so, we developed a mouse model harboring the BRAF^V600E somatic mutation during early brain development to reflect the most frequent mutation, as well as the origin and timing thereof. Therein, the BRAF^V600E mutation arising in progenitor cells during brain development led to the acquisition of intrinsic epileptogenic properties in neuronal lineage cells, whereas tumorigenic properties were attributed to high proliferation of glial lineage cells. RNA sequencing analysis of patient brain tissues with the mutation revealed that BRAF^V600E-induced epileptogenesis is mediated by RE1-silencing transcription factor (REST), which is a regulator of ion channels and neurotransmitter receptors associated with epilepsy. Moreover, we found that seizures in mice were significantly alleviated by an FDA-approved BRAF^V600E inhibitor, vemurafenib, as well as various genetic inhibitions of Rest. Accordingly, this study provides direct evidence of a BRAF somatic mutation contributing to the intrinsic epileptogenicity in pediatric brain tumors and suggests that BRAF and REST could be treatment targets for intractable epilepsy.

Epileptogenicity and pathology - Under consideration of ablative approaches

Besides resective epilepsy surgery, minimally invasive ablation using new diagnostic and therapeutic techniques recently became available. Optimal diagnostic approaches for these treatment options are discussed. The pathophysiology of epileptogenic networks differs depending on the lesion-types and location, requiring a differential use of non-invasive or invasive functional studies. In addition to the definition of epileptogenic zones, a challenge for pre-surgical investigation is the determination of three-dimensional epileptic networks to be removed.

Glial GABA Transporters as Modulators of Inhibitory Signalling in Epilepsy and Stroke

Imbalances in GABA-mediated tonic inhibition are involved in several pathophysiological conditions. A classical way of controlling tonic inhibition is through pharmacological intervention with extrasynaptic GABA_A receptors that sense ambient GABA and mediate a persistent GABAergic conductance. An increase in tonic inhibition may, however, also be obtained indirectly by inhibiting glial GABA transporters (GATs). These are sodium-coupled membrane transport proteins that normally act to terminate GABA neurotransmitter action by taking up GABA into surrounding astrocytes. The aim of the review is to provide an overview of glial GATs in regulating tonic inhibition, especially in epilepsy and stroke. This entails a comprehensive summary of changes known to occur in GAT expression levels and signalling following epileptic and ischemic insults. Further, we discuss the accumulating pharmacological evidence for targeting GATs in these diseases.

Role of GABA(B) receptors in learning and memory and neurological disorders

Although it is evident from the literature that altered GABAB receptor function does affect behavior, these results often do not correspond well. These differences could be due to the task protocol, animal strain, ligand concentration, or timing of administration utilized. Because several clinical populations exhibit learning and memory deficits in addition to altered markers of GABA and the GABAB receptor, it is important to determine whether altered GABAB receptor function is capable of contributing to the deficits. The aim of this review is to examine the effect of altered GABAB receptor function on synaptic plasticity as demonstrated by in vitro data, as well as the effects on performance in learning and memory tasks. Finally, data regarding altered GABA and GABAB receptor markers within clinical populations will be reviewed. Together, the data agree that proper functioning of GABAB receptors is crucial for numerous learning and memory tasks and that targeting this system via pharmaceuticals may benefit several clinical populations.

BRAF V600E mutation in neocortical posterior temporal epileptogenic gangliogliomas

The aim of this study was to verify the presence of BRAF mutations in a series of six patients affected by drug-resistant focal epilepsy associated with neocortical posterior temporal gangliogliomas (GG) who were subjected to lesionectomy between June 2008 and November 2013. GG are an increasingly recognized cause of epilepsy and represent the most common tumor in young patients undergoing surgery for intractable focal epilepsy. BRAF mutations have been identified in up to 50% of GG. Interestingly, these six patients shared a specific anatomical posterior temporal site. In all patients, histological examination confirmed the diagnosis of GG, and two were also associated with a focal cortical dysplasia (FCD) type IIa. BRAF mutations were found in four out of six GG (66.6%). Furthermore, dysplastic tissue of Patient 2 showed a concomitant BRAF V600E mutation. All patients but one (83.3%) achieved Engel Class Ia seizure control. The patient carrying a concomitant BRAF mutation in GG and FCD fell into Engel Class II. Further analyses will be required in order to better understand the meaning of BRAF mutations in epilepsy-associated tumors and FCD and their possible role as a prognostic seizure outcome and tumor behavior marker.

Focal cortical dysplasias in temporal lobe epilepsy surgery: Challenge in defining unusual variants according to the last ILAE classification

OBJECTIVE

Focal cortical dysplasias (FCDs) represent a common architectural cortical disorder underlying pharmacoresistant focal epilepsy. The recent ILAE classification defines different types of FCDs based on their histopathological features, MRI imaging, and presumed pathogenesis; however, their clinical features and their prognostic significance are still incompletely defined. In addition, the combination of different histopathological abnormalities can represent "unusual" subtypes that can be difficult to classify. The aim of our study was to analyze the incidence and the significance of these "unusual" subtypes of FCDs in drug-resistant mesial temporal lobe epilepsy (MTLE).

METHODS

We retrospectively analyzed 133 patients consecutively submitted to tailored anteromesial temporal lobe resection for pharmacoresistant MTLE. Seizure onset, seizure duration, age at surgery, and postoperative seizure outcome were evaluated in relation to the different neuropathological groups defined according to the new ILAE classification.

RESULTS

Focal cortical dysplasias were found in 80 out of 133 patients. Six patients were affected by isolated FCD type I, 12 patients by FCD type II, and 44 patients by FCD type III. Furthermore, we found 18 "atypical" cases (20.5% of all FCD cases and 26.6% of FCDs associated with a principal lesion): 10 cases of associated FCD type II-hippocampal sclerosis (HS) and 8 cases associated with FCD II-epilepsy-associated tumors (EATs).

CONCLUSION

Our results indicate that "unusual" subtypes of FCDs, in particular associated FCD type II, are not uncommon findings, suggesting that they deserve a classification recognition. Similarities in seizure outcome and immunohistochemical and molecular evidences, shared by FCD type II+EATs and EATs, suggest a common pathogenic link. The choice to create a specific unifying class or, on the contrary, to also include "associated FCD type II" in the definition of the new unifying class FCD type III should be further discussed.

Interneurons are necessary for coordinated activity during reversal learning in orbitofrontal cortex

BACKGROUND

Cerebral cortical gamma-aminobutyric acidergic interneuron dysfunction is hypothesized to lead to cognitive deficits comorbid with human neuropsychiatric disorders, including schizophrenia, autism, and epilepsy. We have previously shown that mice that harbor mutations in the Plaur gene, which is associated with schizophrenia, have deficits in frontal cortical parvalbumin-expressing interneurons. Plaur mice have impaired reversal learning, similar to deficits observed in patients with schizophrenia.

METHODS

We examined the role of parvalbumin interneurons in orbitofrontal cortex during reversal learning by recording single unit activity from 180 control and 224 Plaur mouse neurons during a serial reversal task. Neural activity was analyzed during correct and incorrect decision choices and reward receipt.

RESULTS

Neurons in control mice exhibited strong phasic responses both during discrimination and reversal learning to decisions and rewards, and the strength of the response was correlated with behavioral performance. Although baseline firing was significantly enhanced in Plaur mice, neural selectivity for correct or erroneous decisions was diminished and not correlated with behavior, and reward encoding was downscaled. In addition, Plaur mice showed a significant reduction in the number of neurons that encoded expected outcomes across task phases during the decision period.

CONCLUSIONS

These data indicate that parvalbumin interneurons are necessary for the representation of outcomes in orbitofrontal cortex. Deficits in inhibition blunt selective neural firing during key decisions, contributing to behavioral inflexibility. These data provide a potential explanation for disorders of cognitive control that accompany the loss of these gamma-aminobutyric acidergic interneurons in human neuropsychiatric disorders, such as autism, epilepsy, and schizophrenia.

Etomidate, propofol and diazepam potentiate GABA-evoked GABAA currents in a cell line derived from human glioblastoma

GABAA receptors are pentameric chloride ion channels that are opened by GABA. We have screened a cell line derived from human glioblastoma, U3047MG, for expression of GABAA receptor subunit isoforms and formation of functional ion channels. We identified GABAA receptors subunit α2, α3, α5, β1, β2, β3, δ, γ3, π, and θ mRNAs in the U3047MG cell line. Whole-cell GABA-activated currents were recorded and the half-maximal concentration (EC₅₀) for the GABA-activated current was 36 μM. The currents were activated by THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) and enhanced by the benzodiazepine diazepam (1 μM) and the general anesthetics etomidate and propofol (50 μM). In line with the expressed GABAA receptors containing at least the α3β3θ subunits, the receptors were highly sensitive to etomidate (EC₅₀=55 nM). Immunocytochemistry identified expression of the α3 and β3 subunit proteins. Our results show that the GABAA receptors in the glial cell line are functional and are modulated by classical GABAA receptor drugs. We propose that the U3047MG cell line may be used as a model system to study GABAA receptors function and pharmacology in glial cells.

Epilepsy associated tumors: Review article

Long-term epilepsy associated tumors (LEAT) represent a well known cause of focal epilepsies. Glioneuronal tumors are the most frequent histological type consisting of a mixture of glial and neuronal elements and most commonly arising in the temporal lobe. Cortical dysplasia or other neuronal migration abnormalities often coexist. Epilepsy associated with LEAT is generally poorly controlled by antiepileptic drugs while, on the other hand, it is high responsive to surgical treatment. However the best management strategy of tumor-related focal epilepsies remains controversial representing a contemporary issues in epilepsy surgery. Temporo-mesial LEAT have a widespread epileptic network with complex epileptogenic mechanisms. By using an epilepsy surgery oriented strategy LEAT may have an excellent seizure outcome therefore surgical treatment should be offered early, irrespective of pharmacoresistance, avoiding both the consequences of uncontrolled seizures as well as the side effects of prolonged pharmacological therapy and the rare risk of malignant transformation.

Time to focus on brain tumor-related epilepsy trials

Brain tumor-related epilepsy (BTRE) is a common complication of cerebral glioma. It has a serious impact on the patient's confidence and quality of life and can be life threatening. There are significant differences in the management of BTRE and nontumoral epilepsy in adults. Surgery is performed early in management, and resection can be curative. Radiotherapy can also improve seizure frequency. Antiepileptic drugs (AEDs) are started after first seizure but are only effective at stopping attacks in 50% of cases. There are no satisfactory randomized controlled clinical trials, or even good prospective series, to support using one AED over another with respect to efficacy. Guidelines are therefore based on poor levels of evidence. In general, the choice of AED may depend on risk of early side effect (rash, biochemical, or hematological effects) and whether drug interactions with chemotherapy are likely. In patients with suspected low-grade glioma, where use of chemotherapy early in the management is not standard practice and survival in measured in many years, the drug interactions are less relevant, and rational seizure management should focus on drugs with the fewest long-term effects on neurocognition, personality, mood, and fatigue. While intriguing and potentially very important, there is no good evidence that any specific AED has a clinical antitumor effect or improves survival. Development of special interest groups in BTRE within countries, or between countries, may be a model for promoting better BTRE trials in the future.

Epilepsy related to developmental tumors and malformations of cortical development

Structural abnormalities of the brain are increasingly recognized in patients with neurodevelopmental delay and intractable focal epilepsies. The access to clinically well-characterized neurosurgical material has provided a unique opportunity to better define the neuropathological, neurochemical, and molecular features of epilepsy-associated focal developmental lesions. These studies help to further understand the epileptogenic mechanisms of these lesions. Neuropathological evaluation of surgical specimens from patients with epilepsy-associated developmental lesions reveals two major pathologies: focal cortical dysplasia and low-grade developmental tumors (glioneuronal tumors). In the last few years there have been major advances in the recognition of a wide spectrum of developmental lesions associated with a intractable epilepsy, including cortical tubers in patients with tuberous sclerosis complex and hemimegalencephaly. As an increasing number of entities are identified, the development of a unified and comprehensive classification represents a great challenge and requires continuous updates. The present article reviews current knowledge of molecular pathogenesis and the pathophysiological mechanisms of epileptogenesis in this group of developmental disorders. Both emerging neuropathological and basic science evidence will be analyzed, highlighting the involvement of different, but often converging, pathogenetic and epileptogenic mechanisms, which may create the basis for new therapeutic strategies in these disorders.

Prefrontal cognitive deficits in mice with altered cerebral cortical GABAergic interneurons

Alterations of inhibitory GABAergic neurons are implicated in multiple psychiatric and neurological disorders, including schizophrenia, autism and epilepsy. In particular, interneuron deficits in prefrontal areas, along with presumed decreased inhibition, have been reported in several human patients. The majority of forebrain GABAergic interneurons arise from a single subcortical source before migrating to their final regional destination. Factors that govern the interneuron populations have been identified, demonstrating that a single gene mutation may globally affect forebrain structures or a single area. In particular, mice lacking the urokinase plasminogen activator receptor (Plaur) gene have decreased GABAergic interneurons in frontal and parietal, but not caudal, cortical regions. Plaur assists in the activation of hepatocyte growth factor/scatter factor (HGF/SF), and several of the interneuron deficits are correlated with decreased levels of HGF/SF. In some cortical regions, the interneuron deficit can be remediated by endogenous overexpression of HGF/SF. In this study, we demonstrate decreased parvalbumin-expressing interneurons in the medial frontal cortex, but not in the hippocampus or basal lateral amygdala in the Plaur null mouse. The Plaur null mouse demonstrates impaired medial frontal cortical function in extinction of cued fear conditioning and the inability to form attentional sets. Endogenous HGF/SF overexpression increased the number of PV-expressing cells in medial frontal cortical areas to levels greater than found in wildtype mice, but did not remediate the behavioral deficits. These data suggest that proper medial frontal cortical function is dependent upon optimum levels of inhibition and that a deficit or excess of interneuron numbers impairs normal cognition.

Seizure outcome in surgically treated drug-resistant mesial temporal lobe epilepsy based on the recent histopathological classifications

OBJECT

The study was performed to investigate the relation between seizure outcome after surgical treatment of mesial temporal lobe epilepsy (MTLE) and pathological findings, classified according to the recently proposed classifications of mesial temporal sclerosis (MTS), granule cell pathology (GCP), focal cortical dysplasia (FCD) and epilepsy-associated low-grade tumors (ELGT).

METHODS

The authors analyzed data obtained in 120 consecutive cases involving patients presenting with drug-resistant MTLE, who underwent tailored anteromesial temporal lobe resection, and correlated seizure outcome with pathological findings. They identified 5 histopathological groups: Group 1-ELGT, alone or associated with other lesions (30 cases); Group 2-isolated FCD (17 cases); Group 3-MTS, with or without GCP (28 cases); Group 4-MTS associated with FCD, with or without GCP (37 cases); Group 5-other lesions (8 cases).

RESULTS

Engel Class I outcome was observed in 83% of patients with ELGT (Class IA in 63%); in 59% of patients with isolated FCD, with FCD Type II showing a better prognosis than FCD Type I; in 82% of patients with isolated MTS (Class IA in 50%), with MTS Type 1a and MTS Type 1b showing a better prognosis than MTS Type 2 and patients with MTS and GCP having better postsurgical results than those with MTS without GCP. Engel Class I outcome was also achieved in 84% of patients with FCD associated with MTS (Engel Class IA in 62%); also in this group MTS 1a and MTS 1b associated with FCD showed a better prognosis than FCD associated with MTS 2. Finally, Engel Class I was also achieved in 2 patients with vascular malformation and in 1 with a temporal pole encephalocele.

CONCLUSIONS

Patients with MTLE and ELGT, MTS, or MTS associated with FCD showed the best postsurgical seizure outcome (Engel Class I in more than 80% of cases), whereas only 63% of patients with isolated FCD achieved the same type of outcome. Interestingly, the analysis of seizure outcome in histopathological subtypes of FCD and of MTS showed different prognoses in the different pathological subgroups, with worse outcomes for atypical MTS, absence of GCP, and isolated FCD Type I.

Seizure outcome of surgical treatment of focal epilepsy associated with low-grade tumors in children

OBJECT

Low-grade tumor (LGT) is an increasingly recognized cause of focal epilepsies, particularly in children and young adults, and is frequently associated with cortical dysplasia. The optimal surgical treatment of epileptogenic LGTs in pediatric patients has not been fully established.

METHODS

In the present study, the authors retrospectively reviewed 30 patients (age range 3-18 years) who underwent surgery for histopathologically confirmed LGTs, in which seizures were the only clinical manifestation. The patients were divided into 2 groups according to the type of surgical treatment: patients in Group A (20 cases) underwent only tumor removal (lesionectomy), whereas patients in Group B (11 cases) underwent removal of the tumor and the adjacent epileptogenic zone (tailored surgery). One of the patients, who underwent 2 operations, is included in both groups. Follow-up ranged from 1 to 17 years.

RESULTS

Sixteen (80%) of 20 patients in Group A had an Engel Class I outcome. In this group, 3 of 4 patients who were in Engel Classes II and III had temporomesial lesions. All patients in Group B had temporomesial tumors and were seizure free (Engel Class I). In this series, in temporolateral and extratemporal tumor locations, lesionectomy yielded a good seizure outcome. In addition, a young age at seizure onset (in particular < 4 years) was associated with a poor seizure outcome.

CONCLUSIONS

Tailored resection in temporomesial LGTs was associated with excellent seizure outcome, indicating that an adequate presurgical evaluation including extensive neurophysiological evaluation (long-term videoelectroencephalography monitoring) to plan appropriate surgical strategy is advised.

Long-term seizure control outcomes after resection of gangliogliomas

BACKGROUND

Gangliogliomas are rare glioneuronal tumors that typically cause refractory seizures during the first 3 decades of life.

OBJECTIVE

To determine the prognosticators of seizure outcome after surgery for ganglioglioma.

METHODS

We reviewed the cases of 66 patients who underwent resection of gangliogliomas at the University of California, San Francisco. Demographic, seizure history, and operative data were examined for statistical association with postoperative seizure outcomes.

RESULTS

Of the 66 patients who underwent surgical resection of ganglioglioma, 49 patients (74%) presented with a history of seizures. Of those 49 patients, 50% presented with intractable epilepsy. Temporal lobe gangliogliomas were present in 76% of the patients who presented with a history of seizures. Electrocorticography was performed on 35% of the patients, and of those patients, 82% underwent extended lesionectomy to remove abnormally epileptogenic extralesional tissue. The median follow-up duration was 6.9 years, during which tumor progression occurred in 38% of patients who underwent subtotal resection and in 8% of patients who underwent gross total resection (P = .02). Overall, 85% of patients were seizure free (International League Against Epilepsy class I or II) 5 years after surgery. Subtotal resection was associated with poor seizure outcomes 1 year after resection (odds ratio = 14.6; 95% confidence interval = 2.4-87.7): rates of seizure freedom were 54% after subtotal resection, 96% after gross total resection, and 93% after gross total resection with intraoperative electrocorticography-guided extended lesionectomy.

CONCLUSION

We report excellent long-term seizure control outcomes after surgery for gangliogliomas. Intraoperative electrocorticography may be a useful adjunct for guiding extended resection in certain pharmacoresistant epilepsy patients with gangliogliomas. Subtotal resection is associated with higher rates of tumor progression and nonoptimal seizure outcomes.

Long-term epilepsy-associated tumors

The term long-term epilepsy associated tumor (LEAT) encompasses lesions identified in patients investigated for long histories (often 2 years or more) of drug-resistant epilepsy. They are generally slowly growing, low grade, cortically based tumors, more often arising in younger age groups and in many cases exhibit neuronal in addition to glial differentiation. Gangliogliomas and dysembryoplastic neuroepithelial tumors predominate in this group. LEATs are further united by cyto-architectural changes that may be present in the adjacent cortex which have some similarities to developmental focal cortical dysplasias (FCD); these are now grouped as FCD type IIIb in the updated International League Against Epilepsy (ILAE) classification. In the majority of cases, surgical treatments are beneficial from both perspectives of managing the seizures and the tumor. However, in a minority, seizures may recur, tumors may show regrowth or recurrence, and rarely undergo anaplastic progression. Predicting and identifying tumors likely to behave less favorably are key objectives of the neuropathologist. With immunohistochemistry and modern molecular pathology, it is becoming increasingly possible to refine diagnostic groups. Despite this, some LEATs remain difficult to classify, particularly tumors with "non-specific" or diffuse growth patterns. Modification of LEAT classification is inevitable with the goal of unifying terminological criteria applied between centers for accurate clinico-pathological-molecular correlative data to emerge. Finally, establishing the epileptogenic components of LEAT, either within the lesion or perilesional cortex, will elucidate the cellular mechanisms of epileptogenesis, which in turn will guide optimal surgical management of these lesions.

GABA-A channel subunit expression in human glioma correlates with tumor histology and clinical outcome

GABA (γ-aminobutyric acid) is the main inhibitory neurotransmitter in the CNS and is present in high concentrations in presynaptic terminals of neuronal cells. More recently, GABA has been ascribed a more widespread role in the control of cell proliferation during development where low concentrations of extrasynaptic GABA induce a tonic activation of GABA receptors. The GABA-A receptor consists of a ligand-gated chloride channel, formed by five subunits that are selected from 19 different subunit isoforms. The functional and pharmacological properties of the GABA-A channels are dictated by their subunit composition. Here we used qRT-PCR to compare mRNA levels of all 19 GABA-A channel subunits in samples of human glioma (n = 29) and peri-tumoral tissue (n = 5). All subunits except the ρ1 and ρ3 subunit were consistently detected. Lowest mRNA levels were found in glioblastoma compared to gliomas of lower malignancy, except for the θ subunit. The expression and cellular distribution of the α1, γ1, ρ2 and θ subunit proteins was investigated by immunohistochemistry on tissue microarrays containing 87 gliomas grade II. We found a strong co-expression of ρ2 and θ subunits in both astrocytomas (r = 0.86, p<0.0001) and oligodendroglial tumors (r = 0.66, p<0.0001). Kaplan-Meier analysis and Cox proportional hazards modeling to estimate the impact of GABA-A channel subunit expression on survival identified the ρ2 subunit (p = 0.043) but not the θ subunit (p = 0.64) as an independent predictor of improved survival in astrocytomas, together with established prognostic factors. Our data give support for the presence of distinct GABA-A channel subtypes in gliomas and provide the first link between specific composition of the A-channel and patient survival.

Localization of mGluR5, GABAB, GABAA, and cannabinoid receptors on the vago-vagal reflex pathway responsible for transient lower esophageal sphincter relaxation in humans: an immunohistochemical study

BACKGROUND

  Transient lower esophageal sphincter relaxations (TLESRs) are the predominant mechanisms underlying gastro-esophageal reflux. TLESRs are mediated by a vago-vagal reflex, which can be blocked by interaction with metabotropic Glutamate Receptor 5 (mGluR5), γ-aminobutyric acid type B (GABA(B)), γ-aminobutyric acid type A (GABA(A)), and cannabinoid (CB) receptors. However, the distribution of these receptors in the neural pathway underlying the triggering of TLESRs has not been evaluated in humans.

METHODS

  Using immunohistochemistry, we investigated the distribution of mGluR5, GABA(A), GABA(B), CB1, and CB2 receptors in the human nodose ganglion, the brain stem, and the myenteric plexus of the esophagus.

KEY RESULTS

  MGluR5, GABA(B), CB1, and CB2 receptors are abundantly expressed in neurons of the myenteric plexus of the LES, nodose ganglion cell bodies and nerve fibers, the dorsal motor nucleus, and nucleus of the solitary tract in the brain stem. GABA(A) receptors are expressed in the same regions except in the nodose ganglion and myenteric plexus of the LES.

CONCLUSIONS & INFERENCES

  Human mGluR5, GABA(A,B), and CB(1,2) receptors are abundantly expressed along the vago-vagal neural pathway and involved in the triggering of TLESRs. These findings are not only in line with the central side effects observed during treatment with reflux inhibitors such as GABA(B) receptor agonists and mGluR5 antagonists, but also suggest that peripherally acting compounds may be effective.

Epilepsy in patients with a brain tumour: focal epilepsy requires focused treatment

Brain tumours frequently cause epileptic seizures. Medical antiepileptic treatment is often met with limited success. Pharmacoresistance, drug interactions and adverse events are common problems during treatment with antiepileptic drugs. The unpredictability of epileptic seizures and the treatment-related problems deeply affect the quality of life of patients with a brain tumour. In this review, we focus on both clinical and basic aspects of possible mechanisms in epileptogenesis in patients with a brain tumour. We provide an overview of the factors that are involved in epileptogenesis, starting focally at the tumour and the peritumoral tissue and eventually extending to alterations in functional connectivity throughout the brain. We correlate this knowledge to the known mechanisms of antiepileptic drugs. We conclude that the underlying mechanisms of epileptogenesis in patients with a brain tumour are poorly understood. The currently available antiepileptic drugs have little to no influence on the known epileptogenic mechanisms that could contribute to the poor efficacy. Better understanding of focal changes that are involved in epileptogenesis may provide new tools for optimal treatment of both the seizures and the underlying tumour. In our opinion, therapy for every patient with a brain tumour suffering from epilepsy should first and foremost aim at eliminating the tumour as well as the epileptic focus through resection combined with postoperative treatment, and only if this strategy does not result in adequate seizure control should medical antiepileptic treatment be intensified. If this strategy, however, results in sustained seizure freedom, tapering of antiepileptic drugs should be considered in the long term.

Surgical management of glioneuronal tumors with drug-resistant epilepsy

In this review, we discuss the options for the surgical management of glioneuronal tumors (GNTs) associated with drug-resistant epilepsy, with an emphasis on the surgical issues involved in addressing the epileptogenic nature of these lesions. We briefly summarize the pathological hallmarks of these lesions in order to outline how these tumors contribute to seizure activity. Understanding the pathophysiology of these lesions is important in discussing the advantages and disadvantages of different surgical strategies. There have been a number of studies that have investigated the utility of different surgical approaches in improving seizure outcome, and we highlight some of these studies in order to shed light on surgical issues related to these tumors.

Focal epilepsy associated with glioneuronal tumors

Glioneuronal tumors are an increasingly recognized cause of partial seizures that occur primarily in children and young adults. Focal epilepsy associated with glioneuronal tumors is often resistant to pharmacological treatment. The cellular mechanisms underlying the epileptogenicity of glioneuronal tumors remain largely unknown. The involved mechanisms are certain to be multifactorial and depend on specific tumor histology, integrity of the blood-brain barrier, characteristics of the peritumoral environment, circuit abnormalities, or cellular and molecular defects. Glioneuronal tumors presenting with epilepsy were observed to have relatively benign biological behavior. The completeness of the tumor resection is of paramount importance in avoiding tumor progression and malignant transformation, which are rare in cases of epileptogenic glioneuronal tumors. An evolving understanding of the various mechanisms of tumor-related epileptogenicity may also lead to a more defined surgical objective and effective therapeutic strategies, including antiepileptogenic treatments, to prevent epilepsy in at-risk patients.

Targets for preventing epilepsy following cortical injury

Prophylaxis of posttraumatic epilepsy will require a detailed knowledge of the epileptogenic pathophysiological processes that follow brain injury. Results from studies of experimental models and human epilepsy highlight alterations in GABAergic interneurons and formation of excessive new excitatory synaptic connectivity as prominent targets for prophylactic therapies. Promising laboratory results suggest that it will be possible to experimentally modify these aberrant processes and interfere with epileptogenesis. However, a number of key issues must be addressed before these results can be used to frame clinical antiepileptogenic therapy.

Early surgical intervention in adult patients with ganglioglioma is associated with improved clinical seizure outcomes

Gangliogliomas are rare central nervous system tumors, most commonly affecting children and young adults. Chronic seizure and epilepsy are the most frequent presentation of patients with gangliogliomas. In this report, we review the modern literature regarding the effects of early surgical intervention on the clinical outcome of patients with ganglioglioma. A boolean search of PubMed using key words "ganglioglioma", "adult", "seizure control", "treatment", "surgical intervention", and "observation", alone and in combination was performed. The inclusion criteria for articles were that: (i) clinical outcomes were reported specifically for gangliogliomas; (ii) data were reported for adult patients older than the age of 18 years; (iii) treatment data were included for the treatment of gangliogliomas; and (iv) ganglioglioma was the only pathological diagnosis for the evaluation of the tumor. Data were analyzed as a whole then stratified into two groups: early and late treatment intervention. The query identified a total of 99 articles including 1,089 cases of ganglioglioma meeting our inclusion and exclusion criteria. There was a 55% prevalence of males, representing a statistically significant predilection (51-59%, 95% confidence interval). Seizure control was significantly improved when surgical intervention occurred less than 3 years after symptom onset (78% versus 48%; p = 0.0001). Ganglioglioma in adults represents a rare group of tumors, and our systematic analysis suggests a higher prevalence in males. Our findings also support that an early surgical intervention is significantly associated with improved clinical seizure control.

Pediatric epileptogenic gangliogliomas: seizure outcome and surgical results

OBJECT

Ganglioglioma is the most common neoplasm causing focal epilepsy, accounting for approximately 40% of all epileptogenic tumors and for 1-4% of all pediatric CNS tumors. The optimal surgical treatment for pediatric epileptogenic ganglioglioma has not been fully established. The authors present their experience in the surgical management of these lesions.

METHODS

The authors retrospectively analyzed seizure outcome and surgical results of pediatric patients with ganglioglioma treated with resection. The patients' charts were reviewed for demographic data, clinical presentation, surgical therapy, and follow-up.

RESULTS

The 30 patients (17 boys, 13 girls) had a history of medically intractable epilepsy. Total resection of tumor was achieved with or without adjacent epileptogenic tissue resection in all patients except 1, who underwent cyst fenestration and biopsy. Intraoperative electrocorticography (ECoG) was used in 21 patients. If an active spike focus or profound attenuation was observed in adjacent tissues, resection of those tissues was performed in addition to complete tumor resection (lesionectomy). The interval between onset of seizures and surgery ranged from 1 month to 9 years (mean 1.6 years). Patient age at the time of surgery ranged from 9 months to 16.3 years (mean 8.6 years). Twenty-five patients (83.3%) had complex partial seizures and 5 (16.7%) had simple partial seizures. Eighteen tumors (60%) were temporal (14 temporomesial, 4 temporolateral), and 12 (40%) were extratemporal. The mean follow-up period was 3.4 years (range 1 month-8.16 years). In 2 cases (6.7%), tumor recurrence was observed. Outcome was Engel Class I in 27 cases (90.0%; 14 temporomesial, 4 temporolateral, 9 extratemporal) and Engel Class II in 3 (10.0%; all extratemporal). Tumor resection allowed good seizure control, especially in the 18 cases of temporal ganglioglioma (all Engel Class I postoperatively). Eleven patients underwent removal of extratumoral epileptogenic tissue (anterior temporal neocortex resection in 10, anterior temporal neocortex resection with anterior hippocampectomy in 1) in addition to lesionectomy using intraoperative ECoG.

CONCLUSIONS

Lesionectomy with adjacent temporal neocortex resection using intraoperative ECoG provided good seizure control of pediatric temporal ganglioglioma. For extratemporal ganglioglioma, lesionectomy alone can provide fairly good seizure control. Considering the memory function of the hippocampus, lesionectomy with adjacent temporal neocortical resection can be a safe, feasible, and effective treatment option for epileptogenic gangliogliomas in pediatric patients.

Seizure outcome of epilepsy surgery in focal epilepsies associated with temporomesial glioneuronal tumors: lesionectomy compared with tailored resection

OBJECT

The authors retrospectively analyzed and compared seizure outcome in a series of 28 patients with temporomesial glioneuronal tumors associated with epilepsy who underwent 1 of 2 different epilepsy surgery procedures: lesionectomy or tailored resection.

METHODS

The 28 patients were divided into 2 groups, with 14 cases in each group. In Group A, surgery was limited to the tumor (lesionectomy), whereas Group B patients underwent tailored resection involving removal of the tumor and the epileptogenic zone as identified by a neurophysiological noninvasive presurgical study.

RESULTS

In Group A (10 male and 4 female patients) the interval between onset of seizures and surgery ranged from 1 to 33 years (mean 10.6 years). Patients' ages ranged from 3 to 61 years (mean 23.1 years). The epileptogenic lesion was on the left side in 6 patients and the right in 8 patients. Mean follow-up was 9.8 years (range 6.5-15 years). The Engel classification system, used to determine postoperative seizure outcome, showed 6 patients (42.8%) were Engel Class I and 8 (57.1%) were Engel Class II. In Group B (6 male and 8 female patients) the interval between onset of seizures and surgery ranged from 0.5 to 25 years (mean 8.6 years). Patients' ages ranged from 3 to 48 years (mean 22.3 years). The tumor and associated epileptogenic area was on the right side in 8 patients and the left in 6 patients. Mean follow-up duration was 3.5 years (range 1-6.5 years). Postoperative seizure outcome was Engel Class I in 13 patients (93%) and Engel Class II in 1 (7.1%).

CONCLUSIONS

The authors' results demonstrate a better seizure outcome for temporomesial glioneuronal tumors associated with epilepsy in patients who underwent tailored resection rather than simple lesionectomy (p = 0.005). For temporomesial glioneuronal tumors associated with epilepsy, performing a presurgical noninvasive neurophysiological study intended to identify the epileptogenic zone is necessary for planning a tailored surgery. Using this surgical strategy, the presence of temporomesial glioneuronal tumors constitutes a predictive factor of excellent seizure outcome, and therefore surgical treatment can be offered early to avoid both the consequences of uncontrolled seizures as well as the side effects of pharmacological therapy.

Expression of synaptic vesicle protein 2A in epilepsy-associated brain tumors and in the peritumoral cortex

Synaptic vesicle protein 2A (SV2A) has been identified as the binding site for the antiepileptic drug levetiracetam and is thought to decrease neuronal excitability. Since knockout of SV2A in mice leads to seizures, we hypothesized that a reduction in SV2A expression promotes seizure generation in epilepsy-associated brain tumors. We compared the SV2A expression and distribution in surgically removed tumor tissue (n = 63) and peritumoral cortex (n = 31) of patients with glial and glioneuronal tumors to normal control cortex obtained at autopsy in nonbrain tumor patients (n = 6). Additionally, we compared the SV2A expression and distribution in tumor patients with epilepsy (n = 39) with SV2A expression in tumor patients without epilepsy (n = 24). Immunohistochemistry in control cortex demonstrated strong and diffuse SV2A immunoreactivity (IR) throughout all cortical layers. Similar strong SV2A IR (with the same diffuse distribution pattern) was observed in the peritumoral cortical specimens in both patients with and without epilepsy. Modest SV2A IR was observed within the tumor area. The SV2A-positive cells detected within the tumor area were mainly entrapped neurons. Oligodendrogliomas and glioneuronal tumors displayed variable SV2A neuropil staining. In ganglioglioma (GG), strong SV2A IR was present along the dysplastic neuronal cell borders and processes. In both GG and dysembryoplastic neuroepithelial tumors, SV2A IR was occasionally observed within the neuronal perikarya. We found no differences in SV2A expression in the peritumoral cortex between the patients with and without epilepsy, which suggests that the role of SV2A in epileptogenesis in patients with glial tumors is questionable. The distinct pattern of SV2A IR in glioneuronal tumors suggests a redistribution of SV2A.

Calretinin immunoreactivity in focal cortical dysplasias and in non-malformed epileptic cortex

Focal cortical dysplasias (FCDs) represent a prominent cause of pharmacologically intractable epilepsy. In FCD, the decrease of parvalbumin immunoreactive (PV+) inhibitory interneurons has been repeatedly documented. Here, we wanted to show whether another interneuronal population, the calretinin immunoreactive (CR+) neurons, exhibits any change in human FCD. We also investigated samples of morphologically normal temporal neocortex resected together with sclerotic hippocampus (nHSTN), where decrease of PV+ interneurons was previously documented as well. Brain tissue from 24 patients surgically treated for pharmacoresistant epilepsy was examined. Calretinin immunoreactivity was qualitatively evaluated and the density of CR+ neuronal profiles was quantified. As a control, post-mortem acquired neocortical samples of nine patients without any brain affecting disease were used. CR+ neurons were located predominantly in superficial cortical layers both in controls and pathological samples. Similarly, the morphology of CR+ neurons was unaffected in pathological samples. The overall density of CR+ neurons was significantly decreased in FCD type I (to approximately 70% of control values) and even more in FCD type II (to approximately 50% of controls). In nHSTN, no change compared to controls was found in CR+ neuronal density. Our results may contribute to the better understanding of the role of individual interneuronal populations in epileptogenesis.

Gene expression analysis of tuberous sclerosis complex cortical tubers reveals increased expression of adhesion and inflammatory factors

Cortical tubers in patients with tuberous sclerosis complex are associated with disabling neurological manifestations, including intractable epilepsy. While these malformations are believed to result from the effects of TSC1 or TSC2 gene mutations, the molecular mechanisms leading to tuber formation, as well as the onset of seizures, remain largely unknown. We used the Affymetrix Gene Chip platform to provide the first genome-wide investigation of gene expression in surgically resected tubers, compared with histological normal perituberal tissue from the same patients or autopsy control tissue. We identified 2501 differentially expressed genes in cortical tubers compared with autopsy controls. Expression of genes associated with cell adhesion, for example, VCAM1, integrins and CD44, or with the inflammatory response, including complement factors, serpinA3, CCL2 and several cytokines, was increased in cortical tubers, whereas genes related to synaptic transmission, for example, the glial glutamate transporter GLT-1, and voltage-gated channel activity, exhibited lower expression. Gene expression in perituberal cortex was distinct from autopsy control cortex suggesting that even in the absence of tissue pathology the transcriptome is altered in TSC. Changes in gene expression yield insights into new candidate genes that may contribute to tuber formation or seizure onset, representing new targets for potential therapeutic development.

Local and remote epileptogenicity in focal cortical dysplasias and neurodevelopmental tumours

During the pre-surgical evaluation of drug-resistant epilepsy, the assessment of the extent of the epileptogenic zone and its organization is a crucial objective. Indeed, the epileptogenic zone may be organized as a simple focal lesional site or as a more complex network (often referred to as the 'epileptogenic network') extending beyond the lesion. This distinction is particularly relevant in developmental lesions such as focal cortical dysplasias or dysembryoplastic neuroepithelial tumours and may determine both the surgical strategy and the prognosis. In this study, we have quantified the epileptogenic characteristic of brain structures explored by depth electrodes in 36 patients investigated by stereoelectroencephalography and suffering from focal drug-resistant epilepsy associated with focal cortical dysplasias or dysembryoplastic neuroepithelial tumours. This quantification was performed using the 'Epileptogenicity Index' method that accounts for both the propensity of a brain area to generate rapid discharges and the time for this area to get involved in the seizure. Epileptogenicity Index values range from 0 (no epileptogenicity) to 1 (maximal epileptogenicity). We determined Epileptogenicity Index from signals recorded in distinct brain structures including the lesional site. We studied the type of epileptogenic zone organization (focal versus network) and looked for a correlation with clinical data and post-surgical outcome. Mean Epileptogenicity Index in lesional regions was 0.87 (+/-0.25), and 0.29 (+/-0.30) in 'non-lesional' structures. The number of highly epileptogenic structures (defined by Epileptogenicity Index value >or=0.4) was 3.14 (+/-1.87) in the whole population. We found that 31% of patients had only one epileptogenic structure (N(EI>or=0.4) = 1), therefore disclosing a strictly focal epileptogenic zone organization while 25 patients had more than one epileptogenic region, disclosing a network (61%) or bilateral (8%) epileptogenic zone organization. We observed a trend for a difference in seizure outcome according to the type of epileptogenic zone organization. Indeed, 57% of patients with network organization and 87% with focal organization were seizure-free while none of those with bilateral organization became seizure-free. The determination of Epileptogenicity Index computed from electrophysiological signals recorded according to the stereoelectroencephalography technique is a novel tool. Results suggest that it can help in the delineation of the epileptogenic zone associated with brain lesions and that it could be used in the definition of the subsequent surgical resection.

GABA's control of stem and cancer cell proliferation in adult neural and peripheral niches

Aside from traditional neurotransmission and regulation of secretion, gamma-amino butyric acid (GABA) through GABA(A) receptors negatively regulates proliferation of pluripotent and neural stem cells in embryonic and adult tissue. There has also been evidence that GABAergic signaling and its control over proliferation is not only limited to the nervous system, but is widespread through peripheral organs containing adult stem cells. GABA has emerged as a tumor signaling molecule in the periphery that controls the proliferation of tumor cells and perhaps tumor stem cells. Here, we will discuss GABA's presence as a near-universal signal that may be altered in tumor cells resulting in modified mitotic activity.

Neuropathology of focal epilepsies: a critical review

A broad spectrum of structural lesions can be histopathologically identified in surgical brain specimens obtained from patients with focal, therapy-refractory epilepsies. In our experience with 4512 tissue samples collected at the German Neuropathological Reference Center for Epilepsy Surgery, three clinicopathological entities are most common: mesial temporal sclerosis (40%), long-term epilepsy-associated tumors (27%), and malformations of cortical development (13%). Notwithstanding, a systematic histopathological and molecular-genetic analysis is mandatory to unravel the underlying pathogenic mechanism of epilepsy-associated lesions and may contribute to our current understanding of pharmacoresistance and epileptogenesis. However, an interdisciplinary approach is necessary to further explore predictive parameters with respect to postsurgical seizure relief and memory impairment, and also to identify new pharmacological targets.

Expression patterns of synaptic vesicle protein 2A in focal cortical dysplasia and TSC-cortical tubers

PURPOSE

Synaptic vesicle protein 2A (SV2A), the binding site for the antiepileptic drug (AED) levetiracetam, has been shown to be involved in the control of neuronal excitability. The aim of the study was to define the expression and cell-specific distribution of SV2A in developmental focal lesions associated with medically intractable epilepsy.

METHODS

SV2A immunocytochemistry and Western blotting was performed in focal cortical dysplasia (FCD type IIB) and cortical tubers from patients with tuberous sclerosis complex (TSC).

RESULTS

Autopsy and surgical control neocortical specimens were characterized by strong SV2A immunoreactivity throughout all cortical layers, with punctate labeling around the somata and dendrites of neurons. In FCD and cortical tuber specimens less intense, SV2A immunoreactivity was observed in the neuropil. The reduction in expression was confirmed by Western blot analysis. In both FCD and tuber specimens, clusters of punctate labeling were detected along cell borders and processes (perisomatic synapses) of dysplastic neuronal cells localized in both gray and white matter. The large majority of balloon cells in FCD, or giant cells in tubers, did not show punctate labeling around their somata. SV2A immunoreactivity was observed occasionally within the neuronal perikarya.

CONCLUSIONS

The pattern of SV2A immunoreactivity with reduced neuropil expression and altered cellular and subcellular distribution suggests a possible contribution of SV2A to the epileptogenicity of these malformations of cortical development. Knowledge of the expression pattern of SV2A in epilepsy-associated pathologies may be valuable for the evaluation of the effectiveness of AEDs targeting this protein.

Factors contributing to resectability and seizure outcomes in 44 patients with ganglioglioma

OBJECTIVES

The purpose of this retrospective study was to evaluate causes contributing to surgical resectability and seizure outcomes depending on various clinical and surgical factors.

PATIENTS AND METHODS

The records of 44 patients with gangliogliomas surgically treated between April 1986 and March 2007, were retrospectively reviewed to assess presenting symptoms, resectability and seizure outcomes.

RESULTS

Tumors were located in the supratentorial areas in 33 cases, the infratentorial area in 9 cases and the spinal cord in 2 cases. Thirty-five cases underwent gross total removal and 9 cases underwent subtotal resection. Only 2 cases underwent postoperative radiotherapy and 2 cases underwent gamma knife surgery. Twenty-six patients presented seizure symptoms of which 22 cases were located in temporal lobe and 4 cases were located in the extratemporal lobe. Twenty-three patients (88.5%) were seizure-free after surgery. Two patients were Engel class II and another was Engel class III.

CONCLUSION

We concluded that tumor location and seizure-presenting symptoms are good predictors of gross total removal. Gross total removal of ganglioglioma had a better chance of leaving the patient seizure free after surgery rather incomplete resection. Our data do not support the concept that surgical methods, invasive monitoring and surrounding cortical malformation correlated with seizure-free outcome.

Gene expression profile analysis of epilepsy-associated gangliogliomas

Gangliogliomas (GG) constitute the most frequent tumor entity in young patients undergoing surgery for intractable epilepsy. The histological composition of GG, with the presence of dysplastic neurons, corroborates their maldevelopmental origin. However, their histogenesis, the pathogenetic relationship with other developmental lesions, and the molecular alterations underlying the epileptogenicity of these tumors remain largely unknown. We performed gene expression analysis using the Affymetrix Gene Chip System (U133 plus 2.0 array). We used GENMAPP and the Gene Ontology database to identify global trends in gene expression data. Our analysis has identified various interesting genes and processes that are differentially expressed in GG when compared with normal tissue. The immune and inflammatory responses were the most prominent processes expressed in GG. Several genes involved in the complement pathway displayed a high level of expression compared with control expression levels. Higher expression was also observed for genes involved in cell adhesion, extracellular matrix and proliferation processes. We observed differential expression of genes as cyclin D1 and cyclin-dependent kinases, essential for neuronal cell cycle regulation and differentiation. Synaptic transmission, including GABA receptor signaling was an under-expressed process compared with control tissue. These data provide some suggestions for the molecular pathogenesis of GG. Furthermore, they indicate possible targets that may be investigated in order to dissect the mechanisms of epileptogenesis and possibly counteract the epileptogenic process in these developmental lesions.

Mechanisms of epileptogenesis in tuberous sclerosis complex and related malformations of cortical development with abnormal glioneuronal proliferation

Malformations of cortical development (MCDs) are increasingly recognized as causes of medically intractable epilepsy. In order to develop more effective, rational therapies for refractory epilepsy related to MCDs, it is important to achieve a better understanding of the underlying mechanisms of epileptogenesis, but this is complicated by the wide variety of different radiographic, histopathological, and molecular features of these disorders. A subset of MCDs share a number of characteristic cellular and molecular abnormalities due to early defects in neuronal and glial proliferation and differentiation and have a particularly high incidence of epilepsy, suggesting that this category of MCDs with abnormal glioneuronal proliferation may also share a common set of primary mechanisms of epileptogenesis. This review critically analyzes both clinical and basic science evidence for overlapping mechanisms of epileptogenesis in this group of disorders, focusing on tuberous sclerosis complex, focal cortical dysplasia with balloon cells, and gangliogliomas. Specifically, the role of lesional versus perilesional regions, circuit versus cellular/molecular defects, and nonneuronal factors, such as astrocytes, in contributing to epileptogenesis in these MCDs is examined. An improved understanding of these various factors involved in epileptogenesis has direct clinical implications for optimizing current treatments or developing novel therapeutic approaches for epilepsy in these disorders.