Multimodal imaging reveals the role of γ activity in eating-reflex seizures

[Insular lobe epilepsy. Part 1: semiology]

The insula is often referred to as "the fifth lobe" of the brain, and its accessibility used to be very limited due to the deep location under the opercula as well as the sylvian vasculature. It was not until the availability of modern stereo-electroencephalography (SEEG) technique that the intracranial electrodes could be safely and chronically implanted within the insula, thereby enabling anatomo-electro-clinical correlations in seizures of this deep origin. Since the first report of SEEG-recorded insular seizures in late 1990s, the knowledge of insular lobe epilepsy (ILE) has rapidly expanded. Being on the frontline for the diagnosis and management of epilepsy, neurologists should have a precise understanding of ILE to differentiate it from epilepsies of other lobes or non-epileptic conditions. Owing to the multimodal nature and rich anatomo-functional connections of the insula, ILE has a wide range of clinical presentations. The following symptoms should heighten the suspicion of ILE: somatosensory symptoms involving a large/bilateral cutaneous territory or taking on thermal/painful character, and cervico-laryngeal discomfort. The latter ranges from slight dyspnea to a strong sensation of strangulation (laryngeal constriction). Other symptoms include epigastric discomfort/nausea, hypersalivation, auditory, vestibular, gustatory, and aphasic symptoms. However, most of these insulo-opercular symptoms can easily be masked by those of extra-insular seizure propagation. Indeed, sleep-related hyperkinetic (hypermotor) epilepsy (SHE) is a common clinical presentation of ILE, which shows predominant hyperkinetic and/or tonic-dystonic features that are often indistinguishable from those of fronto-mesial seizures. Subtle objective signs, such as constrictive throat noise (i.e., laryngeal constriction) or aversive behavior (e.g., facial grimacing suggesting pain), are often the sole clue in diagnosing insular SHE. Insular-origin seizures should also be considered in temporal-like seizures without frank anatomo-electro-clinical correlations. All in all, ILE is not the epilepsy of an isolated island but rather of a crucial hub involved in the multifaceted roles of the brain.

Symptomatic eating epilepsy: two novel pediatric patients and review of literature

Eating epilepsy (EE) is a form of reflex epilepsy in which seizures are triggered by eating. It is a rare condition but a high prevalence has been reported in Sri Lanka. In EE, the ictal semiology includes focal seizures with or without secondary generalization or generalized seizures. Some cases are idiopathic while focal structural changes on imaging, if present, are often confined to the temporal lobe or perisylvian region. On the other hand, some cases support the hypothesis of a genetic aetiology. The prognosis of EE is extremely variable due to the different nature of the underlying disorder. We describe two patients with symptomatic eating epilepsy, a 13-year-old boy with a bilateral perisylvian polymicrogyria and a 2-year-old boy with a genetic cause. The presence of structural lesions or the dysfunction of specific cortical regions in the context of a germline genetic alteration might lead to a hyperexcitation fostering the epileptogenesis. We review the available literature to clarify the aetiopathogenesis and the mechanisms underlying EE to improve the diagnosis and the management of these rare conditions.

Insular seizures and epilepsies: Ictal semiology and minimal invasive surgery

PURPOSE OF REVIEW

The increased identification of seizures with insular ictal onset, promoted by the international development of stereo-electroencephalography (SEEG), has led to the recent description of larger cohorts of patients with insular or insulo-opercular epilepsies than those previously available. These new series have consolidated and extended our knowledge of the rich ictal semiology and diverse anatomo-clinical correlations that characterized insular seizures. In parallel, some experiences have been gained in the surgical treatment of insular epilepsies using minimal invasive procedures.

RECENT FINDINGS

The large majority of patients present with auras (mostly somatosensory and laryngeal) and motor signs (predominantly elementary and orofacial), an underlying focal cortical dysplasia, and an excellent postoperative seizure outcome. Many other subjective and objective ictal signs, known to occur in other forms of epilepsies, are also observed and clustered in five patterns, reflecting the functional anatomy of the insula and its overlying opercula, as well as preferential propagation pathways to frontal or temporal brain regions. A nocturnal predominance of seizure is frequently reported, whereas secondary generalization is infrequent. Some rare ictal signs are highly suggestive of an insular origin, including somatic pain, reflex seizures, choking spells, and vomiting. Minimal invasive surgical techniques have been applied to the treatment of insular epilepsies, including Magnetic Resonance Imaging-guided laser ablation (laser interstitial thermal therapy (LITT)), radiofrequency thermocoagulation (RFTC), gamma knife radiosurgery, and responsive neurostimulation. Rates of seizure freedom (about 50%) appear lower than that reported with open-surgery (about 80%) with yet a significant proportion of transient neurological deficit for LITT and RFTC.

SUMMARY

Significant progress has been made in the identification and surgical treatment of insular and insulo-opercular epilepsies, including more precise anatomo-clinical correlations to optimally plan SEEG investigations, and experience in using minimal invasive surgery to reduce peri-operative morbidity.

Eight years follow-up of a generalized epilepsy patient with eating-induced late-onset epileptic spasms and atypical absence with myoclonic jerks

PURPOSE

Eating epilepsy was previously known as a kind of focal reflex epilepsy. However, the development of eating-induced multiple generalized seizures and the associated EEG changes were rarely reported. Herein, we present a 13-year-old generalized epilepsy patient with eating-induced generalized seizures since the age of 5.

CASE PRESENTATION

The 13-year-old male patient had suffered from late-onset eating-induced epileptic spasms during the meal since the age of 5. Meanwhile, he also experienced spontaneous epileptic spasms during the period of sleep. The seizure frequency and type gradually increased from 7 years of age. In addition to epileptic spasms, he started experiencing atypical absence with myoclonic jerks during the meal. Ictal EEG presented as the appearance of an irregular slow-wave mixed with generalized polyspike wave with the intake of food, and gradually evolved to bursts of generalized polyspike wave complexes. At the end of the meal, the EEG returned to normal. Nevertheless, at the age of 13, his seizure frequency increased and appeared new seizure type, and besides epileptic spasm and atypical absence, he began to experience myoclonic seizure during sleep and awaking-generalized tonic-clonic seizure in the morning. In this period he started taking valproic acid, topiramate and clonazepam, and his seizure frequency was reduced.

CONCLUSION

In conclusion, this case demonstrated the variability of eating induced multiple generalized seizure types, and eight years follow-up also indicates that generalized epilepsy progressed with age. The EEG and clinical changes of our patient contribute to a better understanding of the electro-clinical features of eating-induced multiple generalized seizures and the course of generalized epilepsy with such seizures.

Insular epilepsy, an under-recognized seizure semiology. A review for general neurologist

Understanding seizure semiology is one of the most important and crucial steps in diagnosing a seizure disorder. Insular epilepsy may mimic other focal seizure semiologies, leading to misdiagnosis and failed epilepsy surgery. Insular seizures may begin as brief ictal symptoms, such as laryngeal discomfort and unpleasant throat sensations, and spread rapidly to the temporal or frontal regions, causing prominent ictal symptoms different to the initial insular ictal manifestation. Moreover, insular seizures are associated with complex epileptogenic networks and multiple connections. For this reason, accurate seizure semiology helps to lateralize and localize the seizure onset. The insular cortex is deep, and thus scalp electroencephalography is not always beneficial as the epileptic discharges will not be easily recorded, or they will be seen over other cortical regions like the temporal or frontal areas. Insular surgical resection is generally safe, but it requires extensive presurgical workup and surgical precautions in order to minimize mortality.

Seizures triggered by eating - A rare form of reflex epilepsy: A systematic review

Eating epilepsy is a rare disorder, characterised by reflex seizures induced by food intake. It is highly heterogenous, with clinical signs and EEG findings varying between patients. However, common features do emerge from the reported literature. The aim of this systematic review was to bring together this information to facilitate understanding and recognition. We therefore searched electronic databases (PubMed, Scopus, Medline) for relevant studies using keywords 'epilepsy', 'seizure' and 'eating' in March 2020. Human studies, written in English, that reported on cohorts of patients with eating epilepsy were included. Fifty-two unique papers were consequently identified, describing seizure characteristics and diagnostic features in 378 patients. Eating seizures began in the second decade of life, with a higher incidence in males. They were typically focal-onset, and most commonly of the focal impaired awareness type. Pharmacological therapy with one or multiple agents was noted in 80 % of cases, with poor control reported in approximately 25 % of patients. While this retrospective work highlights key features, it is important that future studies implicate video EEG to fully evaluate this highly unique and interesting disorder.

Non-lesional eating epilepsy with temporo-insular onset: A stereo-EEG study

Eating Epilepsy (EE) is a rare and often under-recognized form of reflex epilepsy, which manifests with seizures triggered during meals, with or without spontaneous seizures. The electro-clinical manifestations of EE are distinct with variable response to antiseizure drugs. We report the case of a 34-year-old man who was seen for a 4-year history of drug-resistant focal impaired awareness seizures associated with eating without a structural cause. Scalp video-EEG delineated a right temporal seizure focus with atypical features. Subsequent stereo-EEG revealed synchronized seizure onset from the right mesial temporal region and the right inferior insula. Resective surgery of the involved areas rendered this patient seizure-free with 3 years' follow-up. In non-lesional cases of drug-resistant EE, the epileptogenic zone can be large and deep, and therefore stereo-EEG was helpful in determining the seizure onset zone.

Epileptogenicity Mapping: A Quantitative Approach to Identify the Seizure Onset

During the presurgical evaluation of patients with focal refractory epilepsies, the spatial mapping of the seizure onset zone (SOZ) and seizure propagation networks critically depends on the use of different features extracted from the intracranial electroencephalogram (IEEG). The identification of the SOZ is usually based on visual inspection by highly qualified neurophysiologists. However, quantitative IEEG analyses have recently been developed by exploiting signal and image characteristics in order to improve and expedite the SOZ detection. Here, the authors briefly review some of the latest methods proposed by different research groups and then present the recent implementation in Brainstorm software.

Epileptogenicity Maps of Intracerebral Fast Activities (60-100 Hz) at Seizure Onset in Epilepsy Surgery Candidates

Fast activities (FA) at seizure onset have been increasingly described as a useful signature of the epileptogenic zone (EZ) in patients undergoing intracranial EEG recordings. Different computer-based signal analysis methods have thus been developed for objectively quantifying ictal FA. Whether these methods detect FA in all forms of focal epilepsies, whether they provide similar information than visual analysis (VA), and whether they might help for the surgical decision remain crucial issues. We thus conducted a retrospective study in 21 consecutive patients suffering from drug-resistant seizures studied by SEEG recordings. Ictal FA were quantified using the Epileptogenicity Maps (EM) method that we recently developed and which generates, by adopting a neuroimaging approach, statistical parametric maps of FA ranging from 60 to 100 Hz (FA⁶⁰⁻¹⁰⁰). Ictal FA were analyzed blindly using VA and EM, and the prognostic significance of removing areas exhibiting FA⁶⁰⁻¹⁰⁰ at seizure onset was evaluated. A significant ictal FA⁶⁰⁻¹⁰⁰ activation was found in all patients, and in 92.6% of all the 68 seizures recorded, whatever the epilepsy type. The overlap ratio (OR) between VA and EM was significantly better for defining the regions spared at seizure onset than those from which seizure arose (p < 0.001), especially in temporal or temporal “plus” epilepsies. EM and VA were much more discordant to define the EZ, with a mean number of electrode contacts involved at seizure onset significantly higher with EM than with VA (p = <0.0001). Seizure outcome correlated with the resection ratio for FA⁶⁰⁻¹⁰⁰, which was significantly higher in seizure-free (Engel's class Ia) than in non seizure-free patients (class Ic-IV) (p = 0.048). The quantification of FA at seizure onset can bring information additional to clinical expertise that might contribute to define accurately the cortical region to be resected.

Distinctive epileptogenic networks for parietal operculum seizures

OBJECTIVE

The present study investigated the electroclinical features and epileptogenic networks of parietal operculum seizures (POS) by using stereoelectroencephalography (SEEG) intracerebral recordings.

METHODS

Comprehensive presurgical evaluation data of seven patients with drug-resistant epilepsy with POS were analyzed retrospectively. Stereoelectroencephalography-recorded seizures were processed visually and quantitatively by using epileptogenicity mapping (EM), which has been proposed to ergonomically quantify the epileptogenicity of brain structures with a neuroimaging approach.

RESULTS

Six patients reported initial somatosensory or viscerosensitive symptoms. Ictal clinical signs comprised frequently nocturnal hypermotor seizures and contralateral focal motor seizures, including tonic, tonic-clonic, or dystonic seizures of the face and limbs. Interictal and ictal scalp EEG provided information regarding lateralization in the majority of patients, but the discharges were widely distributed over perisylvian or "rolandic-like" regions and the vertex. Furthermore, two subgroups of epileptogenic network organization were identified within POS by SEEG, visually and quantitatively, using an EM approach: group 1 (mesial frontal/cingulate networks) was observed in three patients who mainly exhibited hypermotor seizures; group 2 (perisylvian networks) was observed in four patients who mainly exhibited contralateral focal motor seizures.

CONCLUSION

This study indicated that POS could be characterized by initial specific somatosensory sensations, followed by either frequently nocturnal hypermotor seizures or contralateral focal motor seizures. The distinctive seizure semiology depended on the organization of two primary epileptogenic networks. This article is part of the Special Issue "Individualized Epilepsy Management: Medicines, Surgery and Beyond.

The Insula and Its Epilepsies

Insular seizures are great mimickers of seizures originating elsewhere in the brain. The insula is a highly connected brain structure. Seizures may only become clinically evident after ictal activity propagates out of the insula with semiology that reflects the propagation pattern. Insular seizures with perisylvian spread, for example, manifest first as throat constriction, followed next by perioral and hemisensory symptoms, and then by unilateral motor symptoms. On the other hand, insular seizures may spread instead to the temporal and frontal lobes and present like seizures originating from these regions. Due to the location of the insula deep in the brain, interictal and ictal scalp electroencephalogram (EEG) changes can be variable and misleading. Magnetic resonance imaging, magnetic resonance spectroscopy, magnetoencephalography, positron emission tomography, and single-photon computed tomography imaging may assist in establishing a diagnosis of insular epilepsy. Intracranial EEG recordings from within the insula, using stereo-EEG or depth electrode techniques, can prove insular seizure origin. Seizure onset, most commonly seen as low-voltage, fast gamma activity, however, can be highly localized and easily missed if the insula is only sparsely sampled. Moreover, seizure spread to the contralateral insula and other brain regions may occur rapidly. Extensive sampling of the insula with multiple electrode trajectories is necessary to avoid these pitfalls. Understanding the functional organization of the insula is helpful when interpreting the semiology produced by insular seizures. Electrical stimulation mapping around the central sulcus of the insula results in paresthesias, while stimulation of the posterior insula typically produces painful sensations. Visceral sensations are the next most common result of insular stimulation. Treatment of insular epilepsy is evolving, but poses challenges. Surgical resections of the insula are effective but risk significant morbidity if not carefully planned. Neurostimulation is an emerging option for treatment, especially for seizures with onset in the posterior insula. The close association of the insula with marked autonomic changes has led to interest in the role of the insula in sudden unexpected death in epilepsy and warrants additional study with larger patient cohorts.

Precipitation and inhibition of seizures in focal epilepsies

INTRODUCTION

There is growing awareness that reflex epileptic seizures offer unique insight into natural seizure generation in humans. In the last years, focus has mostly been on reflex seizures in generalized epilepsies whereas a comprehensive review of their role in focal epilepsies has been missing. Areas covered: This paper reviews reflex seizures strictly in focal epilepsies, not including focal reflex seizures in system epilepsies that also exist. They were categorized according to their triggers which can be sensory or cognitive, simple or complex. Numerous diverse conditions exist some of which are much better investigated than others. They required separate individual literature search in PubMed. Where recent review papers exist, it refers to these, but several conditions have never been reviewed, and here it refer to and discusses original reports. Miscellaneous case reports were only exceptionally included when they contributed aspects otherwise missing. Expert commentary: Research on focal reflex seizures with advanced methods of imaging and neurophysiology to elucidate mechanisms of focal ictogenesis will probably be rapidly increasing and will soon provide much new insight. Sensory and cognitive inhibition, i.e. the counterpart of reflex ictogenesis, is promising but needs more structured and controlled research to establish robust therapeutic approaches.

Correlation of FDG-PET hypometabolism and SEEG epileptogenicity mapping in patients with drug-resistant focal epilepsy

OBJECTIVE

Interictal [18F]fluorodeoxyglucose-positron emission tomography (FDG-PET) is used in the presurgical evaluation of patients with drug-resistant focal epilepsy. We aimed at clarifying its relationships with ictal high-frequency oscillations (iHFOs) shown to be a relevant marker of the seizure-onset zone.

METHODS

We studied the correlation between FDG-PET and epileptogenicity maps in an unselected series of 37 successive patients having been explored with stereo-electroencephalography (SEEG).

RESULTS

At the group level, we found a significant correlation between iHFOs and FDG-PET interictal hypometabolism only in cases of temporal lobe epilepsy. This correlation was found with HFOs, and the same comparison between FDG-PET and ictal SEEG power of lower frequencies during the same epochs did not show the same significance.

SIGNIFICANCE

This finding suggests that interictal FDG-PET and ictal HFOs may share common underlying pathophysiologic mechanisms of ictogenesis in temporal lobe epilepsy, and combining both features may help to identify the seizure-onset zone.

Surgery for Nontumoral Insular Epilepsy Explored by Stereoelectroencephalography

BACKGROUND

Hidden by the perisylvian operculi, insular cortex has long been underexplored in the context of epilepsy surgery. Recent studies advocated stereoelectroencephalography (SEEG) as a reliable tool to explore insular cortex and its involvement in intractable epilepsy and suggested that insular seizures could be an underestimated entity. However, the results of insular resection to treat pharmacoresistant epilepsy are rarely reported.

OBJECTIVE

We report 6 consecutive cases of right insular resection performed based on anatomoelectroclinical correlations provided by SEEG.

METHODS

Six right-handed patients (3 male, 3 female) with drug-resistant epilepsy underwent comprehensive presurgical evaluation. Based on video electroencephalographic recordings, they all underwent SEEG evaluation with bilateral (n = 4) or unilateral right (n = 2) insular depth electrode placement. All patients had both orthogonal and oblique (1 anterior, 1 posterior) insular electrodes (n = 4-6 electrodes). Preoperative magnetic resonance imaging findings were normal in 4 patients, 1 patient had right insular focal cortical dysplasia, and 1 patient had a right opercular postoperative scar (cavernous angioma). All patients underwent right partial insular corticectomy via the subpial transopercular approach.

RESULTS

Intracerebral recordings demonstrated an epileptogenic zone confined to the right insula in all patients. After selective insular resection, 5 of 6 patients were seizure free (Engel class I) with a mean follow-up of 36.2 months (range, 18-68 months). Histological findings revealed focal cortical dysplasia in 5 patients and a gliosis scar in 1 patient. All patients had minor transient neurological deficit (eg, facial paresis, dysarthria).

CONCLUSION

Insular resection based on SEEG findings can be performed safely with a significant chance of seizure freedom.

"Eating" epilepsy revisited- an electro-clinico-radiological study

This study aimed to evaluate the clinical, video electroencephalographic and MRI attributes of patients with eating epilepsy (EE). Consecutive patients who were diagnosed with EE and underwent potential pre-surgical work-up from 2003 to 2012 formed the study cohort. Their electro-clinico-radiological and seizure outcome data were obtained from our prospectively maintained medical records. Out of 7094 patients who underwent evaluation for refractory seizures, 47 patients satisfied the criteria for EE. Twenty-three (48.9%) had exclusive EE; the remainder had a combination of predominantly eating-induced and unprovoked seizures with no differences noted in timing of seizures in relation to meals. Lesional epilepsy was seen in 34% of patients, with posterior cortex (PC; posterior temporo-parieto-occipital) predominance. In MRI negative patients, PC interictal epileptiform discharges were present in 34.4% of patients and multifocal in 20.6% of patients compared to the MRI positive group with 12.5% and 6.5%, respectively (p=0.003). Among 24 patients (51.1%) with co-existent unprovoked seizures, developmental delay and PC ictal onset was more prevalent (p=0.013 and 0.029) as compared to exclusive EE. The seizure frequency and outcome did not significantly differ between patients with or without MRI abnormality. Two patients underwent anterior temporal lobectomy, with persistence of their eating seizures postoperatively. EE is a complex reflex epilepsy of cryptogenic and symptomatic etiology. As opposed to the traditionally implied temporo-limbic mechanisms behind epileptogenesis, a multilobar network originating from the PC receiving sensory and visual inputs linked to the limbic-opercular pathways represents a plausible mechanism. Surgical selection should be diligent and cautious in this group of patients.

Reflex epileptic mechanisms in ictogenesis and therapeutic consequences

Recent studies of reflex epileptic mechanisms in human epilepsy using advanced methods of neurophysiology and functional neuroimaging have contributed much to elucidate pathophysiological processes of seizure generation. Whereas in lesional focal epilepsies reflex mechanisms usually relate directly to the anatomical focus, in system epilepsies they have helped to define which functional anatomical systems serving physiological function are recruited by the ictogenic mechanisms. Reflex epileptic seizures can often be prevented by avoidance or modification of triggers or by prophylactic benzodiazepine administration. Surgical options apply to focal cases. According to restricted experiences with pharmacotherapy, without controlled studies and little information on new AEDs, reflex seizures in system epilepsies appear to respond best to valproic acid and in focal epilepsies, to carbamazepine.

The role of functional neuroimaging in pre-surgical epilepsy evaluation

The prevalence of epilepsy is about 1% and one-third of cases do not respond to medical treatment. In an eligible subset of patients with drug-resistant epilepsy, surgical resection of the epileptogenic zone is the only treatment that can possibly cure the disease. Non-invasive techniques provide information for the localization of the epileptic focus in the majority of cases, whereas in others invasive procedures are required. In the last years, non-invasive neuroimaging techniques, such as simultaneous recording of functional magnetic resonance imaging and electroencephalogram (EEG-fMRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), electric and magnetic source imaging (MSI, ESI), spectroscopy (MRS), have proved their usefulness in defining the epileptic focus. The combination of these functional techniques can yield complementary information and their concordance is crucial for guiding clinical decision, namely the planning of invasive EEG recordings or respective surgery. The aim of this review is to present these non-invasive neuroimaging techniques, their potential combination, and their role in the pre-surgical evaluation of patients with pharmaco-resistant epilepsy.

The role of functional neuroimaging in pre-surgical epilepsy evaluation

The prevalence of epilepsy is about 1% and one-third of cases do not respond to medical treatment. In an eligible subset of patients with drug-resistant epilepsy, surgical resection of the epileptogenic zone is the only treatment that can possibly cure the disease. Non-invasive techniques provide information for the localization of the epileptic focus in the majority of cases, whereas in others invasive procedures are required. In the last years, non-invasive neuroimaging techniques, such as simultaneous recording of functional magnetic resonance imaging and electroencephalogram (EEG-fMRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), electric and magnetic source imaging (MSI, ESI), spectroscopy (MRS), have proved their usefulness in defining the epileptic focus. The combination of these functional techniques can yield complementary information and their concordance is crucial for guiding clinical decision, namely the planning of invasive EEG recordings or respective surgery. The aim of this review is to present these non-invasive neuroimaging techniques, their potential combination, and their role in the pre-surgical evaluation of patients with pharmaco-resistant epilepsy.

Eating epilepsy: phenotype, MRI, SPECT and video-EEG observations

BACKGROUND

Eating epilepsy is one of the rare forms of reflex epilepsy precipitated by eating. Previous studies have demonstrated lesions due to variable aetiology involving the temporolimbic and suprasylvian regions.

OBJECTIVE

To study anatomical correlates of reflex eating epilepsy using multimodality investigations (MR imaging, video-EEG and SPECT).

METHODOLOGY

Six patients (M:F=3:3; mean age: 20.7±4.9 years) with eating epilepsy were subjected to MRI of brain, video-EEG studies and SPECT scan. These were correlated with phenotypic presentations.

RESULTS

Among the five patients with ictal recording of eating epilepsy during video-EEG, semiology was characterized by behavioural arrest followed by either flexion or extension of trunk and neck and two patients had speech arrest and four had salivation from angle of mouth. Another patient had EEG changes during "thought about eating". Four patients had perisylvian frontal lobe lesions and one had high frontal lesion on MRI. Ictal EEG (n=6) showed ictal rhythmic slowing/fast activity in parieto-temporal (n=2) or fronto-temporal (n=4) regions with subsequent secondary generalization in three. Ictal and interictal SPECT imaging showed changes in frontal lobe (n=1), anterior temporal lobe (n=1), and parieto-insular region (n=1) suggesting it to be seizure onset zone. Three of four patients with structural lesions in MRI had concordant ictal EEG and ictal SPECT changes.

CONCLUSION

Lesions near the perisylvian region might play a major role in eating epilepsy.

Imaging the seizure onset zone with stereo-electroencephalography

Stereo-electroencephalography is used to localize the seizure onset zone and connected neuronal networks in surgical candidates suffering from intractable focal epilepsy. The concept of an epileptogenicity index has been proposed recently to represent the likelihood of various regions being part of the seizure onset zone. It quantifies low-voltage fast activity, the electrophysiological signature of seizure onset usually assessed visually by neurologists. Here, we revisit epileptogenicity in light of neuroimaging tools such as those provided in statistical parametric mapping software. Our goal is to propose a robust approach, allowing easy exploration of patients' brains in time and space. The procedure is based upon statistical parametric mapping, which is an established framework for comparing multi-dimensional image data that allows one to correct for inherent multiple comparisons. Statistics can also be performed at the group level, between seizures in the same patient or between patients suffering from the same type of epilepsy using normalization of brains to a common anatomic atlas. Results are obtained from three case studies (insular reflex epilepsy, cryptogenic frontal epilepsy and lesional occipital epilepsy) where tailored resection was performed, and from a group of 10 patients suffering from mesial temporal lobe epilepsy. They illustrate the basics of the technique and demonstrate its very good reproducibility and specificity. Most importantly, the proposed approach to the quantification of the seizure onset zone allows one to summarize complex signals in terms of a time-series of statistical parametric maps that can support clinical decisions. Quantitative neuroimaging of stereo-electroencephalographic features of seizures might thus help to provide better pre-surgical assessment of patients undergoing resective surgery.

Comparison of five directed graph measures for identification of leading interictal epileptic regions

Directed graphs (digraphs) derived from interictal periods of intracerebral EEG (iEEG) recordings can be used to estimate the leading interictal epileptic regions for presurgery evaluations. For this purpose, quantification of the emittance contribution of each node to the rest of digraph is important. However, the usual digraph measures are not very well suited for this quantification. Here, we compare the efficiency of recently introduced local information (LI) measure and a new measure called total global efficiency with classical measures like global efficiency, local efficiency and node degree. For evaluation, the estimated leading interictal epileptic regions based on five measures are compared with seizure onset zones obtained by visual inspection of epileptologists for five patients. The comparison revealed the superior performance of the LI measure. We showed efficiency of different digraph measures for the purpose of source and sink node identification.