Seizure Onset Zone Localization from Ictal High-Density EEG in Refractory Focal Epilepsy

ObjectiveTo determine whether seizure onset zone can be accurately localized prior to surgical planning in focal epilepsy patients, we performed non-invasive EEG recordings and source localization analyses on 39 patients.MethodsIn a total of 39 focal epilepsy patients, we recorded and extracted 138 seizures and 1,325 interictal epileptic discharges using high-density EEG. We have investigated a novel approach for directly imaging sources of seizures and interictal spikes from high density EEG recordings, and rigorously validated it for noninvasive localization of seizure onset zone (SOZ) determined from intracranial EEG findings and surgical resection volume. Conventional source imaging analyses were also performed for comparison.ResultsIctal source imaging showed a concordance rate of 95% when compared to intracranial EEG or resection results. The average distance from estimation to seizure onset (intracranial) electrodes is 1.35 cm in patients with concordant results, and 0.74 cm to surgical resection boundary in patients with successful surgery. About 41% of the patients were found to have multiple types of interictal activities; coincidentally, a lower concordance rate and a significantly worse performance in localizing SOZ were observed in these patients.ConclusionNoninvasive ictal source imaging with high-density EEG recording can provide highly concordant results with clinical decisions obtained by invasive monitoring or confirmed by resective surgery. By means of direct seizure imaging using high-density scalp EEG recordings, the added value of ictal source imaging is particularly high in patients with complex interictal activity patterns, who may represent the most challenging cases with poor prognosis.

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Clinical Validation of the Champagne Algorithm for Epilepsy Spike Localization

Frontiers in Human Neuroscience ◽

10.3389/fnhum.2021.642819 ◽

2021 ◽

Vol 15 ◽

Author(s):

Chang Cai ◽

Jessie Chen ◽

Anne M. Findlay ◽

Danielle Mizuiri ◽

Kensuke Sekihara ◽

...

Keyword(s):

Refractory Epilepsy ◽

Focal Epilepsy ◽

Epileptiform Activity ◽

Consecutive Series ◽

Source Reconstruction ◽

Seizure Onset ◽

Current Dipole ◽

Seizure Onset Zone ◽

Complementary Techniques ◽

Epilepsy Localization

Magnetoencephalography (MEG) is increasingly used for presurgical planning in people with medically refractory focal epilepsy. Localization of interictal epileptiform activity, a surrogate for the seizure onset zone whose removal may prevent seizures, is challenging and depends on the use of multiple complementary techniques. Accurate and reliable localization of epileptiform activity from spontaneous MEG data has been an elusive goal. One approach toward this goal is to use a novel Bayesian inference algorithm—the Champagne algorithm with noise learning—which has shown tremendous success in source reconstruction, especially for focal brain sources. In this study, we localized sources of manually identified MEG spikes using the Champagne algorithm in a cohort of 16 patients with medically refractory epilepsy collected in two consecutive series. To evaluate the reliability of this approach, we compared the performance to equivalent current dipole (ECD) modeling, a conventional source localization technique that is commonly used in clinical practice. Results suggest that Champagne may be a robust, automated, alternative to manual parametric dipole fitting methods for localization of interictal MEG spikes, in addition to its previously described clinical and research applications.

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Statistical Features in High-Frequency Bands of Interictal iEEG Work Efficiently in Identifying the Seizure Onset Zone in Patients with Focal Epilepsy

Entropy ◽

10.3390/e22121415 ◽

2020 ◽

Vol 22 (12) ◽

pp. 1415

Author(s):

Most. Sheuli Akter ◽

Md. Rabiul Islam ◽

Toshihisa Tanaka ◽

Yasushi Iimura ◽

Takumi Mitsuhashi ◽

...

Keyword(s):

High Frequency ◽

State Of The Art ◽

Focal Epilepsy ◽

Epileptic Seizures ◽

Gradient Boosting ◽

Statistical Features ◽

Seizure Onset ◽

Seizure Onset Zone ◽

Frequency Components ◽

Final Score

The design of a computer-aided system for identifying the seizure onset zone (SOZ) from interictal and ictal electroencephalograms (EEGs) is desired by epileptologists. This study aims to introduce the statistical features of high-frequency components (HFCs) in interictal intracranial electroencephalograms (iEEGs) to identify the possible seizure onset zone (SOZ) channels. It is known that the activity of HFCs in interictal iEEGs, including ripple and fast ripple bands, is associated with epileptic seizures. This paper proposes to decompose multi-channel interictal iEEG signals into a number of subbands. For every 20 s segment, twelve features are computed from each subband. A mutual information (MI)-based method with grid search was applied to select the most prominent bands and features. A gradient-boosting decision tree-based algorithm called LightGBM was used to score each segment of the channels and these were averaged together to achieve a final score for each channel. The possible SOZ channels were localized based on the higher value channels. The experimental results with eleven epilepsy patients were tested to observe the efficiency of the proposed design compared to the state-of-the-art methods.

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Temporal Lobe Epilepsy Semiology

Epilepsy Research and Treatment ◽

10.1155/2012/751510 ◽

2012 ◽

Vol 2012 ◽

pp. 1-10 ◽

Cited By ~ 19

Author(s):

Robert D. G. Blair

Keyword(s):

Temporal Lobe Epilepsy ◽

Temporal Lobe ◽

Focal Epilepsy ◽

Intractable Epilepsy ◽

Febrile Seizures ◽

Mesial Temporal Sclerosis ◽

Careful Study ◽

Seizure Onset ◽

Seizure Semiology ◽

Seizure Onset Zone

Epilepsy represents a multifaceted group of disorders divided into two broad categories, partial and generalized, based on the seizure onset zone. The identification of the neuroanatomic site of seizure onset depends on delineation of seizure semiology by a careful history together with video-EEG, and a variety of neuroimaging technologies such as MRI, fMRI, FDG-PET, MEG, or invasive intracranial EEG recording. Temporal lobe epilepsy (TLE) is the commonest form of focal epilepsy and represents almost 2/3 of cases of intractable epilepsy managed surgically. A history of febrile seizures (especially complex febrile seizures) is common in TLE and is frequently associated with mesial temporal sclerosis (the commonest form of TLE). Seizure auras occur in many TLE patients and often exhibit features that are relatively specific for TLE but few are of lateralizing value. Automatisms, however, often have lateralizing significance. Careful study of seizure semiology remains invaluable in addressing the search for the seizure onset zone.

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The comparative study of invasive electroencephalography modalities in temporal lobe epilepsy

Russian journal of neurosurgery ◽

10.17650/1683-3295-2021-23-3-14-22 ◽

2021 ◽

Vol 23 (3) ◽

pp. 14-22

Author(s):

V. M. Dzhafarov ◽

A. B. Dmitriev ◽

N. P. Denisova ◽

D. A. Rzaev

Keyword(s):

Temporal Lobe Epilepsy ◽

Temporal Lobe ◽

Focal Epilepsy ◽

Epileptogenic Zone ◽

Foramen Ovale ◽

Seizure Onset ◽

Depth Electrodes ◽

Seizure Onset Zone ◽

Temporal Lobe Seizures ◽

Mesial Temporal Lobe

Introduction. Invasive video-EEG monitoring (invasive EEG) is indicated in patients with refractory focal epilepsy while localization of the epileptogenic zone is unclear. Methods of invasive EEG in different groups of patients demonstrate variable results.Objective: to analyse the results of invasive EEG via subdural and depth electrodes in patients with refractory temporal lobe epilepsy with mesial temporal lobe seizures.Materials and methods. The series of 37 patients who underwent invasive EEG from 2013 to 2020 was retrospectively analysed. The study includes primary adult patients with structural refractory focal epilepsy with mesial temporal lobe seizures without tumor and vascular pathology. Patients were divided onto 3 groups: 1) with foramen ovale electrodes 2) subdural strip electrodes and 3) combination of subdural strips and depths electrodes. The results of anteromedial temporal lobectomy after 6 months were classified according to Engel scale.Results. A group with foramen ovale electrodes included 7 patients, subdural strips – 23, combination – 7. The seizure onset zone was detected in 36 (97 %) cases. Serious complications were observed in 2 (29 %) cases in the group with foramen ovale electrodes. The mean follow-up in 23 (76 %) patients after resective surgery was 28.3 months. Favourable results (Engel I, II) were observed in 4 (80 %) patients with foramen ovale electrodes, in 8 (67 %) patients with subdural electrodes, in 6 (100 %) with combination. Unfavourable results (Engel III, IV) were noted in 1 (20 %) patient with foramen ovale electrode, in 4 (33 %) patients with subdural strips.Conclusion. All the presented modalities of invasive EEG are effective for localizing of seizure onset zone in this category of patients. Foramen ovale electrode using may be limited due to increased risk of complications.

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Mapping of Seizure Networks

Invasive Studies of the Human Epileptic Brain ◽

10.1093/med/9780198714668.003.0038 ◽

2018 ◽

pp. 511-519

Author(s):

Olivier David

Keyword(s):

Data Analysis ◽

Focal Epilepsy ◽

Seizure Onset ◽

High Frequency Oscillations ◽

Signal Features ◽

Seizure Onset Zone ◽

Presurgical Assessment ◽

Computer Based ◽

Intracranial Electroencephalography ◽

Quantitative Neuroimaging

Intracranial electroencephalography (iEEG) is used to localize the seizure onset zone (SOZ) and connected neuronal networks in surgical candidates suffering from intractable focal epilepsy. Identification of the SOZ is usually based on visual inspection of iEEG signals, but new computer-based quantitative iEEG analyses are being developed to improve and expedite SOZ detection. Two main questions arise. First, which signal features are the best proxys to identify the SOZ and the propagation pathways constituting epileptic networks? Second, how can the results of data analysis be represented in a clinically useful and meaningful manner? This chapter adopts an epileptogenicity mapping approach based on maps of ictal high-frequency oscillations superimposed on neuroanatomy and illustrates the main concepts underlying mapping of seizure networks. Future quantitative iEEG approaches should complete and operationalize understanding of seizure networks. Quantitative neuroimaging of iEEG features of seizures should help provide better presurgical assessment of patients undergoing resective surgery.

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Distinction of Physiologic and Epileptic Ripples: An Electrical Stimulation Study

Brain Sciences ◽

10.3390/brainsci11050538 ◽

2021 ◽

Vol 11 (5) ◽

pp. 538

Author(s):

Jan Schönberger ◽

Anja Knopf ◽

Kerstin Alexandra Klotz ◽

Matthias Dümpelmann ◽

Andreas Schulze-Bonhage ◽

...

Keyword(s):

Electrical Stimulation ◽

Slow Wave Sleep ◽

Focal Epilepsy ◽

Epileptic Activity ◽

Interictal Spikes ◽

Seizure Onset ◽

Receiver Operating Characteristic Curves ◽

Seizure Onset Zone ◽

Intracranial Electroencephalography ◽

Better Than

Ripple oscillations (80–250 Hz) are a promising biomarker of epileptic activity, but are also involved in memory consolidation, which impairs their value as a diagnostic tool. Distinguishing physiologic from epileptic ripples has been particularly challenging because usually, invasive recordings are only performed in patients with refractory epilepsy. Here, we identified ‘healthy’ brain areas based on electrical stimulation and hypothesized that these regions specifically generate ‘pure’ ripples not coupled to spikes. Intracranial electroencephalography (EEG) recorded with subdural grid electrodes was retrospectively analyzed in 19 patients with drug-resistant focal epilepsy. Interictal spikes and ripples were automatically detected in slow-wave sleep using the publicly available Delphos software. We found that rates of spikes, ripples and ripples coupled to spikes (‘spike–ripples’) were higher inside the seizure-onset zone (p < 0.001). A comparison of receiver operating characteristic curves revealed that spike–ripples slightly delineated the seizure-onset zone channels, but did this significantly better than spikes (p < 0.001). Ripples were more frequent in the eloquent neocortex than in the remaining non-seizure onset zone areas (p < 0.001). This was due to the higher rates of ‘pure’ ripples (p < 0.001; median rates 3.3/min vs. 1.4/min), whereas spike–ripple rates were not significantly different (p = 0.87). ‘Pure’ ripples identified ‘healthy’ channels significantly better than chance (p < 0.001). Our findings suggest that, in contrast to epileptic spike–ripples, ‘pure’ ripples are mainly physiological. They may be considered, in addition to electrical stimulation, to delineate eloquent cortex in pre-surgical patients. Since we applied open source software for detection, our approach may be generally suited to tackle a variety of research questions in epilepsy and cognitive science.

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The UK experience of stereoelectroencephalography in children: An analysis of factors predicting the identification of a seizure onset zone and subsequent seizure freedom

10.1101/2021.03.05.21252613 ◽

2021 ◽

Author(s):

Keyword(s):

Epilepsy Surgery ◽

Surgical Intervention ◽

Focal Epilepsy ◽

Neurological Deficits ◽

Seizure Freedom ◽

Seizure Onset ◽

Operative Outcomes ◽

Seizure Onset Zone ◽

Nationally Representative ◽

The Uk

AbstractImportanceStereoelectroencephalography (SEEG) is more frequently being used in the pre-surgical evaluation of children with focal epilepsy. Many factors affect the rate of identification of a definable seizure onset zone (SOZ) and subsequent seizure freedom following SEEG-guided epilepsy surgery, which have not been systematically examined in multi-centre studies.ObjectivesDetermine the rates and factors that predict (a) whether or not a definable putative SOZ was identified on SEEG and (b) subsequent seizure freedom following surgical intervention.DesignRetrospective cohort studySettingMulticentre study involving 6 of 7 UK Children’s Epilepsy Surgery Service centres that perform paediatric SEEG in the UK.ParticipantsAll children undergoing SEEG from 2014 - March 2019 were included. Demographic, non-invasive evaluation, SEEG and operative factors were collected retrospectively from patient records.Main OutcomesThe two main outcome measures were (a) whether or not a definable putative SOZ was identified on SEEG (binary yes/no outcome) and (b) subsequent seizure freedom following surgical intervention (Engel classification)FindingsOne hundred and thirty-five patients underwent 139 SEEG explorations using a total of 1767 electrodes. A definable SOZ was identified in 117 patients (85.7%); odds of successfully finding a SOZ were 6.4x greater for non-motor seizures compared to motor seizures (p=0.02) and 3.6x more if ≥ 4 seizures were recorded during SEEG (p=0.03). Of 100 patients undergoing surgical treatment, 47 (47.0%) had an Engel class I outcome at a median follow-up of 1.3 years; the only factor associated with outcome was indication for SEEG (p=0.03). SEEG was safe with one (0.7%) haematoma requiring surgical evacuation and no long-term neurological deficits as a result of the procedure.Conclusions and RelevanceThis large nationally representative cohort illustrates that, in these patients who may not have otherwise been offered resective surgery, SEEG-guided surgery can still achieve high rates of seizure freedom. Seizure semiology and the number of seizures recorded during SEEG are important factors in the identification of a definable SOZ and the indication for SEEG is an important factor in post-operative outcomes.

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Synchrony in Normal and Focal Epileptic Brain: The Seizure Onset Zone is Functionally Disconnected

Journal of Neurophysiology ◽

10.1152/jn.00368.2010 ◽

2010 ◽

Vol 104 (6) ◽

pp. 3530-3539 ◽

Cited By ~ 101

Author(s):

Christopher P. Warren ◽

Sanqing Hu ◽

Matt Stead ◽

Benjamin H. Brinkmann ◽

Mark R. Bower ◽

...

Keyword(s):

Focal Epilepsy ◽

Brain Regions ◽

Seizure Onset ◽

Neuronal Synchrony ◽

Seizure Onset Zone ◽

Paradoxical Finding ◽

Eeg Recordings ◽

Learning And Cognition ◽

Patients With Epilepsy ◽

And Control

Synchronization of local and distributed neuronal assemblies is thought to underlie fundamental brain processes such as perception, learning, and cognition. In neurological disease, neuronal synchrony can be altered and in epilepsy may play an important role in the generation of seizures. Linear cross-correlation and mean phase coherence of local field potentials (LFPs) are commonly used measures of neuronal synchrony and have been studied extensively in epileptic brain. Multiple studies have reported that epileptic brain is characterized by increased neuronal synchrony except possibly prior to seizure onset when synchrony may decrease. Previous studies using intracranial electroencephalography (EEG), however, have been limited to patients with epilepsy. Here we investigate neuronal synchrony in epileptic and control brain using intracranial EEG recordings from patients with medically resistant partial epilepsy and control subjects with intractable facial pain. For both epilepsy and control patients, average LFP synchrony decreases with increasing interelectrode distance. Results in epilepsy patients show lower LFP synchrony between seizure-generating brain and other brain regions. This relative isolation of seizure-generating brain underlies the paradoxical finding that control patients without epilepsy have greater average LFP synchrony than patients with epilepsy. In conclusion, we show that in patients with focal epilepsy, the region of epileptic brain generating seizures is functionally isolated from surrounding brain regions. We further speculate that this functional isolation may contribute to spontaneous seizure generation and may represent a clinically useful electrophysiological signature for mapping epileptic brain.

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Localisation in focal epilepsy: a practical guide

Practical Neurology ◽

10.1136/practneurol-2019-002341 ◽

2021 ◽

pp. practneurol-2019-002341

Author(s):

Fahmida A Chowdhury ◽

Rui Silva ◽

Benjamin Whatley ◽

Matthew C Walker

Keyword(s):

Current Literature ◽

Focal Epilepsy ◽

Correct Diagnosis ◽

Epileptic Seizures ◽

Seizure Onset ◽

Practical Guide ◽

Seizure Onset Zone ◽

Insight Into

The semiology of epileptic seizures reflects activation, or dysfunction, of areas of brain (often termed the symptomatogenic zone) as a seizure begins and evolves. Specific semiologies in focal epilepsies provide an insight into the location of the seizure onset zone, which is particularly important for presurgical epilepsy assessment. The correct diagnosis of paroxysmal events also depends on the clinician being familiar with the spectrum of semiologies. Here, we summarise the current literature on localisation in focal epilepsies using illustrative cases and discussing possible pitfalls in localisation.

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