Identification Of Epileptogenic Zone Research Articles

Ictal Semiology Important for Electrode Implantation and Interpretation of Stereoelectroencephalography.

Scalp video-electroencephalography (video-EEG) monitoring should be analyzed thoroughly to preoperatively evaluate stereoelectroencephalography (SEEG). Formulating the working hypotheses for the epileptogenic zone (EZ) considering "anatomo-electroclinical correlations" is the most crucial step, which determines the placement of SEEG electrodes. If these hypotheses are insufficient, precise EZ identification may not be achieved during SEEG recording.In ictal semiology analysis, temporal and spatial patterns with reference to ictal EEG changes are emphasized. In frontal lobe epilepsy, seizures often begin with relatively widespread synchronous activity, and complex motor symptoms manifest within seconds. Due to the wide area involved and intense interhemispheric connectivity, a comprehensive evaluation is often required. Hypotheses are formulated on the basis of the motor symptoms and emotional manifestations that are related to the prefrontal cortices. In temporal lobe epilepsy, EEG onset often precedes clinical onset. Propagation from the EZ to locations within and outside of the temporal lobe is examined from both the EEG and semiological standpoint. The characteristics of contralateral versive seizures, contralateral tonic seizures, and frequent focal onset bilateral tonic-clonic seizures indicate a higher risk of temporo-perisylvian epilepsy. In parietal/occipital lobe epilepsy, despite that some symptoms result from activity in the immediate vicinity, stronger connectivity with other regions usually contributes to the generation of prominent ictal semiology. Hence, multilobar electrode placement is often useful in practice. For insular epilepsy, it is important to understand the anatomy, function, and networks between other regions. A semiological approach is one of the most important clues for electrode implantation and interpretation of SEEG.

Determinants of epileptogenic zone identification and seizure outcome in children with refractory epilepsy undergoing stereoelectroencephalography.

The objective of this paper was to investigate the factors associated with successful epileptogenic zone (EZ) identification and postsurgical seizure freedom in pediatric patients with drug-resistant epilepsy who underwent first-time stereoelectroencephalography (SEEG). The authors conducted a retrospective cohort study of all consecutive patients younger than 18 years of age at the time of recommendation for invasive evaluation with SEEG who were treated from July 2009 to June 2020. The authors excluded patients who had undergone failed prior resective epilepsy surgery or prior intracranial electrode evaluation for seizure localization. For their primary outcome, the authors evaluated the relationship between clinical and radiographic factors and successful identification of a putative EZ. For their secondary outcome, the authors investigated whether these factors had a significant relationship with seizure freedom (according to the Engel classification) at last follow-up. The authors included 101 patients in this study. SEEG was safe, with no major morbidity or mortality experienced. The population was complex, with an MRI lesion present in less than 40% of patients and patients as young as 2.9 years included. A proposed EZ was identified in 88 (87%) patients. Patients with an older onset of epilepsy (OR 1.20/year, p = 0.04) or epilepsy etiology suspected to be due to a developmental lesion (OR 8.38, p = 0.02) were more likely to have proposed EZ identification. Patients with a preimplantation bilateral seizure-onset hypothesis (OR 0.29, p = 0.047) and those who underwent longer periods of monitoring (OR 0.86/day, p = 0.006) were somewhat less likely to have proposed EZ identification. The presence of an MRI lesion was a positive factor on secondary analyses (OR 4.18, p = 0.049; 1-tailed test). Fifty percent of patients who underwent surgical treatment with resection or laser ablation achieved Engel class I outcomes, in contrast to 0% of patients who underwent neuromodulation. Patients with a preimplantation hypothesis in the frontal/parietal lobes had increased odds of seizure freedom compared with patients with a hypothesis in other locations (OR 3.64, p = 0.01). Pediatric SEEG is safe and often identifies a proposed resectable EZ. These results suggest that SEEG is effective in patients with frontal/parietal preimplantation hypothesis, with or without identified lesions on MRI.

Spontaneous fast-ultradian dynamics of polymorphic interictal events in drug-resistant focal epilepsy.

We studied the rate dynamics of interictal events occurring over fast-ultradian time scales, as commonly examined in clinics to guide surgical planning in epilepsy. Stereo-electroencephalography (SEEG) traces of 35 patients with good surgical outcome (Engel I) were analyzed. For this we developed a general data mining method aimed at clustering the plethora of transient waveform shapes including interictal epileptiform discharges (IEDs) and assessed the temporal fluctuations in the capability of mapping the epileptogenic zone (EZ) of each type of event. We found that the fast-ultradian dynamics of the IED rate may effectively impair the precision of EZ identification, and appear to occur spontaneously, that is, not triggered by or exclusively associated with a particular cognitive task, wakefulness, sleep, seizure occurrence, post-ictal state, or antiepileptic drug withdrawal. Propagation of IEDs from the EZ to the propagation zone (PZ) could explain the observed fast-ultradian fluctuations in a reduced fraction of the analyzed patients, suggesting that other factors like the excitability of the epileptogenic tissue could play a more relevant role. A novel link was found between the fast-ultradian dynamics of the overall rate of polymorphic events and the rate of specific IEDs subtypes. We exploited this feature to estimate in each patient the 5 min interictal epoch for near-optimal EZ and resected-zone (RZ) localization. This approach produces at the population level a better EZ/RZ classification when compared to both (1) the whole time series available in each patient (p = .084 for EZ, p < .001 for RZ, Wilcoxon signed-rank test) and (2) 5 min epochs sampled randomly from the interictal recordings of each patient (p < .05 for EZ, p < .001 for RZ, 105 random samplings). Our results highlight the relevance of the fast-ultradian IED dynamics in mapping the EZ, and show how this dynamics can be estimated prospectively to inform surgical planning in epilepsy.

Use of the Globus ExcelsiusGPS System for Robotic Stereoelectroencephalography: An Initial Experience

Stereoelectroencephalography (SEEG) is a critical tool used in the identification of epileptogenic zones. While stereotactic frame-based SEEG procedures have been performed traditionally, newer robotic assisted SEEG procedures have become increasingly common. To evaluate the accuracy, efficacy, and safety of the ExcelsiusGPS® robot in SEEG procedures. Five consecutive adult patients with drug resistant epilepsy were identified as SEEG candidates via a multi-disciplinary epilepsy surgery committee. Preoperative scans were merged onto the robot to plan electrode placement. With the use of a camera system, dynamic reference base, and surveillance markers, the robotic arm was used to establish the trajectory of the electrodes. Post-operative CT scans were merged onto the preoperatively planned trajectory and the radial, depth, and entry errors we calculated. Fiducial registration error was calculated for four cases to determine error between the patient and intraoperative CT merge. A total of 59 electrodes were placed. The mean age at surgery was 41.6 ± 15.1 years. Mean operating room time, anesthesia time, and surgical time was 301.6 ± 44.4 min, 261.6 ± 50.2 min, and 155.8 ± 48.8 min, respectively. The overall mean depth, radial, and entry errors were 2.5 ± 1.9 mm, 1.9 ± 1.5 mm, and 1.6 ± 1.2 mm. Mean fiducial registration error retrospectively calculated for four of five cases were 0.13 ± 0.04 mm.There were no perioperative complications. The initial performance of the ExcelsiusGPS® robotic system yielded comparable results to other systems currently in use for adult SEEG procedures.

Chronological changes in phase-amplitude coupling during epileptic seizures in temporal lobe epilepsy

ObjectiveTo analyze chronological changes in phase-amplitude coupling (PAC) and verify whether PAC analysis can diagnose epileptogenic zones during seizures. MethodsWe analyzed 30 seizures in 10 patients with mesial temporal lobe epilepsy who had ictal discharges with preictal spiking followed by low-voltage fast activity patterns on intracranial electroencephalography. We used the amplitude of two high-frequency bands (ripples: 80–200 Hz, fast ripples: 200–300 Hz) and the phase of three slow wave bands (0.5–1 Hz, 3–4 Hz, and 4–8 Hz) for modulation index (MI) calculation from 2 minutes before seizure onset to seizure termination. We evaluated the accuracy of epileptogenic zone detection by MI, in which a combination of MI was better for diagnosis and analyzed patterns of chronological changes in MI during seizures. ResultsMIRipples/3–4 Hz and MIRipples/4–8 Hz in the hippocampus were significantly higher than those in the peripheral regions from seizure onset. Corresponding to the phase on intracranial electroencephalography, MIRipples/3–4 Hz decreased once and subsequently increased again. MIRipples/4–8 Hz showed continuously high values. ConclusionsContinuous measurement of MIRipples/3–4 Hz and MIRipples/4–8 Hz could help identify epileptogenic zones. SignificancePAC analysis of ictal epileptic discharges can help epileptogenic zone identification.

Multimodal combination of neuroimaging methods for localizing the epileptogenic zone in MR-negative epilepsy

The objective was to determine the optimal combination of multimodal imaging methods (IMs) for localizing the epileptogenic zone (EZ) in patients with MR-negative drug-resistant epilepsy. Data from 25 patients with MR-negative focal epilepsy (age 30 ± 10 years, 16M/9F) who underwent surgical resection of the EZ and from 110 healthy controls (age 31 ± 9 years; 56M/54F) were used to evaluate IMs based on 3T MRI, FDG-PET, HD-EEG, and SPECT. Patients with successful outcomes and/or positive histological findings were evaluated. From 38 IMs calculated per patient, 13 methods were selected by evaluating the mutual similarity of the methods and the accuracy of the EZ localization. The best results in postsurgical patients for EZ localization were found for ictal/ interictal SPECT (SISCOM), FDG-PET, arterial spin labeling (ASL), functional regional homogeneity (ReHo), gray matter volume (GMV), cortical thickness, HD electrical source imaging (ESI-HD), amplitude of low-frequency fluctuation (ALFF), diffusion tensor imaging, and kurtosis imaging. Combining IMs provides the method with the most accurate EZ identification in MR-negative epilepsy. The PET, SISCOM, and selected MRI-post-processing techniques are useful for EZ localization for surgical tailoring.

Fast oscillations >40 Hz localize the epileptogenic zone: An electrical source imaging study using high-density electroencephalography

ObjectiveFast Oscillations (FO) >40 Hz are a promising biomarker of the epileptogenic zone (EZ). Evidence using scalp electroencephalography (EEG) remains scarce. We assessed if electrical source imaging of FO using 256-channel high-density EEG (HD-EEG) is useful for EZ identification. MethodsWe analyzed HD-EEG recordings of 10 focal drug-resistant epilepsy patients with seizure-free postsurgical outcome. We marked FO candidate events at the time of epileptic spikes and verified them by screening for an isolated peak in the time-frequency plot. We performed electrical source imaging of spikes and FO within the Maximum Entropy of the Mean framework. Source localization maps were validated against the surgical cavity. ResultsWe identified FO in five out of 10 patients who had a superficial or intermediate deep generator. The maximum of the FO maps was localized inside the cavity in all patients (100%). Analysis with a reduced electrode coverage using the 10–10 and 10–20 system showed a decreased localization accuracy of 60% and 40% respectively. ConclusionsFO recorded with HD-EEG localize the EZ. HD-EEG is better suited to detect and localize FO than conventional EEG approaches. SignificanceThis study acts as proof-of-concept that FO localization using 256-channel HD-EEG is a viable marker of the EZ.

Arterial spin-labelling and magnetic resonance spectroscopy as imaging biomarkers for detection of epileptogenic zone in non-lesional focal impaired awareness epilepsy

BackgroundThe proper identification of an epileptic focus is a pivotal diagnostic issue; particularly in non-lesional focal impaired awareness epilepsy (FIAE). Seizures are usually accompanied by alterations of regional cerebral blood flow (rCBF) and metabolism. Arterial spin labeling-MRI (ASL-MRI) and proton magnetic resonance spectroscopy (1H-MRS) are MRI techniques that can, non-invasively, define the regions of cerebral perfusion and metabolic changes, respectively. The aim of the current study was to recognize the epileptogenic zone in patients with non-lesional FIAE by evaluating the interictal changes in rCBF and cerebral metabolic alterations, using PASL-MRI and 1H-MRS.ResultsFor identification of the epileptogenic zone, increased ASLAI% assessed by PASL-MRI (at a cut-off value ≥ 5.96%) showed 95.78% accuracy, and increased %AF (at a cut-off value ≥ 9.98%) showed 98.14% accuracy, while decreased NAA/(Cho + Cr) ratio estimated by multi-voxels (MV) 1H-MRS (at a cut-off value ≥ 0.59) showed 97.74% accuracy. Moreover, the combined use of PASL-MRI and MV 1H-MRS yielded 100% sensitivity, 98.45% specificity and 98.86% accuracy.ConclusionThe combined use of PASL-MRI and MV 1H-MRS can be considered as in-vivo proficient bio-marker for proper identification of epileptogenic zone in patients with non-lesional FIAE.

Identifying the epileptogenic zone by four non-invasive imaging techniques versus stereo-EEG in MRI-negative pre-surgery epilepsy patients

ObjectiveWe evaluated four imaging techniques, i.e. Electroencephalography (EEG)-functional Magnetic Resonance Imaging (MRI) (EEG-fMRI), High-resolution EEG (HR-EEG), Magnetoencephalography (MEG) and 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (PET), for the identification of the epileptogenic zone (EZ) in 41 patients with negative MRI, candidate to neurosurgery. MethodsFor each technique, results were compared to the Stereo-EEG. Diagnostic measures were calculated with respect to the post-surgical outcome, either for all the patients (39/41, two patients excluded) and for the subgroup of patients with the EZ involving more than one lobe (20/41). ResultsWhen considered individually, each functional technique showed accuracy values ranging 54,6%–63,2%, having PET, MEG and HR-EEG higher sensitivity, and EEG-fMRI higher specificity. In patients with multilobar epileptogenic zone, functional techniques achieved the best accuracies (up to 80%) when three techniques, including EEG-fMRI, were considered together. ConclusionsThe study highlights the accuracy of a combination of functional imaging techniques in the identification of EZ in MRI negative focal epilepsy. The best diagnostic yield was obtained if the combination of PET, MEG (or HR-EEG as alternative), EEG-fMRI were considered together. SignificanceThe functional imaging techniques may improve the presurgical workup of MRI negative focal epilepsy, if epileptogenic zone involves more than one lobe.

The Potential of Stereotactic-EEG for Brain-Computer Interfaces: Current Progress and Future Directions.

Stereotactic electroencephalogaphy (sEEG) utilizes localized, penetrating depth electrodes to measure electrophysiological brain activity. It is most commonly used in the identification of epileptogenic zones in cases of refractory epilepsy. The implanted electrodes generally provide a sparse sampling of a unique set of brain regions including deeper brain structures such as hippocampus, amygdala and insula that cannot be captured by superficial measurement modalities such as electrocorticography (ECoG). Despite the overlapping clinical application and recent progress in decoding of ECoG for Brain-Computer Interfaces (BCIs), sEEG has thus far received comparatively little attention for BCI decoding. Additionally, the success of the related deep-brain stimulation (DBS) implants bodes well for the potential for chronic sEEG applications. This article provides an overview of sEEG technology, BCI-related research, and prospective future directions of sEEG for long-term BCI applications.

Identification of epileptogenic zone based on network-connectivity analysis derived from the frequency spectrum of the recorded EEG

Identification of epileptogenic zone based on network-connectivity analysis derived from the frequency spectrum of the recorded EEG

The value of epileptogenicity index in operation of epilepsy post viral encephalitis

Objective To explore application value of epileptogenicity index (EI) in operation of epilepsy post viral encephalitis (VE). Methods From January 2014 to August 2017, we retrospectively identified 10 patients with epilepsy post VE undergoing surgery at Epilepsy Center of Yuquan Hospital Tsinghua University. All patients underwent comprehensive presurgical evaluation. SEEG (stereo-electroencephalograhy) was necessary in those patients whose noninvasive investigation results did not reveal clear identification of epileptogenic zone (EZ). Habitual seizures were recorded and EI was calculated. We set a cut-off EI value as EI>0.4 (positive). Meanwhile, we superimposed the EI value on the patient's MRI image to better clarify the starting range. Ten patients underwent epileptic focus resection or SEEG-guided radiofrequency thermocoagulation. The outcome was evaluated by using international Engel epilepsy surgery outcome scale after 21 to 43 months of follow-up. Results Ten patients were followed up from 21 to 43 months, Engel class Ⅰ was achieved in 3 patients, Engel class Ⅱ in 3, Engel class Ⅲ in 2 and Engel class Ⅳ in 2. The number of electrodes classified as epileptogenic revealed by SEEG was closely correlated with number of EI positive ones (Spearman′s correlation r=0.794, P=0.006). EI analysis was consistent with SEEG visual onset and no completely contradictory results were found. Patients with good surgical outcome(Engel class Ⅰ-Ⅱ) showed a high value restricted to focal area and those with poor surgical outcome(Engel class Ⅲ-Ⅳ)revealed a diffuse EI value which involved widely spread onset. Conclusions EI plays an important role in localization of seizure onset of patients with epilepsy after VE and thus could serve as a strong evidence and supplement for SEEG onset. EI could assist in identification of EZ and accurate surgical resection. Key words: Epilepsy; Encephalitis, viral; Neurosurgical procedures; Epileptogenicity index; Stereoelectroencephalography

Precision study of stereotactic electroencephalograph electrode implantation under neuronavigation in children with refractory epilepsy

Objective To explore the accuracy of stereotactic electroencephalograph (SEEG) electrode implantation under neuronavigation in children with refractory epilepsy. Methods Twenty-one children with refractory epilepsy underwent SEEG electrode implantation for identification of epileptogenic zone at Neurosurgery Department of Shenzhen Children's Hospital from March 2016 to December 2017 and were retrospective enrolled into this study MR surface registration and CT registration with anatomic markers were used for the electrode implantation. The accuracy of electrode implantation was compared between the 2 registration methods. The correlation between the depth of electrode implantation (the distance from cortical entry point to target) and the error of target and the error of entry point was analyzed. Results A total of 139 electrodes were implanted in 21 patients. Among them, 56 electrodes were implanted by MR surface registration method, and 83 implanted electrodes were placed by CT anatomical marker registration method. The registration time, registration error, electrode entry error and target error of MR Surface registration group were (37±9) min, (2.3±0.5) mm, (2.7±0.7) mm and (3.1±0.5) mm; those in anatomical marker registration group were (10±4) min, (1.1±0.3) mm, (1.5±0.5) mm, (2.2±0.6) mm respectively. The differences were statistically significant (all P<0.05) in the comparison between the 2 groups. In 139 electrodes, the electrode implantation depth was (4.7±1.7) mm, the entry point error was (2.1±1.3) mm, and the target error was (2.8±1.2) mm. Correlation analysis showed that the depth of electrode implantation was positively correlated with the target error (r=0.57, P=0.034), and there was no correlation with the error of the entry point (r=0.27, P=0.121). None of the patients had complications such as bleeding and infection after electrode implantation. After epileptogenic zonectomy, all patients were followed up for 6 months and included 20 cases as Engel Ⅰ and 1 case as Engel Ⅱ. Conclusion In children with refractory epilepsy, the accuracy of SEEG electrode implantation under neuronavigation seems to be relatively high. Compared with MR surface registration method, the registration efficiency and the accuracy of electrode implantation can be improved by using CT anatomical marker registration. Key words: Epilepsy; Child; Error; Neuronavigation; Stereoelectroencephalography

Stereoelectroencephalography-guided radiofrequency thermocoagulation in periventricular nodular heterotopia related epilepsy

Objective To investigate the seizure outcome in a case series of patients with periventricular nodular heterotopia related epilepsy treated by stereo-EEG (SEEG)-guided radio-frequency thermocoagulation (RF-TC). Methods Five patients with periventricular nodular heterotopia related epilepsy admitted to Department of Neurosurgery, Beijing Fengtai Hospital from March 2015 to May 2017 were retrospectively studied. Following video-EEG monitoring, patients underwent SEEG recording for further identification of epileptogenic zone. All patients underwent RF-TC of periventricular nodular heteropia using contiguous contacts of the electrodes employed for recording. The contacts for RF-TC lesions were chosen according to anatomical and electrical criteria. Postoperative follow-up was conducted by outpatient visits or telephone, and the prognosis was assessed by Engel classification. Results This cohort included 5 cases and 23 electrodes. No serious complications were observed after operation. During the follow-up of 9-27 months, 4 patients were seizure-free (Engel Ⅰ), and 1 patient did not benefit from RF-TC (Engel Ⅳ). No obvious complications were reported during or after RF-TC in this series. Conclusions SEEG-guided RF-TC seems to have important clinical value in epileptogenicity validation and treatment of relatively limited periventricular nodular heterotopia. Key words: Epilepsy; Neurosurgical procedures; Stereoelectroencephalography; Radiofrequency thermocoagulation; Periventricular nodular heterotopia

Application of intracranial electrode implantation using stereotactic frame in identification of epileptogenic zone

Objective To explore the safety and reliability of intracranial electrode implantation based on stereotactic frame. Methods Sixty patients with refractory epilepsy were retrospectively included from June 2015 to June 2016 in Beijing Tiantan-Fengtai Epilepsy Center. We analyzed relevant indexes which might influence the SEEG (stereo-electroencephalograhy) electrode implantation target deviations and complications related to the implantation. Video-EEG monitoring was conducted after the electrode implantation before operation was performed to remove the seizure focus according to the preoperative evaluation. Outcomes were followed-up. Results Sixty patients underwent a total of 474 intracranial electrodes implantation with an average electrode number of 8.0 ± 2.5 and an average application time of 13.5 ± 3.1 min per electrode. The entrance point deviation, target deviation, electrode-skull angle and electrode length in the brain were 0.0-8.3 mm (median: 1.1 mm), 0-12 mm (median: 1.4 mm), 44.0-90.0° (median: 67.5°) and 15-97 mm (median: 43 mm), respectively. The target deviation was positively correlated with the deviation of entry point (r=0.426, P<0.01). The target deviation was negatively correlated with the electrode skull angle (r=-0.247, P<0.01). The target deviation was positively correlated with the length of electrode in the brain (r=0.145, P<0.01). There are totally 6(10%) cases developing complications including small amount of cerebral hematoma in 3(5%), brain abscess in 1(2%) and electrode bending in 2(3%). Fifty-three patients were followed up for 1-2 (1.5±0.5) years post resection surgery. There was 72%(38/53) of the patients achieving seizure free (Engel Ⅰ). Meanwhile, seizures remained in the other 28%(15/53) of the patients (Engel Ⅱ-Ⅳ). Conclusion The stereotactic frame-based intracranial electrode implantation technique seems safe and reliable. Combined with postoperative video-EEG analysis, it could be applied for localization of epileptogenic zone. Key words: Epilepsy; Neurosurgical procedures; Stereoelectroencephalogram; Prognosis

Using Interictal HFOs to Improve the Identification of Epileptogenic Zones in Preparation for Epilepsy Surgery.

For the more than 15 million patients who have drug-resistant epilepsy, surgical resection of the region where seizure arise is often the only alternative therapy. However, the identification of this epileptogenic zone (EZ) is often imprecise. Generally, insufficient EZ identification and resection may cause seizures to continue and too much resection may lead to unnecessary neurological deficits. In this paper, an automatic high frequency oscillations (HFOs) detection method based on noise-assisted multivariate EMD (NA-MEMD) is proposed to improve the localization of the EZ for epilepsy patients. In this method, different detected HFO types such as fast-ripple (FR), ripple (R), and fast-ripple concurrent with ripple (FRandR) are utilized to investigate their clinical relevance in identifying EZ. The proposed method may significantly improve the precision by which pathological brain tissue can be identified.

Impact of radiotracer injection latency and seizure duration on subtraction ictal SPECT co-registered to MRI (SISCOM) performance in children

ObjectiveWe evaluated the impact of radiotracer injection latency and post-injection seizure duration on subtraction ictal SPECT co-registered to MRI (SISCOM) test performance in identifying the epileptogenic zone (EZ) in children with drug-resistant epilepsy who had undergone a resective epilepsy surgery. MethodsSISCOM concordance with the EZ was retrospectively reviewed to evaluate its performance in 113 children. The impact of radiotracer injection latency and post-injection seizure duration was evaluated for their predictive value of SISCOM localization accuracy. ResultsThe overall sensitivity and specificity of SISCOM in identifying an EZ was 64.8% (95%CI = 50.6–77.3) and 40.7% (95%CI = 28.1–54.3). The positive likelihood ratio and diagnostic odd ratio was 1.09 (95%CI = 0.80–1.48) and 1.26 (95%CI = 0.59–2.71), respectively. Logistic regression showed that injection latency and post-injection seizure duration did not significantly predict the probability of true positive SISCOM (p-value = 0.45 and 0.29, respectively). ConclusionRadiotracer injection latency and post-injection seizure duration were not shown to have a statistical significant impact on SISCOM performance in identifying the EZ. SignificanceThis study demonstrates that further study of factors contributing to the performance of SISCOM in EZ identification in children is needed.

F09. Predictors of post-surgical seizure outcomes in refractory temporal lobe epilepsy

Introduction The effectiveness of epilepsy surgery depends on precise identification of epileptogenic zone and historically temporal lobe epilepsy has been described to have highest seizure freedom rates after surgery. Researches have previously analyzed multiple variables with distinct predictive values of postsurgical outcome. We attempted to identify prognostic variables in temporal lobe epilepsy using the diagnostic studies that are routinely performed during presurgical evaluation. Methods Retrospective analysis of electroencephalogram (EEG), Magnetic resonance imaging (MRI), Positron emission tomography (PET), Single-photon emission computed tomography (SPECT) and Magnetoencephalography (MEG) was performed on 93 adult patients with refractory temporal lobe epilepsy who underwent selective temporal lobectomy was performed. Outcomes was assessed on a clinical basis using modified Engel’s classification. Results At one year follow up, there were 73 patients (78.5%) with good surgical outcome (E1 & E2) and 10 patients (10%) with poor outcome (E3 & E4) and 10 patients were lost to follow up. EEG findings such as consistently unilateral interictal epileptiform discharges (IEDs) during NREM sleep (91%), consistent lateralized focal ictal onset (90%) and IEDs concordant with ictal onset on scalp and intracranial EEG were highly predictive of a good outcome. Mesial temporal sclerosis and other hippocampal abnormalities on MRI correlated with good outcome (82–100%). Concordant findings on ictal and interictal EEG MRI, PET and MEG also correlated with good outcome. The type of ictal onset pattern did not have significant difference. In patients with poor outcome (E3 & E4), there was lack of correlation between MRI/PET with interictal and ictal EEG. The presence of any lesion on the MRI did not seem to make any difference in outcome, especially in patients who skipped an invasive monitoring. In two-thirds of the patients with poor outcome, having concordant MRI findings and ictal onset did not change the surgical outcome. Subset analysis of non-lesional patients with hypometabolism on PET had a good outcome (33%). Conclusion Several factors have been identified with some postsurgical predictive value and majority of the studies have included patients with mesial temporal sclerosis (MTS), which is usually considered to be of excellent prognostic value. Contrary to this, the presence of MTS on MRI, did not improve the outcome in our study. This may indicate that the presence of MTS is an independent variable, and other diagnostic studies should be considered to make a reasonable prognostication and such information can be used to counsel the patients appropriately.

Diagnostic evaluation and surgical management of pediatric insular epilepsy utilizing magnetoencephalography and invasive EEG monitoring

IntroductionThe diagnosis and surgical management of pediatric patients with insular epilepsy is challenging due to variable and indistinct seizure semiology arising within the insular cortex. In addition, surgical approaches are associated with potential morbidity given the regional neurosurgical and vascular anatomy. Our institutional experience in evaluation and surgical management of insular epilepsy patients is presented. Diagnostic evaluation, surgical treatment and seizures outcomes are highlighted. MethodsThe institutional database for all pediatric surgical epilepsy patients was reviewed over a period of 15 years (2000–2015). Study subjects were defined as patients who had undergone surgical resection of the epileptogenic zone involving the insular cortex. Diagnostic imaging, electrophysiological studies and surgical records were assessed. ResultsSix (n = 6) patients with insular epilepsy were identified with a mean follow up of 2.8 years (range: 0.8–6.8 years). Mean age at surgical resection was 9.5 ± 2.5 years (range: 2.5–16 years). Majority of patients (n = 4/6, 67%) underwent more than 1 surgical procedure. Magnetoencephalography (MEG) identified insular cortex involvement presurgically in all cases. MEG cluster localization was useful in guiding invasive EEG monitoring in 5 patients and was concordant with identification of epileptogenic zone through intracranial monitoring in all 5 patients. Surgical resection of the epileptogenic zone, as delineated through MEG spike sources and invasive EEG monitoring, was associated with favorable seizure outcome in 4 of 6 patients (67%; Engel Class I). Cortical dysgenesis was identified on histopathology in 4 cases. ConclusionDiagnostic evaluation through invasive and noninvasive electrophysiological studies is critical to identify pediatric patients with insular epilepsy. Our findings suggest that MEG may help with identifying the epileptogenic zone within the insular cortex, which could be confirmed with invasive intracranial monitoring.

Study of broadband frequency analysis in stereo-electroencephalography for intractable epilepsy

Objective To investigate the characteristics of preictal and ictal stereo-electroencephalography (SEEG) in intractable epilepsy using multifrequency quantity analysis and to provide neuro-electrophysiological evidence for accurate identification of epileptogenic zone. Methods We retrospectively analyzed the data of 95 intractable epilepsy patients, who underwent preoperative evaluation involving stereo-electroencephalography(SEEG) and subsequent epileptogenic zonectomy between January 2015 and March 2016 at Beijing Tiantan Hospital, Capital Medical University. Preictal and ictal SEEG data of 16 patients, with the sampling rate over 2, 000 Hz, were analyzed using multifrequency quantity method and that patients were followed up for 10.0 ± 2.7 months. Results The ictal onset rhythm in those 16 patients covered the frequency bands of 0.2-4.0 Hz and 8-500 Hz. Notably, the quantitative analysis showed that the infraslow activity (0.2-1.0 Hz), fast activity(12-30 Hz) and high-frequency oscillations (80-500 Hz) were more correlated with the seizure onset zone rather than non-seizure onset zone(P<0.001). Conclusions The infraslow activity (0.2-1.0 Hz) and high-frequency oscillations (80-500 Hz) in the seizure onset zone seem to demonstrate pronounced increase in preictal period. Broadband frequency analysis of ictal electroencephalography (EEG) could facilitate accurate localization of epileptogenic zone by identifying subtle changes that might be difficult to recognize in conventional analysis. Key words: Epilepsy; Electroencephalography; Stereoelectroencephalography; High-frequency oscillations