Magnetoencephalographic study of rhythmic mid-temporal discharges in non-epileptic and epileptic patients.

To evaluate the source location and clinical significance of rhythmic mid-temporal theta discharges (RMTD) by MEG in non-epileptic and epileptic patients, we conducted simultaneous MEG and EEG recordings with a whole-scalp 306-channel neuromagnetometer in three patients: one with right temporal lobe epilepsy (TLE), one with right frontal lobe epilepsy (FLE), and one with tension headache. We visually detected the RMTD activity and interictal spikes, and then localised their generators by MEG source modelling. We repeated MEG measurement 3 months after right anterior temporal lobectomy (ATL) in the TLE patient; 3 months after anticonvulsant medication in the FLE patient. In epileptic patients, RMTD activities were found during drowsiness over the left temporal channels of both MEG and EEG recordings, and their generators were localised to the left posterior inferior temporal region. In the patient with tension headache, RMTD was localised in the right inferior temporal area. When the epileptic patients became seizure free with disappearance of epileptic spikes, RMTD was still found over the left temporal channels. Besides, some bursts of RMTD appeared also in the right temporal channels in our TLE patient after ATL. Our results indicate that the source of RMTD activity is located in the fissural cortex of the posterior inferior temporal region. As a physiologic rhythm related to dampened vigilance, RMTD has no direct relation to epileptogenic activity.     

Magnetoencephalographic and electroencephalographic evaluation in patients with cryptogenetic partial epilepsy.

Magnetoencephalography (MEG) has been applied for more than 20 years to the localization of the epileptic focus in partial epilepsies, but correlation with electroencephalographic (EEG) data in homogeneous groups of patients is scarce. OBJECTIVE: The aim of our work was to use EEG and MEG for the study of a group of adults and children affected by cryptogenetic partial epilepsy. METHODS: We analyzed the traces obtained from electroencephalographic and magnetoencephalographic recordings of 10 patients of ages ranging from 7 to 38 years affected by cryptogenetic partial epilepsy. We evaluated the presence of commonly detected or uniquely detected spikes, and, whenever possible, we used MEG for localization of the epileptic focus. RESULTS: Three patients showed no epileptic activity during the EEG and MEG sessions. Overall agreement between EEG and MEG (presence of concordant spikes with the same localization shown by both techniques) was obtained in five patients. In one patient the spikes detected by EEG and MEG were different, and in another patient interictal activity was demonstrated exclusively by EEG. CONCLUSIONS: EEG in this series was not inferior to MEG in terms of spike detection. Combination of EEG and MEG is feasible, better than each technique alone, and may be useful for non-invasive diagnosis and monitoring of pediatric and adult patients with partial epilepsies.     

Interictal and ictal magnetoencephalographic study in patients with medial frontal lobe epilepsy

PURPOSE: To determine whether magnetoencephalography (MEG) has any clinical value for the analysis of seizure discharges in patients with medial frontal lobe epilepsy (FLE). METHODS: Four patients were studied with 74-channel MEG. Interictal and ictal electroencephalographic (EEG) and MEG recordings were obtained. The equivalent current dipoles (ECDs) of the MEG spikes were calculated. RESULTS: In two patients with postural seizures, interictal EEG spikes occurred at Cz or Fz. The ECDs of interictal MEG spikes were localized around the supplementary motor area. In the other two patients with focal motor or oculomotor seizures, interictal EEG spikes occurred at Fz or Cz. The ECDs of interictal MEG spikes were localized at the top of the medial frontal region. The ECDs detected at MEG ictal onset were also localized in the same area as those of the interictal discharges. CONCLUSIONS: In medial FLE patients, interictal and ictal MEG indicated consistent ECD localization that corresponded to the semiology of clinical seizures. Our findings demonstrate that MEG is a useful tool for detecting epileptogenic focus.     

Ictal magnetoencephalography in temporal and extratemporal lobe epilepsy

PURPOSE: We evaluated visual patterns and source localization of ictal magnetoencephalography (MEG) in patients with intractable temporal lobe epilepsy (TLE) and extratemporal epilepsy (ETE). METHODS: We performed spike and seizure recording simultaneously with EEG and MEG on two patients with TLE and five patients with ETE. Scalp EEG was recorded from 21 channels (10-20 international system), whereas MEG was recorded from two 37-channel sensors. We compared ictal EEG and MEG onset, frequency, and evolution and performed MEG dipole source localization of interictal spikes and early ictal discharges and co-registered dipoles to brain magnetic resonance imaging (MRI). We correlated dipole characteristics with intracranial EEG, surgical resection, and outcome. RESULTS: Ictal MEG lateralized seizure onset in both TLE patients and demonstrated ictal onset, frequency, and evolution in accordance with EEG. Ictal MEG source analysis revealed tangential vertical dipoles in the anterolateral angle in one patient, and anterior dipoles with anteroposterior orientation in the other. Intracranial EEG revealed regional entorhinal seizure onset in the first patient. Both patients became seizure free after temporal lobectomy. In ETE, ictal MEG demonstrated visual patterns similar to ictal EEG and had concordant localization with interictal MEG in all five patients. Two patients underwent surgery. Ictal MEG localization was concordant with intracranial EEG in both cases. One patient had successful outcome after surgery. The second patient did not improve after limited resection and multiple subpial transections. CONCLUSIONS: Ictal MEG can demonstrate ictal onset frequency and evolution and provide useful localizing information before epilepsy surgery.     

Neuromagnetic source localization of auditory evoked fields and intracerebral evoked potentials: a comparison of data in the same patients.

OBJECTIVE: To compare the localizations of different neural sources (a) obtained from intracerebral evoked responses and (b) calculated from surface auditory evoked field responses recorded in the same subjects. Our aim was to evaluate the resolving power of a source localization method currently used in our laboratory, which is based on a recent spatio-temporal algorithm used in magneto-encephalography (MEG). METHODS: Auditory evoked responses were studied in 4 patients with medically intractable epilepsy. These responses were recorded from depth electrodes implanted in the auditory cortex for pre-surgical evaluation (stereo-electro-encephalography (SEEG)), as well as from surface captors (for MEG) placed on the scalp after removal of the depth electrodes. Auditory stimuli were clicks and short tone bursts with different frequencies. RESULTS: All middle-latency components (from 13 to 70 ms post-stimulus onset) were recorded and localized (via SEEG) along Heschl's gyrus (HG). MEG reliably localized Pam and P1m in the same area of HG that intracerebral recordings localized them in. No significant delay between SEEG and MEG latencies was observed. Both methods suggest that N1 is generated from different sources in the intermediate and lateral parts of the HG and in the planum temporale (PT). The source of P2 (PT and/or Area 22) remains unclear and was in one case, localized in different regions according to the method used. This latter component may therefore also be generated by different sources. CONCLUSIONS: The results suggest that both techniques are useful and may be used together in a complementary fashion. Intracerebral recordings allow the researcher to validate and interpret surface recordings.     

Inverse modeling in magnetic source imaging: Comparison of MUSIC,SAM(g2), and sLORETA to interictal intracranial EEG

Magnetoencephalography (MEG) is used in the presurgical work‐up of patients with focal epilepsy. In particular, localization of MEG interictal spikes may guide or replace invasive electroencephalography monitoring that is required in difficult cases. From literature, it is not clear which MEG source localization method performs best in this clinical setting. Therefore, we applied three source localization methods to the same data from a large patient group for which a gold standard, interictal spikes as identified in electrocorticography (ECoG), was available. The methods used were multiple signal classification (MUSIC), Synthetic Aperture Magnetometry kurtosis [SAM(g2)], and standardized low‐resolution electromagnetic tomography. MEG and ECoG data from 38 patients with refractory focal epilepsy were obtained. Results of the three source localization methods applied to the interictal MEG data were assigned to predefined anatomical regions. Interictal spikes as identified in ECoG were also assigned to these regions. Identified regions by each MEG method were compared to ECoG. Sensitivity and positive predictive value (PPV) of each MEG method were calculated. All three MEG methods showed a similar overall correlate with ECoG spikes, but the methods differ in which regions they detect. The choice of the inverse model thus has an unexpected influence on the results of magnetic source imaging. Combining inverse methods and seeking consensus can be used to improve specificity at the cost of some sensitivity. Combining MUSIC with SAM(g2) gives the best results (sensitivity = 38% and PPV = 82%). Hum Brain Mapp 34:2032–2044, 2013. © 2012 Wiley Periodicals, Inc.     

Magnetoencephalography is more successful for screening and localizing frontal lobe epilepsy than electroencephalography

PURPOSE: The diagnosis of frontal lobe epilepsy may be compounded by poor electroclinical localization, due to distributed or rapidly propagating epileptiform activity. This study aimed at developing optimal procedures for localizing interictal epileptiform discharges (IEDs) of patients with localization related epilepsy in the frontal lobe. To this end the localization results obtained for magnetoencephalography (MEG) and electroencephalography (EEG) were compared systematically using automated analysis procedures. METHODS: Simultaneous recording of interictal EEG and MEG was successful for 18 out of the 24 patients studied. Visual inspection of these recordings revealed IEDs with varying morphology and topography. Cluster analysis was used to classify these discharges on the basis of their spatial distribution followed by equivalent dipole analysis of the cluster averages. The locations of the equivalent dipoles were compared with the location of the epileptogenic lesions of the patient or, if these were not visible at MRI with the location of the interictal onset zones identified by subdural electroencephalography. RESULTS: Generally IEDs were more abundantly in MEG than in the EEG recordings. Furthermore, the duration of the MEG spikes, measured from the onset till the spike maximum, was in most patients shorter than the EEG spikes. In most patients, distinct spike subpopulations were found with clearly different topographical field maps. Cluster analysis of MEG spikes followed by dipole localization was successful (n = 14) for twice as many patients as for EEG source analysis (n = 7), indicating that the localizability of interictal MEG is much better than of interictal EEG. CONCLUSIONS: The automated procedures developed in this study provide a fast screening method for identifying the distinct categories of spikes and the brain areas responsible for these spikes. The results show that MEG spike yield and localization is superior compared with EEG. This finding is of importance for the diagnosis and preoperative evaluation of patients with frontal lobe epilepsy.     

Automated interictal spike detection and source localization in magnetoencephalography using independent components analysis and spatio-temporal clustering.

OBJECTIVE: Magnetoencephalography (MEG) dipole localization of epileptic spikes is useful in epilepsy surgery for mapping the extent of abnormal cortex and to focus intracranial electrodes. Visually analyzing large amounts of data produces fatigue and error. Most automated techniques are based on matching of interictal spike templates or predictive filtering of the data and do not explicitly include source localization as part of the analysis. This leads to poor sensitivity versus specificity characteristics. We describe a fully automated method that combines time-series analysis with source localization to detect clusters of focal neuronal current generators within the brain that produce interictal spike activity. METHODS: We first use an ICA (independent components analysis) method to decompose the multichannel MEG data and identify those components that exhibit spike-like characteristics. From these detected spikes we then find those whose spatial topographies across the array are consistent with focal neural sources, and determine the foci of equivalent current dipoles and their associated time courses. We then perform a clustering of the localized dipoles based on distance metrics that takes into consideration both their locations and time courses. The final step of refinement consists of retaining only those clusters that are statistically significant. The average locations and time series from significant clusters comprise the final output of our method. RESULTS AND SIGNIFICANCE: Data were processed from 4 patients with partial focal epilepsy. In all three subjects for whom surgical resection was performed, clusters were found in the vicinity of the resectioned area. CONCLUSIONS: The presented procedure is promising and likely to be useful to the physician as a more sensitive, automated and objective method to help in the localization of the interictal spike zone of intractable partial seizures. The final output can be visually verified by neurologists in terms of both the location and distribution of the dipole clusters and their associated time series. Due to the clinical relevance and demonstrated promise of this method, further investigation of this approach is warranted.     

Intracranial EEG potentials estimated from MEG sources: A new approach to correlate MEG and iEEG data in epilepsy

Detection of epileptic spikes in MagnetoEncephaloGraphy (MEG) requires synchronized neuronal activity over a minimum of 4cm2. We previously validated the Maximum Entropy on the Mean (MEM) as a source localization able to recover the spatial extent of the epileptic spike generators. The purpose of this study was to evaluate quantitatively, using intracranial EEG (iEEG), the spatial extent recovered from MEG sources by estimating iEEG potentials generated by these MEG sources. We evaluated five patients with focal epilepsy who had a pre‐operative MEG acquisition and iEEG with MRI‐compatible electrodes. Individual MEG epileptic spikes were localized along the cortical surface segmented from a pre‐operative MRI, which was co‐registered with the MRI obtained with iEEG electrodes in place for identification of iEEG contacts. An iEEG forward model estimated the influence of every dipolar source of the cortical surface on each iEEG contact. This iEEG forward model was applied to MEG sources to estimate iEEG potentials that would have been generated by these sources. MEG‐estimated iEEG potentials were compared with measured iEEG potentials using four source localization methods: two variants of MEM and two standard methods equivalent to minimum norm and LORETA estimates. Our results demonstrated an excellent MEG/iEEG correspondence in the presumed focus for four out of five patients. In one patient, the deep generator identified in iEEG could not be localized in MEG. MEG‐estimated iEEG potentials is a promising method to evaluate which MEG sources could be retrieved and validated with iEEG data, providing accurate results especially when applied to MEM localizations. Hum Brain Mapp 37:1661–1683, 2016. © 2016 Wiley Periodicals, Inc .     

Complementary use of video-electroencephalography and magnetoencephalography in frontal lobe epilepsy

PurposeThe aim of this study was to compare magnetoencephalography (MEG) and video-electroencephalography (VEEG) source localization in frontal lobe epilepsy (FLE) and determine if these methods can be complementary to each other in clinical practice.MethodThirty patients with pharmaco-resistant FLE who underwent epilepsy surgery were retrospectively enrolled. Video EEG was recorded using an IT-med system using 10/20 system. Regional localization of spikes in VEEG was defined as spikes discharged from adjacent electrodes and no further propagation to a large and/or contralateral area. Magnetoencephalography was recorded for the purpose of focus assessment. Magnetoencephalography spikes were detected for dipole localization of the epileptogenic cortex and the epileptogenic area was classified as mono- or multi-focal.ResultsRegional spike discharges were identified in the interictal VEEG of 20 patients and in the ictal VEEG of 17 patients. Thirteen patients had regional spikes in both interictal and ictal VEEG. Mono-focal localization was identified in the MEG of 20 patients. Fourteen of these patients had regional spike discharges in VEEG. In the remaining six patients, sources localization was only identified by MEG and there were no regional spike discharges either interictal or ictal VEEG.ConclusionIn clinical practice, VEEG is the routine procedure in the presurgical evaluation of FLE. However, we found six cases in which VEEG failed to locate the epileptogenic area that was identified by MEG. We therefore propose that combining VEEG and MEG will optimize the noninvasive presurgical evaluation of epileptiform activities in FLE.     

Correlation Between Interictal Regional Cerebral Blood Flow and Depth-Recorded Interictal Spiking in Temporal Lobe Epilepsy

Summary: Purpose: Single photon emission computed tomography (SPECT) is used as an adjunctive method in preoperative localization of epileptic foci. In temporal lobe epilepsy (TLE), interictal hypoperfusion is observed in 60–70% of cases. Correlation with ictal EEG changes is observed in ～50–60% of cases. Relationships with interictal EEG have been studied less. We compared interictal SPECT data obtained in 20 patients with their interictal intracerebral electrical activity recorded by depth electrodes to evaluate a potential relationship. Methods: We studied 20 sequential patients whose clinical, surface, and depth EEG data indicated seizure originating in the temporal lobe and who had interictal [^99mTc]hexamethyl-propylene amine oxime (HMPAO)-SPECT stereo-EEG (SEEG). Intracerebral electrodes were placed according to the patient's profile. The interictal extent of epileptiform activity allowed delineation of the irritative zone. Interictal spike frequency was also analyzed semiquantitatively. Visual and numerical SPECT analysis was performed blind to SEEG data. Results: Interictal hypoperfusion was observed in 16 patients, involving the epileptogenic temporal lobe in 14. Except for 1 patient who manifested lateral temporal hypoperfusion corresponding to a mass lesion, two distinctive patterns of hypoperfusion were noted: (a) mesial hypoperfusion (5 patients), and (b) global temporal hypoperfusion (8 patients). In 8 patients, hypoperfusion had also extended into the adjacent cortex. Temporal mesial hypoperfusion was associated with spiking limited to the mesial structures, whereas global temporal hypoperfusion or hypoperfusion extending beyond the temporal lobe was associated with a similar topographic pattern of spikes. Conclusions: Comparison between SPECT and SEEG data collected in the interictal phase indicated that the extent of the hypoperfused area correlated topographically with that of the underlying irritative zone.     

Benign partial epilepsy in childhood: selective cognitive deficits are related to the location of focal spikes determined by combined EEG/MEG

Summary:  Purpose: Benign partial epilepsy (BPE) in childhood is characterized by the occurrence of interictal stereotyped focal spikes with variable localization in the EEG. Children with BPE often exhibit neuropsychological deficits. It is unclear whether a correlation exists between these deficits and the localization of spikes, several EEG studies giving inconsistent results. Magnetoencephalography (MEG) improves the accuracy of spike localization. Therefore by using combined MEG/EEG, we investigated the topographic relation between focal spikes and neuropsychological findings in children with BPE.
Methods: Twenty-seven children diagnosed consecutively with BPE were enrolled in the study. All were examined by combined MEG/EEG and magnetic resonance imaging (MRI). Location of spikes was determined by dipole source estimation. A standardized neuropsychological assessment was conducted, including Kaufman ABC battery, language tests, and motor performance series. All children with sufficient MEG data were included in the correlation analysis (N = 20).
Results: Focal spikes were located in the perisylvian region in 13 children, in the occipital region in seven, and in the frontal region in one. Five children had bilateral or multiple foci. Children with left perisylvian spikes did not differ from the others in global IQ, but performed significantly lower in language tests (p = 0.01). Children with occipital spikes performed significantly lower in simultaneous information processing (p = 0.01), especially in visual transformation tasks.
Conclusions: Combined MEG/EEG investigation is a useful tool to examine interictal focal spikes. Our results show a correlation between the location of spikes and selective cognitive deficits in children with BPE. These findings indicate that focal interictal spikes may interfere with complex cognitive functions.     

High resolution spatio-temporal EEG-MEG analysis of rolandic spikes.

Using high resolution EEG and MEG and a realistic volume conductor model, the authors investigated spatio-temporal aspects of the sources of spikes in children with benign rolandic epilepsy. A 64-channel EEG and simultaneous 151-channel MEG of interictal spike activity in five children all having general and/or focal seizures were recorded. A spatio-temporal multiple signal classification (MUSIC) analysis was performed on the spike data. Sources having a complex spatio-temporal configuration as well as single stationary sources were found. Results for the EEG and MEG were different. In this group of five patients, both high resolution EEG and MEG revealed that in some cases sources well separated in space and time exist, whereas in other cases only single source activity can be resolved. For multiple sources, differences for EEG and MEG in timing and localization of activity suggest that sources are spatio-temporally distributed. Sources can propagate from initial activity in the finger/hand area around the central sulcus down to the mouth/tongue area.     

EEG and MEG source analysis of single and averaged interictal spikes reveals intrinsic epileptogenicity in focal cortical dysplasia

PURPOSE: Simultaneous interictal EEG and magnetoencephalography (MEG) recordings were used for noninvasive analysis of epileptogenicity in focal cortical dysplasia (FCD). The results of two different approach methods (multiple source analysis of averaged spikes and single dipole peak localization of single spikes) were compared with pre- and postoperative anatomic magnetic resonance imaging (MRI). PATIENTS: We studied nine children and adolescents (age, 3.5-15.9 years) with localization-related epilepsy and FCD diagnosis based on MRI. Five patients underwent epilepsy surgery, two of them after long-term recording with subdural grid electrodes, and one after intraoperative electrocorticography. METHODS: The 122-channel whole-head MEGs and 33-channel EEGs were recorded simultaneously for 25 to 40 min. Interictal spikes were identified visually and used as templates to search for similar spatiotemporal spike patterns throughout the recording. With the BESA program, similar spikes (r > 0.85) were detected, averaged, high-pass filtered (5 Hz) to enhance spike onset, and subjected to multiple spatiotemporal source analysis with a multishell spherical head model. Peak activity from single spikes was modeled by single dipoles for the same subset of spikes. Source localization was visualized by superposition on T1-weighted MRI and compared with the lesion identified in T1- and T2-weighted MRI. In the five cases undergoing epilepsy surgery, the results were correlated with invasive recordings, postoperative MRI, and outcome. RESULTS: In all cases, the analysis of averaged spikes showed a localization of onset- and peak-related sources within the visible lesion for both EEG and MEG. Of the single spikes, 128 (45%; total 284) were localizable at the peak in MEG, and 170 (60%) in EEG. Of these, 91% localized within the lesion with MEG, and 93.5% with EEG. In three of five patients operated on, the resected area included the onset zones of averaged EEG and MEG spike activity. These patients had excellent postoperative outcome, whereas the others did not become seizure free. CONCLUSIONS: Consistent MEG and EEG spike localization in the lesional zone confirmed the hypothesis of intrinsic epileptogenicity in FCD.     

Reproducibility of EEG‐MEG fusion source analysis of interictal spikes: Relevance in presurgical evaluation of epilepsy

Fusion of electroencephalography (EEG) and magnetoencephalography (MEG) data using maximum entropy on the mean method (MEM‐fusion) takes advantage of the complementarities between EEG and MEG to improve localization accuracy. Simulation studies demonstrated MEM‐fusion to be robust especially in noisy conditions such as single spike source localizations (SSSL). Our objective was to assess the reliability of SSSL using MEM‐fusion on clinical data. We proposed to cluster SSSL results to find the most reliable and consistent source map from the reconstructed sources, the so‐called consensus map. Thirty‐four types of interictal epileptic discharges (IEDs) were analyzed from 26 patients with well‐defined epileptogenic focus. SSSLs were performed on EEG, MEG, and fusion data and consensus maps were estimated using hierarchical clustering. Qualitative (spike‐to‐spike reproducibility rate, SSR) and quantitative (localization error and spatial dispersion) assessments were performed using the epileptogenic focus as clinical reference. Fusion SSSL provided significantly better results than EEG or MEG alone. Fusion found at least one cluster concordant with the clinical reference in all cases. This concordant cluster was always the one involving the highest number of spikes. Fusion yielded highest reproducibility (SSR EEG = 55%, MEG = 71%, fusion = 90%) and lowest localization error. Also, using only few channels from either modality (21EEG + 272MEG or 54EEG + 25MEG) was sufficient to reach accurate fusion. MEM‐fusion with consensus map approach provides an objective way of finding the most reliable and concordant generators of IEDs. We, therefore, suggest the pertinence of SSSL using MEM‐fusion as a valuable clinical tool for presurgical evaluation of epilepsy.     

Magnetoencephalography using total intravenous anesthesia in pediatric patients with intractable epilepsy: lesional vs nonlesional epilepsy

Purpose: Magnetoencephalography (MEG) provides source localization of interictal spikes. We use total intravenous anesthesia (TIVA) with propofol to immobilize uncooperative children. We evaluate the effect of TIVA on interictal spikes in children who have intractable epilepsy with or without MRI lesions. Methods: We studied 28 children (3–14 years; mean, 6.6). We intravenously administered propofol (30–60 μg/kg/min) to record MEG with simultaneous EEG. We evaluated MEG spike sources (MEGSSs). We compared spikes on simultaneous EEG under TIVA with those on scalp video-EEG without TIVA. Results: There was a significant decrease in frequent spikes (10 patients, 36%) on simultaneous EEG under TIVA compared to those (22 patients, 79%) on scalp video-EEG without TIVA (P < 0.01). MEGSSs were present in 21 (75%) of 28 patients. Clustered MEGSSs occurred in 15 (83%) of 18 lesional patients but in 3 (30%) of 10 nonlesional patients (P < 0.05). MEGSSs were more frequently absent in nonlesional (6 patients, 60%) than lesional (one patient, 5%) patients (P < 0.01). Thirteen patients with MRI and/or histopathologically confirmed neuronal migration disorder most frequently showed clustered MEGSSs (11 patients, 85%) compared to those of other lesional and nonlesional patients. Conclusion: Propofol-based TIVA reduced interictal spikes on simultaneous EEG. TIVA for MEG still had utility in identifying spike sources in a subset of pediatric patients with intractable epilepsy who were uncooperative and surgical candidates. In lesional patients, MEG under TIVA frequently localized the clustered MEGSSs. Neuronal migration disorders were intrinsically epileptogenic and produced clustered MEGSSs under TIVA. Nonlesional patients often had no MEGSS under TIVA.     

Reliability of dipole models of epileptic spikes.

OBJECTIVE: In order to validate dipole-modeling results, we compared dipole localizations with the distribution of intracerebral potentials occurring simultaneously with scalp EEG paroxysms. METHODS: Firstly, scalp EEGs were recorded from 11 patients. Dipole sources were estimated on averaged spikes and projected on 3D-MRIs. Secondly, stereoelectroencephalography (SEEG) was recorded from implanted electrodes with direct identification onto MRI. Simultaneously with SEEG, control scalp electrodes were pasted where spikes peaked during the first session. SEEG was averaged, triggered by the main peak of scalp spikes. RESULTS: SEEG activity during scalp spikes always involved several contacts. In 13 of 14 spikes, maximal fields occurred in neocortical regions. In 4 of 5 cases where intracerebral activity was simple, spikes could be modeled by one source. In all cases where intracerebral activity was complex, spikes had to be modeled by several sources. The main dipole source was 11 +/- 4.2 mm from the SEEG contact showing the maximal intracerebral potential. Early and late dipole localization and SEEG fields were concordant in two thirds of cases. CONCLUSION: Results indicate that in our group of patients scalp spikes reflect activity in large neocortical areas and never activity limited to mesial structures. Dipole locations and time activation were confirmed most often and were more reliable for sources representing the main negative component than for early or late sources.     

Automated electrical source imaging with scalp EEG to define the insular irritative zone: Comparison with simultaneous intracranial EEG

Objective To evaluate the accuracy of automated interictal low-density electrical source imaging (LD-ESI) to define the insular irritative zone (IZ) by comparing the simultaneous interictal ESI localization with the SEEG interictal activity.Methods Long-term simultaneous scalp electroencephalography (EEG) and stereo-EEG (SEEG) with at least one depth electrode exploring the operculo-insular region(s) were analyzed. Automated interictal ESI was performed on the scalp EEG using standardized low-resolution brain electromagnetic tomography (sLORETA) and individual head models. A two-step analysis was performed: i) sublobar concordance between cluster-based ESI localization and SEEG-based IZ; ii) time-locked ESI-/SEEG analysis. Diagnostic accuracy values were calculated using SEEG as reference standard. Subgroup analysis was carried out, based on the involvement of insular contacts in the seizure onset and patterns of insular interictal activity.Results Thirty patients were included in the study. ESI showed an overall accuracy of 53% (C.I. 29–76%). Sensitivity and specificity were calculated as 53% (C.I. 29–76%), 55% (C.I. 23–83%) respectively. Higher accuracy was found in patients with frequent and dominant interictal insular spikes.Conclusions LD-ESI defines with good accuracy the insular implication in the IZ, which is not possible with classical interictal scalp EEG interpretation.SignificanceAutomated LD-ESI may be a valuable additional tool to characterize the epileptogenic zone in epilepsies with suspected insular involvement.     

Electro- and magneto-encephalographic spike source localization of small focal cortical dysplasia in the dorsal peri-rolandic region

ObjectiveSmall focal cortical dysplasia (FCD) may be ambiguous or overlooked on magnetic resonance (MR) imaging. Source localization of EEG and magnetoencephalography (MEG) spikes was evaluated to confirm the diagnosis of small FCD.MethodsThis study included 6 epilepsy patients with a single small lesion on MR imaging suggesting FCD within a single gyrus among 181 consecutive epilepsy patients admitted to our epilepsy monitoring unit over 27 months. Stereotypical interictal spikes were detected on simultaneous EEG and MEG recordings and the onset-related source of averaged spikes was estimated.ResultsAll 6 patients had unique clinical characteristics as follows: leg sensori-motor seizures in 5 patients and eye version in 1 patient; a small MR imaging lesion suggesting FCD in the dorsal peri-rolandic region, which had been overlooked until our evaluation; and both EEG and MEG dipoles were estimated adjacent to the MR imaging lesion.ConclusionsSource localization of EEG and MEG spikes can confirm the diagnosis of FCD based on a single small MR imaging lesion, which was overlooked by previous examination of MR images.SignificanceExamination of MR images should be based on spike source localization as well as seizure semiology to identify subtle MR imaging abnormalities.     

The magnetic field of epileptic spikes agrees with intracranial localizations in complex partial epilepsy

The magnetoencephalogram (MEG) and electroencephalogram (EEG) were measured during interictal epileptic spikes in nine patients with complex partial seizures. The MEG localization estimates were compared with localizations by intraoperative cortical electrodes, subdural electrodes, stereotaxic depth electrodes, anatomic imaging, postoperative pathologic analysis, and postoperative follow-up. In all patients, MEG localization estimates were in the same lobe as the epileptic focus determined by invasive methods and EEG. In two patients, it was possible to quantify precisely the accuracy of MEG localization by mapping a spike focus that was visually indistinguishable on MEG and cortical recordings. In both patients, MEG localization was approximately 12 mm from the center of the cortical spike focus on intracranial recordings. In eight patients, MEG showed tangential dipolar field patterns on the spontaneous record, but EEG did not. In one patient, a cortical epileptic discharge was detected only on MEG for some discharges and only on EEG for other discharges. The MEG did not detect deep spikes with present levels of environmental noise.