Sensitivity and specificity of seizure-onset zone estimation by ictal magnetoencephalography

Purpose: Ictal video–electroencephalography (EEG) is commonly used to establish ictal onset‐zone location. Recently software development has enabled systematic studies of ictal magnetoencephalography (MEG). In this article, we evaluate the ability of ictal MEG signals to localize the seizure‐onset zone. Methods: Twenty‐six patients underwent ictal MEG and epilepsy surgery. Prediction of seizure‐onset zone by ictal and interictal MEG was retrospectively compared with ictal‐onset area found by intracranial EEG in 12 patients. The specificity and sensitivity of the prediction were calculated at hemisphere‐lobe (HL) and at hemisphere‐lobe‐surface (HLS) levels. Key Findings: The sensitivity of ictal MEG source localization was 0.958 on HL and 0.706 on HLS levels, and its specificity was 0.900 on HL and 0.731 on HLS levels. The interictal MEG dipole cluster, defined as >10 dipoles on one lobar surface, had sensitivity of 0.400 and specificity of 0.769. Ictal MEG was equally sensitive and specific on dorsolateral and nondorsolateral neocortical surfaces up to a depth of 4 cm from the scalp. Significance: Sources of ictal‐onset MEG signals and interictal dipole clusters are essentially equally specific in estimation of the ictal‐onset zone on lobar surface resolution, but ictal MEG is more sensitive. On the lobe resolution, ictal MEG estimates ictal‐onset zone with high sensitivity and specificity.     

Magnetoencephalography source localization and surgical outcome in temporal lobe epilepsy.

OBJECTIVE: We prospectively investigated the role of magnetoencephalography (MEG) in localizing the seizure focus and in predicting outcome to surgical resections for intractable temporal lobe epilepsy (TLE). METHODS: We performed simultaneous interictal EEG and MEG recording (two 37-channel system) in 26 TLE patients followed by MEG source localization. We correlated early modeling dipoles with intracranial EEG, temporal surgical resection and surgical outcome. RESULTS: There were 12 patients who had anterior temporal horizontal or tangential dipoles to the anterior infero-lateral temporal tip cortex. Two patients underwent selective amygdalo-hippocampectomy (SAH) and nine patients had antero-medial temporal lobectomy (AMTL). All patients had successful outcome except for one patient who initially failed SAH, but became seizure-free after AMTL. There were 11 patients who demonstrated anterior temporal vertical or tangential oblique dipoles. Five patients had AMTL and three had SAH; all became seizure free. Five of above 23 patients had invasive EEG and demonstrated mesial seizure onset. Three TLE patients had lateral vertical dipoles that were concordant with intracranial EEG and these became seizure free after temporal neocortical resections. CONCLUSIONS: MEG source analysis produces distinct source patterns that provide useful localizing information, predict surgical outcome, and may aid in planning limited surgical resection in TLE.     

Ictal onset localization of epileptic seizures by magnetoencephalography

OBJECTIVES: The aim of this study was to localize the ictal onset zone of focal epileptic seizures by magnetoencephalography (MEG) and to compare the results with interictal MEG localizations, ictal and interictal electroencephalography (EEG) results and magnetic resonance imaging (MRI) in epilepsy surgery candidates. MATERIALS AND METHODS: Data of 13 patients with partial seizures during MEG recording were analysed. Measurements were performed with a Magnes II dual unit system. RESULTS: In six of 13 cases, the ictal onset zone could be localized by MEG, with all interictal MEG findings being confirmed by ictal MEG results. In four cases, the ictal MEG localization results were corresponding to the ictal EEG localization results. In two cases, EEG yielded no comparable information. CONCLUSION: Ictal onset localization is feasible with MEG. Both interical and ictal MEG contribute valuable information to the presurgical assessment of epilepsy patients.     

Dipole Modeling in Epilepsy Surgery Candidates

Summary: Purpose : The validity and clinical significance of dipole modeling in epilepsy surgery candidates is not fully established.
Patients and Methods : Interictal and ictal dipole modeling was performed in 43 patients with refractory complex partial seizures (CPS) and intracranial structural abnormalities demonstrated with optimum magnetic resonance imaging (MRI: space–occupying, n = 15; atrophic, n = 26; dysplastic, n = 2). Video–EEG monitoring showed CPS in all patients. In 12 patients, additional intracranial EEG monitoring demonstrated hippocampal seizure onset in 11 patients and medial occipital ictal onset in 1.
Results : Spatiotemporal dipole mapping of averaged interictal spikes and epochs of early ictal discharges revealed two distinct dipole patterns. Patients with lesions located in the medial (± lateral) temporal lobe (n = 34) and medial occipital lobe (n = 1) uniformly presented a combined interictal dipole that consisted of a radial and a tangential component with a high degree of elevation relative to the axial plane. Eight of 9 patients with extratemporal lesions had a less stable dipole with a predominant radial component. Ictal dipole modeling identified the ictal onset zone correctly as compared with intracranial EEG recordings from bilateral hippocampal depth electrodes. Ictal dipoles showed a striking correspondence with the interictal dipoles in individual patients.
Conclusions : Interictal and ictal dipole mapping provided additional, reliable, and relevant localizing information in surgical candidates for refractory CPS. Ictal dipole analysis may limit the number of patients who require intracranial electrodes.     

Ictal magnetoencephalographic study in a patient with ring 20 syndrome

OBJECTIVE: To report the ictal magnetoencephalography (MEG) in a patient with ring chromosome 20 mosaicism, a rare chromosomal anomaly associated with intractable epilepsy. METHODS: MEG and simultaneous EEG were recorded with a 204 channel whole head MEG system. Ten habitual seizures occurred during the acquisition, which was done twice. The equivalent current dipoles (ECDs) for ictal discharges on MEG were calculated using a single dipole model. The ECDs were superimposed on a magnetic resonance image. RESULTS: During the seizures, EEG showed prolonged bursts of 5-6 Hz high voltage slow waves with spike components, dominantly in the bilateral frontal region. MEG showed epileptiform discharges corresponding to the ictal EEG. Ictal discharges on MEG were dominant in the frontal area in the initial portion, and then spread in the bilateral temporal area in the middle of the seizure. ECDs obtained from the spikes of the initial portion were clustered in the medial frontal lobe. CONCLUSIONS: The source of the ictal MEG was localised in the medial frontal lobe. The findings suggest that the mechanism underlying epilepsy in this case might be similar to medial frontal lobe epilepsy. Ictal MEG is a valuable tool for detecting the site of seizure onset.     

Ictal MEG in two children with partial seizures

We report on the successful identification of epileptic foci in two children with partial epilepsy using ictal magnetoencephalography (MEG). Case 1 is a 12-year-old male suffering with simple partial seizures with leftwards nystagmus. Ictal SPECT revealed a hyperperfusion area in the right lateral occipital area, and MRI revealed cortical dysplasia in the same area. Interictal EEG dipoles were concentrated in the right mesial occipital lobe. Both interictal and ictal MEG dipoles were concentrated in the right mesial occipital lobe, which corresponded well with neuroimaging data and his clinical features. Case 2 is a 5-year-old female suffering with simple partial seizures with left-side facial twitching. Interictal EEG dipoles were located in her left motor area, the pre-sylvian fissure, close to the location of the interictal MEG-estimated dipoles. Ictal EEGs showed no remarkable changes associated with her clinical manifestations. However, ictal MEG showed high-voltage slow waves over her left hemisphere, and ictal MEG iso-contour maps revealed a clear dipolar pattern, which suggested that the MEG dipole was located in the area of the sylvian fissure. Ictal SPECT revealed hyperperfusion areas around the left sylvian fissure. Conclusion: Ictal MEG is useful for determining the precise location of epileptic focus in patients with motionless seizures, including children.     

Continuous Source Imaging of Scalp Ictal Rhythms in Temporal Lobe Epilepsy

Summary: Purpose: We wished to determine whether continuous EEG source imaging can predict the location of seizure onset with sublobar accuracy in temporal lobe epilepsy (TLE).
Methods : We retrospectively analyzed the earliest scalp ictal rhythms, recorded with 23- to 27-channel EEG, in 40 patients with intractable TLE. A continuous source analysis technique with multiple fixed dipoles (Focus 1.1) decomposed the EEG into source components representing the activity of major cortical sublobar surfaces. For the temporal lobe, these were basal, anterior tip, anterolateral, and posterolateral cortex. Ictal EEG onset was categorized according to its most prominent and leading source component. All patients underwent intracranial EEG studies before epilepsy surgery, and all had a successful surgical outcome (follow-up >1 year).
Results : Most patients with ictal rhythms having a predominant basal source component had hippocampal-onset seizures, whereas those with seizures with prominent lateral source activity had predominantly temporal neocortical seizure origins. Seizures with a prominent anterior temporal tip source component mostly had onset in entorhinal cortex. Seizures in some patients had several equally large and nearly synchronous source components. These seizures, which could be modeled equally well by a single oblique dipole, had onset predominantly in either entorhinal or lateral temporal cortex.
Conclusions : Multiple fixed dipole analysis of scalp EEG can provide information about the origin of temporal lobe seizures that is useful in presurgical planning. In particular, it can reliably distinguish seizures of mesial temporal origin from those of lateral temporal origin.     

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.     

Role of immediate postictal diffusion-weighted MRI in localizing epileptogenic foci of mesial temporal lobe epilepsy and non-lesional neocortical epilepsy.

OBJECTIVE: To determine whether meaningful changes in signal intensity or in the apparent diffusion coefficient of water (ADC) in the ictal onset zone can be detected through immediate postictal and interictal diffusion-weighted magnetic resonance imaging (DWMRI) in patients with localization-related epilepsy. METHOD: In randomly selected 10 medial and lateral temporal lobe epilepsy (TLE) and four extratemporal epilepsy patients, DWMRI was performed immediately after a seizure and during the interictal period. All 14 patients were non-lesional except for hippocampal sclerosis detected on MRI. The mean time interval from seizure onset to postictal DWMRI was 81 min. Regions of interest (ROI) were selected in both the cortex, which was believed to be the ictal onset zone, and the corresponding anatomical region of the contralateral hemisphere in the postictal and interictal DWMRI. The mean ADC measured from all ROIs was compared. Ictal onset zones were determined by ictal electroencephalography (EEG) and seizure semiology. RESULTS: On visual inspection of postictal and interictal DWMRI, signal changes in the ictal onset zone could be identified in only one patient with medial TLE. The mean ADC values from the ictal onset zones were not significantly different from those of the corresponding contralateral regions of the cortices in both postictal and interictal DWMRI. However, the postictal ADC values of the epileptogenic foci of neocortical epilepsy or neocortical temporal portion of TLE without hippocampal sclerosis were decreased compared with interictal ones in whom both interictal and postictal DWMRIs were obtained (P = 0.028). CONCLUSION: Our results demonstrate that water diffusion can change even after a single seizure in non-lesional neocortical epilepsy.     

Ictal and Interictal Activity in Partial Epilepsy Recorded with Multichannel Magnetoelectroencephalography: Correlation of Electroencephalography/Electrocorticography, Magnetic Resonance Imaging, Single Photon Emission Computed Tomography, and Positron Emission Tomography Findings

Ictal and interictal epileptic activity was recorded for the first time by multichannel magnetoencephalography (MEG) in three patients with partial epilepsy. Pre- and intra-operative localization of the epileptogenic region was compared. The interictal epileptic activity was localized at the same region of the temporal or frontal lobe as the ictal activity. Main zones of ictal activity were shown to evolve from the tissue at the centers of interictal activity. Pre- and intra-operative electrocorticography (ECoG) as well as postoperative outcome confirmed localization in the temporal and frontal lobe. Results also correlated with findings from scalp EEG, interictal and ictal single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance imaging (MRI). Combined multichannel MEG/EEG recording permitted dipole localization of interictal and ictal activity.     

Lobar localization information in epilepsy patients: MEG--a useful tool in routine presurgical diagnosis

Epilepsy surgery is an established therapy for pharmacoresistant focal epilepsy. This study investigated the contribution of routinely used magnetoencepahlography (MEG) in addition to long term video-EEG-monitoring in presurgical evaluation. The distribution of localization results to anatomical lobes was compared with special focus to MEG spike localization results in cases without or with ambiguous EEG findings. A total of 105 consecutive patients with intractable focal epilepsy and epilepsy surgery after investigation by video-EEG-monitoring and MEG were included. The percentages of monolobar results were analysed and compared, especially with respect to the resection lobe. Postoperative outcome was used for further validation. No spikes were recorded on MEG in 30% (32 of 105). In cases with a diagnostic finding by the respective method, MEG localized in 82% (60 of 73 patients) within one anatomical lobe. Ictal EEG localized within one lobe in 72% (66 of 92 patients), interictal EEG in 60% (59 of 98 patients). In 25 of 105 patients (24%) no clear localization within one lobe was found either in interictal or in ictal EEG. In 11 of these cases MEG localized within the resection lobe. Six patients of these became seizure free, the other five had at least 50% reduction of their seizure rate 1 year after surgery. In summary MEG is a useful tool in the routine workup for epilepsy surgery contributing information to focus hypothesis in addition to video-EEG.     

Is ictal recording mandatory in temporal lobe epilepsy? Not when the interictal electroencephalogram and hippocampal atrophy coincide

OBJECTIVE: To investigate the concordance between scalp electroencephalogram (EEG) lateralization and side of hippocampal atrophy in patients with temporal lobe epilepsy (TLE). METHODS: We studied 184 consecutive patients with TLE without lesions other than those compatible with mesial temporal sclerosis. In this study, we studied specifically hippocampal atrophy and the results of scalp EEG investigation. Patients were classified according to the localization of interictal epileptiform discharges as unilateral, bilateral asymmetric, and bilateral symmetric. The EEG seizure onsets were also classified separately as unilateral, bilateral asymmetric, and bilateral symmetric. The hippocampal atrophy was determined by volumetric measurements using high-resolution magnetic resonance imaging (MRIVol). RESULTS: Only 3% of patients had discordance between the ictal and interictal EEG lateralizations; however, none of these had unilateral interictal EEG abnormalities. Interictal EEGs were considered unilateral in 62.0% of patients, bilateral asymmetric in 31.5%, and bilateral symmetric in 6.5%. Ictal EEGs were considered unilateral in 63.5% of patients, bilateral asymmetric in 30.0%, and bilateral symmetric in 6.5%. The MRIVol showed unilateral hippocampal atrophy in 60.9% of patients, bilateral asymmetric hippocampal atrophy in 19.0%, symmetric hippocampal atrophy in 3.8%, and normal volumes in 16.3%. There was a significant concordance between MRIVol lateralization and both interictal and ictal EEG lateralization (P<.001). All patients with unilateral hippocampal atrophy had concordant interictal and ictal EEG lateralization. Six (18.2%) of the 33 patients with bilateral asymmetric hippocampal atrophy had MRI lateralization discordant with EEG lateralization. CONCLUSIONS: We found a strong concordance between EEG and MRIVol lateralization in patients with TLE. Unilateral hippocampal atrophy predicted ipsilateral interictal epileptiform abnormalities and ipsilateral seizure onsets with no false lateralization. Previous studies in addition to the present series support that a concordant outpatient EEG evaluation in patients with TLE and unilateral hippocampal atrophy would obviate the need for inpatient EEG monitoring.     

A Comparison of Magnetoencephalography, MRI, and V-EEG in Patients Evaluated for Epilepsy Surgery

PURPOSE: To determine the efficacy and relative contribution of several diagnostic methods [ictal and interictal scalp and intracranial EEG, magnetic resonance imaging (MRI), and magnetoencephalography (MEG)] in identifying the epileptogenic zone for resection. METHODS: This was a prospective study using a masked comparison-to-criterion standard. Fifty-eight consecutive patients with refractory partial epilepsy from two university comprehensive epilepsy programs were studied. Patients who were evaluated for and underwent epilepsy surgery were recruited. The main outcome measure was the efficacy of each diagnostic method to identify the resected epileptogenic zone, when referenced to surgical outcome. RESULTS: MEG (52%) was second only to ictal intracranial V-EEG in predicting the epileptogenic zone for the entire group of patients who had an excellent surgical outcome (seizure free or rare seizure). In a subanalysis, for patients who had temporal lobe surgery, this same relation was seen (MEG, 57%, ictal intracranial V-EEG, 62%). With extratemporal resection, ictal (81%) and interictal (75%) intracranial EEG were superior to MEG (44%) in predicting the surgery site in those patients with an excellent outcome. Finally, for all patients who had a good surgical outcome, MEG (52%) was better than ictal (33%) or interictal (45%) scalp VEEG in predicting the site of surgery. CONCLUSIONS: These results indicate that MEG is a very promising diagnostic method and raise the possibility that it may obviate the need for invasive EEG in some cases or reduce the length of scalp EEG evaluation in others.     

Source localization in refractory partial epilepsy.

In this paper, 51 patients with refractory complex partial seizures (CPS) and intracranial structural abnormalities demonstrated with optimum MR (space-occupying: n = 16; atrophic: n = 32; dysplastic: n = 3) were studied. Video-EEG monitoring showed CPS in all patients. In 13 patients, additional intracranial EEG monitoring demonstrated hippocampal seizure onset in 12 and medial occipital ictal onset in 1 patient. Interictal and ictal dipole modeling using a spherical head model and realistic electrode coordinates were performed. Spatiotemporal dipole mapping of interictal epileptic discharges revealed two distinct dipole patterns. Patients with lesions located in the medial temporal lobe (n = 41) and medial occipital lobe (n = 2) uniformly presented a dipole with an elevation of more than 15 degrees relative to the axial plane. Eight out of ten patients with extratemporal lesions and 1 patient with a pure neocortical temporal lesion had a less stable dipole with an elevation less than 15 degrees relative to the axial plane. Dipole modeling of epochs of early ictal discharges revealed a striking correspondence with the interictal findings in individual patients. Ictal dipole modeling identified the ictal onset zone correctly when compared with intracranial EEG recordings from bilateral hippocampal depth electrodes in patients with medial temporal seizure onset. Mapping of dipoles on MR images of individual patients facilitated clinical interpretation of the EEG data. Interictal and ictal dipole mapping provided additional and clinically relevant information and may obviate the need for intracranial EEG studies in some surgical candidates for refractory CPS.     

Source localization of interictal spike-locked neuromagnetic oscillations in pediatric neocortical epilepsy

ObjectiveTo evaluate the utility of an event-related beamforming (ERB) algorithm in source localization of interictal discharges.MethodsWe analyzed interictal magnetoencephalography data in 35 children with intractable neocortical epilepsy. We used a spatiotemporal beamforming method to estimate the spatial distribution of source power in individual interictal spikes. We compared ERB results to source localization using the equivalent current dipole model and to the seizure onset zones on intracranial EEG.ResultsFocal beamformer localization was observed in 66% of patients and multifocal in the remaining 34%. ERB localized within 2 cm of the equivalent current dipole cluster centroid in 77% of the patients. ERB localization was concordant with the seizure onset zone on intracranial EEG at the gyral level in 69% of patients. Focal ERB localization area was included in the resection margin in 22/23 patients. However, focal ERB localization was not statistically associated with better surgical outcome.ConclusionsERB can be used for source localization of interictal spikes and can be predictive of the ictal onset zone in a subset of patients with neocortical epilepsy.SignificanceThese results support the utility of beamformer source localization as a fast semi-automated method for source localization of interictal spikes and planning the surgical strategy.     

Seizure outcome after anterior temporal lobectomy and its predictors in patients with apparent temporal lobe epilepsy and normal MRI

PURPOSE: Very little reliable information is available regarding the role of anterior temporal lobectomy (ATL), optimal presurgical evaluation strategy, post-ATL seizure outcome, and the factors that predict the outcome in patients with medically refractory temporal lobe epilepsy (TLE) and normal high-resolution magnetic resonance imaging (MRI). To be cost-effective, epilepsy surgery centers in developing countries will have to select candidates for epilepsy surgery by using the locally available technology and expertise. METHODS: We reviewed the electroclinical and pathological characteristics and seizure outcome of 17 patients who underwent ATL for medically refractory TLE after being selected for ATL based on a noninvasive selection protocol without the aid of positron emission tomography (PET) or single-photon emission computed tomography (SPECT), despite a normal preoperative high-resolution MRI. RESULTS: Seven (41%) patients achieved an excellent seizure outcome; five of them were totally seizure free. An additional five (29%) patients had >75% reduction in seizure frequency. The following pre-ATL factors predicted an excellent outcome: antecedent history of febrile seizures, strictly unilateral anterior temporal interictal epileptiform discharges (IEDs), and concordant type 1 ictal EEG pattern. All the five patients with pathologically verified hippocampal formation neuronal loss were seizure free. The presence of posterior temporal, bilateral temporal, and generalized IEDs portended unfavorable post-ATL seizure outcome. CONCLUSIONS: A subgroup of patients destined to have an excellent post-ATL outcome can be selected from MRI-negative TLE patients by using history and scalp-recorded interictal and ictal EEG data. The attributes of these patients are antecedent history of febrile seizures, strictly unilateral anterior IEDs, and concordant type 1 ictal EEG pattern.     

Toward the substitution of invasive electroencephalography in epilepsy surgery.

The authors compared the localization accuracy of interictal magnetoencephalography (MEG) with ictal and interictal invasive video electroencephalography (VEEG) in identifying the epileptogenic zone in epilepsy surgery candidates. Forty-one patients, 29 with temporal lobe epilepsy (TLE) and 12 with extratemporal lobe epilepsy (ETLE), participated. Only patients with interictal changes during the MEG recordings were included. A comparison of the accuracy of invasive VEEG and MEG seizure zone identification was based on the degree of overlap between the location of the actual surgical resection and the zone identified by each method, and the success of surgery in reducing seizure activity. No statistical differences were observed between the accuracy of invasive VEEG and MEG in determining the location of the seizure zone across TLE and ETLE cases. Invasive VEEG and MEG localization judgments were correct in 54% and 56% of the cases, respectively. Separate group analyses suggested that MEG may be less beneficial relative to invasive VEEG in ETLE than TLE cases. MEG is of statistically equivalent accuracy to invasive VEEG, despite the fact that its use has not reached optimal conditions. The authors predict the replacement of the more invasive procedure with MEG in the near future for TLE cases, subsequent to the optimization of the conditions under which preoperative MEG is performed.     

MEG predicts outcome following surgery for intractable epilepsy in children with normal or nonfocal MRI findings

PURPOSE: To identify the predictors of postsurgical seizure freedom in children with refractory epilepsy and normal or nonfocal MRI findings. METHODS: We analyzed 22 children with normal or subtle and nonfocal MRI findings, who underwent surgery for intractable epilepsy following extraoperative intracranial EEG. We compared clinical profiles, neurophysiological data (scalp EEG, magnetoencephalography (MEG) and intracranial EEG), completeness of surgical resection and pathology to postoperative seizure outcomes. RESULTS: Seventeen children (77%) had a good postsurgical outcome (defined as Engel class IIIA or better), which included eight (36%) seizure-free children. All children with postsurgical seizure freedom had an MEG cluster in the final resection area. Postsurgical seizure freedom was obtained in none of the children who had bilateral MEG dipole clusters (3) or only scattered dipoles (1). All five children in whom ictal onset zones were confined to < or = 5 adjacent intracranial electrodes achieved seizure freedom compared to three of 17 children with ictal onset zones that extended over >5 electrodes (p = 0.002). None of six children with more than one type of seizure became seizure-free, compared to eight of 16 children with a single seizure type (p = 0.04). Complete resection of the preoperatively localized epileptogenic zone resulted in seizure remission in 63% (5/8) and incomplete resections, in 21% (3/14) (p = 0.06). Age of onset, duration of epilepsy, number of lobes involved in resection, and pathology failed to correlate with seizure freedom. CONCLUSIONS: Surgery for intractable epilepsy in children with normal MRI findings provided good postsurgical outcomes in the majority of our patients. As well, restricted ictal onset zone predicted postoperative seizure freedom. Postoperative seizure freedom was less likely to occur in children with bilateral MEG dipole clusters or only scattered dipoles, multiple seizure types and incomplete resection of the proposed epileptogenic zone. Seizure freedom was most likely to occur when there was concordance between EEG and MEG localization and least likely to occur when these results were divergent.     

Imag(in)ing seizure propagation: MEG‐guided interpretation of epileptic activity from a deep source

Identification and accurate localization of seizure foci is vital in patients with medically‐intractable focal epilepsy, who may be candidates for potentially curative resective epilepsy surgery. We present a patient with difficult‐to‐control seizures associated with an occult focal cortical dysplasia residing within the deeper left parietal operculum and underlying posterior insula, which was not detected by conventional MRI analysis. Propagated activities from this deeper generator produced misleading EEG patterns both on surface and subdural electrode recordings suggesting initial activation of the perirolandic and mesial frontal regions. However, careful spatio‐temporal analysis of stereotyped interictal activities recorded during MEG, using sequential dipole modeling, revealed a consistent pattern of epileptic propagation originating from the deeper source and propagating within few milliseconds to the dorsal convexity. In this instance, careful dissection of noninvasive investigations (interictal MEG along with ictal SPECT findings) allowed clinicians to dismiss the inaccurate and misleading findings of the traditional “gold‐standard” intracranial EEG. In fact, this multimodal noninvasive approach uncovered a subtle dysplastic lesion, resection of which rendered the patient seizure‐free. This case highlights the potential benefits of dynamic analysis of interictal MEG in the appropriate clinical context. Pathways of interictal spike propagation may help elucidate essential neural networks underlying focal epilepsy. Hum Brain Mapp, 2012. © 2012 Wiley Periodicals, Inc     

Pre-surgical evaluation and surgical outcome of 41 patients with non-lesional neocortical epilepsy.

Pre-surgical evaluation and the surgical treatment of non-lesional neocortical epilepsy is one of the most challenging areas in epilepsy surgery. The aim of this study was to evaluate the surgical outcome and the diagnostic role of ictal scalp electroencephalography (EEG), interictal (18)F-fluorodeoxyglucose-positron emission tomography (FDG-PET), and ictal technetium-99m hexamethylpropyleneamine oxime single photon emission tomography ( (99m)Tc-HMPAO SPECT). In 41 non-lesional neocortical epilepsy patients (16 frontal lobe epilepsy, 11 neocortical temporal lobe epilepsy, seven occipital lobe epilepsy, four parietal lobe epilepsy, and three with multifocal onset) who underwent surgical treatment between December 1994 and July 1998, we evaluated the surgical outcome with a follow-up of at least 1 year. The localizing and lateralizing values of ictal scalp EEG, interictal FDG-PET, and ictal SPECT were evaluated in those patients with good surgical outcome. Ictal scalp EEG had the highest diagnostic sensitivity in the localization of epileptogenic foci (69.7% vs. 42.9% for FDG-PET and 33.3% for ictal SPECT; P= 0.027). However, no significant difference was found in the lateralization of the epileptogenic hemisphere among the three modalities (78.8% for ictal scalp EEG, 57.2% for FDG-PET, and 55.5% for ictal SPECT; P= 0.102). During a mean follow-up of 2.77 +/- 1.12 years, 33 (80.5%) showed good surgical outcome (seizure free or seizure reduction >90%), including 16 (39.0%) seizure free patients. Ictal scalp EEG was the most useful diagnostic tool in the localization of epileptogenic foci. Interictal FDG-PET and ictal SPECT were found to be useful as complementary and, sometimes, independent modalities. Many patients with non-lesional neocortical epilepsy would benefit from surgical treatment.