Somatosensory-evoked fields on magnetoencephalography for epilepsy infants younger than 4 years with total intravenous anesthesia.

OBJECTIVE: Patients must remain immobile for magnetoencephalography (MEG) and MRI recordings to allow precise localization of brain function for pre-surgical functional mapping. In young children with epilepsy, this is accomplished with recordings during sleep or with anesthesia. This paper demonstrates that MEG can detect, characterize and localize somatosensory-evoked fields (SEF) in infants younger than 4 years of age with or without total intravenous anesthesia (TIVA). METHODS: We investigated the latency, amplitude, residual error (RE) and location of the N20m of the SEF in 26 infants (mean age=2.6 years). Seventeen patients underwent TIVA and 9 patients were tested while asleep, without TIVA. RESULTS: MEG detected 44 reliable SEFs (77%) in 52 median nerve stimulations. We found 27 reliable SEFs (79%) with TIVA and 13 reliable SEFs (72%) without TIVA. TIVA effects included longer latencies (p<0.001) and lower RE (p<0.05) compared to those without TIVA. Older patients and larger head circumferences also showed significantly shorter latencies (p<0.01). CONCLUSIONS: TIVA resulted in reliable SEFs with lower RE and longer latencies. SIGNIFICANCE: MEG can detect reliable SEFs in infants younger than 4 years old. When infants require TIVA for MEG and MRI acquisition, SEFs can still be reliably observed.

Surgical treatment for acute symptomatic refractory status epilepticus: a case report.

A previously healthy 10-year-old boy developed generalized convulsive status epilepticus following a mild febrile illness. Prolonged video-electroencephalographic monitoring revealed frequent right hemispheric electrographic seizures that were refractory to high-dose suppressive therapy. Ictal and interictal magnetoencephalography demonstrated dipole sources projecting from the right mesial temporal region. Diffusion-weighted imaging showed restricted diffusion involving the right hippocampus. Right anterior temporal lobectomy resulted in cessation of status epilepticus. At 1-year follow-up, he attends regular school and has infrequent nocturnal seizures on chronic antiepileptic drug therapy. Surgical treatment should be considered to stop status epilepticus in selected cases of acute symptomatic refractory status epilepticus with no preexisting epilepsy or magnetic resonance imaging abnormalities and may avoid the complications associated with prolonged high-dose suppressive therapy.

Preoperative simulation of intracerebral epileptiform discharges: synthetic aperture magnetometry virtual sensor analysis of interictal magnetoencephalography data.

OBJECT: Magnetoencephalography (MEG) has been used for the preoperative localization of epileptic equivalent current dipoles (ECDs) in neocortical epilepsy. Spatial filtering can be applied to MEG data by means of synthetic aperture magnetometry (SAM), and SAM virtual sensor analysis can be used to estimate the strength and temporal course of the epileptic source in the region of interest. To evaluate the clinical usefulness of this approach, the authors compare the results of SAM virtual sensor analysis to the results of ECD analysis, subdural electroencephalography (EEG) findings, and surgical outcomes in pediatric patients with neocortical epilepsy. METHODS: Ten pediatric patients underwent MEG, invasive subdural EEG, and cortical resection for neocortical epilepsy. The authors compared the morphological characteristics, quantity, location, and distribution of the epileptiform discharges assessed using SAM and ECD analysis, and subdural EEG findings (interictal discharges and ictal onset zones). In nine patients, MEG revealed clustered ECDs. The region exhibiting the maximum percentage (> or = 70%) of spikes/sharp waves on SAM was colocalized to clustered ECDs in seven patients. In six patients, SAM demonstrated focal spikes; in two, diffuse spikes; and in two others, focal rhythmic sharp waves. These epileptiform discharges were similar to those recorded on subdural EEG. In nine patients, concordant regions containing the maximum percentage of spikes/sharp waves were revealed by SAM and subdural EEG data. The region of the maximum percentage of spikes/sharp waves as demonstrated by SAM was colocalized to the ictal onset zone identified by subdural EEG findings in seven patients and partially colocalized in two. CONCLUSIONS: The SAM virtual sensor analysis revealed morphological characteristics, location, and distribution of epileptiform discharges similar to those shown by subdural EEG recordings. By using SAM it is possible to predict intracerebral interictal epileptiform discharges in the region of interest from noninvasively collected preoperative MEG data. The maximum interictal discharge zone identified by SAM virtual sensors correlated to clustered ECDs and the ictal onset zone on subdural EEG findings. Complementary analyses of ECDs and SAM on three-dimensional MR images can improve delineation of epileptogenic zones and lesions in neocortical epilepsy.

Pediatric magnetoencephalography and magnetic source imaging.

Magnetoencephalography (MEG) and magnetic source imaging (MSI) together represent a uniquely powerful functional imaging modality because of their capabilities of directly observing the electrophysiologic activity of neurons with exquisite temporal detail and accurately localizing corresponding neuromagnetic field sources onto high-resolution MR images. These features have and should continue to advance our understanding of the complex spatiotemporal basis of normal and abnormal brain function and development in children. By more clearly delineating and characterizing epileptogenic foci and their relation to eloquent cortex, MSI enables earlier and more effective neurosurgery to be performed, thus resulting in improved seizure outcomes. Although MEG and MSI cannot replace scalp electroencephalography, neuropsychologic testing, and the need for meticulous intraoperative cortical mapping in patients undergoing excision of epileptogenic lesions, their increasing availability should ultimately persuade many clinicians of their key, if not essential, role in the evaluation and treatment of children with epilepsy.

Magnetoencephalography spike sources interrelate the extensive epileptogenic zone of tuberous sclerosis complex.

OBJECTIVE: We hypothesized that the extensive epileptic network in patients with tuberous sclerosis complex (TSC) manifests as clustered and scattered distributions of magnetoencephalography spike sources (MEGSS). METHODS: We retrospectively analyzed pre-surgical MEG in 15 patients with TSC. We performed single moving dipole analysis to localize and classify clustered and scattered MEGSS. We compared the number of electrodes within the resected area (RA) and the proportions of clustered and scattered MEGSS within RA with the seizure outcome. RESULTS: The number of electrodes within RA ranged from 29 to 83 (mean=51). The MEGSS were distributed over multiple lobes (3-8; mean=5.9) and bilaterally in 14 patients. Clusters of MEGSS ranged from 1 to 4 (mean=1.4). The number of MEGSS ranged in total from 28 to 139 (mean=70); in the clusters, 10-128 (mean=49); and in the scatters, 0-45 (mean=21). Four patients achieved an Engel class I surgical outcome, four, a class II outcome; five, a class III outcome; and two, a class IV outcome. The proportion of MEGSS ranged in total from 0 to 92% (mean=57%) within RA; 0-100% (mean=67%) in the resection hemisphere; 0-100% (mean=63%) in the clusters; and 0-81% (mean=28%) in the scatters. Univariate ordinal logistic regression analyses showed that the proportion of scattered MEGSS within RA (p=0.049) significantly correlated with seizure outcomes. Multivariate analyses using three covariates (number of electrodes, proportions of clustered and scattered MEGSS within RA) showed that only the proportion of scattered MEGSS within RA significantly correlated with seizure outcomes (p=0.016). SIGNIFICANCE: MEG data showed a wide distribution of multilobar MEGSS in patients with TSC. The seizure outcome was not related to the clustered MEGSS within RA, since the grids were essentially planned to cover and resect the clustered MEGSS surrounding tubers. The maximal possible resection of scattered MEGSS correlated with improved seizure outcome in TSC. Some parts of the epileptogenic zone disrupted by multiple tubers did not have a sufficiently large area to produce clustered MEGSS. Although the wide distribution of scattered MEGSS is not interpreted as epileptogenic, they might be interrelated with clustered MEGSS to project a complex epilepsy network and be part of the extensive epileptogenic zones found in TSC.

Characterizing magnetic spike sources by using magnetoencephalography-guided neuronavigation in epilepsy surgery in pediatric patients.

OBJECT: The authors sought to validate magnetoencephalography spike sources (MEGSSs) in neuronavigation during epilepsy surgery in pediatric patients. METHODS: The distributions of MEGSSs in 16 children were defined and classified as clusters (Class I), greater than or equal to 20 MEGSSs with 1 cm or less between MEGSSs; small clusters (Class II), 6 to 19 with 1 cm or less between; and scatters (Class III), less than 6 or greater than 1 cm between spike sources. Using neuronavigation, the MEGSSs were correlated to epileptic zones from intra- and extraoperative electrocorticography (ECoG), surgical procedures, disease entities, and seizure outcomes. Thirteen patients underwent MEGSSs: nine had clusters; two had small clusters, one with and one without clusters; and three had scatters alone. All 13 had scatters. Clusters localized within and extended from areas of cortical dysplasia and at margins of tumors or cystic lesions. All clusters were colocalized to ECoG-defined epileptic zones. Four of 10 patients with clusters and/or small clusters underwent complete excisions, and six underwent partial excision with or without multiple subpial transections. In the three patients with scatters alone, ECoG revealed epileptic zones buried within MEGSS areas; these regions of scatters were completely excised and treated with multiple subpial transections. Coexisting scatters were left untreated in nine of 10 patients. Postoperatively, nine of 13 patients were seizure free; the four patients with residual seizures had clusters in unresected eloquent cortex. Three patients in whom no MEGSSs were demonstrated underwent lesionectomies and were seizure free. CONCLUSIONS: Magnetoencephalography spike source clusters indicate an epileptic zone requiring complete excision. Coexisting scatters remote from clusters are nonepileptogenic and do not require excision. Scatters alone, however, should be examined by ECoG; an epileptic zone may exist within these distributions.

Neurophysiologic findings of neuronal migration disorders: intrinsic epileptogenicity of focal cortical dysplasia on electroencephalography, electrocorticography, and magnetoencephalography.

We define specific neurophysiologic characteristics for focal cortical dysplasia, a neuronal migration disorder. We reviewed data from published reports and our patients with focal cortical dysplasia. Our patients underwent preoperative scalp video-electroencephalography (EEG), magnetic resonance imaging (MRI), magnetoencephalography, and intraoperative or extraoperative electrocorticography monitoring. Scalp EEG showed trains of rhythmic epileptiform spike or sharp waves. Positive spikes correlated with early seizure onset, MRI lesion around the rolandic fissure, hemiparesis, and a less favorable outcome. Interictal electrocorticography showed continuous epileptogenic discharges: repetitive electrographic seizures and bursting discharges or continuous or quasicontinuous rhythmic spiking. Ictal electrocorticography showed paroxysmal fast and/or repetitive spiking. Magnetoencephalography showed clustered spike sources within and extending from the lesion. Cortical stimulation gave more frequent, lower-threshold afterdischarges and higher-threshold primary motor function. Focal cortical dysplasias are highly and intrinsically epileptogenic. For surgical seizure control, EEG, electrocorticography, and magnetoencephalography must delineate the intrinsic epileptogenic zone within and extending from the focal cortical dysplasia identified by MRI.

Recurrent intractable seizures in children with cortical dysplasia adjacent to dysembryoplastic neuroepithelial tumor.

The purpose of this study was to identify the pathologic features that predict postoperative outcome in children with cortical dysplasia adjacent to dysembryoplastic neuroepithelial tumors. We reviewed the records of children with dysembryoplastic neuroepithelial tumor who underwent epilepsy surgery and who had at least 1 year of surgical follow-up. We divided the dysembryoplastic neuroepithelial tumors into three pathology classes (simple, complex, and nonspecific), categorized adjunctive cortical dysplasia into four types, and compared histopathology with seizure outcomes. We identified 26 children with dysembryoplastic neuroepithelial tumors. Dysembryoplastic neuroepithelial tumors were complex in 19 patients (73%), simple in 6 (23%), and nonspecific in 1 (4%). Cortical dysplasia was adjacent to dysembryoplastic neuroepithelial tumors in 18 patients. Six patients had type IA cortical dysplasia, 5 had type IB, 3 had type IIA, and 1 had type IIB. The 3 remaining patients had repeated surgeries; of these, 2 patients had cortical dysplasias of type IA/IB and 1 was type IIA/IIB. Eight (39%) of 18 patients with dysembryoplastic neuroepithelial tumors and cortical dysplasia required further surgery for recurrent intractable seizures (P < .05), whereas none of 8 patients without cortical dysplasia required additional surgery. Of 13 patients with type I cortical dysplasia, only 4 had a poor seizure outcome, whereas all 5 patients with type II had a poor seizure outcome postoperatively (P < .05). Children with dysembryoplastic neuroepithelial tumor and cortical dysplasia often had recurrent intractable seizures postoperatively and required further epilepsy surgery. Cortical dysplasia adjacent to dysembryoplastic neuroepithelial tumor can play a role in the epileptogenicity of dysembryoplastic neuroepithelial tumor. Complete resection of a dysembryoplastic neuroepithelial tumor and its adjacent cortical dysplasia should be considered.

Identifying the primary epileptogenic hemisphere from electroencephalographic (EEG) and magnetoencephalographic dipole lateralizations in children with intractable epilepsy.

We used electroencephalographic (EEG) and magnetoencephalographic dipole lateralizations to identify the primary epileptogenic hemisphere in 41 children with intractable localization-related epilepsy. We compared EEG and magnetoencephalographic dipole lateralizations, EEG ictal onsets, and magnetic resonance images (MRIs). Concordant lateralization of EEG and magnetoencephalographic dipoles (> 50% of each lateralizing to the same hemisphere) occurred in 34 patients, with EEG ictal onsets in the same hemisphere in 23 (68%) and concordant MRI lesions in 23 (68%). Focal resection in 16 of 20 patients resulted in a good surgical outcome. Of the seven children with nonconcordant magnetoencephalographic and EEG lateralizations, one (14%) had EEG ictal onset and one (14%) had MRI lesions that lateralized; none had surgery. The relationship between lateralized EEG and magnetoencephalographic dipoles forecasts surgical candidacy. Concordant lateralizations predict good seizure control after surgery by identifying the primary epileptogenic hemisphere. Discordant lateralizations signify an undetermined epileptogenic hemisphere and contraindicate surgery without further testing.

Spatial relationship between fast and slow components of ictal activities and interictal epileptiform discharges in epileptic spasms.

OBJECTIVE: We analyzed the spatial distribution and concordance of fast (>10Hz) and slow (<5Hz) electroencephalogram (EEG) components of ictal activities and interictal epileptiform discharges (IIED) recorded by intracranial video EEG (IVEEG) in children with epileptic spasms (ES). METHODS: We studied eight children with ES, who underwent IVEEG before resective surgery for epilepsy. We quantified the root-mean-square (RMS) amplitude of the fast and slow components of ictal activities during ES and IIED. We compared the concordance between the spatial distributions of the fast and slow components of ES and IIED. RESULTS: There was a larger concordance between the spatial distributions of the fast and slow components in IIED than in ES (p=0.0206 and 0.0401). CONCLUSIONS: The spatial concordance between the fast and slow EEG components was significantly different between ES and IIED. SIGNIFICANCE: The mechanisms underlying the generation of slow EEG components may differ between ES and IIED. The slow EEG components of ES might indicate an extensive epileptic network involving remote symptomatic zones for ES in either the cortical or subcortical areas. The high spatial concordance between the fast and slow components of IIED suggests the involvement of a local inhibitory process within the epileptic cortex.

Sound motion evoked magnetic fields.

OBJECTIVE: The aim of present study was to determine which brain regions are involved in the conscious perception of sound motion in humans. METHODS: Six kinds of sound stimuli were studied. Two static sound stimuli with durations of 100 or 1000 ms remained at a fixed position during the stimulation period. Four moving sound stimuli with duration of 100 or 1000 ms were moving from left to right, or right to left, during the stimulation period. Evoked magnetic fields were recorded using a 151-channel whole cortex magnetoencephalographic system. RESULTS: The response identified in all sound stimuli was M100. Responses identified only in moving sound stimuli were M180, M280 and M680. Contour maps and dipoles overlapped on magnetic resonance imaging indicated that both the M100 and M680 responses were generated in the superior temporal cortex (left and right), while M180 and M280 were generated in the parietal cortex (right). CONCLUSIONS: The results of this MEG study indicated that the right parietal cortex was involved in sound motion processing. We hypothesize that the right parietal cortex, in association with the left and right superior temporal cortex, forms a network to process sound motion information.

Electroencephalographic dipoles of spikes with and without myoclonic jerks caused by epilepsia partialis continua.

We used electroencephalographic (EEG) dipole analysis to investigate the generators of spikes with and without myoclonic jerks in a 12-year-old patient with epilepsia partialis continua secondary to left parietal cortical dysplasia. We recorded EEG and right wrist extensor electromyography (EMG) and collected 42 spikes with jerks (jerking spikes) and 42 spikes without jerks (nonjerking spikes). We applied a single moving dipole model to the individual and averaged spikes. Dipoles at the negative peak of individual jerking and nonjerking spikes were localized in the dysplastic area. At the onset of the averaged jerking spike that preceded the EMG discharges by 20 ms, the dipole was in the motor cortex, whereas for the averaged nonjerking spike, the dipole was in the sensory cortex. The dipole moment at averaged jerking spike onset was twice that of the averaged nonjerking spike. Electroencephalographic dipole analysis of averaged spikes differentiated the generator of jerking and nonjerking spikes in epilepsia partialis continua. Individual dipoles demonstrated the area of epileptogenic cortical dysplasia.

Localization of auditory N1 in children using MEG: source modeling issues.

Techniques for localizing auditory (AEF) sources are a topic of on-going discussion and this is particularly pertinent in pediatric research. Smaller head sizes are: (1) subject to bilateral temporal lobe source interference from both temporal lobes; and (2) further from MEG sensors resulting in poorer signal-to-noise ratios. An additional consideration in children is that the components of the AEF have distinct contributions along the development spectrum resulting in an ever-changing morphology for the pediatric AEF. These factors present a complicated picture for dipole fitting and raise the question of the most effective fitting strategy. We examined the AEF localizations in five children from 151, 70 and 47 MEG channels of data. We found evidence that bilateral source interaction could result in localization errors along the medial-lateral axis of up to 1 cm. We suggest that any modeling strategy needs to sufficiently account for this interaction and more precise models allowing for multiple sources need to be developed.

Magnetoencephalography helps delineate the extent of the epileptogenic zone for surgical planning in children with intractable epilepsy due to porencephalic cyst/encephalomalacia.

OBJECT: Porencephalic cyst/encephalomalacia (PC/E) is a brain lesion caused by ischemic insult or hemorrhage. The authors evaluated magnetoencephalography (MEG) spike sources (MEGSS) to localize the epileptogenic zone in children with intractable epilepsy secondary to PC/E. METHODS: The authors retrospectively studied 13 children with intractable epilepsy secondary to PC/E (5 girls and 8 boys, age range 1.8-15 years), who underwent prolonged scalp video-electroencephalography (EEG), MRI, and MEG. Interictal MEGSS locations were compared with the ictal and interictal zones as determined from scalp video-EEG. RESULTS: Magnetic resonance imaging showed PC/E in extratemporal lobes in 3 patients, within the temporal lobe in 2 patients, and in both temporal and extratemporal lobes in 8 patients. Magnetoencephalographic spike sources were asymmetrically clustered at the margin of PC/E in all 13 patients. One cluster of MEGSS was observed in 11 patients, 2 clusters in 1 patient, and 3 clusters in 1 patient. Ictal EEG discharges were lateralized and concordant with MEGSS in 8 patients (62%). Interictal EEG discharges were lateralized and concordant with MEGSS hemisphere in 9 patients (69%). Seven patients underwent lesionectomy in addition to MEGSS clusterectomy with (2 patients) and without (5 patients) intracranial video-EEG. Temporal lobectomy was performed in 1 patient and hemispherectomy in another. Eight of 9 patients achieved seizure freedom following surgery. CONCLUSIONS: Magnetoencephalography delineated the extent of the epileptogenic zone adjacent to PC/E in patients with intractable epilepsy. Complete resection of the MEGSS cluster along with PC/E can provide favorable seizure outcomes.

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

OBJECTIVE: To evaluate the utility of an event-related beamforming (ERB) algorithm in source localization of interictal discharges. METHODS: We 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. RESULTS: Focal 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. CONCLUSIONS: ERB 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. SIGNIFICANCE: These 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.

Total intravenous anesthesia affecting spike sources of magnetoencephalography in pediatric epilepsy patients: focal seizures vs. non-focal seizures.

PURPOSE: Magnetoencephalography (MEG) provides source localization of interictal spikes. This study evaluated the inhibitory effects of propofol on MEG spike sources (MEGSSs) among different types of seizures in patients who underwent two separate MEG studies with and without total intravenous anesthesia (TIVA) using propofol. METHODS: We studied 19 children (1-14 years; mean, 6.2 years) who had MEG with and without TIVA. TIVA was administered using propofol (0.03-0.06 mg/kg/min) to record MEG with simultaneous EEG. We analyzed number of spikes of MEG and MEGSSs comparing MEG studies done with and without TIVA. RESULTS: Seizures were divided into nine focal seizure (FS) with/without secondary generalization, five epileptic spasm (ES), and five generalized seizure (GS). TIVA significantly decreased the number of MEG spikes/min (from 4.5 to 2.0) in five FS without secondary generalization (p<0.05). The number of MEG spikes/min was significantly lower (1.9) in FS than that in non-FS (ES+GS, 6.1) (p<0.01). MEGSSs without TIVA were clustered in 15 patients (6FS; 4ES; 5GS), scattered in four (3FS; 1ES). MEG under TIVA showed clusters in 10 patients (1FS; 4ES; 5GS), scatters in three (2FS; 1ES) and no MEGSS in six patients with FS. Under TIVA, nine (90%) of ten patients with non-FS showed MEGSSs clusters compared to one (11%) of nine patients with FS (p<0.01). CONCLUSIONS: Reduction of MEGSSs occurred in patients with FS under TIVA. Diffuse/generalized spikes in non-FS are not affected by TIVA. Propofol may decrease focal spikes in the epileptic cortex in FS. Cortical hyperexcitability in non-FS group would be stronger or more extensive than that in the FS group of patients.

The role of magnetoencephalography in children undergoing hemispherectomy.

OBJECT: Hemispherectomy is an established neurosurgical procedure for medication-resistant epilepsy in children. Despite the effectiveness of this technique, there are patients who do not achieve an optimum outcome after surgery; possible causes of suboptimal results include the presence of bilateral independent epileptogenic foci. Magnetoencephalography (MEG) is an emerging tool that has been found to be useful in the management of lesional and nonlesional epilepsy. The authors analyzed the relative contribution of MEG in patient selection for hemispherectomy. METHODS: The medical records of children undergoing hemispherectomy at the Hospital for Sick Children were reviewed. Those patients who underwent MEG as part of the presurgical evaluation were selected. RESULTS: Thirteen patients were included in the study. Nine patients were boys. The mean age at the time of surgery was 66 months (range 10-149 months). Seizure etiology was Rasmussen encephalitis in 6 patients, hemimegalencephaly in 2 patients, and cortical dysplasia in 4 patients. In 8 patients, video-EEG and MEG results were consistent to localize the primary epileptogenic hemisphere. In 2 patients, video-EEG lateralized the ictal onset, but MEG showed bilateral spikes. Two patients had bilateral video-EEG and MEG spikes. Engel Class I, II, and IV outcomes were seen in 10, 2, and 1 patients, respectively. In 2 of the patients who had an outcome other than Engel Class I, the MEG clusters were concentrated in the disconnected hemisphere. The third patient had bilateral clusters and potentially independent epileptogenic foci from bilateral cortical dysplasia. CONCLUSIONS: The presence of unilateral MEG spike waves correlated with good outcomes following hemispherectomy. In some cases, MEG provides information that differs from that obtained from video-EEG and conventional MR imaging studies. Further studies with a greater number of patients are needed to assess the role of MEG in the preoperative assessment of candidates for hemispherectomy.

Localization of epileptic foci in children with intractable epilepsy secondary to multiple cortical tubers by using synthetic aperture magnetometry kurtosis.

OBJECT: Magnetoencephalography (MEG) has been typically used to localize epileptic activity by modeling interictal activity as equivalent current dipoles (ECDs). Synthetic aperture magnetometry (SAM) is a recently developed adaptive spatial filtering algorithm for MEG that provides some advantages over the ECD approach. The SAM-kurtosis algorithm (also known as SAM[g2]) additionally provides automated temporal detection of spike sources by using excess kurtosis value (steepness of epileptic spike on virtual sensors). To evaluate the efficacy of the SAM(g2) method, the authors applied it to readings obtained in children with intractable epilepsy secondary to tuberous sclerosis complex (TSC), and compared them to localizations obtained with ECDs. METHODS: The authors studied 13 children with TSC (7 girls) whose ages ranged from 13 months to 16.3 years (mean 7.3 years). Video electroencephalography, MR imaging, and MEG studies were analyzed. A single ECD model was applied to localize ECD clusters. The SAM(g2) value was calculated at each SAM(g2) virtual voxel in the patient's MR imaging-defined brain volume. The authors defined the epileptic voxels of SAM(g2) (evSAM[g2]) as those with local peak kurtosis values higher than half of the maximum. A clustering of ECDs had to contain > or = 6 ECDs within 1 cm of each other, and a grouping of evSAM(g2)s had to contain > or = 3 evSAM(g2)s within 1 cm of each other. The authors then compared both ECD clusters and evSAM(g2) groups with the resection area and correlated these data with seizure outcome. RESULTS: Seizures started when patients were between 6 weeks and 8 years of age (median 6 months), and became intractable secondary to multiple tubers in all cases. Ictal onset on scalp video electroencephalography was lateralized in 8 patients (62%). The MEG studies showed multiple ECD clusters in 7 patients (54%). The SAM(g2) method showed multiple groups of epileptic voxels in 8 patients (62%). Colocalization of grouped evSAM(g2) with ECD clusters ranged from 20 to 100%, with a mean of 82%. Eight patients underwent resection of single (1 patient) and multiple (7 patients) lobes, with 6 patients achieving freedom from seizures. Of 8 patients who underwent surgery, in 7 the resection area covered ECD clusters and grouped evSAM(g2)s. In the remaining patient the resection area partially included the ECD cluster and grouped evSAM(g2)s. Six of the 7 patients became seizure free. CONCLUSIONS: The combination of SAM(g2) and ECD analyses succeeded in localizing the complex epileptic zones in children with TSC who had intractable epilepsy secondary to multiple cortical tubers. For the subset of children with TSC who present with early-onset and nonlateralized seizures, MEG studies in which SAM(g2) and ECD are used might identify suitable candidates for resection to control seizures.

Changing ictal-onset EEG patterns in children with cortical dysplasia.

PURPOSE: Cortical dysplasia (CD) is intrinsically epileptogenic. We hypothesize that CDs clinically emerging in the early developing brain tend to extend into multifocal or larger epileptic networks to pronounce intractability in contrast to CDs which clinically emerge at a later age. METHODS: We evaluated the spatial and temporal profiles of ictal-onset EEG patterns in children with histopathologically confirmed CD. We designated Group A as children with changing ictal-onset EEG patterns over time, and Group B without change. We compared seizure profiles, consecutive scalp video-EEGs (VEEGs), MRI, MEG, and surgical outcomes. RESULTS: We found 14 children consisting of 10 Group A patients (7 girls) and 4 Group B patients (all boys). Eight (80%) Group A patients had their seizure onset <5 years while all Group B patients had seizure onset >or=5 years (p<.05). Changes of ictal onset EEG pattern in Group A consisted of bilateral (4 patients), extending (2); extending and bilateral (2); and generalized (2). We saw MRI lesions (6) and single clustered MEG spike sources (MEGSSs) in (5). Six patients underwent surgery before 15 years of age, and 4 of them attained seizure freedom. All 4 Group B patients had MRI lesions and single clustered MEGSSs. Three patients underwent surgery after 15 years of age. All 4 patients attained seizure freedom. CONCLUSION: Ictal-onset EEG patterns change over time in children with early seizure onset and intractable epilepsy caused by CD. Younger epileptic children with CD more frequently have multifocal epileptogenic foci or larger epileptogenic foci. Early resection of CD, guided by MRI, MEG, and intracranial video EEG, resulted in seizure freedom despite changes in ictal-onset EEG patterns.