S H Chuang

University of Toronto, Toronto, Ontario, Canada

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Publications (120)271.69 Total impact

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    ABSTRACT: 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.
    Journal of Neurosurgery Pediatrics 07/2014; · 1.63 Impact Factor
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    ABSTRACT: 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 (0.03-0.06mg/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.
    Epilepsy research 04/2013; · 2.48 Impact Factor
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    ABSTRACT: 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 2cm 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.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 03/2013; · 3.12 Impact Factor
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    ABSTRACT: Children with new-onset seizures may have antecedent neurobiologic alterations that predispose them to developing seizures. Our aim was to evaluate hippocampal and thalamic volumes and lobar cortical thickness of children with new-onset seizures. Twenty-nine children with new-onset seizures and normal MR imaging findings were recruited. Ten patients had generalized seizures, 19 had partial seizures, and 15 were on antiepileptic medications. Twenty-three age-matched healthy controls were also recruited. Hippocampal and thalamic volumes and lobar cortical thickness, including frontal, medial temporal, lateral temporal, parietal, cingulate, and occipital cortical thickness, were assessed by using volumetric T1-weighted imaging and were compared between patients and controls. There were no significant differences in hippocampal and thalamic volumes of patients with new-onset seizures, including the subgroups with generalized and partial seizures and those on and off antiepileptic medications, compared with controls (P > .01). There was significant reduction in cortical thickness in right cingulate (P = .004), right medial temporal (P = .006), and left frontal (P = .007) cortices in patients with new-onset seizures. Patients with generalized seizures did not demonstrate a significant reduction in cortical thickness (P > .01). Patients with partial seizures demonstrated a significant reduction in cortical thickness in the right frontal (P = .008), right parietal (P = .003), and left frontal (P = .007) cortices. There were no significant differences in cortical thickness among patients on or off antiepileptic medications (P > .01). We found reduced cortical thickness in children with new-onset seizures. Further studies are necessary to elucidate the neurobiologic relevance of these structural changes.
    American Journal of Neuroradiology 01/2012; 33(4):673-7. · 3.17 Impact Factor
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    ABSTRACT: 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. 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. 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. 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.
    Journal of Neurosurgery Pediatrics 12/2011; 8(6):575-83. · 1.63 Impact Factor
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    ABSTRACT: Cortical and white matter changes have been identified outside the MR imaging-visible cortical/subcortical tubers in the tuberous sclerosis complex. The aim of this study was to evaluate DTI changes in the corpus callosum and internal capsules and to correlate the DTI changes with cortical/subcortical tuber load. Twelve TSC patients and 23 controls underwent MR imaging including DTI. FA, trace, D( ||), and D() of genu and splenium of corpus callosum and right and left internal capsules were assessed. The number and volume of cortical/subcortical tubers were correlated with DTI indices of corpus callosum and internal capsules. In the genu and splenium, FA was lower and trace (P < .01) and D() were higher (P < .01), and in the internal capsules, trace was higher (P = .04) in TSC patients compared with controls. The total tuber volume correlated positively with trace of genu (r = 0.77, P < .01) and splenium (r = 0.69, P = .01) and with D() of splenium (r = 0.68, P = .01), and negatively with FA of splenium (r = -0.60, P = .04) of corpus callosum. The left and right hemispheric tuber volume correlated positively with trace of left (r = 0.56, P = .05) and right (r = 0.67, P = .02) internal capsules. Our findings of reduced FA, elevated trace, and elevated D() in the corpus callosum and internal capsules may be related to abnormalities in myelin. The correlations between tuber volume and DTI indices in corpus callosum and internal capsules suggested that more extensive malformation as demonstrated by larger tuber load was more likely to be associated with more severe DTI changes in the commissural and projection white matter.
    American Journal of Neuroradiology 03/2010; 31(7):1273-7. · 3.17 Impact Factor
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    ABSTRACT: 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. 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. 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. 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.
    Journal of Neurosurgery Pediatrics 12/2009; 4(6):515-22. · 1.63 Impact Factor
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    ABSTRACT: PurposeCortical 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.MethodsWe 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.ResultsWe 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 ⩾ 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.ConclusionIctal-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.
    Brain & development 01/2009; · 1.74 Impact Factor
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    ABSTRACT: 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. We studied 28 children (3-14 years; mean, 6.6). We intravenously administered propofol (30-60 microg/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. 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. 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.
    Brain & development 10/2008; 31(1):34-41. · 1.74 Impact Factor
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    ABSTRACT: Cortical dysplasia (CD) has been classified as Taylor's focal cortical dysplasia (FCD type II) or other CD (FCD type I and mild malformation of cortical development) based on histological findings. The aims of this study were to determine whether MRI and magnetoencephalography (MEG) could distinguish between these two groups and to evaluate surgical outcomes. We evaluated the MRI features, MEG spike source (MEGSS) patterns (clusters or scatters) and postsurgical seizure outcomes of 27 children with CD. Thirteen patients had Taylor's FCD and 14 had other CD. MRI showed visible lesion in 22 (81%) patients. Tapering of abnormal white matter signals to the ventricles and cortical thickening were more prevalent in Taylor's FCD; focal hypoplasia and white matter atrophy were more prevalent in other CD. MEG showed spike sources in 26 (96%) patients. Taylor's FCD showed clustered MEGSSs in 6, both clustered and scattered MEGSSs in 5 and scattered MEGSSs in 2; other CD demonstrated clusters in 2, cluster and scatter in 10 and scatter in 1. Eleven (85%) of 13 patients who had complete resection of clustered MEGSSs achieved Engel class I outcome, but 4 (44%) of 9 patients with incomplete resections achieved class I. Fifteen (88%) of 17 patients who had complete resection of MRI lesions achieved class I, but 1 (33%) of 3 patients with incomplete lesionectomy was class I. There was no difference in surgical outcomes between Taylor's FCD and other CD. Surgical outcome was the same in both groups following complete removal of areas containing clustered MEGSSs and MR lesions.
    Epilepsy research 10/2008; 82(2-3):147-55. · 2.48 Impact Factor
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    ABSTRACT: 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). 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. 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). TIVA resulted in reliable SEFs with lower RE and longer latencies. 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.
    Clinical Neurophysiology 06/2008; 119(6):1328-34. · 3.14 Impact Factor
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    ABSTRACT: To study the role of magnetoencephalography (MEG) in the surgical evaluation of children with recurrent seizures after epilepsy surgery. We studied 17 children with recurrent seizures after epilepsy surgery using interictal and ictal scalp EEG, intracranial video EEG (IVEEG), MRI, and MEG. We analyzed the location and distribution of MEG spike sources (MEGSSs) and the relationship of MEGSSs to the margins of previous resections and surgical outcome. Clustered MEGSSs occurred at the margins of previous resections within two contiguous gyri in 10 patients (group A), extended spatially from a margin by < or =3 cm in three patients (group B), and were remote from a resection margin by >3 cm in six patients (group C). Two patients had concomitant group A and C clusters. Thirteen patients underwent second surgeries. IVEEG was used in four patients. Six of seven patients with group A MEGSS clusters did not require IVEEG for second surgeries. Follow-up periods ranged from 0.6 to 4.3 years (mean: 2.6 years). Eleven children, including eight who became seizure-free, achieved Engel class I or II. Our data demonstrate the utility of MEG for evaluating patients with recurrent seizures after epilepsy surgery. Specific MEGSS cluster patterns delineate epileptogenic zones. Removing cluster regions adjacent to the margins of previous resections, in addition to removing recurrent lesions, achieves favorable surgical outcome. Cluster location and extent identify which patients require IVEEG, potentially eliminating IVEEG for some. Patients with remotely located clusters require IVEEG for accurate assessment and localization of the entire epileptogenic zone.
    Epilepsia 11/2007; 48(11):2150-9. · 3.91 Impact Factor
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    ABSTRACT: Abnormal cortical development will lead to abnormal axons in white matter. The purpose was to investigate (1) the microstructural changes in subcortical white matter adjacent to malformations of cortical development (MCD) and (2) the deep white matter tracts using diffusion tensor imaging (DTI). Thirteen children with a variety of MCD were recruited. The fractional anisotropy (FA), trace, and eigenvalues (lambdamajor, lambdamedium, lambdaminor) of subcortical white matter of MCD were compared with contralateral normal side. The deep white matter tracts were graded based on the size, color hues and displacement of the tracts as visualized on color vector maps and tractography; grade 1 was normal tract size and color hue, grade 2 was reduced tract size but preserved color hue and grade 3 was loss of color hue or failure of tracking on tractography. The subcortical white matter adjacent to abnormal cortex demonstrated reduced FA (p < 0.05) and tendency to increase trace (p = 0.06). There was a significant elevation in lambdamedium and lambdaminor (p < 0.05), but no significant change in lambdamajor (p > 0.05). Twelve cases demonstrated alteration in white matter tracts. Seven cases of focal cortical dysplasia and two cases of transmantle MCD demonstrated grade 3 pattern of white matter tract. Reduced FA is a sensitive but nonspecific marker of alteration in microstructure of white matter. The elevated lambdamedium and lambdaminor may reflect a dominant effect of abnormal myelin. Alteration in white matter tracts was observed in most cases of MCD.
    Epilepsia 09/2007; 48(8):1460-9. · 3.91 Impact Factor
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    ABSTRACT: 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.
    Journal of Child Neurology 05/2007; 22(4):435-9. · 1.39 Impact Factor
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    ABSTRACT: Magnetoencephalography (MEG) provides accurate localizing information of the epileptogenic zones in localization-related epilepsies. Refractory status epilepticus (RSE) is a life-threatening emergency that often requires prolonged high-dose suppressive therapy (HDST) to stop frequent and prolonged seizures. Surgical treatments for patients with RSE secondary to pre-existing epilepsy were reported. This article addresses the role of MEG in localizing the epileptogenic zone for the surgical treatment of patients with RSE. Five pediatric patients with RSE underwent epilepsy surgery using MEG, scalp video EEG and magnetic resonance imaging (MRI). Ictal MEG spike sources (MEGSSs) were localized in the clustered interictal MEGSSs in right Rolandic region (patient 3) and right temporal region (patient 5). Interictal MEG revealed unilateral clustered MEGSSs in four patients (patients 1, 2, 4, and 5) and bilateral (patient 3). Ictal-onset EEG findings were localized to one region in three patients (patients 1, 3, and 5) and two regions in the other two patients (patients 2 and 4). In all five patients, interictal discharges were widespread involving over two lobes (patients 2 and 4) or three lobes (patients 1, 3, and 5). Suppression burst pattern was obtained by HDST (patient 5). MRI showed cortical dysplasia in three patients (patients 1, 3, and 4). Patient 2 had a normal MRI. Patient 5 had normal MRI at the onset. Repeat MRI 5 days later showed diffusion restriction in the right hippocampus associated with increased signal intensity on T2 and FLAIR sequences. We performed cortical excision in two patients (patients 1 and 4), hemispherectotomy one (patient 3) and anterior temporal lobectomy two patients (patients 2 and 5). Two patients (patients 1 and 3) became seizure free, the other three patients experienced residual seizures. MEG showed clustered MEGSSs during the RSE in the pre-existing epilepsy patients and at an early time window in the acute symptomatic RSE patients. The complete resection of clustered MEGSSs can control RSE and possibly lead to a seizure free outcome.
    Acta neurologica Scandinavica. Supplementum 02/2007; 186:29-36.
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    ABSTRACT: MEG somatosensory evoked fields (SEF) have been used in pre-surgical functional mapping to localize sensory cortex. Although the localization accuracy of the SEF has been compared to functional MRI, there have not been any direct comparisons between the SEF and sensory cortex identified by electrocorticography. In this retrospective study, we identified 9 children (5 males, 4 females; aged 4–17 yrs) who had pre-surgical functional mapping with MEG and then proceeded to epilepsy surgery with subdural grid recording. We compared the pre-operative localization of the MEG SEF with the location identified extra-operatively with subdural grid electrodes. We found 78% (7/9) concordance for gyral localization between pre-operative MEG and extra-operative grid recording. In the other two patients, MEG SEF was located in the central sulcus. We conclude that MEG demonstrates high accuracy in localizing sensory cortex and is a valuable tool in pre-surgical functional mapping.
    International Congress Series 01/2007; 1300:637-640.
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    ABSTRACT: Temporal lobectomy is a well-established neurosurgical procedure for temporal lobe epilepsy. In this study, we conducted a retrospective review of children with drug-resistant temporal lobe epilepsy to evaluate seizure outcome after temporal lobe surgery. We reviewed the medical records of 126 children who had surgery for temporal lobe epilepsy at The Hospital for Sick Children between 1983 and 2003. The records were examined for preoperative and intraoperative factors that could predict patient outcome after surgery. The mean age at seizure onset was 5.9 years. The mean seizure duration before surgery was 5.6 years. All patients had preoperative computed tomographic scans, magnetic resonance imaging scans, or both. The mean age at the time of surgery was 13.5 years. Sixty-two patients underwent left temporal resections and 64 patients underwent right temporal resections. The histopathology of the temporal resections revealed low-grade brain tumors in 65 children (52%) and cavernous malformations in four children. Ganglioglioma and astrocytoma were the most common tumors encountered. Mesial temporal sclerosis was found in 16 patients (13%), astrogliosis in 15 patients (12%), and cortical dysplasia in eight patients (7%). Postoperative follow-up of at least 2 years was available for 106 patients and ranged up to 13.0 years. Seventy-four percent of patients had an Engel Class I or II outcome. Patients with temporal lobe lesions had better outcomes compared with those without lesions (P < 0.05). Patients without a history of secondary generalization of seizures also had a better outcome when compared with those with secondary generalization. Complications in the form of contralateral homonymous hemianopsia, dysphasia, and infection were found in 5% of patients. Twelve patients had a second temporal lobe procedure for intractable recurrent seizures. After a second procedure, seven patients returned to a seizure-free state. Temporal lobe resections for epilepsy in children are effective and safe procedures, with a favorable impact on seizure control. Repeat temporal resections for recurrent seizures may also be effective in restoring a seizure-free outcome to children.
    Neurosurgery 01/2007; 59(6):1203-13; discussion 1213-4. · 2.53 Impact Factor
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    ABSTRACT: To go beyond using magnetoencephalography (MEG) for visual identification of epileptic spikes, this study was to quantitatively estimate epileptic spectral power and volumetrically localize the neuromagnetic activity associated with epilepsy. MEG data were recorded from 16 patients with epilepsy using a whole-cortex MEG system. Focal increases of spectral power were identified using wavelet; the three-dimensional neuromagnetic distributions of the focal increases of spectral power were estimated using synthetic aperture magnetometry (SAM). SAM images and dipoles pointed to a same area in 12 patients (75% 12/16), SAM revealed focal epileptic activity but dipole modelling failed in 2 patients (12.5%, 2/16), and SAM detected more epileptic foci than dipole modelling did in 2 patients (12.5%, 2/16). Interestingly, spectrogram revealed focal increases of spectral power just before magnetic spikes; and SAM peaks were close to the dipoles of the initial portion of the spikes. The results suggest that wavelet-based SAM analysis has the potential to localize the onset of epileptic seizures, and seems superior to dipole modelling for estimation of multiple epileptic foci. In comparison to the conventional visual identification of spike, wavelet-based SAM analysis is objective and quantitative. Thus, wavelet-based SAM analysis has the potential to be extremely useful for clinical management of epilepsy.
    International Congress Series 01/2007; 1300:697-700.
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    ABSTRACT: The use of magnetoencephalography (MEG) has become increasingly accepted in the clinical realm as a valid and valuable investigational tool in the assessment of patients with epilepsy and in the mapping of functional and eloquent cortices. The clinical MEG lab at The Hospital for Sick Children, Toronto, Ontario, Canada was established in 2000 and focused specifically on pediatric examinations. The MEG laboratory has established pediatric protocols, based on guidelines from the American Electroencephalography Society. This paper will outline the routine clinical protocols that we have established in our lab for the acquisition of MEG data from pediatric patients with intractable epilepsy.
    International Congress Series 01/2007; 1300:685-688.
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    ABSTRACT: The aim of our study is to describe the hyperintense ring sign on fluid-attenuated inversion recovery (FLAIR) images in patients with dysembryoplastic neuroepithelial tumors (DNET), to discuss the radiopathologic correlation for this appearance, and to determine its role in preoperative diagnosis of DNETs. We retrospectively analyzed imaging features in 11 patients with pathological diagnosis of DNET. All patients had undergone surgery for refractory seizures. All had FLAIR imaging sequences performed on a 1.5-T magnetic resonance scanner. Clinical and pathological details in all cases were examined. Twenty-one age matched patients with pathologically confirmed low-grade glioma (n = 11), oligodendroglioma (n = 2), and ganglioglioma (n = 8) in similar locations acted as control cases. Ten patients had follow-up imaging. There were 11 patients with DNET (5 girls and 6 boys). The age of presentation varied from 4 to 18 years (average, 9 years 1 month). Tumors were located in the temporal (n = 5), frontal (n = 4), parietal (n = 1), and occipital (n = 1) lobes. In 9 patients (82% sensitivity), the FLAIR images showed a well-defined hyperintense ring around these tumors, either as a complete or incomplete ring. Among the 21 control cases, the hyperintense ring sign was seen in 2 cases (90% specificity): one with low-grade glioma and one with ganglioglioma. Pathological evaluation of the DNETs suggested the hyperintense ring might correspond to the presence of peripheral loose neuroglial elements. Postoperative imaging showed partial residual ring in 3 patients, all of whom had persistent seizures. One patient had recurrent DNET at second surgery. Magnetic resonance imaging findings of DNET are well described. We describe an additional imaging sign, the hyperintense ring sign on FLAIR images, which is distinct and is fairly sensitive and specific for DNET. We believe this sign is a helpful adjuvant to preoperatively diagnose these tumors. The presence of this ring on postoperative imaging may indicate residual or recurrent tumor.
    Journal of Computer Assisted Tomography 01/2007; 31(3):348-53. · 1.58 Impact Factor

Publication Stats

2k Citations
271.69 Total Impact Points


  • 1990–2013
    • University of Toronto
      • • Division of Neurology
      • • Hospital for Sick Children
      Toronto, Ontario, Canada
  • 1979–2011
    • SickKids
      • • Division of Neurosurgery
      • • Division of Neurology
      • • Department of Diagnostic Imaging
      Toronto, Ontario, Canada
  • 2007
    • Cincinnati Children's Hospital Medical Center
      • Division of Neurology
      Cincinnati, OH, United States
  • 1998
    • The University of Sheffield
      Sheffield, England, United Kingdom
  • 1989
    • University of Copenhagen
      • Department of Radiology
      Copenhagen, Capital Region, Denmark