Atsushi Shirasawa

SickKids, Toronto, Ontario, Canada

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Publications (7)21.88 Total impact

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    ABSTRACT: Panayiotopoulos syndrome (PS) is a type of benign childhood partial epilepsy that is frequently associated with abundant multifocal spikes other than main occipital spikes on the EEG. In this study, we investigated the characteristic features of dipoles in PS. We performed dipole analysis of the interictal occipital spike discharges seen in 10 children with PS (group A) and in 10 children with other types of symptomatic localization-related epilepsy (group B). We analyzed the dipoles of the averaged spike in each patient. In group A, the averaged occipital spikes in each patient showed dense dipole locations in the mesial occipital area; in group B, widely scattered dipole locations were observed. In Group A, the geometric centers of the dipoles at each time point (such as at the main negative peak and before or after the main peak) were estimated in the neighboring locations. In contrast, they tended to be scattered in group B. Our study reveals that PS has high dipole stability, similar to that of rolandic epilepsy. From the electroencephalographic view, this seems to indicate a close link between these two syndromes.
    Preview · Article · May 2006 · Epilepsia
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    ABSTRACT: Panayiotopoulos syndrome (PS) is a type of benign childhood partial epilepsy, which has a good prognosis despite the fact that it is frequently associated with abundant multifocal spikes on the electroencephalography (EEG). We investigated whether stable dipoles, as seen in rolandic epilepsy, were also present in PS. We performed dipole analysis of the interictal spike discharges seen in the interictal EEGs of eight children with PS. We chose more than 10 spikes for each kind of spike, and investigated whether or not more than three of these spikes showed consistently stable dipole locations. (1) We observed 15 different kinds of spikes in various regions in the EEGs of the eight children. (2) Twelve of the 15 kinds of spikes had dipoles with a high goodness of fit. Furthermore, 14 of the 15 spikes had stable dipoles with similar locations for more than three individual spikes. (3) Fourteen of the 15 spikes, including frontal spikes, showed dense dipole locations in the mesial occipital area. Thirteen of these 14 spikes also showed other dipole locations in the rolandic area and/or the vertex (Cz). Our study revealed that the various types of spikes observed in PS have similar and stable dipole locations. The dipoles showing high stability, were located in the mesial occipital area, and were accompanied by dipoles located in the rolandic area. The stability and location of these dipoles indicate that there may be a pathogenetic link between PS and rolandic epilepsy.
    No preview · Article · Feb 2005 · Brain and Development
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    ABSTRACT: The aim of this study is to analyze the characteristics of dipoles in clustered individual spikes and averaged spikes, we compared electroencephalography (EEG) dipole localizations from patients with intractable extratemporal lobe epilepsy (IETLE) and from patients with benign epilepsy with centrotemporal spikes (BECTS). We studied 10 patients; five with IETLE who underwent epilepsy surgery after subdural EEG and five with BECTS. We recorded 19-channel digital scalp EEGs and used clustering analysis for individual spikes to characterize interictal spikes. We selected and averaged one representative spike group at the maximum negative peak electrode. We used a single dipole method with three-shell spherical head model. We compared dipole localizations of both averaged and individual spikes.IETLE data had more identifiable spike clusters and fewer spikes in each cluster than BECTS (P<0.05). Dipole sources with goodness-of-fit >or=95% in averaged spikes were less frequent in IETLE than in BECTS (P<0.05). For IETLE, averaged spikes showed no dipoles (two patients), while individual spikes gave dipole sources reliably in the epileptic region. For BECTS, individual and averaged spike sources were clustered. More than 80% of dipoles in averaged spikes were stable, in close proximity, for prolonged periods in BECTS. More spike groups after clustering and fewer acceptable dipoles from averaged spikes in IETLE reflect variable spike activity over extensive epileptic regions. Fewer spike groups producing more acceptable dipoles in BECTS correlate with stable spike sources within the isolated epileptic central region. Characteristics of clustered interictal spikes need careful examination before the use of dipole analysis of averaged spikes for epilepsy evaluation.
    No preview · Article · Jan 2003 · Brain and Development
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    ABSTRACT: The purpose of this paper is to describe the use of computerized brain-surface voltage topographic mapping to localize and identify epileptic discharges recorded on electrocorticographic (ECoG) studies in which a subdural grid was used during intracranial video electroencephalographic (IVEEG) monitoring. The authors studied 12 children who underwent surgery for intractable extrahippocampal epilepsy. Cortical surfaces and subdural grid electrodes were photographed during the initial surgery to create an electrode map that could be superimposed onto a picture of the brain surface. Spikes were selected from ictal discharges recorded at the beginning of clinically confirmed seizures and from interictal discharges seen on ECoG studies during IVEEG recording. A computer program was used to calculate the sequential amplitude of the spikes by using squared interpolation, and they were then superimposed onto the electrode map. Interictal discharges and high-amplitude spike complexes at seizure onset were plotted on the map. This mapping procedure depicted the ictal zone in nine patients and the interictal zone in 12, and proved to be an accurate and useful source of information for planning corrective surgery.
    No preview · Article · Jul 2001 · Journal of Neurosurgery
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    ABSTRACT: To assess the reliability of dipole localization based on residual variances (RV), using equivalent current dipole analysis of interictal EEG spikes in children with extratemporal lobe epilepsy. Four pediatric patients with extratemporal lobe epilepsy were studied. Digital EEG was recorded from 19 scalp electrodes. Computer programs for spike detection and clustering analysis were used to select spikes. Dipoles were calculated 5 times for each spike using different initial guesses by the moving dipole model. Standard deviation (SD) of the dipole positions was calculated at each time point in the 5 trials. We analyzed the dipoles at 1097 time points from 4 patients. Among 106 time points with RV < 2%, the SD was < 1 mm in 78 (74%), while in those with SD > 1 mm the dipole positions varied between 2.8 and 52.6 mm. Of dipoles with RV < 1%, 26 of 27 (96%) had an SD < 1 mm; the one dipole with SD > 1 mm varied within 2.5 mm. The dipole localizations with RV < 2% corresponded to the epileptogenic zones identified on intracranial invasive video EEG and intraoperative ECoG. The systematic approach of equivalent current dipole analysis using spike detection, clustering analysis, and an RV < 2% as a standard is useful for identifying extratemporal epileptic regions.
    No preview · Article · Jan 2000 · Clinical Neurophysiology
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    ABSTRACT: This study was undertaken to assess the utility of digital camera-derived intraoperative images in the planning of neurosurgery for children with epilepsy. A hand-held digital camera was used to capture the exposed surgical field at the time of craniotomy for 11 children with medically intractable seizure disorders. Intraoperative somatosensory evoked potential recordings of phase reversals and direct cortical stimulation were used to map areas of eloquent brain tissue. Digital camera images were obtained to mark regions of functional brain tissue with respect to cortical surface landmarks and subdural grid placement. The digital camera images were then immediately downloaded, in the operating room, to a laptop computer, which was placed next to the electroencephalographic recording device. Using computer software, the epileptologist highlighted the primary and secondary zones of epileptogenesis, as well as the functional brain areas identified during the monitoring period, on the digital camera images on the computer screen. A neurosurgical map was thus created to aid the neurosurgeon and the epileptologist with the proposed cortical resections and multiple subpial transections. With the images obtained using the digital camera, the epilepsy team was able to observe the contacts of the grid electrodes with the brain during the procedure. Color printouts of the images served as references during the period of invasive monitoring. Zones of primary and secondary epileptogenesis, as well as areas of functional brain tissue, were identified and plotted on the digital camera images. Other benefits of the digital camera-derived images included the ability to accurately reposition the grids or letters marking eloquent brain tissue if they were inadvertently shifted during the procedure, the ease with which the images could be obtained and manipulated, the ability to assess postresection epileptiform activity of the surrounding brain tissue with images obtained while an electrocorticographic array was in place, the ability to provide the entire epilepsy team with updated information on the neurosurgical field while minimizing movement in the operating room, and facilitation, with neurosurgical maps, of discussions with the patients and their families concerning proposed cortical resections. Digital camera images have become essential components for the planning of cortical resections for children with intractable epilepsy at our institution. We envision widespread application of this technology to other neurosurgical fields.
    No preview · Article · Dec 1999 · Neurosurgery
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    ABSTRACT: We used coherence analysis to test for leading discharges on an ipsilateral right mesial temporal lesion in a 5 year old boy with flexor spasms. Digital EEG analysis with video-EEG telemetry was performed preparatory to epilepsy surgery. Study of 10 spasms with head drop and subsequent flexion of both arms demonstrated an interhemispheric time lag with secondary bilateral synchrony, with a mean difference of 17 ms. The right hemisphere led. After a lesionectomy with resection of epileptic regions (performed with electrocorticographical guidance), the patient has been seizure-free for 4 years. Pathology confirmed a low-grade mixed glioma and cortical dysgenesis. The coherence analysis demonstrated a pathway of secondary generalization, confirming that the lesional side was leading during ictal generalized discharges in flexor spasms.
    No preview · Article · Mar 1999 · Clinical Neurophysiology

Publication Stats

149 Citations
21.88 Total Impact Points


  • 1999-2001
    • SickKids
      • Division of Neurology
      Toronto, Ontario, Canada
    • University of Toronto
      • Division of Neurology
      Toronto, Ontario, Canada