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Hiroshi Otsubo, Atsushi Shirasawa, Shiro Chitoku, James T. Rutka, Scott B. Wilson and O. Carter Snead III

✓ 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.

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Jeffrey P. Blount, Wayne Langburt, Hiroshi Otsubo, Shiro Chitoku, Ayako Ochi, Shelly Weiss, O. Carter Snead and James T. Rutka

Object. The technique involved in multiple subpial transections (MSTs) allows the surgeon treating patients with epilepsy the capability to make disconnective lesions in epileptogenic regions of eloquent cortex. Although there have been increasing numbers of reports in adults of the efficacy and relative safety of this technique, there are relatively few such reports in children. The authors present their experience in 30 children who underwent MSTs during the surgical management of the seizure disorder.

Methods. Thirty consecutive children who underwent MSTs with or without cortical excision form the basis of this retrospective review. An analysis of neurological adverse effects following MSTs and seizure outcome was performed.

Between 1996 and 2000, MSTs were performed either as stand-alone therapy (four patients) or in conjunction with planned cortical excisions (26 patients). Twenty-three children underwent invasive monitoring after placement of subdural grid electrodes, and in seven intraoperative electrocorticography alone was performed. The mean follow-up period for the group was 3.5 years (minimum 30 months in all cases). All 20 patients in whom MSTs were performed in the primary motor cortex experienced transient hemiparesis (mild in 12 and moderate in eight) lasting up to 6 weeks; however, no patient suffered a permanent motor deficit in the long-term follow-up period. In 26 patients who underwent cortical resections followed by MSTs, 12 (46%) were seizure free (Engel Class I) following surgery. Eleven patients (42%) (Engel Classes II and III) continued to suffer seizures but improvement in seizure control was adequate following surgery. In the 23 patients in whom subdural grids were placed to capture the ictal onset zone by invasive video-electroencephalography, MSTs comprised a mean of 37% of the surgically treated area under the grid.

Conclusions. The results of this series demonstrate that MSTs can be performed with acceptable morbidity in children undergoing epilepsy surgery. The precise role of MSTs in controlling seizure frequency and outcome, especially when combined with planned cortical resections, awaits further study.

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Walter J. Hader, Mark Mackay, Hiroshi Otsubo, Shiro Chitoku, Shelly Weiss, Lawrence Becker, O. Carter Snead III and James T. Rutka

Object. The authors conducted a study to determine seizure-related outcomes in a group of pediatric patients with pathologically proven focal cortical dysplasia (FCD) treated by focal cortical resections and multiple subpial transections (MSTs).

Methods. The authors performed a retrospective review of pediatric patients in whom surgery was conducted to treat medically refractory epilepsy secondary to cortical dysplasia between April 1989 and January 2001. Diagnostic studies included preoperative scalp electroencephalography (EEG), magnetic resonance (MR) imaging, positron emission tomography (PET), and magnetoencephalography (MEG). Intraoperative electrocorticography (ECoG) or extraoperative subdural grid EEG monitoring was performed in all patients. Seizure outcome was classified using the Engel scheme. The authors analyzed nine data points and compared these with seizure outcome, including seizure semiology, MR imaging, PET and MEG data, as well as location of resection, intracranial video-EEG findings, MSTs, postresection ECoG data, and histological findings.

The authors analyzed data obtained in 39 children in whom the follow-up interval after epilepsy surgery was at least 18 months. Patients had suffered epilepsy for a mean of 7.7 years prior to surgical intervention and their mean age at treatment was 9.6 years (range 2 months–18 years). A good seizure-related outcome was demonstrated in 28 patients (72%), including 21 (54%) who were free of seizures (Engel Class I) and seven (18%) in whom seizures were rare (Engel Class II). In 11 patients seizure-related outcome was less favorable, including six (15%) with worthwhile improvement involving some seizures (Engel Class III) and five (13%) with no postoperative seizure improvement (Engel Class IV). There was no significant correlation between seizure outcome and data related to seizure characteristics, MR imaging, PET scanning, MEG, location of resection, intracranial video-EEG, postresection ECoG, and histological findings. Eight (50%) of 16 patients who underwent MSTs in addition to incomplete resection of FCD experienced a good outcome (Engel Class I and II). Twenty (87%) of 23 patients in whom resection of FCD was complete and in whom MSTs were not performed experienced a good seizure outcome (p < 0.05).

Conclusions. Complete resection of FCD results in good seizure outcome in a majority of children. When conducted in conjunction with incomplete cortical resection, MSTs do not improve seizure outcome in patients with FCD. Focal cortical dysplasia located outside of eloquent cortex and complete excision of the lesion are the most important predictors of seizure outcome.

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Çagatay Önal, Hiroshi Otsubo, Takashi Araki, Shiro Chitoku, Ayako Ochi, Shelly Weiss, William Logan, Irene Elliott, O. Carter Snead III and James T. Rutka

Object. This study was performed to evaluate the complications of invasive subdural grid monitoring during epilepsy surgery in children.

Methods. The authors retrospectively reviewed the records of 35 consecutive children with intractable localization-related epilepsy who underwent invasive video electroencephalography (EEG) with subdural grid electrodes at The Hospital for Sick Children between 1996 and 2001. After subdural grid monitoring and identification of the epileptic regions, cortical excisions and/or multiple subpial transections (MSTs) were performed. Complications after these procedures were then categorized as either surgical or neurological.

There were 17 male and 18 female patients whose mean age was 11.7 years. The duration of epilepsy before surgery ranged from 2 to 17 years (mean 8.3 years). Fifteen children (43%) had previously undergone surgical procedures for epilepsy. The number of electrodes on the grids ranged from 40 to 117 (mean 95). During invasive video EEG, cerebrospinal fluid leaks occurred in seven patients. Also, cerebral edema (five patients), subdural hematoma (five patients), and intracerebral hematoma (three patients) were observed on postprocedural imaging studies but did not require surgical intervention. Hypertrophic scars on the scalp were observed in nine patients. There were three infections, including one case of osteomyelitis and two superficial wound infections. Blood loss and the amounts of subsequent transfusions correlated directly with the size and number of electrodes on the grids (p < 0.001). Twenty-eight children derived significant benefit from cortical resections and MSTs, with a more than 50% reduction of seizures and a mean follow-up period of 30 months.

Conclusions. The results of this study indicate that carefully selected pediatric patients with intractable epilepsy can benefit from subdural invasive monitoring procedures that entail definite but acceptable risks.