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Koji Iida, Hiroshi Otsubo, Yuuri Matsumoto, Ayako Ochi, Makoto Oishi, Stephanie Holowka, Elizabeth Pang, Irene Elliott, Shelly K. Weiss, Sylvester H. Chuang, O. Carter Snead III and James T. Rutka

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 six patients with clusters and/or small clusters underwent complete excisions, and two 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.

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Koji Iida, Hiroshi Otsubo, Yuuri Matsumoto, Ayako Ochi, Makoto Oishi, Stephanie Holowka, Elizabeth Pang, Irene Elliott, Shelly K. Weiss, Sylvester H. Chuang, O. Carter Snead III and James T. Rutka

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 six patients with clusters and/or small clusters underwent complete excisions, and two 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.

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Erin N. Kiehna, Elysa Widjaja, Stephanie Holowka, O. Carter Snead III, James Drake, Shelly K. Weiss, Ayako Ochi, Eric M. Thompson, Cristina Go, Hiroshi Otsubo, Elizabeth J. Donner and James T. Rutka

OBJECT

Hemispherectomy for unilateral, medically refractory epilepsy is associated with excellent long-term seizure control. However, for patients with recurrent seizures following disconnection, workup and investigation can be challenging, and surgical options may be limited. Few studies have examined the role of repeat hemispherotomy in these patients. The authors hypothesized that residual fiber connections between the hemispheres could be the underlying cause of recurrent epilepsy in these patients. Diffusion tensor imaging (DTI) was used to test this hypothesis, and to target residual connections at reoperation using neuronavigation.

METHODS

The authors identified 8 patients with recurrent seizures following hemispherectomy who underwent surgery between 1995 and 2012. Prolonged video electroencephalography recordings documented persistent seizures arising from the affected hemisphere. In all patients, DTI demonstrated residual white matter association fibers connecting the hemispheres. A repeat craniotomy and neuronavigation-guided targeted disconnection of these residual fibers was performed. Engel class was used to determine outcome after surgery at a minimum of 2 years of follow-up.

RESULTS

Two patients underwent initial hemidecortication and 6 had periinsular hemispherotomy as their first procedures at a median age of 9.7 months. Initial pathologies included hemimegalencephaly (n = 4), multilobar cortical dysplasia (n = 3), and Rasmussen's encephalitis (n = 1). The mean duration of seizure freedom for the group after the initial procedure was 32.5 months (range 6–77 months). In all patients, DTI showed limited but definite residual connections between the 2 hemispheres, primarily across the rostrum/genu of the corpus callosum. The median age at reoperation was 6.8 years (range 1.3–14 years). The average time taken for reoperation was 3 hours (range 1.8–4.3 hours), with a mean blood loss of 150 ml (range 50–250 ml). One patient required a blood transfusion. Five patients are seizure free, and the remaining 3 patients are Engel Class II, with a minimum follow-up of 24 months for the group.

CONCLUSIONS

Repeat hemispherotomy is an option for consideration in patients with recurrent intractable epilepsy following failed surgery for catastrophic epilepsy. In conjunction with other modalities to establish seizure onset zones, advanced MRI and DTI sequences may be of value in identifying patients with residual connectivity between the affected and unaffected hemispheres. Targeted disconnection of these residual areas of connectivity using neuronavigation may result in improved seizure outcomes, with minimal and acceptable morbidity.

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Shobhan Vachhrajani, Sandrine de Ribaupierre, Hiroshi Otsubo, Ayako Ochi, Shelly K. Weiss, Elizabeth J. Donner, Elysa Widjaja, Elizabeth Kerr, Mary Lou Smith, James Drake, O. Carter Snead III and James T. Rutka

Object

Pediatric frontal lobe epilepsy (FLE) remains a challenging condition for neurosurgeons and epileptologists to manage. Postoperative seizure outcomes remain far inferior to those observed in temporal lobe epilepsies, possibly due to inherent difficulties in delineating and subsequently completely resecting responsible epileptogenic regions. In this study, the authors review their institutional experience with the surgical management of FLE and attempt to find predictors that may help to improve seizure outcome in this population.

Methods

All surgically treated cases of intractable FLE from 1990 to 2008 were reviewed. Demographic information, preoperative and intraoperative imaging and electrophysiological investigations, and follow-up seizure outcome were assessed. Inferential statistics were performed to look for potential predictors of seizure outcome.

Results

Forty patients (20 male, 20 female) underwent surgical management of FLE during the study period. Patients were an average of 5.6 years old at the time of FLE onset and 11.7 years at the time of surgery; patients were followed for a mean of 40.25 months. Most patients displayed typical FLE semiology. Twenty-eight patients had discrete lesions identified on MRI. Eight patients underwent 2 operations. Cortical dysplasia was the most common pathological diagnosis. Engel Class I outcome was obtained in 25 patients (62.5%), while Engel Class II outcome was observed in 5 patients (12.5%). No statistically significant predictors of outcome were found.

Conclusions

Control of FLE remains a challenging problem. Favorable seizure outcome, obtained in 62% of patients in this series, is still not as easily obtained in FLE as it is in temporal lobe epilepsy. While no statistically significant predictors of seizure outcome were revealed in this study, patients with FLE continue to require extensive workup and investigation to arrive at a logical and comprehensive neurosurgical treatment plan. Future studies with improved neuroimaging and advanced invasive monitoring strategies may well help define factors for success in this form of epilepsy that is difficult to control.

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Eisha A. Christian, Elysa Widjaja, Ayako Ochi, Hiroshi Otsubo, Stephanie Holowka, Elizabeth Donner, Shelly K. Weiss, Cristina Go, James Drake, O. Carter Snead and James T. Rutka

OBJECTIVE

Small lesions at the depth of the sulcus, such as with bottom-of-sulcus focal cortical dysplasia, are not visible from the surface of the brain and can therefore be technically challenging to resect. In this technical note, the authors describe their method of using depth electrodes as landmarks for the subsequent resection of these exacting lesions.

METHODS

A retrospective review was performed on pediatric patients who had undergone invasive electroencephalography with depth electrodes that were subsequently used as guides for resection in the period between July 2015 and June 2017.

RESULTS

Ten patients (3–15 years old) met the criteria for this study. At the same time as invasive subdural grid and/or strip insertion, between 2 and 4 depth electrodes were placed using a hand-held frameless neuronavigation technique. Of the total 28 depth electrodes inserted, all were found within the targeted locations on postoperative imaging. There was 1 patient in whom an asymptomatic subarachnoid hemorrhage was demonstrated on postprocedural imaging. Depth electrodes aided in target identification in all 10 cases.

CONCLUSIONS

Depth electrodes placed at the time of invasive intracranial electrode implantation can be used to help localize, target, and resect primary zones of epileptogenesis caused by bottom-of-sulcus lesions.

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Makoto Oishi, Hiroshi Otsubo, Koji Iida, Yasuhiro Suyama, Ayako Ochi, Shelly K. Weiss, Jing Xiang, William Gaetz, Douglas Cheyne, Sylvester H. Chuang, James T. Rutka and O. Carter Snead III

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 (≥ 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.