Focal Epileptiform Discharges Can Mimic Electrode Artifacts When Recorded on the Scalp Near a Skull Defect (original) (raw)

Evaluation of Postoperative Sharp Waveforms Through EEG and Magnetoencephalography

Journal of Clinical Neurophysiology, 2010

EEGs obtained after craniotomy are difficult to read because of a breach rhythm consisting of unfiltered sharply contoured physiologic waveforms that can mimic interictal epileptiform discharges. Magnetoencephalography (MEG) is less affected by the skull breach. The postcraniotomy EEG and MEG scans of 20 patients were reviewed by two experienced electroencephalographers. Larger interrater variability was found for EEG as compared with MEG. Review of patients who had postoperative seizures suggested that EEG was more sensitive but less specific than MEG in detecting interictal epileptiform discharges. Furthermore, several instances of sharp waveforms that were difficult to evaluate on EEG were found to be more easily interpretable on MEG. MEG may also help determine whether asymmetries in physiologic rhythms on EEG result from the skull defect or are pathologic. MEG should be considered as an adjunctive study in patients with a breach rhythm for evaluation of interictal epileptiform discharges and cerebral dysfunction.

Scalp EEG in Temporal Lobe Epilepsy Surgery

The Canadian Journal of Neurological Sciences, 2000

Scalp EEG telemetry is an electrophysiologic technique that involves continuous recording of EEG and patient behavior (image and sound) over prolonged periods. In the context of epilepsy surgery, this investigation is used to assist in defining the ictal and interictal epileptogenic cortical areas by obtaining EEG signals with synchronized assessment of the patient's behavior during recorded seizures. In optimum circumstances for surgical intervention there will be a congruence of the EEG with clinical, radiological, and neuropsychological data. This review will focus on the use of scalp EEG in the evaluation of candidates for temporal lobe epilepsy surgery. SOME TECHNICAL CONSIDERATIONS The International Standard ten-twenty electrode system continues to be the most widely accepted method of measurement and application of EEG scalp electrodes. 1 Other systems describing additional electrode positions have been proposed. 2 A variety of additional "nonstandard" electrodes have been described to more completely evaluate the EEG ABSTRACT: Electroencephalography (EEG) with standard scalp and additional noninvasive electrodes plays a major role in the selection of patients for temporal lobe epilepsy surgery. Recent studies have provided data supporting the value of interictal and postictal EEG in assessing the site of ictal onset. Scalp ictal rhythms are morphologically complex but at least one pattern (a five cycles/second rhythm maximum at the sphenoidal or anterior temporal electrode) occurs in >50% of patients and has a high predictive value and interobserver reliability for temporal lobe originating seizures. Thorough interictal and ictal scalp EEG evaluation, in conjunction with modern neuroimaging, is sufficient for proceeding to surgery without invasive recordings in some patients. Further studies are required to define the scalp ictal characteristics of mesial vs. lateral temporal lobe epilepsy. RÉSUMÉ: L'ÉEG de surface dans la chirurgie de l'épilepsie temporale. L'électroencéphalographie (ÉEG) enregistré au moyen d'électrodes standard de surface et d'électrodes non effractives additionnelles a un rôle majeur dans la sélection des patients pour la chirurgie de l'épilepsie temporale. Des études récentes supportent la valeur de l'ÉEG interictal et postictal dans l'évaluation du site de déclenchement de la crise. Les rythmes de l'enregistrement de surface de la crise ont une morphologie complexe, mais au moins un patron (un rythme de 5 cycles/seconde enregistré par l'électrode sphénoïdale ou temporale antérieure) qu'on retrouve chez plus de 50% des patients, a une valeur prédictive et une fiabilité inter-observateur élevées dans les crises originant dans le lobe temporal. L'évaluation minutieuse par l'ÉEG de surface interictal et ictal, conjointement avec la neuroimagerie moderne sont suffisantes pour procéder à la chirurgie sans enregistrement invasif chez certains patients. D'autres études sont nécessaires pour définir les caractéristiques de l'épilepsie temporale mésiale par rapport à l'épilepsie temporale latérale, à l'enregistrement ictal de surface.

Morbidity Associated With the Use of Intracranial Electrodes for Epilepsy Surgery

The Canadian Journal of Neurological Sciences, 2006

ABSTRACT:Background:Invasive monitoring for the investigation of medically intractable epilepsy may be associated with undesirable morbidity. We performed a review of our recent experience to determine the incidence of major complications.Methods:We reviewed the clinical records of all patients who underwent invasive EEG monitoring at our institution between 2000 and 2004.Results:One-hundred and sixteen patients (57 males, 59 females) with a mean age of 32 years of age underwent intracranial placement of electrodes for epilepsy surgery investigation. Subdural strips were placed in 115 patients with a mean of eight strips per patient. Subdural grids were inserted in 11 patients and depth electrodes in five. Fourteen of the 15 patients with grids or depth electrodes also had strips. Coverage was unilateral in 37 patients and bilateral in 79 patients. Electrodes were placed over the frontal lobe in 78 cases, temporal in 93, parietal in 24, and occipital in 27 patients. The average dura...

Electrocorticographic Patterns in Epilepsy Surgery and Long-Term Outcome

Journal of Clinical Neurophysiology, 2017

The role of intraoperative electrocorticography (iECoG) and of its patterns in epilepsy surgery have shown contradictory results. Our aim was to describe iECoG patterns and their association with outcome in epilepsy surgery. Methods: We retrospectively analyzed 104 patients who underwent epilepsy surgery (2009-2015) with pre-and postresection iECoG. We described clinical findings, type of surgery, preresection iECoG patterns according to Palmini et al., 1995 (sporadic, continuous, burst, and recruiting interictal epileptiform dischargesdIEDs) and postresection iECoG outcome (de novo, residual, and without IEDs). The Engel scale was used to evaluate the outcome. Descriptive statistics, Kaplan-Meier, the logistic regression model, and analysis of variance tests were used. Results: We included 60.6% (63/104) females, with a mean age of 35 (610.2) years at the time of epilepsy surgery. The etiologies were hippocampal sclerosis (63.5%), cavernomas (14.4%), cortical dysplasia (11.5%), and low-grade tumors (10.6%). The most common preresection iECoG pattern was sporadic IEDs (47%). Postresection iECoG patterns were de novo (55.7%), residual (27.8%), and without IEDs (16.3%). Mean follow-up was 19.2 months. Engel scale was as follows: Engel I (91 patients, 87.5%), Engel II (10 patients, 9.6%), and Engel III (three patients, 2.9%). Analysis by mixed-design analysis of variance showed a significant difference between etiology groups with a strong size effect (P ¼ 0.021, h 2 ¼ 0.513) and also between preresection iECoG patterns (P ¼ 0.008, h 2 ¼ 0.661). Conclusions: Preresection iECoG patterns and etiology influence Engel scale outcome in lesional epilepsy surgery.

Intraoperative Electrocorticography in Temporal Lobe Epilepsy Surgery

The Canadian Journal of Neurological Sciences, 2000

The purpose of this paper is mainly to introduce and compare and contrast the concepts of undifferentiated and differentiated ECoG in temporal lobe epilepsy surgery. These will be illustrated with previously unpublished data from the University of British Columbia (UBC) supporting ECoG differentiation. Since a comprehensive critical review of ECoG has recently been published, 2 we have chosen to only briefly review the pathophysiology, methodology and current status of ECoG here.

Diagnostic utility of invasive EEG for epilepsy surgery: Indications, modalities, and techniques

Epilepsia, 2016

Many patients with medically refractory epilepsy now undergo successful surgery based on noninvasive diagnostic information, but intracranial electroencephalography (IEEG) continues to be used as increasingly complex cases are considered surgical candidates. The indications for IEEG and the modalities employed vary across epilepsy surgical centers; each modality has its advantages and limitations. IEEG can be performed in the same intraoperative setting, that is, intraoperative electrocorticography, or through an independent implantation procedure with chronic extraoperative recordings; the latter are not only resource intensive but also carry risk. A lack of understanding of IEEG limitations predisposes to data misinterpretation that can lead to denying surgery when indicated or, worse yet, incorrect resection with adverse outcomes. Given the lack of class 1 or 2 evidence on IEEG, a consensus-based expert recommendation on the diagnostic utility of IEEG is presented, with emphasis ...

Iatrogenic seizures during intracranial EEG monitoring

Epilepsia, 2011

Cerebral edema with declining neurologic status is a known complication of intracranial electroencephalography (EEG) monitoring. The frequency and consequences of iatrogenic edema that is not clinically evident are presently poorly defined. We investigated the potential for intracranial electrodes to cause subclinical cerebral edema, and for such edema to cause iatrogenic seizures. In a retrospective review of 33 adults who had head magnetic resonance imaging (MRI) while undergoing epilepsy surgery evaluation with intracranial EEG, 28% (6 of 21) depth electrode implantations had subclinical vasogenic edema. Of these, 50% (3 of 6) had nonhabitual electrographic seizures that appear to result from iatrogenic edema. No long-term adverse sequelae were noted, however, if unrecognized, iatrogenic seizures could lead to unnecessary exclusion from definitive surgical intervention for refractory epilepsy.

Depth Electrodes in Pediatric Epilepsy Surgery

The Canadian Journal of Neurological Sciences, 2013

Epilepsy surgery has become a treatment option for children with medically intractable epilepsy 1-6. Accurate localization and removal of the epileptogenic zone is crucial in order to achieve seizure control. most centers like ours reserve intracranial recording for complex cases, such as those with potential multiple foci or dual pathology, or to resolve discordant data in which surface electroencephalogram (EEG) and magnetic resonance imaging (mRi) do not provide enough information to correctly recognize the ictal onset zone. the goal of the surgery is to accurately identify and remove the epileptogenic zone while minimizing new functional deficits from surgery. our main objective though remains the attainment of complete seizure freedom without harm to the patient. intracranial recording includes epidural pegs, subdural grid placement, and depth electrode insertion. in the past, like most pediatric epilepsy centers we have implanted large subdural grids in patients with epilepsy in order to further map the ABSTRACT: Background: the surgical removal of the epileptogenic zone in medically intractable seizures depends on accurate localization to minimize the neurological sequelae and prevent future seizures. to date, few studies have demonstrated the use of depth electrodes in a pediatric epilepsy population. Here, we report our study of pediatric epilepsy patients at our epilepsy center who were successfully operated for medically intractable seizures following the use of intracranial depth electrodes. in addition, we detail three individuals with distinct clinical scenarios in which depth electrodes were helpful and describe our technical approach to implantation and surgery. Methods: We retrospectively reviewed 18 pediatric epilepsy patients requiring depth electrode studies who presented at the University of Alberta Comprehensive Epilepsy Program between 1999 and 2010 with medically intractable epilepsy. Patients underwent cortical resection following depth electrode placement according to the Comprehensive Epilepsy Program surgical protocols after failure of surface electroencephalogram and magnetic resonance imaging to localize ictal onset zone. Result: the ictal onset zone was successfully identified in all 18 patients. treatment of all surgical patients resulted in successful seizure freedom (Engel class i) without neurological complications. Conclusion: intracranial depth electrode use is safe and able to provide sufficient information for the identification of the epileptogenic zone in pediatric epilepsy patients previously not considered for epilepsy surgery. RÉSUMÉ: Électrodes profondes dans la chirurgie de l'épilepsie en pédiatrie. Contexte : l'ablation chirurgicale de la zone épileptogène chez les patients atteints de crises d'épilepsie réfractaires au traitement médical dépend d'une localisation précise du foyer épileptogène afin de minimiser les séquelles neurologiques et de prévenir les crises. À ce jour, peu d'études ont démontré l'utilité d'électrodes profondes chez une population pédiatrique atteinte d'épilepsie. notre étude porte sur des patients d'âge pédiatrique atteints d'épilepsie réfractaire au traitement médical, opérés avec succès après implantation d'électrodes profondes dans notre centre de traitement de l'épilepsie. de plus, nous décrivons en détail trois patients présentant des scénarios cliniques distincts chez qui des électrodes profondes ont été utiles et nous décrivons notre approche technique d'implantation de ces électrodes et de la chirurgie. Méthode : nous avons révisé rétrospectivement les dossiers de 18 enfants atteints d'épilepsie nécessitant des études au moyen d'électrodes profondes pour une épilepsie réfractaire au traitement médical dans le cadre du University of Alberta Comprehensive Epilepsy Program entre 1999 et 2010. les patients ont subi une résection corticale après implantation d'électrodes profondes effectuée selon les protocoles chirurgicaux du Comprehensive Epilepsy Program parce que l'électroencéphalogramme de surface et l'imagerie par résonance magnétique n'aient pas pu localiser la zone épileptogène. Résultats : la zone épileptogène a été identifiée avec succès chez ces 18 patients. le traitement chirurgical de tous ces patients a entraîné une absence complète de crises (Classe i de Engal) sans complication neurologique. Conclusion : l'utilisation d'électrodes intracrâniennes profondes est sûre et fournit des informations suffisantes pour l'identification de la zone épileptogène chez les patients d'âge pédiatrique atteints d'épilepsie chez qui un traitement chirurgical n'était pas envisagé dans le passé.