Subdural Grid Electrodes Research Articles

3D source localization derived from subdural strip and grid electrodes: A simulation study

Little experience exists in the application of source reconstruction methods to recordings from subdural strip and grid electrodes. This study addressed the question, whether reliable and accurate 3D source localization is possible from the Electrocorticogram (ECoG). The accuracy of source reconstruction was investigated by simulations and a case study. Simulated sources were used to compute potentials at the electrode positions derived from the MRI of a patient with subdural electrodes. Used procedures were the linear estimation (minimum norm) algorithm and the MUSIC (MUltiple SIgnal Classification) scan. Maxima of linear estimation were attracted to adjacent electrodes. Reliable localization with a localization error 15 mm was only achieved for about 35% of the original source positions. Maxima of the MUSIC metric were identical to original positions for simulations without noise. Noise reduced the percentage of reliable solutions down to a 79.0%. Electrode contacts distant to the source had small influence on localization accuracy. The case study supported simulation results. Reliable source reconstruction derived from ECoG can be achieved by the application of the MUSIC algorithm. Linear estimation needs additional compensation mechanisms. MUSIC based 3D localization based on ECoG has the potential improving epilepsy diagnosis and cognitive research.

Spatial localization and time‐dependant changes of electrographic high frequency oscillations in human temporal lobe epilepsy

High frequency oscillations (HFOs) >200 Hz are believed to be associated with epileptic processes. The spatial distribution of HFOs and their evolution over time leading up to seizure onset is unknown. Also, recording HFOs through conventional intracranial electrodes is not well established. We therefore wished to determine whether HFOs could be recorded using commercially available depth macroelectrodes. We also examined the spatial distribution and temporal progression of HFOs during the transition to seizure activity. Intracranial electroencephalography (EEG) recordings of 19 seizures were obtained from seven patients with temporal lobe epilepsy using commercial depth or subdural electrodes. EEG recordings were analyzed for frequency content in five spectral bands spanning DC-500 Hz. We examined the spatial distribution of the different spectral bands 5 s before and 5 s after seizure onset. Temporal changes in the spectral bands were studied in the 30-s period leading up to seizure onset. Three main observations were made. First, HFOs (100-500 Hz) can be recorded using commercial depth and subdural grid electrodes. Second, HFOs, but not <100 Hz oscillations, were localized to channels of ictal onset (100-200, 400-500 Hz, p < 0.05; 300-400 Hz, p < 0.001). Third, temporal analysis showed increased HFO power for approximately 8 s prior to electrographic onset (p < 0.05). These results suggest that HFOs can be recorded by depth macroelectrodes. Also, HFOs are localized to the region of primary ictal onset and can exhibit increased power during the transition to seizure. Thus, HFOs likely represent important precursors to seizure initiation.

Successful localization of the Broca area with short-train pulses instead of ‘Penfield’ stimulation

Direct electrical stimulation of functional cortical areas is a standard procedure in epilepsy and glioma surgery. Many previous studies support that stimulation of the motor cortex with short-train pulses is a less epileptogenic alternative to the 50–60 Hz ‘Penfield’ technique. However, whether the short-train stimulation is useful also in mapping of speech areas is unclear. In this case report we present a patient with oligodendroglioma near the Broca area. Extraoperative electrical stimulation via a subdural grid electrode was primarily performed to locate the speech area. The cortex was stimulated with short-train pulses (5 pulses, 0.5 pulse duration and 3 ms interpulse interval) in addition to 1–3 s 50 Hz stimulation. The patient had speech arrest from both types of stimulation techniques during a naming task. It was however critical that the short (14.5 ms) train stimulation was synchronized with the presentation of the naming objects. If not, there was no speech arrest. Despite this possible pitfall, this case has encouraged us to further try short-train stimulation in attempts to reduce stimulus-triggered seizures during mapping of eloquent areas.

Similarities of electrical stimulation induced slow oscillation in different vigilance states in epileptic patients.

Event Abstract Back to Event Similarities of electrical stimulation induced slow oscillation in different vigilance states in epileptic patients. Laszlo Entz1, 2*, Daniel Fabo1, 2, L. Eross2, P. Halasz3, Lucia Wittner1, G. Karmos1, 3 and I. Ulbert1, 2, 3 1 Institute for Psychology, Hungarian Academy of Sciences, Hungary 2 National Institute of Neurosurgery, Hungary 3 Péter Pázmány Catholic University, Hungary Cortical electrical stimulation in epilepsy surgery is broadly used for functional mapping of the underlying cortex and also for seizure focus localization. Recently, scalp EEG studies showed that transcranial electrical (TES) and magnetic stimulation (TMS) can trigger Slow Oscillation (SO) in deeper stages of non-REM sleep, but not in wakefulness. In order to investigate the effect of different vigilance states on triggered SO, single pulse cortical electrical stimulation (CES) was combined with subdural electrocorticography (ECoG) and intracortical laminar recordings in humans. Patients with drug resistant epilepsy were implanted with subdural grid and strip electrodes and intracortical laminar multielectrodes. Brief single current pulses were injected into adjacent grid contacts and responses were averaged both from the grids and the laminar electrodes in awake, sleeping and anesthetized state. We have found that CES awake an initial biphasic activation, which is followed by a single wave of SO, characterized by a long lasting negative ECoG potential (down state) and a rebound positivity (up state) in the close (1-2cm) vicinity of the stimulation electrode, regardless of the vigilance state (sleep, awake and anesthesia) of the patient. Comparing the spatial distribution of the stimulus evoked SO between sleep and wakefulness, our preliminary results showed quite similar extent of activation if stimulated between the same electrode pairs. Regarding the amplitude and latency of the triggered SO, we also find similar values between sleep and wake stimulation. Using high resolution mapping methods, our results suggest that contrary to TMS and TES, CES can initiate a single SO cycle in the close vicinity of the stimulation site even in the waking state. Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Pathophysiology and neurology - degenerative disorders Citation: Entz L, Fabo D, Eross L, Halasz P, Wittner L, Karmos G and Ulbert I (2009). Similarities of electrical stimulation induced slow oscillation in different vigilance states in epileptic patients.. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.149 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Mar 2009; Published Online: 05 Mar 2009. * Correspondence: Laszlo Entz, Institute for Psychology, Hungarian Academy of Sciences, Budapest, Hungary, entz@gmx.net Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Laszlo Entz Daniel Fabo L. Eross P. Halasz Lucia Wittner G. Karmos I. Ulbert Google Laszlo Entz Daniel Fabo L. Eross P. Halasz Lucia Wittner G. Karmos I. Ulbert Google Scholar Laszlo Entz Daniel Fabo L. Eross P. Halasz Lucia Wittner G. Karmos I. Ulbert PubMed Laszlo Entz Daniel Fabo L. Eross P. Halasz Lucia Wittner G. Karmos I. Ulbert Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Anatomo‐electro‐clinical correlations: the Great Ormond Street Hospital, UK Case Report ‐ Case 05‐2008: Early‐onset symptomatic focal epilepsy: a dilemma in the timing of surgery

We report the case of a six-year-old boy who presented in infancy with infantile spasms and left focal seizures. An MR scan at two months was suggestive of a right parietal cortical dysplasia, although this was less apparent on repeat scan at 11 months. The initial response to anti-epileptic medications was good; surgery was therefore deferred at that time. Subsequently, seizure control fluctuated and developmental progress was, on the whole, good. However, ultimately seizures increased despite changing the AED, and he began showing developmental problems. Surgery was reconsidered. Again, a repeat MR scan did not define the lesion well. Following full further evaluation, including functional imaging that still implicated the right parietal cortex, subdural grid and depth electrode monitoring were undertaken at 6.5 years, which located the ictal onset zone deep within the lesion. This enabled a right inferior parietal lobe resection to be performed. Four years post-surgery he remains seizure-free and has shown progress in development.

Robotic image-guided depth electrode implantation in the evaluation of medically intractable epilepsy

The authors describe their experience with a technique for robotic implantation of depth electrodes in patients concurrently undergoing craniotomy and placement of subdural monitoring electrodes for the evaluation of intractable epilepsy. Patients included in this study underwent evaluation in the Dartmouth Surgical Epilepsy Program and were recommended for invasive seizure monitoring with depth electrodes between 2006 and the present. In all cases an image-guided robotic system was used during craniotomy for concurrent subdural grid electrode placement. A total of 7 electrodes were placed in 4 patients within the time period. Three of 4 patients had successful localization of seizure onset, and 2 underwent subsequent resection. Of the patients who underwent resection, 1 is now seizure free, and the second has only auras. There was 1 complication after subpial grid placement but no complications related to the depth electrodes. Robotic image-guided placement of depth electrodes with concurrent craniotomy is feasible, and the technique is safe, accurate, and efficient.

Magnetoencephalography-guided epilepsy surgery for children with intractable focal epilepsy: SickKids experience

We introduced magnetoencephalography (MEG)-guided epilepsy surgery for children with intractable focal epilepsy at The Hospital for Sick Children (SickKids) in Toronto, Canada. Surgical candidacy and decisions on surgical procedure for children with intractable focal epilepsy are based on long-term scalp video EEG (VEEG) results, magnetic resonance imaging (MRI) findings, and the distribution of MEG spike sources. After multidisciplinary discussion at the seizure conference, for the patients requiring intracranial VEEG, custom-made subdural electrode grids are designed using three-dimensional MRI superimposed with MEG spike sources to cover the area of clustered MEG spike sources. At the first surgery, neurosurgeons use the intraoperative neuronavigation system to visualize the area of clustered spike dipoles and somatosensory evoked fields on MEG to place the subdural grid and depth electrodes. At the second surgery, the area of seizure onset and active interictal spike discharges on the intracranial VEEG recording, which usually correlates with the zone of clustered MEG spike sources, is resected. This combination leads to successful surgical outcome to control seizures in these challenging paediatric patients. MEG is a useful tool in children with intractable focal epilepsy to determine the surgical candidacy and focal cortical resection to stop seizures.

433: The topographical relationship between the source localization of interictal and ictal EEG discharges recorded with subdural grid electrodes using low-resolution electromagnetic tomography (sLORETA)

Purpose: In patients with medically refractory partial epilepsy, the topographic relationship between the location and the extent of the irritative zone, ictal onset zone, and the epileptogenic zone is controversial. Previous studies investigating the relationship between these zones have been based on a two-dimensional analysis of scalp or intracranial EEG recording, which can give misleading information regarding location of the underlying source generators. In this study patients who underwent chronic intracranial EEG monitoring with subdural electrodes, source localization was utilised using low resolution electromagnetic tomography (sLORETA) and co-registration of MRI and CT images, to examine the three-dimensional topographic relationship of the source of the interictal spikes with the ictal onset zone and regions of immediate spread.

Surgical Complications of Epilepsy Surgery Procedures : Experience of 179 Procedures in a Single Institute

There are a few reports on the complications of surgery for epilepsy. We surveyed our data to present complications of epilepsy surgeries from the neurosurgeon's point of view and compare our results with other previous reports. A total of 179 surgical procedures for intractable epilepsy (41 diagnostic, 138 therapeutic) were performed in 92 consecutive patients (10 adults, 82 children) during the last 9.2 years (February. 1997-April. 2006). Their medical records and radiological findings were reviewed to identify and analyze the surgical complications. The diagnostic procedures encompassed various combinations of subdural grid, subdural strips, and depth electrodes. Four minor transient complications developed in 41 diagnostic procedures (4/41=9.8%). A total of 138 therapeutic procedures included 28 anterior temporal lobectomies, 21 other lobectomies, 6 lesionectomies, 21 topectomies, 13 callosotomies, 20 vagus nerve stimulations, 13 multiple subpial transections, and 16 hemispherectomies. Twenty-six complications developed in therapeutic procedures (26/138=18.8%). Out of the 26 complications, 21 complications were transient and reversible (minor; 21/138=15.2%), and 5 were serious complications (major; 5/138=3.6%). Five major complications were one visual field defect, two mortality cases and two vegetative states. There were 2 additional mortality cases which were not related to the surgery itself. Our results indicate that complication rate was higher than previous other reports in minor complications and was comparable in major complications. However, our results show relatively high frequency of mortality cases and severe morbidity case compared to other previous reports. The authors would like to emphasize the importance of acute postoperative care in young pediatric patients as well as meticulous surgical techniques to reduce morbidity and mortality in epilepsy surgery.

COREGISTRATION OF DIGITAL PHOTOGRAPHY OF THE HUMAN CORTEX AND CRANIAL MAGNETIC RESONANCE IMAGING FOR VISUALIZATION OF SUBDURAL ELECTRODES IN EPILEPSY SURGERY

To develop a method for the coregistration of digital photographs of the human cortex with head magnetic resonance imaging (MRI) scans for invasive diagnostics and resective neocortical epilepsy surgery. Six chronically epileptic patients (two women, four men; mean age, 34 yr; age range, 20-43 yr) underwent preoperative three-dimensional (3D) T1-weighted MRI scans. Digital photographs of the exposed cortex were taken during implantation of subdural grid electrodes. Rendering software (Analyze 3.1; Biomedical Imaging Resource, Mayo Foundation, Rochester, MN) was used to create an MRI-based 3D model of the brain surface. Digital photographs were manually coregistered with the brain surface MRI model using the registration tool in the Analyze software. By matching the digital photograph and the brain surface model, the position of the subdural electrodes was integrated into the coordinate system of the preoperatively acquired 3D MRI dataset. In all patients, the position of the labeled electrode contacts in relation to the cortical anatomy could be visualized on the 3D models of the cortical surface. At the time of resection, the resulting image of the coregistration process provides a realistic view of the cortex and the position of the subdural electrode. The coregistration of digital photographs of the brain cortex with the results of 3D MRI data sets is possible. This allows for identification of anatomic details underlying the subdural grid electrodes and enhances the orientation of the surgeon.

Spatiotemporal dynamics of word processing in the human brain

We examined the spatiotemporal dynamics of word processing by recording the electrocorticogram (ECoG) from the lateral frontotemporal cortex of neurosurgical patients chronically implanted with subdural electrode grids. Subjects engaged in a target detection task where proper names served as infrequent targets embedded in a stream of task-irrelevant verbs and nonwords. Verbs described actions related to the hand (e.g, throw) or mouth (e.g., blow), while unintelligible nonwords were sounds which matched the verbs in duration, intensity, temporal modulation, and power spectrum. Complex oscillatory dynamics were observed in the delta, theta, alpha, beta, low, and high gamma (HG) bands in response to presentation of all stimulus types. HG activity (80–200 Hz) in the ECoG tracked the spatiotemporal dynamics of word processing and identified a network of cortical structures involved in early word processing. HG was used to determine the relative onset, peak, and offset times of local cortical activation during word processing. Listening to verbs compared to nonwords sequentially activates first the posterior superior temporal gyrus (post-STG), then the middle superior temporal gyrus (mid-STG), followed by the superior temporal sulcus (STS). We also observed strong phase-locking between pairs of electrodes in the theta band, with weaker phase-locking occurring in the delta, alpha, and beta frequency ranges. These results provide details on the first few hundred milliseconds of the spatiotemporal evolution of cortical activity during word processing and provide evidence consistent with the hypothesis that an oscillatory hierarchy coordinates the flow of information between distinct cortical regions during goal-directed behavior.

Subdural Electrode-Associated Complications: A 20-Year Experience

Background: Implantation of subdural strip and grid electrodes is a common methodology in the invasive evaluation of patients with medically refractory epilepsy. Although their implantation is safe, the occurrence of implantation-associated complications can occasionally be troublesome. Methods: In our current retrospective study, 185 patients undergoing subdural grid/strip implantation for invasive monitoring were examined. Their ages ranged between 16 and 48 years (mean 23.6). AdTech (Racine, Wisc., USA) strip and grid electrodes were implanted under general endotracheal anesthesia in all our cases. Duration of electroencephalographic monitoring ranged from 2 to 25 days (mean 10.8). The follow-up period ranged from 24 to 60 months (mean 44.6 months). Results: The most common complication in our series was the development of postoperative epidural hematoma in 3 patients (1.6%), while 2 patients (1.1%) suffered a subdural hematoma. Two patients (1.1%) developed significant brain edema postoperatively, 2 others (1.1%) developed an infection, while 2 patients (1.1%) experienced transient aphasia. Two patients (1.1%) had fatal outcomes in our series. Interestingly, in 5 patients (2.7%) nonhabitual seizures were recorded. Conclusion: Thorough understanding, early identification and prompt management of potential complications can minimize the risks associated with the implantation of subdural electrodes.

Transforming Electrocortical Mapping Data into Standardized Common Space

Subdural grid electrodes are implanted routinely for the pre-surgical work up of epilepsy. While different approaches are available, many centers, including ours, visualize electrode locations by co-registering pre-operative 3-D MR images with post-implantation 3-D CT images. This method allows the determination of the electrode positions in relation to the individual patient's anatomy, but does not easily allow comparison across patients. The goal of this study was to develop and validate a method for transforming electrode positions derived from 3-D CT images into standardized space. We analyzed data from twelve patients with subdurally implanted electrodes. Volumetric CT and MRI images were co-registered and then normalized into common stereotactic space. Electrode locations were verified statistically by comparing distances between the anterior commissure and a representative sampling of 8 electrode sites per patient. Results confirm the accuracy of our co-registration method for comparing electrode locations across patients.

STIMULATION MAPPING VIA IMPLANTED GRID ELECTRODES PRIOR TO SURGERY FOR GLIOMAS IN HIGHLY ELOQUENT CORTEX

To evaluate whether preoperative mapping of higher cortical functions with subdural grid electrodes can help to maximize resection in functional areas and avoid permanent injury. A consecutive series of 16 patients (female: n = 7, male: n = 9, mean age of 38 yr) with a history of seizures and without focal deficit was reviewed, harboring gliomas located in the dominant hemisphere adjacent to or in the F3 gyrus/Broca area (n = 11), parietal/perisylvian area (n = 5) and additionally the pre- or postcentral area (n = 15). All patients in this series were operated for cytoreductive purposes only and not for treatment of intractable seizures. To preoperatively define and intraoperatively tailor the extent of resection all patients had a presurgical grid implantation for functional brain mapping. No permanent morbidity/mortality was observed after grid implantation and resective surgery. On postoperative MRI the resection was complete (100%), nearly complete (>90%) in n = 9 and subtotal (60% to <90%) in n = 5 cases. Twice, only biopsies were taken according to the results of mapping. All patients with high-grade gliomas had adjuvant treatment with radiation and chemotherapy. After a mean follow up of 20.4 months, no tumor relapse or growth was seen in all cases of resection. Preoperative grid mapping is a safe and precise instrument to evaluate language and/or associated left perisylvian functions in patients with gliomas. It may be considered a valid alternative to awake craniotomy to maximize safe resection.

Extra-operative somatosensory evoked potentials confirm the accuracy of MEG SEF localizations

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.

The role of neurosurgery in status epilepticus

Status epilepticus remains a life-threatening condition that afflicts both adults and children which although occurs in patients with epilepsy, often presents as new-onset seizure activity also. Refractory status epilepticus poses a management challenge for neurological and neurosurgical teams. Subdural grid electrodes were used to record cortical discharges and guide tumor resection involving eloquent cortex and multiple subpial transections in a 48-year-old man with left hemiparesis in status epilepticus. He had been refractory to multiple medical therapies in persistent epilepsia partialis continua for a prolonged period. As an alternative to higher-dose suppressive medical therapy, the patient elected to proceed with subdural grid mapping after seizure semiology ("negative" scalp electroencephalogram) localized the seizure focus to the right hemisphere, motor cortex. Following tumor removal, multiple subpial transections were subsequently performed over large areas of the motor and sensory strips and successfully resolved the status epilepticus. The patient made an excellent recovery, became seizure free, had improved left-sided strength and was discharged home shortly after. This case illustrates a potentially life-saving technique for the treatment of refractory status epilepticus. Multiple subpial transections and other neurosurgical intervention should be considered for patients with status epilepticus. When localization with surface electrodes is poor, especially in eloquent cortex, subdural grid recording can be used to direct focal resection and/or multiple subpial transections to minimize neurological deficits. A review and summary of previously published neurosurgery cases for status epilepticus is discussed.

Seizures Lead to Elevation of Intracranial Pressure in Children Undergoing Invasive EEG Monitoring

To study the effects of intracranial subdural grid electrode placement and seizures on intracranial pressure (ICP) in children undergoing invasive EEG monitoring. Sixteen children with pharmacoresistant epilepsy who underwent two-stage epilepsy surgery with subdural grid placement were included in the study. The ICP was recorded at baseline and with each seizure prospectively. A variety of seizure parameters including type of seizure, length of seizure, extent of seizure spread, and number of subdural grid electrodes inserted were analyzed retrospectively and correlated with the change in ICP. A total of 48 seizures in 16 children were studied. The mean baseline ICP correlated positively with age of the child. Generalized tonic-clonic seizures were associated with the highest rise in ICP. Similarly, ICP rise was associated with seizures involving more electrodes indicating a larger area of brain participating in the seizure. Seizures in general and generalized tonic-clonic seizures, in particular, increase ICP temporarily in patients who are undergoing invasive EEG monitoring with subdural grids.

Placement of subdural electrode grids for seizure focus localization in patients with a large arachnoid cyst

Subdural electrode arrays are placed to localize seizure foci for possible resection. The procedure is usually straightforward when an electrode grid array is placed on the brain convexity but can become complicated if the surface on which the grids are applied is not convex. Arachnoid cysts can be associated with seizures, but their topography presents a challenge to standard techniques for the placement of subdural grids. The authors report on a technique for electrode grid placement that successfully localized seizure foci in the depths of arachnoid cysts in two patients. Subdural grids were placed to conform to the concave cyst cavity. They were held in place with rolled gelatin foam padding, which filled the arachnoid cyst. The padding was removed before removing the electrode grids and resecting the seizure focus. Although arachnoid cysts present a technical challenge when seizure foci are located within the cyst cavity, the technique of packing the cyst cavity with gelatin foam provides good electrode contact on the concave cyst wall, allowing adequate seizure focus localization.

Complications of invasive subdural electrode monitoring at St. Louis Children’s Hospital, 1994–2005

The purpose of this study was to better define the incidence of complications associated with placement of subdural electrodes for localization of seizure foci and functional mapping in children. The authors retrospectively reviewed the records of 112 consecutive patients (53 boys, 59 girls; mean age 10.9 years, range 10 months-21.7 years) with medically intractable epilepsy who underwent invasive monitoring at the Pediatric Epilepsy Center at St. Louis Children's Hospital between January 1994 and July 2005. There were 122 implantation procedures (85 grids and strips, 32 strips only, five grids only, four with additional depth electrodes), with a mean monitoring period of 7.1 days (range 2-21 days). Operative complications included the need for repeated surgery for additional electrode placement (5.7%); wound infection (2.4%); cerebrospinal fluid leak (1.6%); and subdural hematoma, symptomatic pneumocephalus, bone flap osteomyelitis, and strip electrode fracture requiring operative retrieval (one patient [0.8%] each). There were four cases of transient neurological deficit (3.3%) and no permanent deficit or death associated with invasive monitoring. Placement of subdural grid and strip electrodes for invasive video electroencephalographic monitoring is generally well tolerated in the pediatric population. The authors found that aggressive initial electrode coverage was not associated with higher rates of blood transfusion or perioperative complications, and reduced the frequency of repeated operations for placement of supplemental electrodes.

Definition of the epileptogenic zone in a patient with non‐lesional temporal lobe epilepsy arising from the dominant hemisphere

ABSTRACT Pharmacoresistant epilepsy arising from the dominant temporal region in patients with intact memory and normal anatomical imaging, presents major challenges in the preoperative definition of the epileptogenic zone, and the planning of the extent of the surgical resection. We report on the case of a 42‐year‐old, right‐handed male who presented with recurrent daily seizures that were resistant to antiepileptic drugs. Multiple, non‐invasive (scalp) video‐EEG evaluations revealed focal epilepsy arising from the left fronto‐temporal region. Multiple high resolution MRIs that were performed at multiple Epilepsy Centers failed to show any abnormality. Fluoro‐deoxyglucose PET scan showed extensive, left antero‐mesial temporal hypometabolism, and ictal SPECT showed increased perfusion in the left insula in addition to the left mesial and anterior temporal pole. Neuropsychological testing and intracarotid methohexital testing revealed excellent memory to the left, dominant side. A two‐stage invasive evaluation with subdural grid electrodes followed by depth electrode recordings allowed the localization of the epileptogenic region to the temporal pole. A selective resection of the left temporal pole (that spared the hippocampal formation) resulted in a seizure‐free outcome (one year follow‐up) with no significant consequences on memory function. We conclude that targeted, invasive recording techniques should be used for the accurate localization and delineation of the extent of the epileptogenic zone in cases of suspected, non‐lesional, dominant hemisphere, temporal lobe epilepsy with preserved memory function. The use of the staged invasive approach may increase the chances for memory (function) sparing through tailored, temporal resection.