Placement Of Intracranial Electrodes Research Articles

Comparison of dense array EEG with simultaneous intracranial EEG for Interictal spike detection and localization

To evaluate the clinical utility of dense array electroencephalography (dEEG) for the detection yield and localization of interictal spikes in mesial temporal lobe epilepsy. We simultaneously recorded 256-channel dEEG and intracranial electroencephalography (icEEG) implanted over the lateral and mesial temporal lobe in patients with intractable epilepsy. We calculated the dEEG spike detection rate for mesial temporal spikes which were confirmed by icEEG and applied source estimation to dEEG to compare noninvasive localization to the invasive recordings. 339 of 760 interictal spikes (45%) were detected by dEEG examining the 256-channel head surface array. The average icEEG amplitude of dEEG detectable spikes was 1083 μV, and that of dEEG undetectable spikes was 780 μV (P<0.05). All spikes detected in dEEG were localized to the temporal lobe. 295 of 339 spikes (87%) were well localized in mesial temporal lobe, close to the position confirmed by subdural electrodes. 256-channel dEEG may provide more precise information for the localization of interictal epileptiform discharges than conventional EEG or MEG in patients with deep spike foci. 256-channel dEEG may be clinically useful in the presurgical work-up for epilepsy, providing accurate noninvasive guidance for the placement of intracranial electrodes.

Interictal magnetoencephalographic findings related with surgical outcomes in lesional and nonlesional neocortical epilepsy

Purpose To investigate whether interictal magnetoencephalography (MEG) concordant with other techniques can predict surgical outcome in patients with lesional and nonlesional refractory neocortical epilepsy (NE). Methods 23 Patients with lesional NE and 20 patients with nonlesional NE were studied. MEG was recorded for all patients with a 275 channel whole-head system. Synthetic aperture magnetometry (SAM) with excess kurtosis (g2) and conventional Equivalent Current Dipole (ECD) were used for MEG data analysis. 27 Patients underwent long-term extraoperative intracranial video electroencephalography (iVEEG) monitoring. Surgical outcomes were assessed based on more than 1-year of post-surgical follow-up using Engel classification system. Results As we expected, both favorable outcomes (Engel class I or II) and seizure freedom outcomes (Engel class IA) were higher for the concordance condition (MEG findings are concordant with MRI or iVEEG findings) versus the discordance condition. Also the seizure free rate was significantly higher ( χ 2 = 5.24, P < 0.05) for the patients with lesional NE than for the patients with nonlesional NE. In 30% of the patients with nonlesional NE, the MEG findings proved to be valuable for intracranial electrode implantation. Conclusions This study demonstrates that a favorable post-surgical outcome can be obtained in most patients with concordant MEG and MRI results even without extraoperative iVEEG monitoring, which indicates that the concordance among different modalities could indicate a likelihood of better postsurgical outcomes. However, extraoperative iVEEG monitoring remains prerequisite to the patients with discordant MEG and MRI findings. For nonlesional cases, our results showed that MEG could provide critical information in the placement of intracranial electrodes.

A robust MRI-compatible system to facilitate highly accurate stereotactic administration of therapeutic agents to targets within the brain of a large animal model

Achieving accurate intracranial electrode or catheter placement is critical in clinical practice in order to maximise the efficacy of deep brain stimulation and drug delivery respectively as well as to minimise side-effects. We have developed a highly accurate and robust method for MRI-guided, stereotactic delivery of catheters and electrodes to deep target structures in the brain of pigs. This study outlines the development of this equipment and animal model. Specifically this system enables reliable head immobilisation, acquisition of high-resolution MR images, precise co-registration of MRI and stereotactic spaces and overall rigidity to facilitate accurate burr hole-generation and catheter implantation.To demonstrate the utility of this system, in this study a total of twelve catheters were implanted into the putamen of six Large White Landrace pigs. All implants were accurately placed into the putamen. Target accuracy had a mean Euclidean distance of 0.623mm (standard deviation of 0.33mm). This method has allowed us to accurately insert fine cannulae, suitable for the administration of therapeutic agents by convection-enhanced delivery (CED), into the brain of pigs. This study provides summary evidence of a robust system for catheter implantation into the brain of a large animal model. We are currently using this stereotactic system, implantation procedure and animal model to develop catheter-based drug delivery systems that will be translated into human clinical trials, as well as to model the distribution of therapeutic agents administered by CED over large volumes of brain.

Imaging in the surgical treatment of epilepsy

Medically refractory focal epilepsy is potentially curable by surgery. This Review considers the application of recent advances in structural and functional brain imaging to increase the number of patients with epilepsy who are treated surgically, and to reduce the risk of complications arising from such intervention. Current optimal MRI of brain structure can identify previously undetectable lesions, with voxel-based and quantitative analyses further increasing the diagnostic yield. If MRI proves unremarkable, PET (with (18)F-fluorodeoxyglucose) and single-photon emission CT of ictal-interictal cerebral blood flow might identify the brain region that contains the epileptic focus. Magnetoencephalography plus simultaneous EEG and functional MRI can map the location of interictal epileptic discharges, thereby facilitating placement of intracranial recording electrodes to define the site of seizure onset. Functional MRI can also lateralize language and localize primary motor, somatosensory and language areas, and shows promise for predicting the effects of temporal lobe resection on memory. Tractography can visualize the main cerebral white matter tracts, thereby predicting and reducing surgery risk. Currently, displays of the optic radiation and pyramidal tracts are the most relevant for epilepsy surgery. Reliable integration of structural and functional data into surgical image-guidance systems is being pursued, and promises safer neurosurgery for epilepsy in the future.

Postoperative radiographic findings in patients undergoing intracranial electrode monitoring for medically refractory epilepsy

In this study the authors sought to determine whether any correlations existed between postimplantation head CT findings and the need to perform decompression surgery in patients with grid electrodes. The authors identified 74 patients who underwent intracranial electrode monitoring for medically refractory epilepsy from January 2000 through June 2008. Only the 46 patients who had head CT scans available for review were included in the study. The authors were able to determine the number and types of electrodes placed as well as complications experienced. They reviewed the CT scans for abnormal findings including extraaxial fluid collections, intracranial hemorrhages, and signs of mass effect. All patients developed some degree of extraaxial fluid collection following the placement of intracranial electrodes. The maximum width of the extraaxial fluid collection and the degree of midline shift were not predictive of the need for decompressive surgery. The presence, but not degree, of midline shift was associated with the need for decompressive surgery. Likewise, the presence of ventricular asymmetry was correlated with the need for removal of the electrodes and bone flap. Patients without midline shift or ventricular asymmetry on CT did not require decompressive surgery. After undergoing placement of intracranial electrodes all patients develop extraaxial fluid collections. In addition, many patients develop signs of mass effect including midline shift and ventricular asymmetry. When these findings are absent it is highly unlikely that surgical decompression is required.

Comparing Noninvasive Dense Array and Intracranial Electroencephalography for Localization of Seizures

To compare the localization of the seizure onset zone estimated from ictal recordings with high spatial resolution, 256-channel scalp dense array electroencephalographic video long-term monitoring (LTM) with the aid of source analysis with that obtained from subsequent intracranial ictal recordings. Ten patients with medically refractory epilepsy, all surgical candidates, underwent intracranial LTM after standard noninvasive evaluation failed to provide adequate localizing information regarding ictal origins. Before invasive studies, all patients underwent dense array electroencephalographic LTM in which habitual clinical seizures were recorded for each patient. Source analysis was applied to ictal onsets. Intracranial electrode placement followed conventional guidelines, although the neurosurgeon was aware of the dense array electroencephalographic results. Patients ranged in age from 10 to 49 years (mean age, 24 y); 7 were male. Identified risk factors included closed head injury in 1 patient and childhood meningitis in another. No focal neurological signs were found in any patient. Magnetic resonance imaging findings were normal in 6 patients; 1 patient had cerebellar hypoplasia, 1 had right frontoparietal dysplasia, 1 had bilateral nonspecific white matter abnormalities, and 1 had bilateral cavernous angiomas. Ictal onsets, based on invasive recordings, were in the mesiotemporal lobe (3 patients), lateroparietal (2 patients), mesioparietal (1 patient), laterofrontal (1 patient), superolateral frontocentral (1 patient), frontopolar (1 patient), and posteroinferior temporo-occipital neocortex (1 patient). Dense array electroencephalography localized ictal onsets to the same region as intracranial monitoring in 8 of 10 cases; invasive studies disclosed an additional ictal focus in 2 of these patients. Surgical resections were based only on intracranial electroencephalographic findings. Dense array electroencephalography has the potential to assist in the noninvasive localization of epileptic seizures and to guide the placement of invasive electrodes for localizing seizure onset.

Bilateral Intracranial Electrodes for Lateralizing Intractable Epilepsy

Medically refractory epilepsy is amenable to neurosurgical intervention if the epileptogenic focus is accurately localized. If the scalp video-electroencephalography (EEG) and magnetic resonance imaging are nonlateralizing, yet a single focus is suspected, video-EEG monitoring with bilateral intracranial electrode placement is helpful to lateralize the ictal onset zone. We describe the indications, risks, and utility of such bilateral surveys at our institution. We retrospectively reviewed 26 patients with medically refractory seizures who were treated over a 5-year period and underwent bilateral placement of intracranial electrodes. Subdural strips were used in all cases, and additional stereotactic implantation of depth electrodes into mesial temporal lobes occurred in 50%. The mean patient age was 37.7 years, and 65.4% of patients were male. The most common indication for bilateral invasive monitoring was bilateral ictal onsets on surface video-EEG (76.9%), followed by frequent interictal spikes contralateral to a single ictal focus (7.7%). Intracranial monitoring lasted an average of 8.2 days, with ictal events recorded in all cases. Ten patients (38.5%) subsequently underwent more extensive unilateral monitoring via implantation of subdural and depth electrodes through a craniotomy. A therapeutic procedure was performed in 17 patients (65.4%), whereas 1 patient underwent a palliative corpus callosotomy (3.8%). Nine patients underwent a resection without unilateral invasive mapping. Reasons for no therapeutic surgery (n = 8) included multifocal onsets, failing the Wada test, refusal of further treatment, and negative intraoperative electrocorticogram. There was 1 surgical complication, involving a retained electrode fragment that was removed in a separate minor procedure. Of the 26 patients, 15 (57.7%) are now seizure-free or have seizure disorders that have substantially improved (modified Engel classes I and II). Of the 17 patients who underwent a potentially curative surgery, 13 (76.5%) were Engel classes I and II. Bilateral placement of subdural strip and depth electrodes for epilepsy monitoring in patients with nonlateralizing scalp EEG and/or discordant imaging studies but clinical suspicion for focal seizure origin is both safe and effective. Given the safety and efficacy of this procedure, epileptologists should have a low threshold to consider bilateral implants for suitable patients.

Clinical Application of MEG Source Localization Algorithms in Presurgical Epilepsy Evaluation: Strengths and Limitations

Event Abstract Back to Event Clinical Application of MEG Source Localization Algorithms in Presurgical Epilepsy Evaluation: Strengths and Limitations Douglas Rose1*, Hisako Fujiwara1, Nat Hemasilpin1, Ki Lee1 and Francesco Mangano1 1 University of Cincinnati, Cincinnati Children's Hospital Medical Center, United States MEG source localization algorithms perform well in simulation studies with low noise; little is known regarding relative strengths and limitations of algorithms for real clinical data. We compared algorithms with a common presurgical evaluation clinical dataset. We recorded MEG interictal discharges for 209 patients (ages 1 mo–26 years) with medically intractable epilepsy. We analyzed all recordings with equivalent current dipole models (ECD) and a beamformer, synthetic aperture magnetometry (SAM). We additionally analyzed recordings in 50 patients with dipole scan (DS), (multiple signal classification -MUSIC) and distributed dipole models (DD) (minimum norm estimate - MNE, standardized low resolution brain electromagnetic tomography - sLORETA). We compared each to presurgical scalp interictal/ictal EEG findings. We compared MEG to ECoG localization for 59 patients who had ECD and SAM only and for 17 patients studied with all 5 algorithms. For ECD and DD we had to carefully choose representative samples with low background noise. Use of segmented cortical mantle improved localization for ECD, DS, and DD, but also introduced potential errors. DD tended to localize a single contiguous source region for each patient. SAM tended to identify multiple locations and gave reasonable localizations in the presence of VNS artifact (24 patients) but failed to localize spikes under several conditions. Use of several methodologies limited errors from each; when multiple algorithms indicated a similar region, the localization more often agreed with ictal onset by ECoG. MEG source localization algorithms highlight different aspects of the irritative zone associated with interictal discharges based on different a priori assumptions and different approaches to the inverse problem. Use of several different MEG source localization methodologies may improve localization non-invasively of the irritative zone prior to placement of intracranial electrodes and prior to epilepsy surgery. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Poster Presentation Topic: Epilepsy Citation: Rose D, Fujiwara H, Hemasilpin N, Lee K and Mangano F (2010). Clinical Application of MEG Source Localization Algorithms in Presurgical Epilepsy Evaluation: Strengths and Limitations. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00377 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: 08 Apr 2010; Published Online: 08 Apr 2010. * Correspondence: Douglas Rose, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, United States, douglas.rose@cchmc.org 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 Douglas Rose Hisako Fujiwara Nat Hemasilpin Ki Lee Francesco Mangano Google Douglas Rose Hisako Fujiwara Nat Hemasilpin Ki Lee Francesco Mangano Google Scholar Douglas Rose Hisako Fujiwara Nat Hemasilpin Ki Lee Francesco Mangano PubMed Douglas Rose Hisako Fujiwara Nat Hemasilpin Ki Lee Francesco Mangano 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.

Effect of epilepsy magnetic source imaging on intracranial electrode placement

Intracranial electroencephalography (ICEEG) with chronically implanted electrodes is a costly invasive diagnostic procedure that remains necessary for a large proportion of patients who undergo evaluation for epilepsy surgery. This study was designed to evaluate whether magnetic source imaging (MSI), a noninvasive test based on magnetoencephalography source localization, can supplement ICEEG by affecting electrode placement to improve sampling of the seizure onset zone(s). Of 298 consecutive epilepsy surgery candidates (between 2001 and 2006), 160 patients were prospectively enrolled by insufficient localization from seizure monitoring and magnetic resonance imaging results. Before presenting MSI results, decisions were made whether to proceed with ICEEG, and if so, where to place electrodes such that the hypothetical seizure-onset zone would be sampled. MSI results were then provided with allowance of changes to the original plan. MSI indicated additional electrode coverage in 18 of 77 (23%) ICEEG cases. In 39% (95% confidence interval, 16.4-61.4), seizure-onset ICEEG patterns involved the additional electrodes indicated by MSI. Sixty-two patients underwent surgical resection based on ICEEG recording of seizures. Highly localized MSI was significantly associated with seizure-free outcome (mean, 3.4 years; minimum, >1 year) for the entire surgical population (n = 62). MSI spike localization increases the chance that the seizure-onset zone is sampled when patients undergo ICEEG for presurgical epilepsy evaluations. The clinical impact of this effect, improving diagnostic yield of ICEEG, should be considered in surgery candidates who do not have satisfactory indication of epilepsy localization from seizure semiology, electroencephalogram, and magnetic resonance imaging.

器質性病変を持つてんかんにおける焦点局在診断と頭蓋内電極留置の適応 : てんかん外科を始めるために必要な知識(&lt;特集&gt;器質性病変を持つてんかんの外科治療)

MRIで器質性病変を伴う難治性てんかんは一般に外科治療のよい適応だが,てんかん発作消失を目的として手術を検討する以上,詳細な焦点局在診断が必要である.焦点局在診断には,まず発作症候の記録と解析,間欠期および発作時の頭皮脳波記録,脳磁図,核医学検査など非侵襲的検査を行う.最終的な焦点診断は原則的に頭蓋内脳波記録によってなされるが,特に非侵襲的検査で治療対象とするてんかん焦点が確定できなかった場合,裁断的焦点切除のために高解像度の焦点局在診断が必要な場合には必須となる.一方で頭蓋内脳波は侵襲的であり,海馬硬化を伴う内側側頭葉てんかん以外にもこれを省略できる患者群の同定や,診断治療法の開発が望まれる.

Advances in the Management of Epilepsy

PILEPSY remains one of the most common afflictions in humans, with a prevalence of about 1% in the general population. Since the advent of phenobarbital as a novel therapeutic agent for the prevention of seizures in patients in 1912, the medical and surgical treatments of epilepsy have advanced significantly. There were many early pioneers in epilepsy surgery, including Horsley, Keen, Nancred, and Sachs. 1,4 We must remember that their surgical attack on epilepsy was practiced long before we became familiar with the structure and function of the central nervous system, and the fine histoarchitecture of the neuronal networks within the cerebral cortex. Of course, the work of Penfield 2,3 in the 1930s set the stage for the modern revolution of surgical techniques applied to the study of human epilepsy. In this special issue of Neurosurgical Focus, we have provided an update on the state-of-the-art management of epilepsy from both medical and surgical perspectives. We begin with a description of pharmacologically intractable epilepsy and proceed to a review of imaging strategies to identify neurosurgical candidates. It is becoming increasingly more apparent that neuroimaging is playing a pivotal role in our understanding of the causes of epilepsy in children and adults. We then review current techniques for temporal lobectomy, extratemporal cortical resections, corpus callosotomy, and treatment of hypothalamic hamartomas and tuberous sclerosis. The use of deep brain stimulation for epilepsy is discussed as a novel approach to the management of selected patients with intractable epilepsy. Recent adjuncts in the placement of intracranial electrodes, whether by use of neuronavigation or robotics, are described and can now be made widely accessible to most neurosurgical centers. Finally, some futuristic applications of technologies are presented, such as the use of optical spectroscopy in identifying the seizure focus and the identification of a novel bumentanide-sensitive Na-K-Cl 2 cotransporter. There is much that neurosurgeons can feel proud of in the advancements of techniques that have improved the lives of patients with epilepsy. In the future, I predict that the use of resective surgery, which carries the risk of neurological impairment, will be supplanted by techniques that are more squarely aimed at increasing our understanding of the complexities of the neuronal circuits involved in the generation and propagation of epilepsy. Interrupting these circuits effectively is likely to be accomplished through sophisticated stimulation and electrical interference techniques in which neurosurgeons will continue to play a major role.

FRAMELESS STEREOTACTIC PLACEMENT OF FORAMEN OVALE ELECTRODES IN PATIENTS WITH DRUG-REFRACTORY TEMPORAL LOBE EPILEPSY

Semi-invasive foramen ovale electrodes (FOEs) are used as an alternative to invasive recording techniques in the presurgical evaluation of patients with temporal lobe epilepsy. To maximize patient safety and interventional success, frameless stereotactic FOE placement by use of a variation of an upper jaw fixation device with an external fiducial frame, in combination with an aiming device and standard navigation software, was evaluated by the Innsbruck Epilepsy Surgery Program. Patients were immobilized noninvasively with the Vogele-Bale-Hohner headholder (Medical Intelligence GmbH, Schwabmünchen, Germany) to plan computed tomography and surgery. Frameless stereotactic cannulation of the foramen and intracranial electrode placement were achieved with the help of an aiming device mounted to the base plate of the headholder. Ease of applicability, safety, and results obtained with foramen ovale recording were investigated. Twenty-six FOEs were placed in 13 patients under general anesthesia. The foramen ovale was successfully cannulated in all patients. One patient reported transient painful mastication after the procedure as a complication attributable to use of the Vogele-Bale-Hohner mouthpiece. In one patient, a persistent slight buccal hypesthesia was present 3 months after the procedure. To pass the foramen, slight adjustments in the needle position had to be made in 10 sides (38.4%). To place the intracranial electrodes, adjustments were necessary six times (23.7%). An entirely new path had to be planned once (3.8%). Seizure recording provided conclusive information in all patients (100%). Outcome in operated patients was Engel Class Ia in six patients, Class IId in one patient, Class IIb in one patient, and Class IVa in one patient (minimum follow-up, 6 mo). The Vogele-Bale-Hohner headholder combined with an external registration frame eliminates the need for invasive head clamp fixation. FOE placement can be planned "offline" and performed under general anesthesia later. This can be valuable in patients with distorted anatomy and/or small foramina or in patients not able to undergo the procedure under sedation. Results are satisfactory with regard to patient safety, patient comfort, predictability, and reproducibility. FOEs supported further treatment decisions in all patients.

Deep brain stimulation: Treating neurological and psychiatric disorders by modulating brain activity

Attempts to modulate brain activity for therapeutic purposes by stimulating various cortical and subcortical areas, have been made since the 19th century. Bartholow was one of the first to describe in detail, a case of brain stimulation in 1874 [13]. However, it was not until a century later, when in 1987, Benabid and Pollack proved that chronic high frequency deep brain stimulation (DBS) of thalamus could be used as a safe and effective way of treating the tremor of Parkinson’s disease (PD) [11,19]. A timeline of important milestones in the history of brain stimulation is shown in Fig. 1. In this article we will discuss the currently approved and the experimental uses of DBS. In addition we will give a brief overview of the proposed mechanisms by which DBS is currently thought to modulate brain activity. Sometimes referred to as a ‘brain pacemaker’, DBS involves placement of intracranial electrodes (Fig. 2) which can be connected to a subcutaneously and subclavicularly implanted pulse generator (IPG). The IPG allows noninvasive adjustments of current amplitude, frequency, pulse width and polarity by means of a hand-

Asystole induced by electrical stimulation of the left cingulate gyrus

The cortical control of the autonomic system may account for the clinical phenomenon of ictal asystole which, in turn, has been speculated to be a potential mechanism for sudden unexpected death in epilepsy (SUDEP). We report an 18-year-old patient with frontal lobe epilepsy who had intracranial electrode placement showing bifrontal seizure-onset. This patient received electrical stimulation to the left cingulate gyrus and developed cardiac asystole within 3 seconds of electrical stimulation. Intracranial monitoring showed epileptiform discharges in the left frontal polar, frontal lateral and interhemispheric electrodes. We suggest that the left cingulate gyrus, as part of the central autonomic network, may mediate bradyarrhythmia through the vagal pathway. There remains the possibility that other brain regions were also involved due to the time lag between asystole and epileptiform discharges, and the lack of intracranial exploration in the mesial temporal and insular regions. [Published with video sequences].

EPILEPSY SURGERY FOR NEONATAL OR INFANTILE ONSET SEIZURES: USE OF PET SCANNING

Intractable epilepsy in infants and young children may lead to an epileptic encephalopathy. In such cases, epilepsy surgery should be considered. Surgical results are best when there is concordance between EEG localization and neuroimaging. PET scanning using 2-deoxy-2(18F)fluoro-D-glucose (FDG) identifies epileptic foci when MRI is non-revealing, and when a lesion is present, PET complements MRI by defining the full extent of the lesion and evaluating the integrity of surrounding brain regions. PET abnormalities may guide placement of intracranial electrodes, thus minimizing sampling errors. The size of the hypometabolic zone increases with chronic epilepsy, suggesting dynamic changes in the epileptic network. In infantile spasms, resection of focal PET abnormalities corresponding to focal EEG abnormalities is associated with improved seizure/cognitive outcome. Only about 20% of patients with 'cryptogenic infantile spasms' show a single PET focus amenable to resection. The majority shows multifocal hypometabolism and are not optimal surgical candidates. Bilateral symmetric hypometabolism suggests a nonlesional etiology, more consistent with neurogenetic/neurometabolic disorders. In infants with hemimegalencephaly, the relative integrity of the contralateral hemisphere is assessed using PET for prognostic purposes. In patients with Sturge-Weber syndrome, rapid demise of the affected hemisphere is associated with better seizure/cognitive outcome than slower progression because of brain plasticity. Other PET tracers may provide more specific assessment of seizure foci. 11C-flumazenil (FMZ) labels central benzodiazepine receptors, showing: decreased receptor binding in medial temporal sclerosis, perilesional epileptogenic zones, seizure onset zones, and secondary epileptic foci. 11C-alpha-methyl-L-tryptophan (AMT), an analogue of tryptophan, traces serotonin synthesis and kynurenine pathways and shows increased uptake in epileptogenic cortex interictally. In children with tuberous sclerosis, increased AMT uptake is seen around epileptogenic tubers, but not nonepileptogenic tubers. The list of PET tracers for epilepsy continues to grow and will eventually pinpoint precisely the cortical regions that should be resected to achieve best postoperative outcome.

Surgical Treatment for Extratemporal Epilepsy.

Partial seizures of extratemporal origin may present unique challenges in the patient with medically refractory seizures. The efficacy of an extratemporal focal cortical resection may be less effective than an anterior temporal lobectomy for intractable epilepsy. The potential operative complications may be increased in individuals with extratemporal epilepsy because of functional cerebral cortex involvement and the need for a large cortical resection to significantly reduce seizure tendency. Partial seizures of extratemporal origin are predominantly associated with frontal lobe epilepsy. The most effective treatment for intractable partial epilepsy is a focal cortical resection with excision of the epileptogenic zone, that is, an area of ictal onset and initial seizure propagation. The preoperative evaluation and operative strategy in patients with partial epilepsy of extratemporal origin associated with pharmacoresistant seizures is determined by the anatomic localization of the epileptogenic zone and the presence of a substrate-directed disorder. The goals of surgical treatment in extratemporal epilepsy include rendering the patient seizure-free, avoiding operative morbidity, and allowing the individual to become a participating and productive member of society. Before surgical treatment, the individual with extratemporal epilepsy will require a comprehensive preoperative evaluation, including routine electroencephalogram (EEG), long-term EEG monitoring, neuropsychologic studies, and magnetic resonance imaging (MRI). Patients with a normal MRI study, conflicting preoperative evaluation, or involvement of suspected functional cerebral cortex would require chronic intracranial EEG monitoring. The rationale for intracranial EEG includes localization of the ictal onset zone or intraoperative functional mapping, or both. Two-fluorodeoxyglucose positron emission tomography studies are usually unremarkable in patients with extratemporal epilepsy and normal MRI scans. Subtraction ictal single photon emission computed tomography coregistered to MRI (SISCOM) study may be useful to demonstrate a localized cerebral perfusion alteration in patients with intractable partial epilepsy. The diagnostic yield of SISCOM has been confirmed in patients with extratemporal epilepsy undergoing surgical treatment. The results of the SISCOM study may tailor the placement of intracranial EEG electrodes and affect the operative strategy. Patients with extratemporal epilepsy overall are less favorable operative candidates than individuals with medial temporal lobe epilepsy. However, individuals with MRI-identified lesional pathology of SISCOM-identified perfusion alterations concordant with the epileptogenic zone may be considered for surgical treatment. Chronic intracranial EEG monitoring may be necessary to confirm the localization of the ictal onset zone before epilepsy surgery. Patients with normal neuroimaging studies and extratemporal epilepsy are unlikely to be rendered seizure-free with focal cortical resection and should be considered candidates for other alternative forms of treatment for intractable partial epilepsy. Patients with non-substrate-directed extratemporal epilepsy should undergo a preoperative evaluation and surgical treatment at a comprehensive epilepsy center with extensive experience in chronic intracranial EEG monitoring and contemporary neuroimaging procedures because of the inherently high acuity associated with the operative management clinical disorder.

Positron emission tomography and single photon emission computed tomography in epilepsy care

Radiopharmaceutical brain imaging is clinically applied in planning resective epilepsy surgery. Cerebral sites of seizure generation-propagation are highly associated with regions of hyperperfusion during seizures, and with glucose hypometabolism interictally. For surgical planning in epilepsy, the functional imaging modalities currently established are ictal single photon emission computed tomography (SPECT) with [ 99mTc]technetium-hexamethylpropyleneamine oxime (HMPAO) or with [ 99mTc]technetium-ethylene cysteine dimer (ECD), and interictal positron emission tomography (PET) with 2-[ 18F]fluoro-2-deoxyglucose (FDG). Ictal SPECT and interictal FDG PET can be used in presurgical epilepsy evaluations to reliably: 1) determine the side of anterior temporal lobectomy, and in children the area of multilobar resection, without intracranial electroencephalographic recording of seizures; 2) select high-probability sites of intracranial electrode placement for recording ictal onsets; and, 3) determine the prognosis for complete seizure control following anterior temporal lobe resection. Coregistration of a patient's structural (magnetic resonance) and functional images, and statistical comparison of a patient's data with a normal data set, can increase the sensitivity and specificity of these SPECT and PET applications to the presurgical evaluation. © 2003 Elsevier Inc. All rights reserved.

Magnetoencephalography-directed surgery in patients with neocortical epilepsy

Magnetoencephalography (MEG) and magnetic source (MS) imaging are techniques that have been increasingly used for preoperative localization of epileptic foci and areas of eloquent cortex. The use of MEG examinations must be carefully balanced against the high cost and technological investments required to perform these studies, particularly when less expensive alternative localization methods are available. To help elucidate the value of MEG, the authors have critically reviewed their experience with whole-head MEG in the case management of patients undergoing epilepsy surgery. The authors identified 23 patients with suspected focal epilepsy who underwent whole-head MEG and MS imaging at Huntington Memorial Hospital and, subsequently, underwent invasive intracranial electrode monitoring and electrocorticography (ECoG) to localize the zone of seizure origin for surgical resection. The results of the MS imaging were retrospectively stratified into three groups by the number of interictal spikes recorded during a 4-hour recording session: Class I (no spikes), Class II (< or = five spikes), and Class III (> or = six spikes). Class III was further subdivided according to the clustering density of the interictal spikes: Class IIIA represents a mean distance between interictal spikes of 4 mm or greater (that is, diffusely clustered) and Class IIIB represents a mean distance between interictal spikes of less than 4 mm (that is, densely clustered). The authors analyzed these groups to determine to what extent the results of MS imaging correlated with the ECoG-determined zone of seizure origin. In addition, they assessed whether the MS imaging study provided critical localization data and correlated with surgical outcome following resection. A statistical analysis of these correlations was also performed. Of the 40 patients studied, 23 underwent invasive monitoring, including 13 with neocortical epilepsy, four with mesial temporal lobe epilepsy, and six with suspected neocortical epilepsy that could not be clearly localized by ECoG. Depth electrodes were used in nine cases, subdural grids in nine cases, depth electrodes followed by subdural grids and strips in four cases, and intraoperative ECoG in one case. Electrocorticography was able to localize the zone of seizure origin in 16 (70%) of 23 cases. In 11 (69%) of the 16 cases in which ECoG was able to localize the zone of seizure origin, the interictal spikes on the MS images were classified as Class IIIB (densely clustered) and regionally correlated to the MS imaging-determined localization in all cases (that is, the same lobe). In contrast, no Class IIIB cases were identified when ECoG was unable to localize the zone of seizure origin. This difference showed a trend toward, but did not achieve, statistical significance (p < 0.23), presumably because of the relatively small number of cases available for analysis. In three cases (all Class IIIB), MS imaging was used to guide invasive electrodes to locations that otherwise would not have been targeted and provided unique localization data, not evident from other imaging modalities, that strongly influenced the surgical management of the patient. The classification of findings on MS images into subgroups and subsequent statistical analysis generated a model that predicted that Class IIIB MS imaging data are likely to provide reliable information to guide surgical placement of electrodes, but all other data groups do not provide localization information that is reliable enough to guide surgical decision making. Magnetic source imaging can provide unique localization information that is not available when other noninvasive methods are used. Magnetic source imaging appears most useful for cases of neocortical epilepsy. In particular, when an MS imaging study revealed six or more interictal spikes that were densely clustered in a single anatomical location, the MS image was highly correlated with the zone of seizure origin identified by ECoG. In these cases the MS imaging data may be useful to guide placement of intracranial electrodes.

Localization of ictal and interictal bursting epileptogenic activity in focal cortical dysplasia: Agreement of magnetoencephalography and electrocorticography

Focal cortical dysplasia (FCD) is often associated with severe partial epilepsy. In such cases, interictal frequent rhythmic bursting epileptiform activity (FBREA) on both scalp electroencephalography (EEG) and electrocorticography (ECoG) is generally accepted to be identical to the ictal epileptiform activity. We used magnetoencephalography (or Magnetic Source Imaging (MSI)) to determine the epileptogenic zone in a 6-year-old patient with histopathologically proven FCD and normal magnetic resonance imaging (MRI). MSI was used to localize the sources of both ictal activity and FRBEA, which was then compared with ECoG findings. The intracranial sources of both types of activity co-localized in the left inferior frontal and superior temporal gyri. The location and extent of the epileptogenic area determined by MSI was essentially identical to that determined directly through extra-operative ECoG. In the absence of structural abnormalities detectable on MRI, the noninvasive method of MSI provided valuable information regarding the location and extent of the primary epileptogenic area. This was critical for pre-surgical planning regarding placement of intracranial electrodes and for risk-benefit evaluation. [Neurol Res 2002; 24: 525-530]

Functional imaging in the work-up of childhood epilepsy.

In children with medically intractable lesional epilepsy, surgery is deemed successful if the epileptogenic focus can be removed while major neurological functions are spared. Current techniques rely on invasive intracranial recordings. The new developments in functional imaging offer the possibility of localizing the epileptogenic focus noninvasively (PET/SPECT) and mapping cognitive functions (fMRI). Ictal SPECT shows hyperperfusion in the focus and has proved to have better localizing value than interictal PET or SPECT, which show focal hypometabolism or hypoperfusion. Ictal SPECT is useful for deciding on the placement of intracranial electrodes in extratemporal epilepsies, particularly in young children. Functional MRI has proved highly accurate for localizing motor and language networks, thus offering the possibilities of replacing the Wada test (language hemispheric lateralization) and studying postlesional brain plasticity. Despite the difficulties of functional imaging in children owing to the limited cooperation that can be expected, ethical constraints, and poor normative data, SPECT/PET and fMRI provide clinically useful information for presurgical work-up of childhood epilepsies.