M. Guenot

Neurophysiological Monitoring for Epilepsy Surgery: The Talairach SEEG Method

Object of the Study: In some candidates for epilepsy surgery in whom the decision to operate is difficult to make, invasive presurgical investigations, namely depth electrode recordings, may be needed. The SEEG (StereoElectroEncephaloGraphy) method consists of stereotactic orthogonal implantation of depth electrodes (5 to 15, 11 on average). The object of this study is to clarify the indications for SEEG, to expose its complications, and to display its usefulness in terms of surgical strategy and results. Patients and Methods: 100 patients, suffering from drug-resistant epilepsy and selected as candidates for surgical resection, underwent SEEG between 1996 and 2000. A total of 1,118 electrodes were implanted. For each single case, the sites of implantation of the electrodes were chosen in order to determine either the side of the onset of seizures, or the uni- or multilobar feature of them, or a possible operculo-insular propagation from a temporal onset, and also, using direct electrode stimulation, the proximity of speech or motor area. Results: Complications occurred in 5 patients (2 superficial infections, 2 breakages of electrodes, and 1 intracerebral hematoma responsible for death). SEEG was helpful in most (84%) of the 100 patients to confirm or annul surgical indication, and to adjust the extent of the resection. In some cases (14%), SEEG allowed to propose a resection that might have been disputable based solely on noninvasive investigation data. For frontal epilepsy, SEEG was crucial in all cases to delineate the extent of resection. Conclusion: SEEG proved to be a relatively safe and a very useful method in ‘difficult’ candidates for epilepsy surgery. In addition, in some cases the implanted electrodes can be used to perform therapeutic RF thermocoagulation of epileptic foci or networks.

Precentral Cortex Stimulation for the Treatment of Central Neuropathic Pain

The authors report a series of 23 patients with central neuropathic pain who were treated with the recently developed technique of precentral cortex stimulation (PCS). Of the 20 patients with a follow-up of more than 1 year (mean of 23 months) 25% had an excellent, 35% a good and 15% a fair relief of pain. In 25% the method failed. On the basis of these findings and the literature data (127 reported cases), the authors advocate PCS in patients with severe and medically refractory poststroke pain.

Surgical anatomy of the insula.

The insula is the only cortical part of the brain which is not visible on the surface of the hemisphere. This is due to the fact that it is totally covered by the fronto-parietal and temporal opercula. The insula has a triangular shape, and is separated from the opercula by the anterior, superior, and inferior periinsular sulci. The limen insulae is the antero-inferiorly located insular cortical surface which conjoins the inferior insular point, the anterior perforated surface, and the temporo-mesial surface. The insula is morphologically divided into two parts by the central insular sulcus. The anterior part of the insula bears 3 gyri: the anterior, middle, and posterior short insular gyri, separated by the anterior and precentral insular sulcus. The posterior part of the insula contains the anterior and posterior long insular gyri, separated by the postcentral insular sulcus. The vascular supply of the insula is mainly provided by the M2 segment of the middle cerebral artery, which constitutes a substantial obstacle to any open or stereotactic procedure aiming at the insular region. Histologically, the insula is a part of the paralimbic cortex, as it bears in its antero-inferior part an allo and mesocortical area. The insula is functionally involved in cardiac rhythm and arterial blood pressure control, as well as in viscero-motor control and in viscero-sensitive functions. There is considerable evidence for the involvement of the insula as a somesthetic area, including a major role in the processing of nociceptive inputs. Its possible role in some epilepsies may explain some failures of temporal lobe resection. Surgery of the insular lobe is a technical challenge, whose risks can be minimized by the use of intra-operative direct cerebral stimulation.

SEEG-guided RF-thermocoagulation of epileptic foci: A therapeutic alternative for drug-resistant non-operable partial epilepsies

BACKGROUNDnPrevious literature includes numerous reports of acute stereotactic ablation for epilepsy. Most reports focus on amygdalotomies or amygdalohippocampotomies, some others focus on various extra-limbic targets. These stereotactic techniques proved to have a less favourable outcome than that of standard surgery, so that their rather disappointing benefit/risk ratio explains why they have been largely abandoned. However, depth electrode recordings may be required in some cases of epilepsy surgery to delineate the best region of cortical resection. We usually implant depth electrodes according to Talairachs stereo electroencephalography (SEEG) methodology. Using these chronically implanted depth electrodes, we are able to perform radiofrequency (RF)-thermolesions of the epileptic foci. This paper reports the technical data required to perform such multiple cortical thermolesions, as well as the results in terms of seizure outcome in a group of 41 patients. TECHNICAL DATA: Lesions are placed in the cortex areas showing either a low amplitude fast pattern or spike-wave discharges at the onset of the seizures. Interictal paroxysmal activities are not considered for planning thermocoagulation sites. All targets are first functionally evaluated using electrical stimulation. Only those showing no clinical response to stimulation are selected for thermolesion, including sites located inside or near primary functional area. Lesions are performed using 120mA bipolar current (50 V), applied for 10-30 sec. Each thermocoagulation produces a 5-7mm diameter cortical lesion. A total of 2-31 lesions were performed in each of the 41 patients. Lesions are placed without anaesthesia.nnnRESULTSn20 patients (48.7%) experienced a seizure frequency decrease of at least 50% that was more than 80% in eight of them. One patient was seizure free after RF thermocoagulation. In 21 patients, no significant reduction of the seizure frequency was observed. Amongst the characteristics of the disease (age and sex of the patient, lobar localization of the EZ) and the characteristics of the thermocoagulations (topography, lateralization, number, morphology of the lesions on MRI) no factor was significantly linked to the outcome. However, the best results were clearly observed in epilepsies symptomatic of a cortical development malformation (CDM), with 67% of responders in this group of 20 patients (p = 0.052). Three transient post-procedure side-effects, consisting of paraesthetic sensations in the mouth (2 cases), and mild apraxia of the hand, were observed.nnnCONCLUSIONnSEEG-guided-RF-thermolesioning is a safe technique. Our results indicate that such lesions can lead to a significant reduction of seizure frequency. Our experience suggests that SEEG-guided RF thermocoagulation should be dedicated to drug-resistant epileptic patients for whom conventional resection surgery is risky or contra-indicated on the basis of invasive pre-surgical evaluation, particularly those suffering from epilepsy symptomatic of cortical development malformation.

MRI Assessment of the Anatomy of Optic Radiations after Temporal Lobe Epilepsy Surgery

Objective: The aim of this study was to determine the course of the temporal optic radiations. Material and Methods: Eighteen patients were included in this prospective study. All of them underwent a temporal lobectomy for epilepsy, including the mesial temporal structures and a variable extent of lateral neocortex (from 2 to 7 cm behind the temporal tip). An MRI was performed 2 months postoperatively, allowing assessment of the extent of lateral resection. Postoperative visual fields were determined by automatic static perimetry (ASP). Results: (1) No patient complained of a disabling visual field deficit. (2) ASP, a highly sensitive technique, however, detected postoperative visual field deficits in 83% of patients, confined to the superior homonymous field contralateral to the resection. (3) A strong correlation was found between the presence of a visual field deficit and the extent of laterotemporal resection. (4) The smallest anteroposterior resection resulting in a field defect was limited to 20 mm from the temporal tip. Conclusion: (1) This study confirms a strong correlation between postoperative visual field deficits and the extent of lateral neocortical temporal resection. (2) The anterior limit of Meyer’s loop is likely to be located more rostrally than previously believed. (3) Despite this, lateral resection remains useful in some cases for seizure control.

Towards source volume estimation of interictal spikes in focal epilepsy using magnetoencephalography

Interictal spikes are a hallmark of cortical epileptogenicity; their spatial distribution in the cortex defines the so-called irritative zone or spiking volume (SV). Delineating the SV precisely is a challenge during the presurgical evaluation of patients with epilepsy. Magnetoencephalography (MEG) recordings enable determination of the brain sources of epileptic spikes using source localization procedures. Most previous clinical MEG studies have relied on dipole modeling of epileptic spikes, which does not permit a volumetric estimation of the spiking cortex. In the present study, we propose a new source modeling procedure, Volumetric Imaging of Epileptic Spikes (VIES). In VIES, the SV is identified as the 3D region where sources of the high frequency activities (>20 Hz) associated with epileptic spikes are distributed. We localized these sources using a beamforming approach (DICS, Dynamic Imaging of Coherent Neural Sources). To determine the optimal parameters and accuracy of the method, we compared the SV obtained by VIES with the SV defined by the invasive gold standard, intracranial stereotactic EEG recordings (SEEG), in 21 patients with focal epilepsy. Using rigorous validation criteria based on the exact anatomical location of SEEG contacts, we found that the overall sensitivity of VIES for detecting spiking SEEG contacts was 76% and its specificity for correctly identifying non-spiking SEEG contacts was 67%, indicating a good agreement between VIES and SEEG. Moreover, we found that classical dipole clustering was not informative in 9/21 patients, while VIES enable to delineate the SV in all patients. For the 12 patients having a SV delineated both with VIES and dipole clustering, VIES method had higher sensitivity and lower specificity. This proof-of-concept study shows that VIES is a promising approach to non-invasive estimation of the SV in focal epilepsy.

Restoring consciousness with vagus nerve stimulation

Patients lying in a vegetative state present severe impairments of consciousness [1] caused by lesions in the cortex, the brainstem, the thalamus and the white matter [2]. There is agreement that this condition may involve disconnections in long-range cortico-cortical and thalamo-cortical pathways [3]. Hence, in the vegetative state cortical activity is deafferented from subcortical modulation and/or principally disrupted between fronto-parietal regions. Some patients in a vegetative state recover while others persistently remain in such a state. The neural signature of spontaneous recovery is linked to increased thalamo-cortical activity and improved fronto-parietal functional connectivity [3]. The likelihood of consciousness recovery depends on the extent of brain damage and patients etiology, but after one year of unresponsive behavior, chances become low [1]. There is thus a need to explore novel ways of repairing lost consciousness. Here we report beneficial effects of vagus nerve stimulation on consciousness level of a single patient in a vegetative state, including improved behavioral responsiveness and enhanced brain connectivity patterns.

French guidelines on stereoelectroencephalography (SEEG)

Stereoelectroencephalography (SEEG) was designed and developed in the 1960s in France by J.xa0Talairach and J.xa0Bancaud. It is an invasive method of exploration for drug-resistant focal epilepsies, offering the advantage of a tridimensional and temporally precise study of the epileptic discharge. It allows anatomo-electrical correlations and tailored surgeries. Whereas this method has been used for decades by experts in a limited number of European centers, the last ten years have seen increasing worldwide spread of its use. Moreover in current practice, SEEG is not only a diagnostic tool but also offers a therapeutic option, i.e., thermocoagulation. In order to propose formal guidelines for best clinical practice in SEEG, a working party was formed, composed of experts from every French centre with a large SEEG experience (those performing more than 10 SEEG per year over at least a 5 year period). This group formulated recommendations, which were graded by all participants according to established methodology. The first part of this article summarizes these within the following topics: indications and limits of SEEG; planning and management of SEEG; surgical technique; electrophysiological technical procedures; interpretation of SEEG recordings; and SEEG-guided radio frequency thermocoagulation. In the second part, those different aspects are discussed in more detail by subgroups of experts, based on existing literature and their own experience. The aim of this work is to present a consensual French approach to SEEG, which could be used as a basic document for centers using this method, particularly those who are beginning SEEG practice. These guidelines are supported by the French Clinical Neurophysiology Society and the French chapter of the International League Against Epilepsy.

Mesio-temporal ictal semiology as an indicator for surgical treatment of epilepsies with large multilobar cerebral lesions.

PURPOSEnMesio-temporal ictal semiology is sometimes observed in patients with large multilobar lesion. In this situation, surgery is often discarded because of the lesion size and/or suspicion of extended or multifocal epileptogenic areas. In this retrospective study we evaluated the surgical outcome of such patients in order to assess whether the electro-clinical presentation of seizures could be a prognostic marker of surgical outcome.nnnMETHODSnAmong the temporal lobe epilepsy population explored in our department between 2000 and 2011 (240 patients), we identified 7 patients who presented an extensive lesion on brain Magnetic Resonance Imaging (MRI) (multilobar in four, hemispheric in two, and bilateral in one). All patients underwent (18)Fluorodeoxyglucose Positron Emission Tomography, which showed large, hemispheric or multilobar, areas of glucose hypometabolism. Because of the large lesion size, all patients were explored by stereoelectroencephalography (SEEG) before taking a decision regarding surgical indication.nnnRESULTSnSEEG confirmed the temporal origin of the seizures and discarded the possibility of multiple epileptogenic zones. A temporal lobectomy, tailored on the basis of SEEG data, was proposed to the seven patients. The seven patients are classified Engel class I after the surgery (mean follow-up: 37.4±22.1 months).nnnCONCLUSIONnOur data thus suggest that, even in the absence of hippocampal MRI abnormality, ictal symptoms compatible with a temporal origin of seizures should be considered as a reliable indicator for surgery eligibility regardless of MRI lesion size. On the basis of our findings, the mesio-temporal semiology of seizures appears as one of the most reliable markers of operability in patients with large MRI lesions. These patients should not be excluded a priori from invasive exploration and surgical treatment, even if a large portion of their lesion is likely to be left in place after surgery.

146 ANATOMICAL AND PHYSIOLOGICAL BASES OF THE ROLE OF CEREBRAL CORTEX IN PAIN PERCEPTION

not available at time of printing. 144 QUESTIONS POSED BY EPIDEMIOLOGICAL STUDIES