Pediatric Neuroscience Pathways Fall 2012 - Cleveland Clinic

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In children with refractory and focal epilepsy, subdural mapping techniques have been the hallmark of extraoperative invasive monitoring techniques for refractory epilepsy in the united states for more than 30 years. With subdural methodology, the grid of electrodes is laid directly on the surface of the brain and provides spatially accurate information from the cortical surface in contact with the electrodes. However, the array of electrodes in a grid is limited in the ability to sample deeper brain structures, bilateral brain regions and a wider functional network connecting different brain regions. the stereoelectroencephalogram (seeg) technique is able to overcome these limitations, and it does so with less morbidity risk relative to subdural grid electrodes. For carefully selected candidates who are not ideal for subdural grid electrode evaluation but are potential candidates for surgical treatment, the seeg technique holds promise. The SEEG methodology implies a rigorous pre-implantation scrutiny of all available findings obtained during the noninvasive phase. Based on the noninvasive test results, a hypothesis for the likely seizure-generating zone or seizure network is formulated. this is followed by a tailored implantation of seeg electrodes with the capability to sample depths of brain areas in question to confirm the hypothesis. During this phase, the exploration is focused to sample the anatomic lesion (if present), the more likely structure(s) of seizure onset and the possible pathway(s) of propagation of the seizure discharge. Small 2-mm pinholes are made, and the desired targets are reached using small and flexible electrodes (1.2 mm in diameter) with the precision of the stereotactic technique, allowing them to be recorded from lateral, intermediate or deep brain structures in a 3-D arrangement, thus accounting for the dynamic, multidirectional spatiotemporal organization of the seizures (Figure 1). a surgical resection is offered only after confirmation of the hypothesis and careful delineation of functional and seizure-generating areas. in addition to the general selection criteria for invasive extraoperative monitoring, additional specific indications are used to choose SEEG (vs. other methods of invasive monitoring such as subdural grids/ strips) as the recommended method of invasive monitoring. these criteria include: 1. The possibility of a deep-seated seizure-onset area or a region that cannot be accessed with the help of grid electrodes (e.g., mesial structures of the temporal lobe, opercular areas, cingulate gyrus, interhemispheric regions, posterior orbitofrontal areas, insula and depths of sulci). 2. Failure of a previous subdural invasive study to clearly outline the exact location of the seizure-onset zone. Pediatric ePilePsy aNd Neurosurgery Stereotactic EEG for Surgical Planning in Children with Difficult-to-Localize Epilepsy Jorge Gonzalez-Martinez, MD, PhD, and Deepak Lachhwani, MD “Any sufficiently advanced technology is indistinguishable from magic.” — arthur c. clarke 3. the need for extensive bihemispheric explorations. 4. Presurgical evaluation suggestive of a functional network involvement (e.g., limbic system) in the setting of normal MRI. Between March 2009 and June 2012, 32 children with difficultto-localize refractory focal epilepsy underwent SEEG procedures. The mean age was 8 years (range, 5 to 17 years). All the patients had a diagnosis of refractory focal epilepsy, with an average failure of five antiepileptic drugs per patient. On average, 13 depth electrodes were implanted per patient (range, 7 to 22 electrodes; total of 416 implanted electrodes). analyses of the seeg recordings led to potential electrographic localization of the epileptogenic focus in the majority of patients (n = 30). Twenty-five patients underwent surgical resection following seeg evaluation. From this group, 14 patients (56 percent) were seizure-free at the end of the follow-up period. Only one minor complication related to the SEEG procedures was observed (complication rate was 3 percent), which corresponded to a small frontal intraparenchymal hemorrhage with no clinical significance. No other complications were observed in this series. Given the total number of implanted electrodes, the calculated risk of complications per electrode in this series was 0.2 percent. In conclusion, we have found the SEEG method to be promising in a most challenging group of young patients who were not considered ideal candidates for subdural grid evaluation. the seeg method is a safe, less morbid and more efficient invasive monitoring alternative for children that yields localizing information in the following contexts: (1) in patients with deep-seated or difficult-tocover region(s) such as depths of sulci, mesial structures of the temporal lobe, opercular regions, cingulate gyrus, interhemispheric regions, posterior orbitofrontal cortex and insula; (2) following failure of a previous subdural invasive study to clearly outline the exact location of the seizure-onset zone; (3) in children with multiple multilobar or bihemispheric lesions with a need for extensive bihemispheric explorations; and (4) in children in whom presurgical evaluation shows findings consistent with an anatomofunctional network involvement (e.g., limbic system) in the setting of normal mri. equally important are the seeg method’s minimally invasive characteristics, which are particularly appealing in the pediatric population, as they avoid large craniotomies and minimize blood transfusion and postoperative pain. in performing SEEG in this highly selected group, we were able to overcome the relative limitations of the current standard method of invasive monitoring, offering to this challenging group of patients an additional opportunity for seizure freedom that likely would not be possible with subdural monitoring. 16 Pediatric NeuroscieNce Pathways | 2012 – 2013
Pediatric ePilePsy aNd Neurosurgery Jorge Gonzalez-Martinez, MD, PhD, is an associate staff member in Cleveland Clinic’s Epilepsy Center and the Neurological Surgery and Biomedical Engineering departments. His specialty interests include epilepsy and epilepsy surgery in children and adolescents and medical treatment of epilepsy in children. He can be reached at 216.636.5860 or gonzalj1@ccf.org. Deepak Lachhwani, MD, is a staff pediatric epileptologist in Cleveland Clinic’s Epilepsy Center. His specialty interests include children with complex epilepsies, children with epilepsy and Sturge-Weber syndrome, diagnostic video EEG for pediatric seizure disorders, interpretation of continuous EEG monitoring in the critical care setting, and invasive EEG monitoring for presurgical evaluations. He can be reached at 216.444.5559 or lachhwd@ccf.org. Figure 1 Figure 2 Figure 3 Figure 4 ilustrative case. eight-year-old child with intractable focal epilepsy (bilateral asymmetric motor seizures with extension of the right hand followed by generalized tonic-clonic seizures). mri was normal. Figure 1. Ictal SPECT showing hyperperfusion in right frontal areas. Figure 2. Intraoperative picture, lateral view, showing bilateral frontal and left temporal implantation. Figure 3. Postoperative X-ray showing final aspect of the bilateral SEEG implantation. Figure 4. MRI reconstruction showing (red dots) the location of the contacts associated with the ictal onset zone and the early propagation of the epileptiform activity. suggested readiNg Cossu M, Chabardes S, Hoffmann D, Russo G. Presurgical evaluation of intractable epilepsy using stereo-electro-encephalography methodology: Principles, technique and morbidity. Neurochirurgie. 2008;54(3):367-373. Engel J, Henry T, Risinger M, Mazziotta J, Sutherling W, Levesque M, Phelps m. Presurgical evaluation for partial epilepsy: relative contributions of chronic depth-electrode recordings versus FDG-PET and scalp-sphenoidal ictal EEG. Neurology. 1990;40(11):1670-1677. Jayakar P. Invasive EEG monitoring in children: when, where, and what? J Clin Neurophysiol. 1999;16(5):408-418. Onal C, Otsubo H, Araki T, Chitoku S, Ochi A, Weiss S, Elliott I, Snead O, Rutka J, Logan W. Complications of invasive subdural grid monitoring in children with epilepsy. J Neurosurg. 2003;98 (5):1017-1026. Widdess-Walsh P, Jeha L, Nair D, Kotagal P, Bingaman W, Najm I. subdural electrode analysis in focal cortical dysplasia: predictors of surgical outcome. Neurology. 2007;69(7):660-667. visit clevelaNdcliNicchildreNs.org | 866.588.2264 17
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Page 7 and 8: cover story | diagNostic radiology
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Pediatric Neuroscience Pathways Fall 2012 - Cleveland Clinic

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