Abstracts

Rationale: Background: The development of SEEG electrode implantation plan requires a clear formulation of a specific anatomical and electrophysiological hypothesis to be tested. There is no standardized method to guide the implantation pattern. Objective: To identify patterns of implantations in non lesional frontal lobe epilepsy with the goal of developing a standardized implantation methodology.Methods: MRI and CT images from consecutive frontal lobe epilepsy patients who underwent SEEG guided resection at the Cleveland Clinic Epilepsy Center during the time period July 2009 to March 2013 were used for the study. Patient with less than 6 months post-resection follow up were excluded. The images (CT and MRI) were co-registered and spatially normalized to standard MNI space using SPM toolbox. The standardized images were transferred to the CURRY 7 Neuroimaging Suite software. The AC, PC and additional midline points for each MRI were identified and merged with the CT. We overlaid the Talairach grid on each MRI and CT and recorded the grid parameter for each target point in tri-planar view of the Talairach image. Each block was marked with capital letter and number from the sagittal grid and small letter from the coronal grid, for example (A-1-a). The target point of each electrode was defined as the most distal part of the electrode artifact. Finally, the three dimensional coordinates for each target point in relation to AC point was calculatedResults: Twenty patients were included with a total of 273 implanted electrodes. Of the 273 electrodes, 131 electrodes in the right hemisphere. The average number of electrodes per patient is 13 electrodes (range:10-20). Most of the electrodes trajectories were orthogonal to the midline sagittal plane. Oblique trajectories were mainly for insular and posterior orbitofrontal implantation. The most frequently implanted grid blocks were: B-9-a, C-6-a, D-3-a and F-3-a with 9 electrodes each. Followed by F-6-a (8 electrodes), then D-9-c and H-5-a with 7 electrodes each ( Figure 1). These blocks are located in the frontal pole, orbitofrontal, cingulate, peri-Rolandic and parietal lobe. The median coordinates in relation to AC are as follow; for B-9-a block, X=2.2±1.9, Y=44.2±5.5, Z=8.8±2.5. For C-6-a ; the coordinates are X=1.8±1.5, Y=33.5±5.9, Z=17.2±3.8), for D-3-a; X=1.2±2, Y=15.1±10.5, Z=46.1±3 and for F-3-a; X=1.2± 1.3, Y=32.3±8.5, Z=47.1±3.1).Conclusions: We report a novel technique of localizing SEEG electrodes using both the Talairach grid and the coordinate system in relation to AC. This technique could lead to a standardized method of implantation. Figure 1: (A) Mid-sagittal view showing the target points of the implanted electrodes for all the 20 patients (B) Coronal view at the insular level Figure 2. (A) location of the most frequent implantation Red circle: 9 electrodes, blue: 8 electrodes, orange: 7 electrodes (B) Frequency of implantation in Talairach grid. Only blocks with 5 or more electrodes were included