Abstracts

To compare the localizing yield of sphenoidal (SP) electrodes placed under fluoroscopic guidance and inferior electrodes (SO1/2, F9/10, T9/10, P9/10) in ictal recordings from patients with localization-related epilepsy of frontotemporal origin. Qualitative and quantitative dipole source localization measures were utilized. Ten consecutive patients were prospectively identified, 6 females and 4 males, ages 18-54 with medically intractable localization-related epilepsy (frontotemporal). All patients were in the process of completing a presurgical evaluation.Sixteen electrographic seizures were de-identified and randomly coded. The 10/20 international system was used with 27 single density scalp electrodes. In addition, SP electrodes were placed under fluoroscopic guidance in all 10 patients. Both a referential montage to reference electrode Cz and a bipolar parasagittal montage were simultaneously used. A qualitative comparison of three montages for each EEG was blindly performed as follows: 1) SP with inferior electrodes (IE), 2) SP without IE and, 3) IE without SP electrodes. Measures included ictal onset latency from baseline background activity, and localization of onset. Following identification of the seizure onset epoch, sphenoidal electrodes were excluded from the montage and quantitative dipole source analysis of the ictal data was performed using a spherical head model in BESA Beta 5.0.6 and a realistic head model in Curry 4.6. MRI data for dipole source localization was acquired on a 1.5T GE scanner using 124 gapless coronal slices with a thickness of 1.6mm, 256x192 matrix, and 22 FOV. Qualitatively, a statistically significant difference was seen with respect to seizure onset latency between EEG records using montage 1 (SP + IE) and those using montage 3 (IE - SP), [t = 2.159, df = 16, p = 0.0463]. No significant difference in ictal onset latency was found between all other comparison groups (p [gt] 0.05). Moreover, the addition of the SO1/2 electrodes as part of the IE set added concordant data for those seizures suspected by semiology of involving basal/mesial frontal regions as part of the ictal onset zone. Quantitatively, dipole source localization was influenced by the presence of sphenoidal electrodes when attempting to identify the ictal onset by visual inspection for software analysis. A comparison of sphenoidal electrodes placed fluoroscopically and inferior electrodes yielded an earlier onset when using both IE and SP sets. In addition, localization of seizure onset was improved in those patients suspected of having an ictal onset zone that includes the basal frontal or mesial-basal frontal regions. These data influenced dipole source modeling of the ictal onset zone. These findings can potentially improve surgical outcome by better delineating the ictal onset zone with the concomitant use of sphenoidal and inferior electrodes.