Abstracts

Rationale: MRI has emerged as a leading diagnostic methodology in the field of epilepsy. However, clinical MRI has largely been used as a structural tool. Resting state functional MRI (rsfMRI) allows identification of macroscopic brain networks based on functional connectivity, or co-activation, within nodes comprising a network. Most studies of focal epilepsy using rsfMRI reported reduced functional connectivity of epilepsy producing regions. Most of these studies, however, used either empiric regions of interest or those derived from interictal scalp EEG. In this study, we have probed rsfMRI data using regions of interest along seizure propagation pathways, with directionality derived from icEEG. Methods: Subjects: Patients with medically refractory focal epilepsy of suspected extra-temporal origin undergoing a pre-surgical evaluation with icEEG. icEEG Monitoring: Performed using subdurally placed electrodes in one hemisphere of the brain in a region of suspected seizure onset. MRI Image Acquisition: Each subject undergoes an fMRI scan, per an established protocol, prior to icEEG. Data Analysis: rsfMRI is pre-processed according to established protocols. The icEEG electrode locations are registered to standard MNI space and regions of interest are constructed within the SOZ (5mm ROI over a selected electrode within the SOZ) and of nodes along the propagation pathway. Inter-regional functional connectivity is computed between the SOZ and selected nodes of seizure propagation, as well as between the SOZ and remote uninvolved regions for control. Homologous connectivity pairs are constructed from the non-epileptic hemisphere. Although SOZ are expected to vary from patient to patient, group analysis will be possible by measuring relative differences in functional connectivity between the two hemispheres. Results: To date, we studied six patients, all of whom underwent rsfMRI before invasive video/EEG monitoring. Here we present results of analysis from two patients. The SOZ was extra-temporal in localization. ROIs were placed in the SOZ and in regions determined to be early and secondary regions of seizure propagation. Inter-regional functional connectivity was computed as illustrated in figure 2. Although a group analysis has not been performed to date, there is a suggestion of reduced functional connectivity within the seiuzre propgation networks compared to homologous connections in the non-epileptic hemisphere. Conclusions: In this study, we have asked whether functional seizure propagation networks could also be revealed using MRI in focal, extra-temporal, epilepsy. Based on analysis of two patients to date, it appears that functional connectivity is reduced within the epileptic seizure propagation network compared to homologous connections in the nonepileptic hemisphere. We hope to contribute to a better understanding of seizure propagation networks in patients with non-lesional extra-temporal epilepsy.