Thornton 1 . EEG - correlated fMRI and Post - operative Outcome in Focal Epilepsy

Background: The main challenge in assessing patients with epilepsy for resective surgery is localising seizure onset. Frequently, identification of the irritative and seizure onset zones requires invasive EEG. EEG-correlated fMRI (EEG-fMRI) is a novel imaging technique which may provide localising information with regard to these regions. In patients with focal epilepsy, interictal epileptiform discharges (IED) correlated BOLD (blood oxygen dependent level) signal changes are observed in approximately 50% of patients where IEDs were recorded. In 70% these are concordant with expected seizure onset defined by non-invasive electroclinical information. Assessment of clinical validity requires post-surgical outcome studies which have, to date, been limited to case reports of correlation with intracranial EEG. We assessed the value of EEGfMRI in patients with focal epilepsy who subsequently underwent epilepsy surgery and related IED-correlated fMRI signal changes to the resection area and clinical outcome Methods: We recorded simultaneous EEG-fMRI in 76 patients undergoing presurgical evaluation and compared IEDcorrelated pre-operative BOLD signal change with resected area and post-operative outcome. Results : 21 patients had activations on EEG fMRI of whom 10 underwent surgical resection. 7/10 patients are seizure free following surgery and the area of maximal BOLD signal change was concordant with resection in 6/7. In the remaining 3, with reduced seizure frequency post-surgically, there were areas of significant IED correlated BOLD signal change outside the resection. 55 patients had no activation on EEG fMRI of whom 42 subsequently underwent resection. Conclusion: These results show potential value for EEG-fMRI in pre-surgical evaluation.