EEG dipole source localisation of interictal spikes acquired during routine clinical video-EEG monitoring Stefanie Meckes-Ferber a , Annie Roten a , Christine Kilpatrick a,b , Terence J. O’Brien a,b, * a The Department of Neurology, The Royal Melbourne Hospital, University of Melbourne, Royal Parade, Parkville, Vic. 3050, Australia b The Department of Medicine, The Royal Melbourne Hospital, University of Melbourne, Royal Parade, Parkville, Vic. 3050, Australia Accepted 28 June 2004 Available online 23 August 2004 Abstract Objective: We investigated the feasibility of electroencephalography (EEG) dipole source localisation of interictal epileptiform discharges from data acquired during routine clinical inpatient video-EEG monitoring (VEM) and compared a 19-channel ‘routine montage’ with a 29-channel ‘surgical montage’ that includes an additional row of 10 inferior temporal electrodes. Methods: Twenty consecutive patients who had VEM for the presurgical evaluation of medically refractory partial epilepsy were screened. Thirteen of the patients had focal interictal spikes recorded, and in 11 (85%) these were technically satisfactory for source localisation. Fourteen spike foci were analysed as 3 patients had bilateral independent spikes. EEG data was acquired with 29 electrodes including an inferior temporal row (surgical montage). For comparison, the 10 additional electrodes were excluded from analysis (routine montage). Using NEUROSCANe Source 2.0 software, a computed dipole source localisation of averaged spikes was performed utilising a magnetic resonance imaging-based finite element model. Dipole localisation was compared with that of the Comprehensive Epilepsy Program (CEP) evaluation. Results: Using the surgical montage dipole source localisation was consistent with the CEP spike localisation for 13/14 spikes (93%, P!0.005), compared with only 5/14 spikes (36%) using the routine montage. Conclusions: Data derived from routine clinical inpatient VEM using a routine montage can yield accurate EEG dipole source localisation, but significantly more accurate localisation is obtained using the surgical montage. q 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: Epilepsy; Spike; EEG dipole source localisation; Video EEG monitoring; Electrode 1. Introduction Precise localisation of the epileptogenic zone is crucial for patients considered for surgical treatment of medically refractory epilepsy. Traditionally, visual analysis of interictal routine electroencephalography (EEG) data in addition to prolonged interictal and ictal Video-EEG monitoring (VEM), brain imaging with magnetic reson- ance imaging (MRI), 18-fluorodeoxyglucose positron emission tomography (FDG-PET), single photon emission computed tomography (SPECT), neuropsychologic and neuropsychiatric assessment are the basis for defining seizure localisation. The detection of focal interictal epileptiform EEG discharges during prolonged VEM provides important localising data in the pre-surgical assessment, and has been shown to have prognostic significance with regards to seizure outcome following epilepsy surgery (Radhakrishnan et al., 1998; Steinhoff et al., 1995). However, in clinical practice the localisation of the source of these EEG discharges has continued to rely on visual interpretation of the two-dimensional EEG traces. The clinical usefulness of the data from the various different imaging and neurophysiological methods acquired during the presurgical evaluation can be greatly enhanced by fully integrating them into a common Clinical Neurophysiology 115 (2004) 2738–2743 www.elsevier.com/locate/clinph 1388-2457/$30.00 q 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2004.06.023 * Corresponding author. Tel.: C61-3-8344-3260; fax: C61-3-9348- 2254. E-mail address: obrientj@unimelb.edu.au (T.J. O’Brien).