Epilepsy Research (2012) 99, 147—155 journal homepage: www.elsevier.com/locate/epilepsyres Paradoxical lateralization of non-invasive electroencephalographic ictal patterns in extra-temporal epilepsies Claudia B. Catarino a,b , Christian Vollmar a , Soheyl Noachtar a,* a Epilepsy Center, Department of Neurology, University of Munich, 81377 Munich, Germany b Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, Queen Square, London WC1N 3BG, UK Received 22 September 2011; received in revised form 31 October 2011; accepted 6 November 2011 Available online 30 November 2011 KEYWORDS Electroencephalogra- phy; Partial epilepsy; Epilepsy surgery; Dipole analysis; Parasagittal Summary Video-electroencephalographic (EEG) ictal recordings play an important role in the pre-surgical evaluation of patients with medically refractory focal epilepsy. Paradoxical lateralization of the scalp EEG ictal onset patterns, consistently contralateral to the side of the proven epileptogenic lesion is rare but important to recognize, with possible implications on patient management. We searched the database of the University of Munich Epilepsy Monitoring Unit for patients with extratemporal epilepsies, with scalp EEG ictal patterns consistently contralateral to the proven epileptogenic zone. All available clinical, EEG and imaging data were reviewed. Dipole source analysis of EEG seizure onset was performed where possible. Four patients were identified, who had proven paradoxical lateralization of scalp EEG ictal patterns, demonstrated by seizure freedom after epilepsy surgery, data from invasive elec- troencephalography, or imaging and seizure semiology. Parasagittal lesions on MRI brain scan were found in three cases. Invasive recordings with subdural electrodes were performed in one patient. Dipole source analysis of EEG seizure onset was possible in two patients, helping to correctly lateralize the ictal EEG pattern in one patient. Patients with midline or near midline neocortical seizure foci may show paradoxical lateral- ization of the ictal EEG, likely due to the spatial orientation of the cortical generators in the medial regions of the cerebral hemispheres. These patients may have excellent surgical out- come despite the apparently discordant EEG findings, making this an important phenomenon to be recognized in clinical practice. © 2011 Elsevier B.V. All rights reserved. Abbreviations: DNET, dysembryoplastic neuroepithelial tumor; EEG, electroencephalography; EP, evoked potentials; FCD, focal cortical dysplasia; FLAIR, fluid-attenuated inversion recovery; MPRAGE, magnetization prepared rapid acquisition gradient echo. * Corresponding author at: Epilepsy Center, Department of Neurology, Klinikum Grosshadern, University of Munich, Marchioninistr. 15, 81377 Munich, Germany. Tel.: +49 89 7095 3691; fax: +49 89 7095 6691. E-mail address: noa@med.uni-muenchen.de (S. Noachtar). 0920-1211/$ — see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.eplepsyres.2011.11.002