Paradoxical lateralization of non-invasive electroencephalographic ictal patterns in extra-temporal epilepsies  Claudia B. Catarino, Christian Vollmar, Soheyl Noachtar  Epilepsy Research  Volume 99, Issue 1, Pages 147-155 (March 2012) DOI: 10.1016/j.eplepsyres.2011.11.002 Copyright © 2011 Elsevier B.V. Terms and Conditions

Figure 1 Case 1. MRI brain scan: (A) sagittal T1 and axial T2, show a parasagittal, left frontal, dysembryoplastic neuroepithelial tumor. (B) Three-dimensional reconstructed MRI images show the location of the subdural electrodes (white circles) in relation to the cortex relief. Seizures start in the mesial frontal region (black circle). The area of maximum interictal spiking (dotted black line) during the invasive EEG-video monitoring is also shown on the projection of the subdural electrodes. (C) Non-invasive ictal EEG (Cz referential montage) shows a right centro-parietal seizure pattern at seizure onset (open arrow), which 12s later evolves into a left frontocentral seizure pattern (solid arrow). Epilepsy Research 2012 99, 147-155DOI: (10.1016/j.eplepsyres.2011.11.002) Copyright © 2011 Elsevier B.V. Terms and Conditions

Figure 2 Case 2. (A) MRI brain scan findings. Axial FLAIR, post-traumatic right fronto-temporo-parietal encephalomalacia and right fronto-parieto-occipital gliosis. Source dipole analysis of the EEG seizure pattern at onset superimposed on the brain MRI of the patient (B), and superimposed on a standard brain MRI (C), showing location of the source dipole on the right mesial posterior border of the lesion. (D) Ictal EEG recording, longitudinal bipolar montage, with left parieto-occipital seizure pattern preceding the clinical onset by 180s, contralateral to the right hemispheric lesion, and therefore paradoxically lateralized (open arrow). Five seconds before clinical onset, there was a right occipital seizure pattern (solid arrow). Dipole source analysis at EEG onset correctly lateralized the seizure pattern to the right (B and C). Epilepsy Research 2012 99, 147-155DOI: (10.1016/j.eplepsyres.2011.11.002) Copyright © 2011 Elsevier B.V. Terms and Conditions

Figure 3 Case 3. MRI brain scan: (A) sagittal T1 and axial T1, show the left mesial central cortical malformation. Ictal EEG shows a right centro-parietal seizure pattern, contralateral to the left central lesion at clinical seizure onset (B), characterized by bilateral tonic posturing (open arrow). Twenty-two seconds later, the seizure pattern was located in the left parietal region (P3, Cz) (C, solid arrow); at that time, the seizure clinically evolved into a right clonic seizure. Epilepsy Research 2012 99, 147-155DOI: (10.1016/j.eplepsyres.2011.11.002) Copyright © 2011 Elsevier B.V. Terms and Conditions

Figure 4 Case 4. (A) Ictal EEG, longitudinal bipolar montage, shows left parasagittal polyspikes (solid arrow, and vertical line), synchronous with the EMG artifact, i.e. associated with the left calf jerking. In contrast, isolated spikes (open arrows), with a right central maximum (C4) were not associated with the jerks. EMG L. M. Tib. Ant., EMG left anterior tibialis muscle. (B) Isopotential field map, with electrodes CZ and C4 showing 100% of the amplitude of the potential and the subsequent rings, potential field drops of 10%, demonstrates the left parasagittal polyspikes, and also the isolated spikes with a right central maximum (C4), which had no clinical correlate. Source: (A) Reprinted with permission, from Lüders HO and Noachtar S (1995) Atlas und Klassifikation der Elektroenzephalographie, Ciba Geigy Verlag, Wehr. © Reprinted by permission of Novartis Pharma Verlag, Nürnberg. Epilepsy Research 2012 99, 147-155DOI: (10.1016/j.eplepsyres.2011.11.002) Copyright © 2011 Elsevier B.V. Terms and Conditions

Figure 5 Schematic illustration of the proposed mechanism for paradoxical lateralization. (A) A cortical source situated on the mesial surface of a cerebral hemisphere (outside negative) is oriented with the negative electrical activity projecting obliquely; the highest negative amplitude is recorded on the contralateral side. (B) A source located on the cerebral convexity will be recorded ipsilaterally, given the orientation of the electrical activity vector. Epilepsy Research 2012 99, 147-155DOI: (10.1016/j.eplepsyres.2011.11.002) Copyright © 2011 Elsevier B.V. Terms and Conditions