Combined use of non-invasive techniques for improved functional localization for a selected group of epilepsy surgery candidates A.-M. Vitikainen a,b,c, ⁎, P. Lioumis a,d , R. Paetau a,e , E. Salli d , S. Komssi b,d , L. Metsähonkala e , A. Paetau f , D. Kičić a,g , G. Blomstedt h , L. Valanne d , J.P. Mäkelä a , E. Gaily e a HUSLAB BioMag Laboratory, Hospital District of Helsinki and Uusimaa, Helsinki University Central Hospital, P.O. Box 340, FI-00029 HUS, Finland b HUSLAB Department of Clinical Neurophysiology, Hospital District of Helsinki and Uusimaa, Helsinki University Central Hospital, P.O. Box 280, FI-00029 HUS, Finland c University of Helsinki, Department of Physics, P.O. Box 64, FI-00014 Helsinki, Finland d HUS Helsinki Medical Imaging Center, Hospital District of Helsinki and Uusimaa, Helsinki University Central Hospital, P.O. Box 750, FI-00029 HUS, Finland e Epilepsy Unit, Department of Gynecology and Pediatrics, Hospital District of Helsinki and Uusimaa, Helsinki University Central Hospital, P.O. Box 280, FI-00029 HUS, Finland f University of Helsinki, Hospital District of Helsinki and Uusimaa and Haartman Institute, HUSLAB Department of Pathology, P.O. Box 21, FI-00014, Helsinki, Finland g Department of Biomedical Engineering and Computational Science, Helsinki University of Technology, P.O. Box 3310, FI-02015 TKK, Finland h Department of Neurosurgery, Hospital District of Helsinki and Uusimaa, Helsinki University Central Hospital, P.O. Box 266, FI-00029 HUS, Finland abstract article info Article history: Received 18 April 2008 Revised 4 November 2008 Accepted 8 December 2008 Available online 30 December 2008 Keywords: TMS MEG Intracranial electrodes Cortical localization Preoperative evaluation Epilepsy surgery Invasive cortical mapping is conventionally required for preoperative identification of epileptogenic and eloquent cortical regions before epilepsy surgery. The decision on the extent and exact location of the resection is always demanding and multimodal approach is desired for added certainty. The present study describes two non-invasive preoperative protocols, used in addition to the normal preoperative work-up for localization of the epileptogenic and sensorimotor cortical regions, in two young patients with epilepsy. Magnetoencephalography (MEG) was used to determine the primary somatosensory cortex (S1) and the ictal onset zones. Navigated transcranial magnetic stimulation (nTMS) was used to determine the location and the extent of the primary motor representation areas. The localization results from these non-invasive methods were used for guiding the subdural grid deployment and later compared with the results from electrical cortical stimulation (ECS) via subdural grids, and validated by surgery outcome. The results from MEG and nTMS localizations were consistent with the ECS results and provided improved spatial precision. Consistent results of our study suggest that these non-invasive methods can be added to the standard preoperative work-up and may even hold a potential to replace the ECS in a subgroup of patients with epilepsy who have the suspected epileptogenic zone near the sensorimotor cortex and seizures frequent enough for ictal MEG. © 2008 Elsevier Inc. All rights reserved. Introduction Epilepsy surgery candidates whose epileptic focus is close to eloquent cortical areas need accurate identification of the epilepto- genic zone and the irretrievable cortex. This is usually done with intracranial recordings and electrical cortical stimulation (ECS), pre- sently the standard technique for preoperative localization. However, subdural investigations require diagnostic surgery, associated with significant risk of complications (Hamer et al., 2002). Therefore accu- rate non-invasive methods for localizations with added precision and reliability would be highly appreciated. In two patients who subsequently underwent a weeklong intracranial recording via sub- dural electrodes and resective surgery, we applied two non-invasive methods; magnetoencephalography (MEG) to identify the ictal onset zone and primary somatosensory cortex (S1) (Mäkelä et al., 2006) and navigated transcranial magnetic stimulation (nTMS) to determine the boundaries of the primary motor cortical representation areas of selected muscles (Hannula et al., 2005; Krings et al., 1997a; Wilson et al., 1993). Methods and patients Mapping of the primary motor cortex with nTMS Single-pulse nTMS delivered by a figure-of-eight coil, with con- current electroencephalography (EEG) (eXimia NBS and EEG, NeuroImage 45 (2009) 342–348 Abbreviations: ADM, Adbuctor digiti minimi; AEM, Antiepileptic medication; AH, Abductor hallucis; APB, Abductor pollicis brevis; BB, Biceps brachii; CT, Computed tomography; ECD, Equivalent current dipole; ECS, Electrical cortical stimulation; EDC, Extensor digitorum communis; FCR, Flexor carpi radialis; FDI, First dorsal interosseus; MEG, Magnetoencephalography; MEP, Motor evoked potential; MRI, fMRI, Magnetic resonance imaging, Functional magnetic resonance imaging; MT, Motor threshold; nTMS, TMS, Navigated transcranial magnetic stimulation, Transcranial magnetic stimulation; PET, Positron emission tomography; RF, Rectus femoris; S1, Primary somatosensory cortex; SEF, Somatosensory evoked field; TA, Tibialis anterior. ⁎ Corresponding author. HUSLAB BioMag Laboratory, Haartmaninkatu 4 (P-floor), P.O. Box 340, FI-00029 HUS, Finland. Fax: +358 9 4717 5781. E-mail addresses: anne-mari.vitikainen@helsinki.fi, anne-mari.vitikainen@hus.fi (A.-M. Vitikainen). 1053-8119/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.neuroimage.2008.12.026 Contents lists available at ScienceDirect NeuroImage journal homepage: www.elsevier.com/locate/ynimg