title: Electric source imaging of interictal activity accurately localises the seizure onset zone.
abstract: OBJECTIVE
  It remains controversial whether interictal spikes are a surrogate of the seizure onset zone (SOZ). Electric source imaging (ESI) is an increasingly validated non-invasive approach for localising the epileptogenic focus in patients with drug-resistant epilepsy undergoing evaluation for surgery, using high-density scalp EEG and advanced source localisation algorithms that include the patient's own MRI. Here we investigate whether localisation of interictal spikes by ESI provides valuable information on the SOZ.
  
  
  METHODS
  In 38 patients with focal epilepsy who later underwent intracranial EEG monitoring, we performed ESI of interictal spikes recorded with 128-256-channel EEG. We measured the distance between the ESI maximum and the nearest intracranial electrodes in the SOZ and irritative zone (IZ, the source of interictal spikes). The resection of the region harbouring the ESI maximum was correlated to surgical outcome.
  
  
  RESULTS
  The median distance from the ESI maximum to the nearest electrode involved in the SOZ was 17 mm (IQR 8-27). The IZ and SOZ colocalised in most patients (median distance 0 mm, IQR 0-14), supporting the notion that localising interictal spikes is a valid surrogate for the SOZ. There was no difference in accuracy among patients with temporal or extratemporal epilepsy. In the 32 patients who underwent resective surgery, including the ESI maximum in the resection correlated with favourable outcome (p=0.03).
  
  
  CONCLUSIONS
  Localisation of interictal spikes provides an excellent estimate of the SOZ in the majority of patients. ESI should be taken into account for the management of patients undergoing intracranial recordings.
authors.affiliation: EEG and Epilepsy Unit, Department of Neurology, Geneva University Hospitals, , Geneva, Switzerland.
authors.forename: Pierre
authors.initials: P
authors.lastname: Mégevand
authors.forename: Laurent
authors.initials: L
authors.lastname: Spinelli
authors.forename: Mélanie
authors.initials: M
authors.lastname: Genetti
authors.forename: Verena
authors.initials: V
authors.lastname: Brodbeck
authors.forename: Shahan
authors.initials: S
authors.lastname: Momjian
authors.forename: Karl
authors.initials: K
authors.lastname: Schaller
authors.forename: Christoph M
authors.initials: CM
authors.lastname: Michel
authors.forename: Serge
authors.initials: S
authors.lastname: Vulliemoz
authors.forename: Margitta
authors.initials: M
authors.lastname: Seeck
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D001921:Brain / Q000473:pathology* / Q000503:physiopathology; D002648:Child; D002675:Child, Preschool; D004569:Electroencephalography / Q000379:methods*; D004828:Epilepsies, Partial / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D005260:Female; D006257:Head / Q000033:anatomy & histology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D059906:Neuroimaging / Q000379:methods*; D019635:Neurosurgical Procedures; D012640:Seizures / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D016896:Treatment Outcome; D055815:Young Adult
keywords: EEG; Epilepsy; Functional Imaging; Neurophysiology; Stereotaxic Surgery; Surgery