title: Utility of magnetoencephalography in the evaluation of recurrent seizures after epilepsy surgery.
abstract: OBJECTIVE
  To study the role of magnetoencephalography (MEG) in the surgical evaluation of children with recurrent seizures after epilepsy surgery.
  
  
  METHODS
  We studied 17 children with recurrent seizures after epilepsy surgery using interictal and ictal scalp EEG, intracranial video EEG (IVEEG), MRI, and MEG. We analyzed the location and distribution of MEG spike sources (MEGSSs) and the relationship of MEGSSs to the margins of previous resections and surgical outcome.
  
  
  RESULTS
  Clustered MEGSSs occurred at the margins of previous resections within two contiguous gyri in 10 patients (group A), extended spatially from a margin by < or =3 cm in three patients (group B), and were remote from a resection margin by >3 cm in six patients (group C). Two patients had concomitant group A and C clusters. Thirteen patients underwent second surgeries. IVEEG was used in four patients. Six of seven patients with group A MEGSS clusters did not require IVEEG for second surgeries. Follow-up periods ranged from 0.6 to 4.3 years (mean: 2.6 years). Eleven children, including eight who became seizure-free, achieved Engel class I or II.
  
  
  CONCLUSIONS
  Our data demonstrate the utility of MEG for evaluating patients with recurrent seizures after epilepsy surgery. Specific MEGSS cluster patterns delineate epileptogenic zones. Removing cluster regions adjacent to the margins of previous resections, in addition to removing recurrent lesions, achieves favorable surgical outcome. Cluster location and extent identify which patients require IVEEG, potentially eliminating IVEEG for some. Patients with remotely located clusters require IVEEG for accurate assessment and localization of the entire epileptogenic zone.
authors.affiliation: Division of Neurology, Department of Pediatrics, The Hospital for Sick Children, Unviersity of Toronto, Toronto, Ontario, Canada.
authors.forename: Ismail S
authors.initials: IS
authors.lastname: Mohamed
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Otsubo
authors.forename: Ayako
authors.initials: A
authors.lastname: Ochi
authors.forename: Irene
authors.initials: I
authors.lastname: Elliott
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Donner
authors.forename: Sylvester
authors.initials: S
authors.lastname: Chuang
authors.forename: Rohit
authors.initials: R
authors.lastname: Sharma
authors.forename: Stephanie
authors.initials: S
authors.lastname: Holowka
authors.forename: James
authors.initials: J
authors.lastname: Rutka
authors.forename: O Carter
authors.initials: OC
authors.lastname: Snead
mesh_terms: D000293:Adolescent; D000367:Age Factors; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D004569:Electroencephalography / Q000379:methods / Q000706:statistics & numerical data; D004828:Epilepsies, Partial / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography / Q000379:methods* / Q000706:statistics & numerical data; D008297:Male; D011183:Postoperative Complications / Q000175:diagnosis* / Q000473:pathology / Q000503:physiopathology; D012008:Recurrence; D014743:Videotape Recording