title: The role of magnetoencephalography in children undergoing hemispherectomy.
abstract: OBJECTIVE
  Hemispherectomy is an established neurosurgical procedure for medication-resistant epilepsy in children. Despite the effectiveness of this technique, there are patients who do not achieve an optimum outcome after surgery; possible causes of suboptimal results include the presence of bilateral independent epileptogenic foci. Magnetoencephalography (MEG) is an emerging tool that has been found to be useful in the management of lesional and nonlesional epilepsy. The authors analyzed the relative contribution of MEG in patient selection for hemispherectomy.
  
  
  METHODS
  The medical records of children undergoing hemispherectomy at the Hospital for Sick Children were reviewed. Those patients who underwent MEG as part of the presurgical evaluation were selected.
  
  
  RESULTS
  Thirteen patients were included in the study. Nine patients were boys. The mean age at the time of surgery was 66 months (range 10-149 months). Seizure etiology was Rasmussen encephalitis in 6 patients, hemimegalencephaly in 2 patients, and cortical dysplasia in 4 patients. In 8 patients, video-EEG and MEG results were consistent to localize the primary epileptogenic hemisphere. In 2 patients, video-EEG lateralized the ictal onset, but MEG showed bilateral spikes. Two patients had bilateral video-EEG and MEG spikes. Engel Class I, II, and IV outcomes were seen in 10, 2, and 1 patients, respectively. In 2 of the patients who had an outcome other than Engel Class I, the MEG clusters were concentrated in the disconnected hemisphere. The third patient had bilateral clusters and potentially independent epileptogenic foci from bilateral cortical dysplasia.
  
  
  CONCLUSIONS
  The presence of unilateral MEG spike waves correlated with good outcomes following hemispherectomy. In some cases, MEG provides information that differs from that obtained from video-EEG and conventional MR imaging studies. Further studies with a greater number of patients are needed to assess the role of MEG in the preoperative assessment of candidates for hemispherectomy.
authors: Division of Neurosurgery, Department of Surgery, The Hospital for Sick Children, University of Toronto, Ontario, Canada.
authors: Cristina V
authors: CV
authors: Torres
authors: Aria
authors: A
authors: Fallah
authors: George M
authors: GM
authors: Ibrahim
authors: Samuel
authors: S
authors: Cheshier
authors: Hiroshi
authors: H
authors: Otsubo
authors: Ayako
authors: A
authors: Ochi
authors: Sylvester
authors: S
authors: Chuang
authors: O Carter
authors: OC
authors: Snead
authors: Stephanie
authors: S
authors: Holowka
authors: James T
authors: JT
authors: Rutka
mesh_terms: D002540:Cerebral Cortex / Q000503:physiopathology* / Q000601:surgery; D002675:Child, Preschool; D004569:Electroencephalography; D004827:Epilepsy / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D038421:Hemispherectomy / Q000379:methods; D006801:Humans; D007223:Infant; D015225:Magnetoencephalography / Q000379:methods; D008297:Male; D008499:Medical Records; D012189:Retrospective Studies; D016896:Treatment Outcome