title: The utility of magnetoencephalography in the presurgical evaluation of refractory insular epilepsy.
abstract: OBJECTIVE
  To study the utility of magnetoencephalography (MEG) in patients with refractory insular epilepsy. Covered by highly functional temporal, frontal, and parietal opercula, insular-onset seizures can manifest a variety of ictal symptoms falsely leading to a diagnosis of temporal, frontal, or parietal lobe seizures. Lack of recognition of insular seizures may be responsible for some epilepsy surgery failures.
  
  
  METHODS
  We retrospectively reviewed and analyzed MEG data in 14 patients with refractory insular seizures defined through intracranial electroencephalography (EEG) or by the presence of an epileptogenic lesion in the insula with compatible seizure semiology. MEG was performed as part of the noninvasive presurgical evaluation, using a 275-channel whole head MEG system. MEG data were analyzed using a single equivalent current dipole model. MEG localization was compared to interictal positron emission tomography (PET) and ictal single photon emission computed tomography (SPECT) results and to the resection margin.
  
  
  RESULTS
  Three patterns of MEG spike sources were observed. Seven patients showed an anterior operculoinsular clusters and two patients had a posterior operculoinsular cluster. No spikes were detected in one patient, and the remaining four patients showed a diffuse perisylvian distribution. Spike sources showed uniform orientation perpendicular to the sylvian fissure. Nine patients proceeded to insular epilepsy surgery with favorable surgical outcome. Among patients with anterior operculoinsular cluster who proceeded to have surgery, MEG provided superior information to ictal SPECT in four of six patients and to interictal PET in five of six patients.
  
  
  CONCLUSIONS
  MEG is useful in identifying patients who are likely to benefit from epilepsy surgery targeting the insula, particularly if a tight dipole cluster is identified even if other noninvasive modalities fail to produce localizing results.
authors.affiliation: Division of Neurology, Department of Pediatrics, IIWK Health Center, Halifax, NS, Canada.
authors.forename: Ismail S
authors.initials: IS
authors.lastname: Mohamed
authors.forename: Steve A
authors.initials: SA
authors.lastname: Gibbs
authors.forename: Manon
authors.initials: M
authors.lastname: Robert
authors.forename: Alain
authors.initials: A
authors.lastname: Bouthillier
authors.forename: Jean-Maxime
authors.initials: JM
authors.lastname: Leroux
authors.forename: Dang
authors.initials: D
authors.lastname: Khoa Nguyen
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods; D002648:Child; D004569:Electroencephalography / Q000379:methods; D004827:Epilepsy / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D015225:Magnetoencephalography / Q000379:methods; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods; D011300:Preoperative Care / Q000379:methods; D012189:Retrospective Studies; D016896:Treatment Outcome
keywords: Epilepsy surgery; Insula; Magnetoencephalography; Refractory epilepsy