title: MEG-based identification of the epileptogenic zone in occult peri-insular epilepsy.
abstract: BACKGROUND
  Presurgical work-ups of patients with pharmacoresistant epileptic seizures can require multiple diagnostic methods if magnetic resonance imaging (MRI) combined with video-EEG monitoring fails to show an epileptogenic lesion. Yet, the added value of available methods is not clear. In particular, only a minority of epilepsy centres apply magnetoencephalography (MEG). This study explores the potential of MEG for patients whose previous sophisticated work-ups missed deep-seated, peri-insular epileptogenic lesions.
  
  
  METHODS
  Three patients with well documented, frequent, stereotypical hypermotor seizures without clear focus hypotheses after repeated presurgical work-ups including video-EEG-monitoring, 3Tesla (3T) magnetic resonance imaging (MRI), morphometric MRI analysis, PET and SPECT were referred to MEG source localisation.
  
  
  RESULTS
  In two out of three patients, MEG source localisation identified very subtle morphological abnormalities formerly missed in MRI or classified as questionable pathology. In the third patient, MEG was not reliable due to insufficient detection of epileptic patterns. Here, a 1 mm × 1 mm × 1 mm 3T fluid-attenuated inversion recovery (FLAIR) MRI revealed a potential epileptogenic lesion. A minimal invasive work-up via lesion-focused depth electrodes confirmed the intralesional seizure onset in all patients, and histology revealed dysplastic lesions. Seizure outcomes were Engel 1a in two patients, and Engel 1d in the third.
  
  
  CONCLUSIONS
  MEG can contribute to the identification of epileptogenic lesions even when multiple previous methods failed, and when the lesions are located in deep anatomical structures such as peri-insular cortex. For epilepsy centres without MEG capability, referral of patients with cryptogenic focal epilepsies to centres with MEG systems may be indicated.
authors: Ruhr-Epileptology, University Hospital Knappschaftskrankenhaus Bochum, Germany. marcel.heers@googlemail.com
authors: Marcel
authors: M
authors: Heers
authors: Stefan
authors: S
authors: Rampp
authors: Hermann
authors: H
authors: Stefan
authors: Horst
authors: H
authors: Urbach
authors: Christian E
authors: CE
authors: Elger
authors: Marec
authors: M
authors: von Lehe
authors: Jörg
authors: J
authors: Wellmer
mesh_terms: D000328:Adult; D002540:Cerebral Cortex / Q000473:pathology* / Q000601:surgery; D004569:Electroencephalography; D004828:Epilepsies, Partial / Q000175:diagnosis* / Q000473:pathology / Q000601:surgery*; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography / Q000379:methods*; D008875:Middle Aged; D015899:Tomography, Emission-Computed, Single-Photon; D016896:Treatment Outcome