title: Preoperative evaluation using magnetoencephalography: Experience in 382 epilepsy patients.
abstract: Identifying epilepsy patients for whom clinical MEG is likely to be beneficial avoids or optimizes burdensome ancillary investigations. We determined whether it could be predicted upfront if MEG would be able to generate a hypothesis about the location of the epileptogenic zone (EZ), and in which patients MEG fails to do so.
  
  
  
  MEG recordings of 382 epilepsy patients with inconclusive findings regarding EZ localization prior to MEG were acquired for preoperative evaluation. MEG reports were categorized for several demographic, clinical and MEG variables. First, demographic and clinical variables were associated with MEG localization ability for upfront prediction. Second, all variables were compared between patients with and without MEG location in order to characterize patients without MEG location.
  
  
  
  Our patient group had often complex etiology and did not contain the (by other means) straightforward and well-localized cases, such as those with concordant tumor and EEG location. For our highly-selected patient group, MEG localization ability cannot be predicted upfront, although the odds of a recording with MEG location were significantly higher in the absence of a tumor and in the presence of widespread MRI abnormalities. Compared to the patients with MEG location, patients without MEG location more often had a tumor, widespread EEG abnormalities, non-lateralizing MEG abnormalities, non-concordant MEG/EEG abnormalities and less often widespread MRI abnormalities or epileptiform MEG activity. In a subgroup of 48 patients with known surgery outcome, more patients with concordant MEG and resection area were seizure-free than patients with discordant results.
  
  
  
  MEG potentially adds information about the location of the EZ even in patients with a complex etiology, and the clinical advice is to not withhold MEG in epilepsy surgery candidates. Providing a hypothesis about the location of the EZ using MEG is difficult in patients with inconclusive EEG and MRI findings, and in the absence of specific epileptiform activity. More refined methods are needed for patients where MEG currently does not contribute to the hypothesis about the location of the EZ.
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, Neuroscience Campus Amsterdam, VU University Medical Center, Postbus 7057, 1007 MB, Amsterdam, The Netherlands. Electronic address: i.nissen@vumc.nl.
authors.forename: I A
authors.initials: IA
authors.lastname: Nissen
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, Neuroscience Campus Amsterdam, VU University Medical Center, Postbus 7057, 1007 MB, Amsterdam, The Netherlands. Electronic address: cj.stam@vumc.nl.
authors.forename: C J
authors.initials: CJ
authors.lastname: Stam
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, Neuroscience Campus Amsterdam, VU University Medical Center, Postbus 7057, 1007 MB, Amsterdam, The Netherlands. Electronic address: j.citroen@slaz.nl.
authors.forename: J
authors.initials: J
authors.lastname: Citroen
authors.affiliation: Brain Tumor Center Amsterdam & Department of Neurology, VU University Medical Center, Postbus 7057, 1007 MB, Amsterdam, The Netherlands. Electronic address: jc.reijneveld@vumc.nl.
authors.forename: J C
authors.initials: JC
authors.lastname: Reijneveld
authors.affiliation: Department of Clinical Neurophysiology and MEG Center, Neuroscience Campus Amsterdam, VU University Medical Center, Postbus 7057, 1007 MB, Amsterdam, The Netherlands. Electronic address: a.hillebrand@vumc.nl.
authors.forename: A
authors.initials: A
authors.lastname: Hillebrand
mesh_terms: D000293:Adolescent; D000328:Adult; D000927:Anticonvulsants / Q000627:therapeutic use; D001921:Brain / Q000503:physiopathology* / Q000601:surgery; D001932:Brain Neoplasms / Q000150:complications / Q000503:physiopathology / Q000601:surgery; D004569:Electroencephalography; D004827:Epilepsy / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology* / Q000628:therapy; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D011300:Preoperative Care; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D000927:Anticonvulsants
keywords: Epileptogenic zone; MEG; Refractory epilepsy; Source localization; Surgery