title: Interictal MEG reveals focal cortical dysplasias: special focus on patients with no visible MRI lesions.
abstract: OBJECTIVE
  To investigate the value of interictal magnetoencephalography (MEG) in localizing epileptogenic cortex in epilepsy surgery patients with focal cortical dysplasias (FCD), particularly in patients having no visible MRI lesions.
  
  
  METHODS
  Thirty-four patients with FCD and preoperative MEG were retrospectively evaluated. Interictal MEG spike source localizations in respect to the resected area were studied using postoperative MR imaging. The possible predictive value of MEG-findings in respect to the clinical outcome was evaluated. Results from intracranial recordings were also compared with the MEG localizations.
  
  
  RESULTS
  Interictal MEG spikes were observed in all but one patient. 17 of the 34 (50%) patients became seizure free (Engel class I). In patients with MEG dipole clusters (n=20) and Engel class I or II (n=15) 49% of the source clusters were removed on the average; the corresponding value in patients with Engel class III or IV (n=5) was 5.5% (p=0.02). Seven (54%) of the 13 patients with an MRI-negative lesion achieved Engel class I; the outcomes did not differ from patients having a visible MRI lesion (n=21; p=0.82). The concordance between MEG localizations and the invasive studies was good in nine of the 13 patients with no visible MRI lesions
  
  
  CONCLUSIONS
  MEG is particularly useful in finding small FCDs not visible on MRI. A more complete removal of MEG source cluster area is associated with better clinical outcome These features make it a valuable tool in pre-surgical evaluation of patients with intractable focal-type epilepsy and normal MRI.
authors.affiliation: BioMag Laboratory, HUS Medical Imaging Center, Hospital District of Helsinki and Uusimaa, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Wilenius
authors.forename: Mordekhay
authors.initials: M
authors.lastname: Medvedovsky
authors.forename: Eija
authors.initials: E
authors.lastname: Gaily
authors.forename: Liisa
authors.initials: L
authors.lastname: Metsähonkala
authors.forename: Jyrki P
authors.initials: JP
authors.lastname: Mäkelä
authors.forename: Anders
authors.initials: A
authors.lastname: Paetau
authors.forename: Leena
authors.initials: L
authors.lastname: Valanne
authors.forename: Ritva
authors.initials: R
authors.lastname: Paetau
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D054220:Malformations of Cortical Development / Q000175:diagnosis* / Q000503:physiopathology*; D008875:Middle Aged; D012189:Retrospective Studies; D055815:Young Adult
keywords: Epilepsy; Epilepsy surgery; Focal cortical dysplasia; Magnetoencephalography