title: MRS-lateralisation index in patients with epilepsy and focal cortical dysplasia or a MEG-focus using bilateral single voxels.
abstract: OBJECTIVE
  To evaluate if single voxel proton magnetic resonance spectroscopy (SV-MRS) can help in lateralising and sometimes in localizing an epileptogenic focus. The assumption is that in MRI negative patients the underlying pathology most often is focal cortical dysplasia (FCD). Several studies have shown that in the presence of FCD there are also (1)H-MRS abnormalities on the contralateral side. However, in most cases the studied group was not homogeneous and included different forms of dysplasias, including band heterotopias and polymicrogyria, and the studies used different spectroscopy protocols. In the present study, using bilateral SV-MRS we investigated the presence of a lateralisation index in two groups of patients with localisation related epilepsy: patients with focal cortical dysplasia on MRI and patients without MRI abnormalities with a focus identified by MEG. Aim of the study was to show that in both groups the expected epileptogenic side shows more pronounced metabolic alterations, making MRS a possible screening tool for clarifying lateralisation questions in patients with cryptogenic localisation related epilepsy.
  
  
  METHODS
  In ten patients a single voxel was placed over the FCD and in nine patients over the region of interest (ROI) as indicated by MEG. In all patients a voxel was also placed in the contralateral homologus location. We used metabolite concentrations as peak ratios relative to the creatine (Cr) peak to calculate a lateralisation index.
  
  
  RESULTS
  In both groups NAA/Cr was significantly lower on the affected side whereas the results for Cho/Cr were more diverse. There were no significant differences between the two groups. The limitations of the used methods and the implications of the findings are discussed.
authors.affiliation: Epilepsiecentrum Kempenhaeghe, KNF, Sterkselseweg 65, 5590AB Heeze, Netherlands. dutchcolon@netscape.net
authors.forename: A J
authors.initials: AJ
authors.lastname: Colon
authors.forename: P
authors.initials: P
authors.lastname: Hofman
authors.forename: P P W
authors.initials: PP
authors.lastname: Ossenblok
authors.forename: J F A
authors.initials: JF
authors.lastname: Jansen
authors.forename: L C
authors.initials: LC
authors.lastname: Ter Beek
authors.forename: R
authors.initials: R
authors.lastname: Berting
authors.forename: C J
authors.initials: CJ
authors.lastname: Stam
authors.forename: P
authors.initials: P
authors.lastname: Boon
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D003937:Diagnosis, Differential; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D015225:Magnetoencephalography; D008297:Male; D054220:Malformations of Cortical Development / Q000175:diagnosis* / Q000503:physiopathology; D008875:Middle Aged