title: Occipital lobe lesions result in a displacement of magnetoencephalography visual evoked field dipoles.
abstract: OBJECTIVE
  The pattern-reversal visual evoked potential measured electrically from scalp electrodes is known to be decreased, or absent, in patients with occipital lobe lesions. We questioned whether the measurement and source analysis of the neuromagnetic visual evoked field (VEF) might offer additional information regarding visual cortex relative to the occipital lesion.
  
  
  METHODS
  We retrospectively examined 12 children (6-18 years) with occipital lesions on MRI, who underwent magnetoencephalography and ophthalmology as part of their presurgical assessment. Binocular half-field pattern-reversal VEFs were obtained in a 151-channel whole-head magnetoencephalography. Data were averaged and dipole source analyses were performed for each half-field stimulation.
  
  
  RESULTS
  A significant lateral shift (P < 0.02) in the dipole location was observed in the lesional hemisphere compared with those in the nonlesional hemisphere, regardless of the lesion location. No differences were observed in latency, strength (moment), and residual errors of VEF dipoles between the lesional and nonlesional hemispheres.
  
  
  CONCLUSIONS
  Magnetoencephalography demonstrated the mass effect on the dipole location of VEF in children with occipital lesions. Magnetoencephalography may be useful as a screening test of visual function in young patients. We discuss potential explanations for this lateral shift and emphasize the utility of adding the magnetoencephalography pattern-reversal visual evoked field protocol to the neurologic work-up.
authors.affiliation: *Division of Neurology, The Hospital for Sick Children, Toronto, Ontario, Canada; and †Department of Paediatrics, The University of Toronto, Toronto, Ontario, Canada.
authors.forename: Elizabeth W
authors.initials: EW
authors.lastname: Pang
authors.forename: Bill H W
authors.initials: BH
authors.lastname: Chu
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Otsubo
mesh_terms: D000293:Adolescent; D001927:Brain Diseases / Q000473:pathology*; D001931:Brain Mapping; D002648:Child; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D009778:Occipital Lobe / Q000503:physiopathology*; D010775:Photic Stimulation; D012189:Retrospective Studies