title: Intersubject variability in the anterior extent of the optic radiation assessed by tractography.
abstract: BACKGROUND
  Temporal lobe resection for epilepsy involves a risk of damaging the anterior part of the optic radiation, Meyer's loop, causing a contralateral upper quadrant visual field defect. This study aims to assess the intersubject variability in the course of Meyer's loop in vivo by diffusion tensor imaging and tractography.
  
  
  METHODS
  Seven healthy volunteers and two patients with previous temporal lobe resection were recruited. Diffusion tensor imaging and tractography were used to visualize the optic radiation. The distances from the anterior edge of Meyer's loop to landmarks in the temporal lobe were calculated.
  
  
  RESULTS
  In the healthy subjects, the mean distance between the most anterior part of Meyer's loop and the temporal pole was 44 mm (range 34-51 mm). Meyer's loop did not reach the tip of the temporal horn in any subject. A disruption in Meyer's loop could be demonstrated in the patient with quadrantanopia after temporal lobe resection.
  
  
  CONCLUSIONS
  Meyer's loop has a considerable variability in its anterior extent. Tractography may be a useful method to visualize Meyer's loop, and assess the risk of a visual field defect, prior to temporal lobe resection.
authors.affiliation: Institute of Neuroscience and Physiology, Section of Clinical Neuroscience and Rehabilitation, Epilepsy Research Group, Sahlgrenska Academy at Göteborg University, Sweden. daniel.nilsson@neuro.gu.se
authors.forename: Daniel
authors.initials: D
authors.lastname: Nilsson
authors.forename: Göran
authors.initials: G
authors.lastname: Starck
authors.forename: Maria
authors.initials: M
authors.lastname: Ljungberg
authors.forename: Susanne
authors.initials: S
authors.lastname: Ribbelin
authors.forename: Lars
authors.initials: L
authors.lastname: Jönsson
authors.forename: Kristina
authors.initials: K
authors.lastname: Malmgren
authors.forename: Bertil
authors.initials: B
authors.lastname: Rydenhag
mesh_terms: D000328:Adult; D016880:Anisotropy; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D013702:Temporal Lobe / Q000033:anatomy & histology* / Q000601:surgery*; D014794:Visual Fields / Q000502:physiology; D014795:Visual Pathways / Q000033:anatomy & histology*