Intersubject variability in the anterior extent of the optic radiation assessed by tractography.
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.
Nilsson
Daniel
D
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
Starck
Göran
G
Ljungberg
Maria
M
Ribbelin
Susanne
S
Jönsson
Lars
L
Malmgren
Kristina
K
Rydenhag
Bertil
B
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*