Abstracts

Rationale: Visual field defect (VFD) occurs frequently after temporal lobe resection (TLR) for temporal lobe epilepsy (TLE), as a result of injury to the visual pathways. This study investigated if there was a correlation between perimetry results and tractography (TG) of injury to the optic radiation and whether a postoperative visual field defect could be predicted from preoperative tractography results. Methods: Diffusion tensor imaging-based probabilistic TG and perimetry was done before and after TLR in seven patients with TLE. Distances between the temporal pole and the most anterior part of the visual pathways in the temporal lobe, Meyers loop (TP-ML distance), were measured pre-and postoperatively. Visual inspection of the optic radiations pre-and postop were performed. The results were correlated to postoperative perimetry. Results: Six of seven patients developed a postoperative VFD, 5/7 were less than a quadrant. Preoperative TP-ML varied from 19 mm to 40 mm (mean 31.7 mm for right side, 34.5 mm for the left side). Optic radiation injury could be seen in all subjects with VFD, but not in the subject with normal visual fields. Mean postoperative TP-ML was 36.9 on the operated side and 37.2 mm on the intact side (n.s.). No correlation between preoperative ML-TP distance and postoperative VFD was found. Conclusions: Tractography can localize the visual pathways, and detect injury to the optic radiation causing VFD. Preoperative TG could not accurately predict VFD occurrence after standardized TLR. To minimize injury to the visual pathways, individualized mapping used intraoperatively and TLR tailored to avoid the visual pathways, including subtemporal approach, should be considered.