gms | German Medical Science

Objective: To correlate and predict visual field defects in temporal lobe surgery for pharmaco-resistant epilepsy by comparing reconstructed pre-and intraoperative fiber bundles representing the optic radiation.

Methods: A single-shot spin-echo diffusion weighted echo planar sequence (with 6 diffusion gradients on a 1.5T MR scanner) was used for diffusion tensor imaging (DTI) based fiber tracking in 48 patients undergoing temporal lobectomy for pharmaco-resistant epilepsy. Pre- and intraoperative fiber tracking was used to visualize the optic radiation applying a standard tensor deflection approach (iPlan 2.5, BrainLAB, Feldkirchen, Germany). The differences between pre- and intraoperative reconstruction of the optic radiation were correlated with the visual field defects in a prospective double-blinded study.

Results: The course of the optic radiation could be successfully reconstructed by DTI based fiber tracking. There was a significant correlation between the fiber tracking estimation and the outcome of visual field deficits after surgery. The receiver operating characteristic (ROC) curve analysis confirmed the accuracy and validity of prediction of the post-operative visual field deficits comparing pre- and intra-operative fiber tracking results. The Spearman correlation analysis showed significant correlations of field loss (calculated as visual field defect grades) with optic radiation/Meyer’s loop injury fraction (P<0.001), with an r value of 0.889.

Conclusions: Pre- and intraoperative reconstruction of the optic radiation was possible in all patients. The differences between the reconstructed pre- and intraoperative fiber bundles correlated well with postoperative visual field defects. Blinded analysis of DTI data allowed a reliable prediction of visual field defects.