• Ylva Lilja, Maria Ljungberg, Göran Starck, Kristina Malmgren, Bertil Rydenhag, and Daniel T Nilsson.
• Institute of Neuroscience and Physiology, Department of Clinical Neuroscience and Rehabilitation, The Sahlgrenska Academy at the University of Gothenburg, Per Dubbsgatan 14, 413 46, Gothenburg, Sweden, ylva.lilja@neuro.gu.se.
• Acta Neurochir (Wien). 2015 Jun 1;157(6):947-56; discussion 956.

BackgroundPostoperative visual field defects are common after temporal lobe resection because of injury to the most anterior part of the optic radiation, Meyer's loop. Diffusion tensor tractography is a promising technique for visualizing the optic radiation preoperatively. The aim of this study was to assess the anatomical accuracy of Meyer's loop, visualized by the two most common tractography methods—deterministic (DTG) and probabilistic tractography (PTG)—in patients who had undergone temporal lobe resection.MethodsEight patients with temporal lobe resection for temporal lobe pathology were included. Perimetry and diffusion tensor imaging were performed pre- and postoperatively. Two independent operators analyzed the distance between the temporal pole and Meyer's loop (TP-ML) using DTG and PTG. Results were compared to each other, to data from previously published dissection studies and to postoperative perimetry results. For the latter, Spearman's rank correlation coefficient (r(s)) was used.ResultsMedian preoperative TP-ML distances for nonoperated sides were 42 and 35 mm, as determined by DTG and PTG, respectively. TP-ML assessed with PTG was a closer match to dissection studies. Intraclass correlation coefficients were 0.4 for DTG and 0.7 for PTG. Difference between preoperative TP-ML (by DTG and PTG, respectively) and resection length could predict the degree of postoperative visual field defects (DTG: r(s) = -0.86, p < 0.05; PTG: r(s) = -0.76, p < 0.05).ConclusionBoth DTG and PTG could predict the degree of visual field defects. However, PTG was superior to DTG in terms of reproducibility and anatomical accuracy. PTG is thus a strong candidate for presurgical planning of temporal lobe resection that aims to minimize injury to Meyer's loop.

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