Abstracts

Rationale: MTLE is the most common form of pharmacoresistant focal epilepsy in adults. SAH is a safe and well-recognized surgical procedure for the treatment of MTLE. One of the procedural risks are visual field deficits due to damage of the optic radiation (OR), the so-called Meyer's Loop. Over the years, several approaches for SAH have been introduced - here we compare the transsylvian and the subtemporal approach with regard to VFDs both clinically and with Diffusion Tensor Imaging (DTI). Methods: Overall, 65 consecutive patients with MTLE (right:left 22:43, male:female 37:28, mean age 43 yrs.) underwent temporal resections. Visual fields were determined using Goldmann visual field kinetic perimetry test performed on OCULUS Twinfield2 perimeter both before and after surgery. Conventional MRI is regularly performed as part of the presurgical workup on a Siemens 3T scanner with 60 gradient directions and a resolution of 1.7mm3. DTI data was processed with FSL tools (FMRIB, Oxford, UK) and probabilistic tractography of the OR was carried out using previously described ROIs (Winston, et al., 2011, 2012). Results: A total of 56 patients with SAH had pre- and postoperative perimetry data and were evaluated for this study (33 with transsylvian, 23 with subtemporal approach. Eight patients (24.2%) from the transsylvian approach group showed no VFDs and 3 (10%) had unspecific changes, whereas the remaining 22 exhibited some form of visual field impairment related to surgery (66.7%). Interestingly, only 12 patients (52.1%) with subtemporal approach showed surgery related VFDs (unspecific changes in 1 (4%) patient). Thus, 10 patients (43.2%) from the latter group had no VFD (Figure 1). Visualization of the OR with DTI of good quality (Figure 2) was successfully performed in 49 of 65 patients. The quantitative analysis of the DTI-data is not yet included and further correlation with VFDs is in process. There was no significant difference in seizure outcome between the two groups. Conclusions: The subtemporal approach reduces the risk for VFDs in patients, who undergo SAH. DTI-based tractography can accurately delineate the optic radiation and may help to avoid VFDs in the future by choosing the most appropriate surgical approach. Acknowledgements The study was part of the project A1 of transregional research cluster SFB TR3 "Mesial temporal lobe epilepsies" of the Deutsche Forschungsgemeinschaft. References Winston, G. P., Yogarajah, M., Symms, M. R., McEvoy, A. W., Micallef, C., & Duncan, J. S. (2011). Diffusion tensor imaging tractography to visualize the relationship of the optic radiation to epileptogenic lesions prior to neurosurgery. Epilepsia, 52(8), 1430-1438. Winston, G. P., Daga, P., Stretton, J., Modat, M., Symms, M. R., McEvoy, A. W., Ourselin, S., et al. (2012). Optic radiation tractography and vision in anterior temporal lobe resection. Annals of Neurology, 71(3), 334-341.