191 Methodology for Critical Evaluation of Laser Placement in Stereotactic Laser Ablation for Mesial Temporal Lobe Epilepsy: A Pilot Study

Abstract INTRODUCTION: Stereotactic laser ablation (SLA) is a promising minimally invasive alternative for treating mesial temporal lobe epilepsy (MTLE). While our experience to date has suggested that seizure outcome may not be directly associated with total ablation volume, the specifics of the relevant variables remain unclear. While post-ablation imaging demonstrates laser location, effects of the ablation obscure its location relative to target structures. We therefore formulated and tested a methodology to critically evaluate laser placement in SLA for MTLE. METHODS: We performed a retrospective cohort study involving 10 patients undergoing SLA for MTLE at the Comprehensive Epilepsy Center at Thomas Jefferson University between 2011 and 2013 (Table 1). Preoperative non-contrast magnetic resonance images (MRIs) served as reference images, which were segmented with FreeSurfer. Postoperative gadolinium-enhanced MRIs were coregistered to the preoperative image using SPM8. Laser tracts were segmented from this coregistered image using ITK-SNAP, MatLab, and Slicer. Segmented tracts were superimposed upon the initial MRI to determine its location at the level of the hippocampal head (Figure 1). The length of hippocampus and amygdala cannulated were recorded. RESULTS: The laser tract was segmented and its location was successfully determined in all 10 cases (Figure 2). A laser tract traversing the superior portion of hippocampal head and longer hippocampal cannulations were associated with better seizure outcomes (Figure 3). The length of amygdala and hippocampal cannulations was not clearly associated with the percentage of each structure that was ultimately ablated. CONCLUSION: The presented methodology allowed for critical evaluation of laser placement. Preliminary results suggest the importance of accurate laser placement with a target in the superior hippocampal head to maximize the length of hippocampus that can be cannulated. Further studies with adequate power and long-term follow-up are necessary to substantiate these preliminary findings.