Abstracts

Rationale: One third of patients with focal epilepsy are drug refractory and surgery may provide a cure. Seizure free outcome following surgery is dependent on the correct identification and resection of the putative epileptogenic zone. In patients with no MRI abnormality or where pre-surgical evaluations are discordant invasive Stereoelectroencephalography (SEEG) recordings may be necessary. SEEG is a procedure in which multiple electrodes are stereotactically placed in key targets within the brain to measure ictal and interictal electrophysiological activity. Correlating this activity with the seizure semiology allows identification of the seizure onset zone and key structures within the ictal network. The main risk of SEEG electrode placement is haemorrhage, which occurs in 1% of patients. Planning safe SEEG electrodes requires a meticulous adherence to the following constraints: 1) maximise distance from cerebral vasculature, 2) avoid crossing pial boundaries (sulci), 3) maximize grey matter sampling, 4) minimise electrode length,  5) drilling angle orthogonal to skull, 6) avoid critical neurological structures. We provide a retrospective validation of EpiNav StrategyTM, a multimodal platform that allows automated computer-assisted planning (CAP) of SEEG electrodes by user defined regions of interest. Methods: Thirteen consecutive patients who underwent SEEG implantation of 116 electrodes over a 9 month period were studied. Models of the cortex, grey matter and sulci were generated from a patient specific whole brain parcellation. Vascular segmentation was performed from a pre-operative MR venogram. The multi-disciplinary implantation strategy was reconstructed using CAP and compared to the implemented manual plans. Paired results for safety metric comparison were available for 104 electrodes. Safety metrics included electrode length, drilling angle, minimum distance from vasculature, grey matter sampling ratio and risk (cumulative measure of distance from vasculature along entire length of electrode). External validity of the electrode entry point, trajectory and target point feasibility was sought through 5 independent blinded experts from outside institutions. Statistical analysis was performed by a blinded statistician. Raters appraised two pairs of plans (n = 32) from the same patients to assess inter-rater variability and independently rated a further 3 or 4 pairs of plans (n = 34-41). Results: Table 1 Conclusions: CAP generates clinically feasible electrode plans with statistically improved safety metrics. There was no statistical difference between feasibility of CAP and manual electrodes judged by blinded external raters. CAP generated feasible trajectories where manual plans were rated infeasible in 19%. CAP is a useful tool for automating electrode placement for SEEG but requires operating surgeon review prior to implantation as only 62% of electrodes were rated feasible compared to 69% of manual plans mainly due to proximity to unsegmented vasculature. Improved vascular segmentation may lead to more feasible CAP trajectories. Funding: Funding sources: This work was supported by the Wellcome Trust [Innovation Grant 106882] and the National Institute for Health Research University College London Hospitals Biomedical Research Centre.