gms | German Medical Science

Objective: Stereoelectroencephalography (SEEG) uses surgically implanted intracerebral electrodes to identify a potentially resectable epileptic focus. For a spot-on EEG-Monitoring and avoiding complications, the SEEG-electrodes must follow a carefully planned trajectory. In this study we investigate the level of accuracy of the implanted electrodes compared to the respective planed trajectory depending on the surgical technique used: standard frame-based stereotaxy vs. frame-less stereotaxy using Vario-Guide (Brainlab, München, Germany).

Methods: Data of eight patients (m=6, f=2) undergoing SEEG electrode implantation was analyzed. 11 surgeries were performed, six using the frame-based approach and five using the frame-less approach applying the Vario-Guide system. In both scenarios a head reference array was attached and an automated navigation registration was performed using the AIRO iCT (Brainlab, München, Germany). Afterwards, in frame-based stereotaxy frame localization was performed and arc settings were defined. In total 57 electrodes were implanted (frame-based: 25, frame-less: 32). For each electrode the Euclidian distance of the planned electrode tip and the implanted electrode tip was calculated to quantify the accuracy of electrode implantation. Furthermore the difference in implantation depth between planned and implanted electrode as well as and the radial deviation at the planned electrode tip was calculated.

Results: In case of frame-based surgery the mean Euclidian distance between planned and implanted electrode tip was 3.38±1.71 mm, in case of frame-less surgery 3.12±1.67 mm. No significant difference was seen. Regarding implantation depth a mean deviation of 1.92±1.76 mm for frame-base and 2.10±1.62 mm for frame-less implantation was seen. In case of radial deviation at the planned electrode tip, for frame-based surgery a mean deviation of 2.45±1.27 mm was seen, 1.98±1.28 mm for frame-less surgery also revealing no significant difference between both groups.

Conclusion: Since both methods show a similar displacement error between the planned and implanted electrodes, neither can be advocated as having a superior accuracy. This is however an argument for the use of frame-less stereotactical implantation which, without the need for manual input of coordinates in the frame and checking the accuracy for each electrode using a target-phantom, is also technically faster.