Technical aspects of SEEG limitations and solutions using the Leksell Vantage frame

Stereo-electroencephalography (SEEG) is an invasive electroencephalography method to precisely locate a seizure onset zone (SOZ). While today´s armamentarium allows any compromise between the historically strict orthogonal and oblique trajectories, the following aspects limit its effectiveness and safety. The shorter the distance from entry to the brain and target the less deviation of the electrode. The closer to orthogonal to the scull the more stable the anchor sits in the scull and deviation can be better controlled. Beyond that, limitations due to the stereotactic frame must be considered. In certain cases, a conflict between frame setup and entry point of the trajectory can arise. This conflict spurred us to explore the limits of stereotactic frame and the associated equipment needed for SEEG.

We utilize the Elekta Leksell Vantage frame (LVF) and surgical SEEG-instruments of the company AD-Tech. Planning of the trajectories is performed with a software based on MRI scans. After co-registration with stereotactical CT-angiogram coordinates for the centre-of-arc-principle to set up the LVF are generated. The frame setup focuses on the orientation of the ring-shaped z-axis, which impact SEEG electrode placement. Key factors, such as arc-angle and x-coordinate, influence instrument positioning and potential interference with the frame. Various combinations of ring-scale direction, arc alignment, arc-angle, and x-coordinate were attempted, along with the limitations of the ring angle in relation to y- and z-axis.

Since 2018 our department performed 19 SEEG-implantations of in total 188 SEEG-electrodes. The average age at presentation of the 15 male and 4 female patients was 42 years (range 28 to 58). In 6 of the 19 implantation the ZD Inomed frame was used, while the other 13 cases were performed with the LVF. An average of 9 electrodes were applied using the ZD Inomed frame compared to 11 electrodes with the LVF. Both approaches aimed for bihemispheric targets. The average time of implantation of a single electrode using the ZD Inomed frame was 20,7 min, while the LVF took 4 min less (16,6 min). Other factors such as electrode repositioning or deviation and postoperative complications occurred very rarely. In at least 12 cases concerning 19 out of 188 (10.1%) electrodes an intraoperative trajectory replanning became necessary because of conflict between frame setup and entry point of the trajectory.

Our clinical experience confirmed that the complex planning of SEEG trajectories occasionally leads to a conflict between frame setup and entry points. The systematic analysis of the utilized stereotactic frame and SEEG-instruments can prevent replanning during surgery and improves patient's safety and quality management.