Abstracts

Rationale: Stereoelectroencephalography (SEEG) is an important diagnostic tool in the investigation of patients with intractable epilepsy. At the Montreal Neurological Institute (MNI), intracranial recording electrodes have traditionally been inserted using a manual frameless stereotactic technique. ROSA, a Robotic Surgical Assistant (Medtech, France), has recently been acquired to assist with frameless stereotactic procedures. A paucity of results exists in the literature regarding the accuracy of frameless stereotactic procedures. These are usually small retrospective case series that report around 3 mm in deviation from the axis at the target. One study compared a frame-based to a frameless technique, and found a trend for greater accuracy in the frame-based group (Ortler et al, 2011). This study aims to compare prospectively the accuracy of depth electrode implantation in the early manual frameless technique cohort with the more recent robot-assisted insertion group.Methods: All depth electrode implantation procedures performed at the MNI since July 2010 by two staff neurosurgeons were considered in this study, including the robotic-assisted procedures performed since April 2011. All measurements were assessed by comparing the planned target on the pre-operative MRI to the actual electrode tip on a co-registered post-operative MRI or CT scan. Total error at the target, as well as axial error (error in axis deviation at the target), depth error and entry site error were measured and compared between groups using non-parametric multifactorial statistics.Results: 80 electrodes were inserted in 14 patients using the manual frameless technique, and 27 electrodes were inserted in 4 patients using the robot-assisted technique (total = 107 electrodes in 18 patients). Mean total error (3.0 vs 4.5 mm, p = 0.006) and axial error (2.4 vs 3.2 mm, p = 0.011) were significantly lower in the robot-assisted group compared to the manual group. Error in depth was not significantly different between the two groups (2.0 vs 2.5 mm, p = 0.878). No major morbidity (symptomatic hematoma, peri-electrode edema, infection or mortality) was seen in either groups.Conclusions: The results of this study suggest that robot-assisted frameless stereotaxy is a safe technique that can improve the accuracy of depth electrode insertion compared to manual stereotactic techniques. The accuracy results of manual frameless insertion in this study are comparable to the literature. To the authors' knowledge, this study constitutes the first comparative study of manual versus robotic stereotactic procedures.