Frameless stereotactic drilling for placement of depth electrodes in refractory epilepsy: operative technique and initial experience.

Background: For stereotactic implantation of depth electrodes in refractory epilepsy, both frame-based and frameless techniques have been developed. The higher versatility of current frameless techniques compared with framed-based methods is paid by the need of a standard burr hole for the implantation of 1 electrode.
Objective: To develop a frameless method that allows convenient implantation of the electrode via a percutaneous bolt as used in frame-based methods, thereby avoiding the need for a standard burr hole.
Methods: We adopted our technique from frameless stereotactic biopsy and designed the GIDE, a bone-fixated Guide for Implantation of Depth Electrodes. This reducing sleeve works as a stabilizer of the neuronavigation arm through bony contact and allows percutaneous stereotactic drilling, screwing of an implantation bolt, and placement of the depth electrode.
Results: Twenty-six electrodes in 7 patients (5 male and 2 female patients; median age, 19.6 years; range, 5.5-39.1 years) were successfully implanted. The overall accuracy was comparable to that of frameless stereotactic biopsy with a target deviation of 3.0±1.9 mm (mean±SD). All electrodes were within or touched the targeted anatomic structure with an adequate quality of the recordings. We encountered no hemorrhage or neurological deficit related to the depth electrode.
Conclusion: Our technique combines the high versatility of frameless stereotaxy with the convenient implantation and fixation of the depth electrode via a percutaneous bolt used in frame-based stereotactic methods. Thus, our technique allows fast, efficient implantation of depth electrodes for intracranial electroencephalography recordings.