Nexframe frameless stereotaxy with multitract microrecording: accuracy evaluated by frame-based stereotactic X-ray.

Objective: The development of image-guided systems rendered it possible to perform frameless stereotactic surgery for deep brain stimulation (DBS). As well as stereotactic targeting, neurophysiological identification of the target is important. Multitract microrecording is an effective technique to identify the best placement of an electrode. This is a report of our experience of using the Nexframe frameless stereotaxy with Ben's Gun multitract microrecording drive and our study of the accuracy, usefulness and disadvantages of the system.

Methods: Five patients scheduled to undergo bilateral subthalamic nucleus (STN) DBS were examined. The Nexframe device was adjusted to the planned target, and electrodes were introduced using a microdrive for multitract microrecording. In addition to the Nexframe frameless system, we adopted the Leksell G frame to the same patients simultaneously to use a stereotactic X-ray system. This system consisted of a movable X-ray camera with a crossbar and was adopted to be always parallel to the frame with the X-ray film cassette. The distance between the expected and actual DBS electrode placements was measured on such a stereotactic X-ray system. In addition, the distance measured with this system was compared with that measured by conventional frame-based stereotaxy in 20 patients (40 sides).

Results: The mean deviations from 10 planned targets were 1.3 +/- 0.3 mm in the mediolateral (x) direction, 1.0 +/- 0.9 mm in the anteroposterior (y) direction and 0.5 +/- 0.6 mm in the superoposterior (z) direction. The data from the frame-based stereotaxy in our institute were 1.5 +/- 0.9 mm in the mediolateral (x) direction, 1.1 +/- 0.7 mm in the anteroposterior (y) direction and 0.8 +/- 0.6 mm in the superoposterior (z) direction. Then, differences were not statistically significant in any direction (p > 0.05). The multitract microrecording procedure associated with the Nexframe was performed without any problems in all of the patients. None of these electrodes migrated during and/or after the surgery. However, the disadvantage of the system is the narrow surgical field for multiple electrode insertion. Coagulating the cortex and inserting multiple electrodes under such a narrow visual field were complicated.

Conclusion: The Nexframe with multitract microrecording for STN DBS still has some problems that need to be resolved. Thus far, we do not consider that this technology in its present state can replace conventional frame-based stereotactic surgery. The accuracy of the system is similar to that of frame-based stereotaxy. However, the narrow surgical field is a disadvantage for multiple electrode insertion. Improvement on this point will enhance the usefulness of the system.