Targeting the subthalamic nucleus for deep brain stimulation: technical approach and fusion of pre- and postoperative MR images to define accuracy of lead placement.

OBJECTIVES: To define the role of magnetic resonance imaging (MRI) and intraoperative electrophysiological recording in targeting the subthalamic nucleus (STN) in Parkinson's disease and to determine accuracy of electrode placement. PATIENTS AND METHODS: We implanted 54 electrodes into the STN in 27 patients. Target planning was done by coordinate guidelines and visualising the STN on MRI and defined in relation to the mid-point of the AC-PC line. Intraoperative microelectrode recording was used. We adjusted electrode positions for placement in the centre of the STN electrical activity and verified this on postoperative MRI in 16 cases, which were fused to the preoperative images to measure actual error in electrode placement in the three axes.
RESULTS: Based on coordinate calculation and MRI localisation, the mean of the target was 11.5 mm lateral, 2.5 mm posterior and 4.1 mm inferior to the mid-point of the AC-PC line. Fifty good electrophysiological recordings of the STN (average length 4.65 mm) were achieved and target point adjusted in 90% of lead placements. The mean of the final target after electrophysiological correction was 11.7 mm lateral, 2.1 mm posterior, and 3.8 mm inferior to the mid-point. The distance from the centre of the electrode artefact to the final target used after electrophysiological recording on the fused images was 0.48 mm, 0.69 mm, and 2.9 mm in the x, y, and z axes, respectively. No postoperative MRI related complication was observed.
CONCLUSION: Both direct visualisation of the STN on MRI and intraoperative electrophysiological recording are important in defining the best target. Individual variations exist in the location of the STN target. Fewer tracks were required to define STN activity on the side operated first. Our current stereotactic method of electrode placement is relatively accurate.