Introduction: Deep Brain Stimulation (DBS) is a safe and effective therapy for Parkinson’s disease, essential tremor and dystonia. Increasing use of intraoperative imaging allows near real-time assessment of stereotactic accuracy during implantation of intracranial leads. Frameless stereotactic placement is likewise gaining acceptance with accuracy comparable to frame-based techniques. This study is the largest assessment to date of stereotactic error using these techniques for the placement of DBS electrodes.

Methods: This is a retrospective study. Intraoperative CT imaging was reviewed in patients undergoing DBS placement for Parkinson’s disease and essential tremor at Oregon Health and Sciences University. The AC/PC coordinates of the target electrode were compared to the operative to obtain Euclidean error and absolute error in the anterior-posterior, lateral-medial, and superior-inferior directions.

Results: 169 leads in 94 patients were examined. Targets were GPi (n=86), STN (n=31) and Vim (n=52); 85 were placed on the left and 84 on the right. Average Euclidean error was 1.63 mm (SD: 0.87). Target but not side showed significant effect on error magnitude, being higher for Vim (1.95 mm, SD: 0.88) than for GPi (1.44 mm, SD: 0.84), while STN (1.65 mm, SD: 0.88) did not differ from either Vim or GPi (ANOVA: target, F=6.15, p=0.0027; side, F=0.02, p=0.893). Electrodes targeting Vim were significantly more likely to deviate medially (Vim: 1.28 mm; GPi: 0.49 mm; STN: 1.06 mm; Kruskal-Wallis: Chi-sq=16.15, p=0.00). There was a correlation between a steeper coronal trajectory and larger magnitude of medial deviation when targeting Vim (rho=0.338, p=0.014).

Conclusions: This study shows a significant effect of target on the accuracy of electrode placement for DBS. Trajectories targeting Vim result in greater Euclidean error and greater medial deviation off target. These systematic deviations should be taken into account when using frameless stereotactic placement of DBS electrodes.

Patient Care: Understanding the factors impacting stereotactic error in DBS electrode placement stands to improve targeting accuracy and its likely impact on patient outcomes in the surgical treatment of movement disorders

Learning Objectives: 1. Use of frameless stereotaxy for implantation of DBS electrodes is accurate and precise. 2. Electrodes directed at Vim tend to deviate medially from the operative plan. 3. This deviation is correlated with coronal trajectory

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