Direct Targeting of the Ventral Intermediate Nucleus Using High-Field Proton Density MR Imaging: Functional Outcomes and Comparison to “Indirect” Targeting

Abstract

Abstract INTRODUCTION The ventral intermediate nucleus is typically considered not to be visible on MRI, However, there have been reports of successful imaging of this structure. In this study, the authors describe their experience incorporating “direct targeting” to surgical planning of DBS surgery. METHODS Between July 2017 and September 2018, 41 patients underwent VIM DBS for essential tremor under general anesthesia using direct targeting methods. Images were acquired on a 3.0-tesla MR system, and a proton density sequence was used to visualize the VIM. Clinical outcomes were prospectively collected at baseline and 3-mo follow-up and compared to patients treated previously using indirect targeting methods. RESULTS A total of 77 leads were placed with 36 patients undergoing bilateral surgery and 5 patients undergoing unilateral surgery (mean age 68.6, M: F 25:16). Relative to the mid-commisural point, the mean target coordinates for these patients was (±14.4, −5.9, 0.1). Comparing this to our previous cohort (213 patients) in whom indirect targeting was used, direct targeting led to a more lateral target (P < .05). Three-month follow-up outcomes for 21 patients were compared to to 33 patients who had undergone asleep VIM DBS surgery using indirect targeting. Accuracy was comparable between groups. Direct and Indirect groups did not differ significantly regarding mean postoperative percentages of functional improvement (direct, 36% vs indirect, 48%) or quality of life (direct 68% vs indirect 75%). Mean voltage was 2.09 for the direct group and 2.14 for the indirect group (P = .7). Fewer postoperative stimulation-related speech side effects were reported among the direct targeting group (direct n = 4 vs indirect n = 9). CONCLUSION VIM targeting based upon direct visualization using proton density MRI resulted in more lateral targeting, equivalent functional outcomes, and fewer stimulation-related speech side effects compared to our historical cohorts.