The Medial Subthalamic Nucleus Border as a New Anatomical Reference in Stereotactic Neurosurgery for Parkinson's Disease

Validation of the hotspot for dorsolateral subthalamic nucleus targeting in deep brain stimulation surgery for Parkinson's disease: a post hoc analysis of a randomised controlled trial

BACKGROUND

Visualisation of the dorsolateral subthalamic nucleus (STN) remains challenging on 1.5 and 3Tesla T2-weighted MRI. Our previously defined hotspot, relative to the well-visualised medial STN border, serves as an MRI landmark for dorsolateral STN identification in deep brain stimulation (DBS). We aimed to validate this hotspot in a separate trial cohort of Parkinson's disease (PD) patients and refine its location.

METHODS

In this post hoc analysis of a randomised controlled trial, in which the hotspot was taken into account during target planning, responses to DBS were evaluated using hemibody improvement on the Movement Disorder Society-Unified Parkinson's Disease Rating Scale motor examination and compared with our historical cohort, as well as dopaminergic medication reduction. Then, a refined hotspot was calculated and the Euclidean distance from individual active contacts to the refined hotspot was correlated with motor improvement.

RESULTS

The first quartile of the hemibodies (poor responders) showed an average improvement of 13%, which was higher than the -8% in the historical control group (p=0.044). Dopaminergic medication reduction was greater in the current cohort compared with the historical cohort (p=0.020). Overall variability of hemibody motor improvement was reduced in the current cohort compared with the historical control group (p=0.003). Motor improvement correlated to the Euclidean distance from active contact to the refined hotspot (2.8 mm lateral, 1.1 mm anterior and 2.2 mm superior to the medial STN border) (p=0.001).

CONCLUSION

We validated the hotspot for dorsolateral STN targeting in DBS for patients with PD and showed an improved motor response in poor responders, a reduced variability in motor improvement and a greater dopaminergic medication reduction. We then refined the hotspot at 2.8 mm lateral, 1.1 mm anterior and 2.2 mm superior relative to the medial STN border, which visualises a readily implementable target within the dorsolateral STN on lower field strength MRI.

7-Tesla Magnetic Resonance Imaging Scanning in Deep Brain Stimulation for Parkinson's Disease: Improving Visualization of the Dorsolateral Subthalamic Nucleus

BACKGROUND

Identifying the dorsolateral subthalamic nucleus (STN) for deep brain stimulation (DBS) in Parkinson's disease (PD) can be challenging due to the size and double-oblique orientation. Since 2015 we implemented 7-Tesla T2 weighted magnetic resonance imaging (7 T T2) for improving visualization and targeting of the dorsolateral STN. We describe the changes in surgical planning and outcome since implementation of 7 T T2 for DBS in PD.

METHODS

By comparing two cohorts of STN DBS patients in different time periods we evaluated the influence of 7 T T2 on STN target planning, the number of microelectrode recording (MER) trajectories, length of STN activity and the postoperative motor (UPDRS) improvement.

RESULTS

From February 2007 to January 2014, 1.5 and 3-Tesla T2 guided STN DBS with 3 MER channels was performed in 76 PD patients. Average length of recorded STN activity in the definite electrode trajectory was 3.9 ± 1.5 mm. From January 2015 to January 2022 7 T T2 and MER-guided STN DBS was performed in 182 PD patients. Average length of recorded STN activity in the definite electrode trajectory was 5.1 ± 1.3 mm and used MER channels decreased from 3 to 1. Average UPDRS improvement was comparable.

CONCLUSION

Implementation of 7 T T2 for STN DBS enabled a refinement in targeting. Combining classical DBS targeting with dorsolateral STN alignment may be used to determine the optimal trajectory. The improvement in dorsolateral STN visualization can be used for further target refinements, for example adding probabilistic subthalamic connectivity, to enhance clinical outcome of STN DBS.

Subthalamic deep brain stimulation for primary dystonia: defining an optimal location using the medial subthalamic nucleus border as anatomical reference

Introduction

Although the subthalamic nucleus (STN) has proven to be a safe and effective target for deep brain stimulation (DBS) in the treatment of primary dystonia, the rates of individual improvement vary considerably. On the premise of selecting appropriate patients, the location of the stimulation contacts in the dorsolateral sensorimotor area of the STN may be an important factor affecting therapeutic effects, but the optimal location remains unclear. This study aimed to define an optimal location using the medial subthalamic nucleus border as an anatomical reference and to explore the influence of the location of active contacts on outcomes and programming strategies in a series of patients with primary dystonia.

Methods

Data from 18 patients who underwent bilateral STN-DBS were retrospectively acquired and analyzed. Patients were assessed preoperatively and postoperatively (1 month, 3 months, 6 months, 1 year, 2 years, and last follow-up after neurostimulator initiation) using the Toronto Western Spasmodic Torticollis Rating Scale (for cervical dystonia) and the Burke-Fahn-Marsden Dystonia Rating Scale (for other types). Optimal parameters and active contact locations were determined during clinical follow-up. The position of the active contacts relative to the medial STN border was determined using postoperative stereotactic MRI.

Results

The clinical improvement showed a significant negative correlation with the y-axis position (anterior-posterior; A+, P-). The more posterior the electrode contacts were positioned in the dorsolateral sensorimotor area of the STN, the better the therapeutic effects. Cluster analysis of the improvement rates delineated optimal and sub-optimal groups. The optimal contact coordinates from the optimal group were 2.56 mm lateral, 0.15 mm anterior, and 1.34 mm superior relative to the medial STN border.

Conclusion

STN-DBS was effective for primary dystonia, but outcomes were dependent on the active contact location. Bilateral stimulation contacts located behind or adjacent to Bejjani's line were most likely to produce ideal therapeutic effects. These findings may help guide STN-DBS preoperative planning, stimulation programming, and prognosis for optimal therapeutic efficacy in primary dystonia.