Intra-operative micro-electrode recording in functional neurosurgery: Past, present, future

The Role of Microelectrode Recording and Stereotactic Computed Tomography in Verifying Lead Placement During Awake MRI-Guided Subthalamic Nucleus Deep Brain Stimulation for Parkinson's Disease

BACKGROUND

Bilateral deep brain stimulation of the subthalamic nucleus (STN-DBS) has become a cornerstone in the advanced treatment of Parkinson's disease (PD). Despite its well-established clinical benefit, there is a significant variation in the way surgery is performed. Most centers operate with the patient awake to allow for microelectrode recording (MER) and intraoperative clinical testing. However, technical advances in MR imaging and MRI-guided surgery raise the question whether MER and intraoperative clinical testing still have added value in DBS-surgery.

OBJECTIVE

To evaluate the added value of MER and intraoperative clinical testing to determine final lead position in awake MRI-guided and stereotactic CT-verified STN-DBS surgery for PD.

METHODS

29 consecutive patients were analyzed retrospectively. Patients underwent awake bilateral STN-DBS with MER and intraoperative clinical testing. The role of MER and clinical testing in determining final lead position was evaluated. Furthermore, interobserver variability in determining the MRI-defined STN along the planned trajectory was investigated. Clinical improvement was evaluated at 12 months follow-up and adverse events were recorded.

RESULTS

98% of final leads were placed in the central MER-track with an accuracy of 0.88±0.45 mm. Interobserver variability of the MRI-defined STN was 0.84±0.09. Compared to baseline, mean improvement in MDS-UPDRS-III, PDQ-39 and LEDD were 26.7±16.0 points (54%) (p < 0.001), 9.0±20.0 points (19%) (p = 0.025), and 794±434 mg/day (59%) (p < 0.001) respectively. There were 19 adverse events in 11 patients, one of which (lead malposition requiring immediate postoperative revision) was a serious adverse event.

CONCLUSION

MER and intraoperative clinical testing had no additional value in determining final lead position. These results changed our daily clinical practice to an asleep MRI-guided and stereotactic CT-verified approach.

Full-field MRI measurements of in-vivo positional brain shift reveal the significance of intra-cranial geometry and head orientation for stereotactic surgery

Positional brain shift (PBS), the sagging of the brain under the effect of gravity, is comparable in magnitude to the margin of error for the success of stereotactic interventions ([Formula: see text] 1 mm). This non-uniform shift due to slight differences in head orientation can lead to a significant discrepancy between the planned and the actual location of surgical targets. Accurate in-vivo measurements of this complex deformation are critical for the design and validation of an appropriate compensation to integrate into neuronavigational systems. PBS arising from prone-to-supine change of head orientation was measured with magnetic resonance imaging on 11 young adults. The full-field displacement was extracted on a voxel-basis via digital volume correlation and analysed in a standard reference space. Results showed the need for target-specific correction of surgical targets, as a significant displacement ranging from 0.52 to 0.77 mm was measured at surgically relevant structures. Strain analysis further revealed local variability in compressibility: anterior regions showed expansion (both volume and shape change), whereas posterior regions showed small compression, mostly dominated by shape change. Finally, analysis of correlation demonstrated the potential for further patient- and intervention-specific adjustments, as intra-cranial breadth and head tilt correlated with PBS reaching statistical significance.

Single-Stage Deep Brain Stimulator Placement for Movement Disorders: A Case Series

With more than two decades of experience and thousands of patients treated worldwide, deep brain stimulation (DBS) has established itself as an efficacious and common surgical treatment for movement disorders. However, a substantial majority of patients in the United States still undergo multiple, “staged” surgeries to implant a DBS system. Despite several reports suggesting no significant difference in complications or efficacy between staged and non-staged approaches, the continued use of staging implies surgeons harbor continued reservations about placing all portions of a system during the index procedure. In an effort to eliminate multiple surgeries and simplify patient care, DBS implantations at our institution have been routinely performed in a single surgery over the past four years. Patients who underwent placement of new DBS systems at our institution from January 2016 to June 2019 were identified and their records were reviewed. Revision surgeries were excluded. Total operative time, length of stay and rates of surgical site infections, lead fracture or migration, and other complications were evaluated. This series expands the body of evidence suggesting placement of a complete DBS system during a single procedure appears to be an efficacious and well-tolerated option.

Automatic Segmentation of the Subthalamic Nucleus: A Viable Option to Support Planning and Visualization of Patient-Specific Targeting in Deep Brain Stimulation

BACKGROUND

Automatic segmentation is gaining relevancy in image-based targeting of neural structures.

OBJECTIVE

To evaluate its feasibility, we retrospectively analyzed the concordance of magnetic resonance imaging (MRI)-based automatic segmentation of the subthalamic nucleus (STN) and intraoperative microelectrode recordings (MERs).

METHODS

Electrodes (n = 60) for deep brain stimulation were implanted in the STN of patients (n = 30; median age 57 yr) with Parkinson disease (n = 29) or rapid-onset dystonia parkinsonism (n = 1). Elements (Brainlab, Munich, Germany) were used to segment the STN, using 2 volumetric T1 (±contrast) and volumetric T2 images as input. The stereotactic computed tomography was coregistered with the imaging, and the original stereotactic coordinates were imported. MERs (0.5-1 mm steps) along the anterior, central, and lateral trajectories were used to determine differences between the image-segmented STN boundary and MER-based STN entry and exit.

RESULTS

Of 175 trajectories, 105 penetrated or touched (≤0.7 mm) the STN. The overall median deviation between the segmented STN boundary and electrophysiological recordings was 1.1 mm for MER-based STN entry and 2.0 mm for STN exit. Regarding the entry point of the STN, there was no statistically significant difference between MRI-based automatic segmentation and the electrophysiological trajectories analyzed with intraoperative MER. The exit point was significantly different between both methods in the central and lateral trajectories.

CONCLUSION

MRI-based automatic segmentation of the STN is a viable, patient-specific targeting approach that can be used alongside traditional targeting methods in deep brain stimulation to support preoperative planning and visualization of target structures and aid postoperative optimization of programming.

Structural connectivity-based segmentation of the thalamus and prediction of tremor improvement following thalamic deep brain stimulation of the ventral intermediate nucleus

Objectives

Traditional targeting methods for thalamic deep brain stimulation (DBS) performed to address tremor have predominantly relied on indirect atlas-based methods that focus on the ventral intermediate nucleus despite known variability in thalamic functional anatomy. Improvements in preoperative targeting may help maximize outcomes and reduce thalamic DBS–related complications. In this study, we evaluated the ability of thalamic parcellation with structural connectivity–based segmentation (SCBS) to predict tremor improvement following thalamic DBS.

Methods

In this retrospective analysis of 40 patients with essential tremor, hard segmentation of the thalamus was performed by using probabilistic tractography to assess structural connectivity to 7 cortical targets. The volume of tissue activated (VTA) was modeled in each patient on the basis of the DBS settings. The volume of overlap between the VTA and the 7 thalamic segments was determined and correlated with changes in preoperative and postoperative Fahn-Tolosa-Marin Tremor Rating Scale (TRS) scores by using multivariable linear regression models.

Results

A significant association was observed between greater VTA in the supplementary motor area (SMA) and premotor cortex (PMC) thalamic segment and greater improvement in TRS score when considering both the raw change (P = .001) and percentage change (P = .011). In contrast, no association was observed between change in TRS score and VTA in the primary motor cortex thalamic segment (P ≥ .19).

Conclusions

Our data suggest that greater VTA in the thalamic SMA/PMC segment during thalamic DBS was associated with significant improvement in TRS score in patients with tremor. These findings support the potential role of thalamic SCBS as an independent predictor of tremor improvement in patients who receive thalamic DBS.

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Pre-operative connectivity data may improve thalamic DBS targeting for tremor.

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Tremor control was positively correlated with connectivity-based thalamic segmentation.

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Stimulation of the SMA/PMC connected thalamic region correlated with tremor control.

Information processing from the motor cortices to the subthalamic nucleus and globus pallidus and their somatotopic organizations revealed electrophysiologically in monkeys

To understand how the information derived from different motor cortical areas representing different body parts is organized in the basal ganglia, we examined the neuronal responses in the subthalamic nucleus (STN), and the external (GPe) and internal (GPi) segments of the globus pallidus (input, relay and output nuclei, respectively) to stimulation of the orofacial, forelimb and hindlimb regions of the primary motor cortex (MI) and supplementary motor area (SMA) in macaque monkeys under the awake state. Most STN and GPe/GPi neurons responded exclusively to stimulation of either the MI or SMA, and one‐fourth to one‐third of neurons responded to both. STN neurons responding to the hindlimb, forelimb and orofacial regions of the MI were located along the medial–lateral axis in the posterolateral STN, while neurons responding to the orofacial region of the SMA were located more medially than the others in the anteromedial STN. GPe/GPi neurons responding to the hindlimb, forelimb and orofacial regions of the MI were found along the dorsal–ventral axis in the posterolateral GPe/GPi, and neurons responding to the corresponding regions of the SMA were similarly but less clearly distributed in more anteromedial regions. Moreover, neurons responding to the distal and proximal forelimb MI regions were found along the lateral–medial axis in the STN and the ventral–dorsal axis in the GPe/GPi. Most STN and GPe/GPi neurons showed kinaesthetic responses with similar somatotopic maps. These observations suggest that the somatotopically organized inputs from the MI and SMA are well preserved in the STN and GPe/GPi with partial convergence.