Variability in position of the subthalamic nucleus targeted by magnetic resonance imaging and microelectrode recordings as compared to atlas co-ordinates

A Meta-Analysis of Medication Reduction and Motor Outcomes After Awake Versus Asleep Deep Brain Stimulation for Parkinson Disease

BACKGROUND AND OBJECTIVES

There remains significant debate regarding the performance of deep brain stimulation (DBS) procedures for Parkinson disease (PD) under local or general anesthesia. The aim of this meta-analysis was to compare the clinical outcomes between "asleep" DBS (general anesthesia) and "awake" DBS (local anesthesia) for PD.

METHODS

We conducted a comprehensive literature review of all published studies on DBS for PD following PRISMA guideline on PubMed and Cochrane library from January 2004 to April 2023. Inclusion criteria included cohort ≥15 patients, clinical outcomes data which included Unified Parkinson's Disease Rating Scale (UPDRS) score and levodopa equivalent daily dosage (LEDD), and ≥3 months of follow-up. Analysis was conducted using Stata software.

RESULTS

There were 18 articles that met inclusion criteria. On meta-analysis, there were no significant differences between awake or asleep DBS with regard to percent change in UPDRS III "off" med/"on" DBS condition ( P = .6) and LEDD score ( P = .99). On subgroup analysis, we found that the choice of target had no significant effect on improvement of UPDRS III ( P = 1.0) or LEDD ( P = .99) change for the asleep vs awake operative approach. There were also no statistically significant differences between microelectrode recording (MER) use and no MER use in postoperative UPDRS III ( P = 1.0) or LEDD improvement ( P = .90) between awake and asleep surgery.

CONCLUSION

There was no significant difference in the primary motor outcomes and LEDD improvement between asleep vs awake DBS. The variables of target selection and MER use had no statistically significant impact on outcome. We find that asleep techniques are both safe and effective compared with the awake technique.

The Magnetic Resonance Imaging (MRI)-Directed Implantable Guide Tube Technique: Accuracy and Applications in Deep Brain Stimulation

OBJECTIVE

The magnetic resonance imaging (MRI)-directed implantable guide tube technique allows for direct targeting of deep brain structures without microelectrode recording or intraoperative clinical assessment. This study describes a 10-year institutional experience of this technique including nuances that enable performance of surgery using readily available equipment.

METHODS

Eighty-seven patients underwent deep brain stimulation surgery using the guide tube technique for Parkinson disease (n = 59), essential tremor (n = 16), and dystonia (n = 12). Preoperative and intraoperative MRI was analyzed to measure lead accuracy, volume of pneumocephalus, and the ability to safely plan a trajectory for multiple electrode contacts.

RESULTS

Mean target error was measured to be 0.7 mm (95% confidence interval [CI] 0.6-0.8 mm) in the anteroposterior plane, 0.6 mm (95% CI 0.5-0.7 mm) in the mediolateral plane, and 0.8 mm (95% CI 0.7-0.9 mm) in the superoinferior plane. Net deviation (Euclidean error) from the planned target was 1.3 mm (95% CI 1.2-1.4 mm). Mean intracranial air volume per lead was 0.2 mL (95% CI 0.1-0.4 mL). In total, 52 patients had no intracranial air on postoperative imaging. In all patients, a safe trajectory could be planned to target for multiple electrode contacts without violating critical neural structures, the lateral ventricle, sulci, or cerebral blood vessels.

CONCLUSIONS

The MRI-directed implantable guide tube technique is a highly accurate, low-cost, reliable method for introducing deep brain electrodes. This technique reduces brain shift secondary to pneumocephalus and allows for whole trajectory planning of multiple electrode contacts.

Inner SPACE: 400-Micron Isotropic Resolution MRI of the Human Brain

OBJECTIVES

Clinically relevant neuroanatomy is challenging to teach, learn and remember since many functionally important structures are visualized best using histology stains from serial 2D planar sections of the brain. In clinical patients, the locations of specific structures then must be inferred from spatial position and surface anatomy. A 3D MRI dataset of neuroanatomy has several advantages including simultaneous multi-planar visualization in the same brain, direct end-user manipulation of the data and image contrast identical to clinical MRI. We created 3D MRI datasets of the postmortem brain with high spatial and contrast resolution for simultaneous multi-planar visualization of complex neuroanatomy.

MATERIALS AND METHODS

Whole human brains (N = 6) were immersion-fixed in 4% formaldehyde for 4 weeks, then washed continuously in water for 48 h. The brains were imaged on a clinical 3-T MRI scanner with a 64-channel head and neck coil using a 3D T2-weighted sequence with 400-micron isotropic resolution (voxel = 0.064 mm3; time = 7 h). Besides resolution, this sequence has multiple adjustments to improve contrast compared to a clinical protocol, including 93% reduced turbo factor and 77% reduced effective echo time.

RESULTS

This MRI microscopy protocol provided excellent contrast resolution of small nuclei and internal myelinated pathways within the basal ganglia, thalamus, brainstem, and cerebellum. Contrast was sufficient to visualize the presence and variation of horizontal layers in the cerebral cortex. 3D isotropic resolution datasets facilitated simultaneous multi-planar visualization and efficient production of specific tailored oblique image orientations to improve understanding of complex neuroanatomy.

CONCLUSION

We created an unlabeled high-resolution digital 3D MRI dataset of neuroanatomy as an online resource for readers to download, manipulate, annotate and use for clinical practice, research, and teaching that is complementary to traditional histology-based atlases. Digital MRI contrast is quantifiable, reproducible across brains and could help validate novel MRI strategies for in vivo structure visualization.

3T MRI Whole-Brain Microscopy Discrimination of Subcortical Anatomy, Part 2: Basal Forebrain

BACKGROUND AND PURPOSE

The basal forebrain contains multiple structures of great interest to emerging functional neurosurgery applications, yet many neuroradiologists are unfamiliar with this neuroanatomy because it is not resolved with current clinical MR imaging.

MATERIALS AND METHODS

We applied an optimized TSE T2 sequence to washed whole postmortem brain samples (n = 13) to demonstrate and characterize the detailed anatomy of the basal forebrain using a clinical 3T MR imaging scanner. We measured the size of selected internal myelinated pathways and measured subthalamic nucleus size, oblique orientation, and position relative to the intercommissural point.

RESULTS

We identified most basal ganglia and diencephalon structures using serial axial, coronal, and sagittal planes relative to the intercommissural plane. Specific oblique image orientations demonstrated the positions and anatomic relationships for selected structures of interest to functional neurosurgery. We observed only 0.2- to 0.3-mm right-left differences in the anteroposterior and superoinferior length of the subthalamic nucleus (P = .084 and .047, respectively). Individual variability for the subthalamic nucleus was greatest for angulation within the sagittal plane (range, 15°-37°), transverse dimension (range, 2-6.7 mm), and most inferior border (range, 4-7 mm below the intercommissural plane).

CONCLUSIONS

Direct identification of basal forebrain structures in multiple planes using the TSE T2 sequence makes this challenging neuroanatomy more accessible to practicing neuroradiologists. This protocol can be used to better define individual variations relevant to functional neurosurgical targeting and validate/complement advanced MR imaging methods being developed for direct visualization of these structures in living patients.

Using "Functional" Target Coordinates of the Subthalamic Nucleus to Assess the Indirect and Direct Methods of the Preoperative Planning: Do the Anatomical and Functional Targets Coincide?

Objective: To answer the question of whether the anatomical center of the subthalamic nucleus (STN), as calculated indirectly from stereotactic atlases or by direct visualization on magnetic resonance imaging (MRI), corresponds to the best functional target. Since the neighboring red nucleus (RN) is well visualized on MRI, we studied the relationships of the final target to its different borders. Methods: We analyzed the data of 23 PD patients (46 targets) who underwent bilateral frame-based STN deep brain stimulation (DBS) procedure with microelectrode recording guidance. We calculated coordinates of the active contact on DBS electrode on postoperative MRI, which we referred to as the final “functional/optimal” target. The coordinates calculated by the atlas-based “indirect” and “direct” methods, as well as the coordinates of the different RN borders were compared to these final coordinates. Results: The mean ± SD of the final target coordinates was 11.7 ± 1.5 mm lateral (X), 2.4 ± 1.5 mm posterior (Y), and 6.1 ± 1.7 mm inferior to the mid-commissural point (Z). No significant differences were found between the “indirect” X, Z coordinates and those of the final targets. The “indirect” Y coordinate was significantly posterior to Y of the final target, with mean difference of 0.6 mm (p = 0.014). No significant differences were found between the “direct” X, Y, and Z coordinates and those of the final targets. Conclusions: The functional STN target is located in direct proximity to its anatomical center. During preoperative targeting, we recommend using the “direct” method, and taking into consideration the relationships of the final target to the mid-commissural point (MCP) and the different RN borders.

Application of Preoperative CT/MRI Image Fusion in Target Positioning for Deep Brain Stimulation

<strong>Objective</strong> To explore the efficacy of target positioning by preoperative CT/MRI image fusion technique in deep brain stimulation.<strong>Methods</strong> We retrospectively analyzed the clinical data and images of 79 cases (68 with Parkinson's disease, 11 with dystonia) who received preoperative CT/MRI image fusion in target positioning of subthalamic nucleus in deep brain stimulation. Deviation of implanted electrodes from the target nucleus of each patient were measured. Neurological evaluations of each patient before and after the treatment were performed and compared. Complications of the positioning and treatment were recorded.<strong>Results</strong> The mean deviations of the electrodes implanted on X, Y, and Z axis were 0.5 mm, 0.6 mm, and 0.6 mm, respectively. Postoperative neurologic evaluations scores of unified Parkinson's disease rating scale (UPDRS) for Parkinson's disease and Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) for dystonia patients improved significantly compared to the preoperative scores (P<0.001); Complications occurred in 10.1% (8/79) patients, and main side effects were dysarthria and diplopia.<strong>Conclusion</strong> Target positioning by preoperative CT/MRI image fusion technique in deep brain stimulation has high accuracy and good clinical outcomes.

Magnetic resonance imaging of the subthalamic nucleus for deep brain stimulation

The subthalamic nucleus (STN) is one of the most important stereotactic targets in neurosurgery, and its accurate imaging is crucial. With improving MRI sequences there is impetus for direct targeting of the STN. High-quality, distortion-free images are paramount. Image reconstruction techniques appear to show the greatest promise in balancing the issue of geometrical distortion and STN edge detection. Existing spin echo- and susceptibility-based MRI sequences are compared with new image reconstruction methods. Quantitative susceptibility mapping is the most promising technique for stereotactic imaging of the STN.

Advanced neuroimaging techniques for central neuromodulation

Deep brain stimulation an effective treatment of many neurologic conditions such as Parkinson disease, essential tremor, dystonia, and obsessive-compulsive disorder. Structural and functional neuroimaging studies provide the opportunity to visualize the dysfunctional nodes and networks underlying neurologic and psychiatric disease, and to thereby realize new targets for neuromodulation as well as personalize current therapy. This article reviews contemporary advances in neuroimaging in the basic sciences and how they can be applied to redirect and propel functional neurosurgery toward a goal of functional localization of targets with individualized maps and identification of novel targets for other neuropsychiatric diseases.

Multi-institutional evaluation of deep brain stimulation targeting using probabilistic connectivity-based thalamic segmentation

OBJECT

Due to the lack of internal anatomical detail with traditional MR imaging, preoperative stereotactic planning for the treatment of tremor usually relies on indirect targeting based on atlas-derived coordinates. The object of this study was to preliminarily investigate the role of probabilistic tractography-based thalamic segmentation for deep brain stimulation (DBS) targeting for the treatment of tremor.

METHODS

Six patients undergoing bilateral implantation of DBS electrodes in the thalamus for the treatment of upper-extremity tremor were studied. All patients underwent stereotactic surgical implantation using traditional methods (based on indirect targeting methodologies and intraoperative macrostimulation findings) that were programmed for optimal efficacy, independent of tractography-based segmentations described in this report. Connectivity-based thalamic segmentations were derived by identifying with which of 7 cortical target regions each thalamic voxel had the highest probability of connectivity. The authors retrospectively analyzed the location of the optimal contact for treatment of tremor with connectivity-based thalamic segmentations. Findings from one institution (David Geffen School of Medicine at UCLA) were validated with results from 4 patients at another institution (University of Virginia Health System).

RESULTS

Of 12 electrodes implanted using traditional methodologies, all but one resulted in efficacious tremor control. Connectivity-based thalamic segmentation consistently revealed discrete thalamic regions having unique connectivity patterns with distinct cortical regions. Although the authors initially hypothesized that the most efficacious DBS contact for controlling tremor would colocalize with the thalamic region most highly connected with the primary motor cortex, they instead found it to highly colocalize with those thalamic voxels demonstrating a high probability of connectivity with premotor cortex (center-to-center distance: 0.36 ± 0.55 mm). In contrast to the high degree of colocalization with optimal stimulation site, the precise localization of the premotor cortex-defined thalamic region relative to the anterior and posterior commissures was highly variable. Having defined a connectivity-based target for thalamic stimulation in a cohort of patients at David Geffen School of Medicine at UCLA, the authors validated findings in 4 patients (5 electrodes) who underwent surgery at a different institution (University of Virginia Health System) by a different surgeon.

CONCLUSIONS

This report identifies and provides preliminary external validation of a novel means of targeting a patient-specific therapeutic thalamic target for the treatment of tremor based on individualized analysis of thalamic connectivity patterns. This novel thalamic targeting approach is based on identifying the thalamic region with the highest probability of connectivity with premotor and supplementary motor cortices. This approach may prove to be advantageous over traditional preoperative methods of indirect targeting, providing patient-specific targets that could improve the precision, efficacy, and efficiency of deep brain stimulation surgery. Prospective evaluation and development of methodologies to make these analyses more widely available to neurosurgeons are likely warranted.

Magnetic resonance imaging techniques for visualization of the subthalamic nucleus

The authors reviewed 70 publications on MR imaging-based targeting techniques for identifying the subthalamic nucleus (STN) for deep brain stimulation in patients with Parkinson disease. Of these 70 publications, 33 presented quantitatively validated results. There is still no consensus on which targeting technique to use for surgery planning; methods vary greatly between centers. Some groups apply indirect methods involving anatomical landmarks, or atlases incorporating anatomical or functional data. Others perform direct visualization on MR imaging, using T2-weighted spin echo or inversion recovery protocols. The combined studies do not offer a straightforward conclusion on the best targeting protocol. Indirect methods are not patient specific, leading to varying results between cases. On the other hand, direct targeting on MR imaging suffers from lack of contrast within the subthalamic region, resulting in a poor delineation of the STN. These deficiencies result in a need for intraoperative adaptation of the original target based on test stimulation with or without microelectrode recording. It is expected that future advances in MR imaging technology will lead to improvements in direct targeting. The use of new MR imaging modalities such as diffusion MR imaging might even lead to the specific identification of the different functional parts of the STN, such as the dorsolateral sensorimotor part, the target for deep brain stimulation.

Targeting the subthalamic nucleus for deep brain stimulation--a comparative study between magnetic resonance images alone and fusion with computed tomographic images

BACKGROUND

The aim of this study is to determine whether stereotactic computed tomographic (CT) images fused with magnetic resonance images (MRI) is superior to stereotactic MRI alone in accuracy for targeting the subthalamic nucleus (STN) in deep brain stimulation (DBS).

METHODS

During 2006 to 2007, 21 consecutive patients with Parkinson's disease were enrolled in this retrospective cohort study. CT Fusion group included 10 patients who underwent 20 procedures of STN-DBS under MRI-directed targeting in which the MRIs were fused to stereotactic CT images for surgical coordinates. MRI group included 11 patients who underwent 20 procedures under MRI-directed targeting alone.

RESULTS

After DBS surgery, in comparison to baseline levodopa (L-dopa) OFF, Unified Parkinson Disease Rating Scale, Part III scores improved by 43.6% ± 20.3% and 39.0% ± 15.6% (P = 0.60) in CT Fusion group and MRI group, respectively (L-dopa OFF/DBS ON). The mean decrease in L-dopa equivalent daily dose was 38.9% ± 26.3% and 36.7% ± 30.5% (P = 0.87), respectively. Single microelectrode recording (MER) trajectory procedure was experienced in 65% of patients in the CT Fusion group (13/20) and 45% of patients in the MRI group (9/20). The mean recorded STN length from initial to final MER trajectory in the CT Fusion and MRI groups was 4.3 mm (standard deviation [SD] = 1.8 mm)/5.1 mm (SD = 0.5 mm) and 3.6 mm (SD = 1.7 mm) (P = 0.214)/4.5 mm (SD = 0.7 mm) (P = 0.006), respectively. The final recorded STN length was significantly longer in the CT Fusion group.

CONCLUSIONS

In-frame-based stereotactic STN targeting, an image fusion technique between stereotactic CT and MRI, can record a significantly longer STN length through limited MER compared with MRI alone. Whether this could translate into better clinical outcome and less morbidity still need a large and randomized trial.

Optimal MRI methods for direct stereotactic targeting of the subthalamic nucleus and globus pallidus

OBJECTIVE

Reliable identification of the subthalamic nucleus (STN) and globus pallidus interna (GPi) is critical for deep brain stimulation (DBS) of these structures. The purpose of this study was to compare the visibility of the STN and GPi with various MRI techniques and to assess the suitability of each technique for direct stereotactic targeting.

METHODS

MR images were acquired from nine volunteers with T2- and proton density-weighted (PD-W) fast spin echo, susceptibility-weighted imaging (SWI), phase-sensitive inversion recovery and quantitative T1, T2 and T2* mapping sequences. Contrast-to-noise ratios (CNR) for the STN and GPi were calculated for all sequences. Targeting errors on SWI were evaluated on magnetic susceptibility maps. The sequences demonstrating the best conspicuity of DBS target structures (SWI and T2*) were then applied to ten patients with movement disorders, and the CNRs for these techniques were assessed.

RESULTS

SWI offers the highest CNR for the STN, but standard PD-W images provide the best CNR for the pallidum. Susceptibility maps indicated that the GPi margins may be shifted slightly on SWI, although no shifts were seen for the STN.

CONCLUSION

SWI may improve the visibility of the STN on pre-operative MRI, potentially improving the accuracy of direct stereotactic targeting.

Automated 3-dimensional brain atlas fitting to microelectrode recordings from deep brain stimulation surgeries

OBJECTIVE

Deep brain stimulation (DBS) surgeries commonly rely on brain atlases and microelectrode recordings (MER) to help identify the target location for electrode implantation. We present an automated method for optimally fitting a 3-dimensional brain atlas to intraoperative MER and predicting a target DBS electrode location in stereotactic coordinates for the patient.

METHODS

We retrospectively fit a 3-dimensional brain atlas to MER points from 10 DBS surgeries targeting the subthalamic nucleus (STN). We used a constrained optimization algorithm to maximize the MER points correctly fitted (i.e., contained) within the appropriate atlas nuclei. We compared our optimization approach to conventional anterior commissure-posterior commissure (AC/PC) scaling, and to manual fits performed by four experts. A theoretical DBS electrode target location in the dorsal STN was customized to each patient as part of the fitting process and compared to the location of the clinically defined therapeutic stimulation contact.

RESULTS

The human expert and computer optimization fits achieved significantly better fits than the AC/PC scaling (80, 81, and 41% of correctly fitted MER, respectively). However, the optimization fits were performed in less time than the expert fits and converged to a single solution for each patient, eliminating interexpert variance.

CONCLUSIONS AND SIGNIFICANCE

DBS therapeutic outcomes are directly related to electrode implantation accuracy. Our automated fitting techniques may aid in the surgical decision-making process by optimally integrating brain atlas and intraoperative neurophysiological data to provide a visual guide for target identification.

Subthalamic nucleus deep brain stimulation in elderly patients--analysis of outcome and complications

Background

There is an ongoing discussion about age limits for deep brain stimulation (DBS). Current indications for DBS are tremor-dominant disorders, Parkinson's disease, and dystonia. Electrode implantation for DBS with analgesia and sedation makes surgery more comfortable, especially for elderly patients. However, the value of DBS in terms of benefit-risk ratio in this patient population is still uncertain.

Methods

Bilateral electrode implantation into the subthalamic nucleus (STN) was performed in a total of 73 patients suffering from Parkinson's disease. Patients were analyzed retrospectively. For this study they were divided into two age groups: group I (age <65 years, n = 37) and group II (age ≥ 65 years, n = 36). Examinations were performed preoperatively and at 6-month follow-up intervals for 24 months postoperatively. Age, UPDRS motor score (part III) on/off, Hoehn & Yahr score, Activity of Daily Living (ADL), L-dopa medication, and complications were determined.

Results

Significant differences were found in overall performance determined as ADL scores (group I: 48/71 points, group II: 41/62 points [preoperatively/6-month postoperatively]) and in the rate of complications (group I: 4 transient psychosis, 4 infections in a total of 8 patients, group II: 2 deaths [unrelated to surgery], 1 intracerebral hemorrhage, 7 transient psychosis, 3 infections, 2 pneumonia in a total of 13 patients), (p < 0.05). Interestingly, changes in UPDRS scores, Hoehn & Yahr scores, and L-dopa medication were not statistically different between the two groups.

Conclusion

DBS of the STN is clinically as effective in elderly patients as it is in younger ones. However, a more careful selection and follow-up of the elderly patients are required because elderly patients have a higher risk of surgery-related complications and a higher morbidity rate.

Conventional MRI Is Inadequate to Delineate the Relationship between the Red Nucleus and Subthalamic Nucleus in Parkinson’s Disease

BACKGROUND

An understanding of the relationships between the anterior commissure-posterior commissure line (AC-PC), the subthalamic nucleus (STN), and red nucleus (RN) is imperative if these structures are to be used for targeting in deep brain stimulation. Currently, these relationships are incompletely understood and difficult to assess using conventional MRI. We examined the location and relationships of the STN and the RN to the AC-PC line and to each other in order to provide a greater understanding of their utility when targeting the STN, and the consistency of these anatomic relationships when examined using conventional MRI.

METHODS

A total of 52 STN and RN in 26 patients with Parkinson's disease were evaluated on T2-weighted MR images. The anterior and posterior commissures and the border coordinates of the STN and RN were derived using frame coordinates. The distances from the midcommissural point (mcp) to the centers of the STN and RN, the diameters for each nucleus, and the distances between the nuclei were calculated in the x-, y-, and z-axes.

RESULTS

The mean AC-PC length was 26.1 +/- 1.3 mm. The distance from the mcp to the center of the STN was 10 +/- 0.7 mm in the x-axis, 0.2 +/- 0.7 mm in the y-axis, and 3.3 +/- 0.9 mm in the z-axis. The distance from the mcp to the center of the RN was 4.7 +/- 0.6 mm in the x-axis, -5.9 +/- 1.0 mm in the y-axis, and 6.1 +/- 1.3 mm in the z-axis. The distance between the STN and RN was 2.3 +/- 0.7 mm in the x-axis, 2.1 +/- 1.0 mm in the y-axis, and -0.2 +/- 1.3 mm in the z-axis.

CONCLUSIONS

Although recent studies imply that the RN can be used as a relatively consistent marker for the position of the STN, the present data suggest otherwise. These data indicate that a single targeting method may be inadequate given the resolution of conventional MRI, and that it is imperative to use multiple anatomical measurements when targeting the STN for deep brain stimulation in Parkinson's disease.

Microelectrode recording can be a good adjunct in magnetic resonance image-directed subthalamic nucleus deep brain stimulation for parkinsonism

BACKGROUND

The contribution of MER to improving bilateral STN-DBS is debatable. To resolve the controversy and elucidate the role of MER in DBS, we compared the outcome of bilateral STN-DBS surgery with and without MER in parkinsonian patients.

METHODS

From February 2002 to November 2002, the first 7 of 13 consecutive parkinsonian patients received STN-DBS without MER (group A), and the last 6 received STN-DBS with MER (group B). Pre- and postoperative assessments included scoring of UPDRS with video taping, and MR images.

RESULTS

The mean Hoehn and Yahr stage was 3.6 in group A and 4.0 in group B. The mean follow-up was 7.4 months for group A and 5.3 months for group B. The mean coordinates of the tip of the permanent electrode relative to the mid-commissural point were x = 8.1 mm, y = 4.3 mm, and z = 5.9 mm for group A and x = 10.6 mm, y = 4.1 mm, and z = 6.9 mm for group B. When levodopa was withdrawn from group A for 12 hours at follow-up, the postoperative UPDRS total score improved by 27.6% (P = .01) and the motor score by 25.4% (P = .02); their LEDD decreased by 17.5% (P = .03). In group B, the postoperative UPDRS total score improved by 49.3% (P = .00002) and the motor score by 45.2% (P = .0004); LEDD decreased by 48.5% (P = .01).

CONCLUSIONS

Although STN-DBS is a promising surgical modality for advanced parkinsonian patients, there is an inevitable learning curve associated with adopting this new procedure. Intraoperative MER is an effective way to ensure correct electrode placement in the STN. With the assistance of intraoperative MER, the outcome of STN-DBS can be improved significantly.

Deep brain stimulation: Preoperative issues

Numerous factors need to be taken into account in deciding whether a patient with Parkinson's disease (PD) is a candidate for deep brain stimulation. Patient-related personal factors including age and the presence of other comorbid disorders need to be considered. Neuropsychological and neuropsychiatric concerns relate both to the presurgical status of the patient and to the potential for surgery to result in new problems postoperatively. A number of factors related to the underlying PD need to be considered, including the specific parkinsonian motor indications (e.g., tremor, bradykinesia, gait dysfunction), previous medical therapies, including benefit from current therapy and adverse effects, and past surgical treatments. Definable causes of Parkinsonism, particularly atypical Parkinsonisms, should be considered. Finally, methods of evaluating outcomes should be defined and formalized. This is a report from the Consensus on Deep Brain Stimulation for Parkinson's Disease, a project commissioned by the Congress of Neurological Surgeons and the Movement Disorder Society (MDS). The report has been endorsed by the Scientific Issues Committee of the MDS and the American Society of Stereotactic and Functional Neurosurgery. It outlines answers to a series of questions developed to address all aspects of deep brain stimulation preoperative decision-making.

Electrophysiological mapping for the implantation of deep brain stimulators for Parkinson's disease and tremor

The vast majority of centers use electrophysiological mapping techniques to finalize target selection during the implantation of deep brain stimulation (DBS) leads for the treatment of Parkinson's disease and tremor. This review discusses the techniques used for physiological mapping and addresses the questions of how various mapping strategies modify target selection and outcome following subthalamic nucleus (STN), globus pallidus internus (GPi), and ventralis intermedius (Vim) deep brain stimulation. Mapping strategies vary greatly across centers, but can be broadly categorized into those that use microelectrode or semimicroelectrode techniques to optimize position prior to implantation and macrostimulation through a macroelectrode or the DBS lead, and those that rely solely on macrostimulation and its threshold for clinical effects (benefits and side effects). Microelectrode criteria for implantation into the STN or GPi include length of the nucleus recorded, presence of movement-responsive neurons, and/or distance from the borders with adjacent structures. However, the threshold for the production of clinical benefits relative to side effects is, in most centers, the final, and sometimes only, determinant of DBS electrode position. Macrostimulation techniques for mapping, the utility of microelectrode mapping is reflected in its modification of electrode position in 17% to 87% of patients undergoing STN DBS, with average target adjustments of 1 to 4 mm. Nevertheless, with the absence of class I data, and in consideration of the large number of variables that impact clinical outcome, it is not possible to conclude that one technique is superior to the other in so far as motor Unified Parkinson's Disease Rating Scale outcome is concerned. Moreover, mapping technique is only one out of many variables that determine the outcome. The increase in surgical risk of intracranial hemorrhage correlated to the number of microelectrode trajectories must be considered against the risk of suboptimal benefits related to omission of this technique.

Use of the NeuroMate stereotactic robot in a frameless mode for functional neurosurgery

BACKGROUND

The aim of this paper is to describe the use of the NeuroMate stereotactic robot for functional neurosurgery with a novel frameless ultrasound registration system.

METHODS

A retrospective review of the evaluation and clinical use of the NeuroMate stereotactic robot in a frameless mode for functional neurosurgery.

RESULTS

Prior to its clinical use a phantom study was undertaken to demonstrate an application accuracy of 1.29 mm. Subsequently the robot has been used in 153 functional neurosurgical procedures including 113 deep brain stimulator implantations.

CONCLUSIONS

The NeuroMate stereotactic robot in a frameless mode has sufficient accuracy for a range of functional neurosurgical procedures, including movement disorder surgery.

Motor and non motor effects during intraoperative subthalamic stimulation for Parkinson's disease

Spatial distribution of the clinical effects induced by deep brain stimulation during the intraoperative investigation of the subthalamic nucleus (STN) for Parkinson's disease (PD) was analysed in 17 patients under local anesthesia. The stimulation parameters were 130 hertz, 100 micros, and voltage ranged from 0.05 to 5 volts. Optimal motor response was assessed as the total and lasting disappearance of wrist rigidity on the side opposite to stimulation. Among the adverse effects induced by stimulation, special attention was given to frequently observed autonomic effects (AE). Full motor response was achieved in 49.2% of the 301 points evaluated,with a mean voltage (MV) of 0.94 volts; paresthesiae occurred in 6.6% (MV: 2 volts), dystonia in 10.6% (MV: 3.4 volts), autonomic effects in 19.6% (MV: 3.1 volts) and oculomotor effects in 31.6% (MV: 3 volts). The motor target was located in the posterodorsal part of the nucleus and the optimal point for motor response was close to the superior limit of the nucleus. Whereas other adverse effects occurred relatively far from the motor target, AE occurred with statistic significance near this point. Their neural substrates, such as limbic system and their relationship with postoperative behavioral disorders, are discussed.

Immediate and sustained relief of levodopa-induced dyskinesias after dorsal relocation of a deep brain stimulation lead. Case report

The authors demonstrate that high-frequency electrical stimulation dorsal to the subthalamic nucleus (STN) can directly suppress levodopa-induced dyskinesias. This 63-year-old woman with idiopathic Parkinson disease underwent surgery for placement of bilateral subthalamic deep brain stimulation (DBS) electrodes to control progressive rigidity, motor fluctuations, and levodopa-induced dyskinesias. The model 3389 DBS leads were implanted with microelectrode guidance. Magnetic resonance imaging confirmed proper placement of the leads. Postoperatively the patient exhibited improvement in all of her parkinsonian symptoms; however, her right leg dyskinesias had not improved. Based on their previous experiences treating levodopa-induced dyskinesias with subthalamic stimulation through the more dorsally located contacts of the model 3387 lead, the authors withdrew the implanted 3389 lead 3 mm. Following relocation of the lead they were able to suppress the right leg dyskinesias by using the most dorsal contacts. The patient's dopaminergic medication intake increased slightly. These findings indicate that electrical stimulation dorsal to the STN can directly suppress levodopa-induced dyskinesias independent of dopaminergic medication changes. The 3389 lead may provide inadequate coverage of the subthalamic region for some patients.