Anatomical Determinants of STN Coordinate Shift in Idiopathic Parkinson's Disease DBS Surgery

OBJECTIVE

This study examines how anatomical variations influence the targeting coordinates of the subthalamic nucleus (STN) in patients with Idiopathic Parkinson's Disease (IPD) undergoing Deep Brain Stimulation (DBS), with the goal of enhancing targeting accuracy.

METHODS

A retrospective analysis was performed on 202 STNs from patients who received bilateral STN-DBS surgery. Pre- and postoperative imaging data were used to determine accurate STN coordinates, while brain volume measurements, ventricle size, Evans Index, and AC -PC length were analyzed. Atrophy grading scales were also applied. Correlation and regression analyses assessed the relationship between the STN target location and all anatomical parameters on the x, y, and z axes.

RESULTS

Age showed a significant positive correlation with lateral STN coordinate shift on the x-axis, with each additional year leading to a 0.046 mm shift. An increase in peripheral gray matter volume and a decrease in white matter volume were significantly associated with the lateral displacement of the STN. Total ventricle volume demonstrated a positive correlation with STN shift on both the x-axis (0.0227 mm per cm3 increase) and z-axis (0.0087 mm per cm3 increase). Significant correlations were also found for the Evans Index with lateral shift on the x-axis and for AC-PC length with vertical shifts.

CONCLUSION

Anatomical factors, such as brain volume, ventricle size, Evans Index, AC-PC length, and atrophy scores, significantly influence STN localization in PD patients undergoing DBS. Accounting for these shifts during surgical planning may improve electrode placement accuracy and enhance therapeutic outcomes, underscoring the importance of personalized targeting strategies.

Refining Stereotaxic Deep Brain Stimulation Surgery Procedures for Parkinson Disease in Pursuit of Zero Pneumocephalus: 2-Dimensional Operative Video

BACKGROUND AND OBJECTIVES

Deep brain stimulation (DBS) is a well-established intervention for alleviating both motor and nonmotor symptoms of Parkinson disease. However, a common complication of stereotaxic DBS surgery is pneumocephalus, which can compromise electrode accuracy, complicate postoperative assessments, and negatively affect the long-term outcomes of DBS surgery. This report proposes a comprehensive and robust set of recommendations aimed at optimizing DBS surgical protocols to achieve zero pneumocephalus outcomes.

METHODS

A retrospective analysis was undertaken on 138 patients with Parkinson disease who underwent simultaneous bilateral stereotaxic DBS targeting either the subthalamic nucleus or the globus pallidus internus at a single institution. The study compared the pneumocephalus volume and postsurgical electrode tip displacement between the original surgical technique and a refined procedure that incorporated modified supine position, dural puncture, and liquid sealing.

RESULTS

With the implementation of the refined procedure, the volume of pneumocephalus significantly decreased from 14.40 ± 17.00 to 0.32 ± 1.02 mL, with 92.9% of patients showing no visible pneumocephalus or intracranial air less than 1 mL. In addition, the refined procedure was associated with less electrode tip displacement in the postoperative stage.

CONCLUSION

The refined procedure effectively minimized the average pneumocephalus volume to approximately 0, and bilateral DBS electrodes exhibited enhanced stability during the postoperative stage.

Deep Brain Stimulation Lead Functional Repositioning After Spontaneous Pneumocephalus Resorption: A Clinical Case Presentation and Systematic Review

Deep brain stimulation (DBS) has become a critical intervention for managing advanced Parkinson's disease (PD), particularly for patients whose symptoms are no longer controlled by medication. This report details the case of a 61-year-old male with PD who experienced electrode displacement due to pneumocephalus following DBS surgery targeting the subthalamic nucleus (STN). Initial imaging revealed a significant subdural air volume causing electrode displacement. However, one month later, spontaneous pneumocephalus resorption led to the functional repositioning of the electrodes, restoring proper function and negating the need for reoperation. The accompanying systematic review analyzed 24 studies, involving 1,439 patients across 12 countries, to assess the occurrence and management in this specific scenario. Findings showed electrode displacement occurred in 75% of cases, but spontaneous repositioning happened only in 12.5%, typically with air volumes below 10 cm³. Larger volumes often required surgical intervention, though definitive thresholds for action remain unclear. The review highlights inconsistencies in managing this complication, emphasizing the need for clearer protocols to improve outcomes. This work underscores the rarity of spontaneous electrode realignment and the importance of careful evaluation of pneumocephalus volume and patient symptoms. It advocates for evidence-based management strategies to balance clinical intervention with the potential for natural resolution, aiming to enhance DBS efficacy and patient quality of life. Further research is necessary to establish standardized guidelines for addressing this complication.

Placement accuracy of the second electrode in bilateral deep brain stimulation surgery

PURPOSE

Due to brain shift during bilateral deep brain stimulation (DBS) surgery, placement of the second electrode may be subjected to more error than that of the first electrode. The authors aimed to investigate the accuracy of second electrode placement in this setting.

MATERIALS AND METHODS

Fifty-five patients with Parkinson's disease who underwent bilateral DBS surgery (110 electrodes) were retrospectively evaluated. The targets were subthalamic nucleus (STN) and globus pallidus interna (GPi) in 40 and 15 cases, respectively. Preoperative planning and postoperative electrode images were co-registered to compare the error margin between the two sides.

RESULTS

There is a statistically significant difference in the directional axis error along the y axis only when comparing each laterality (posterior 0.04 ± 1.21 mm vs anterior 0.41 ± 1.07 mm, p = 0.006). There is no significant difference of other error parameters, final track location, and number of microelectrode recording passes between the two sides. In a subgroup analysis, there is a significant difference in directional axis error along the y axis only in the STN subgroup (posterior 0.40 ± 1.05 mm vs anterior 0.18 ± 1.04 mm, p = 0.003).

CONCLUSION

Although a statistically significant difference in directional axis error along the y axis was found between first and second electrode placements in the STN group but not in the GPi group, its magnitude is well below the clinically significant threshold.

Safety and efficiency of deep brain stimulation in the elderly patients with Parkinson's disease

AIMS

Deep brain stimulation (DBS) is not routinely performed in elderly patients (≥75 years old) to date because of concerns about complications and decreased benefit. This study aimed to evaluate the safety and efficacy of DBS in elderly patients with Parkinson's disease.

METHODS

A retrospective analysis was performed using data from 40 elderly patients from four centers who were treated with neurosurgical robot-assisted DBS between September 2016 and December 2021. These patients were followed up for a minimum period of 2 years, with a subgroup of nine patients followed up for 5-7 years. Patient demographic characteristics, surgical information, pre- and postoperative motor scores, non-motor scores, activities of daily living, and complications were retrospectively analyzed.

RESULTS

The mean surgical procedure duration was 1.65 ± 0.24 h, with a mean electrode implantation duration of 1.10 ± 0.23 h and a mean pulse generator implantation duration of 0.55 ± 0.07 h. The mean pneumocephalus volume, electrode fusion error, and Tao's DBS surgery scale were 16.23 ± 12.81 cm3, 0.81 ± 0.23 mm, and 77.63 ± 8.08, respectively. One patient developed a skin infection, and the device was removed. The Unified Parkinson's disease rating scale, Unified Parkinson's disease rating scale of Part III, tremor, rigidity, bradykinesia, axial, and Barthel index for activities of daily living (ADL-Barthel) scores significantly improved at the 2-year follow-up (p < 0.05). The levodopa equivalent daily dose (LEDD) was significantly reduced at the 2-year follow-up (p < 0.05). However, the Montreal cognitive assessment, Hamilton depression scale, and Hamilton anxiety scale scores did not significantly change during the 2-year follow-up (p > 0.05). Additionally, in the subgroup with a 5-year follow-up, the motor symptoms, ADL-Barthel score, and cognitive function worsened over time compared to baseline. However, there was still an improvement in motor symptoms and ADL with DBS on-stimulation compared with the off-stimulation state. The LEDD increased 5 years after surgery compared to that at baseline. Eleven patients had passed away during follow-up, the mean survival time was 38.3 ± 17.3 months after surgery, and the mean age at the time of death was 81.2 (range 75-87) years.

CONCLUSION

Robot-assisted DBS surgery for the elderly patients with Parkinson's disease is accurate and safe. Motor symptoms and ADL significantly improve and patients can benefit from long-term neuromodulation, which may decrease the risk of death.

Preventing Shift from Pneumocephalus During Deep Brain Stimulation Surgery: Don't Give Up the 'Fork in the Brain'

Clinical vignette

We present the case of a patient who developed intra-operative pneumocephalus during left globus pallidus internus deep brain stimulation (DBS) placement for Parkinson's disease (PD). Microelectrode recording (MER) revealed that we were anterior and lateral to the intended target.

Clinical dilemma

Clinically, we suspected brain shift from pneumocephalus. Removal of the guide-tube for readjustment of the brain target would have resulted in the introduction of movement resulting from brain shift and from displacement from the planned trajectory.

Clinical solution

We elected to leave the guide-tube cannula in place and to pass the final DBS lead into a channel that was located posterior-medially from the center microelectrode pass.

Gap in knowledge

Surgical techniques which can be employed to minimize brain shift in the operating room setting are critical for reduction in variation of the final DBS lead placement. Pneumocephalus after dural opening is one potential cause of brain shift. The recognition that the removal of a guide-tube cannula could worsen brain shift creates an opportunity for an intraoperative team to maintain the advantage of the 'fork' in the brain provided by the initial procedure's requirement of guide-tube placement.

Minimizing pneumocephalus during deep brain stimulation surgery

BACKGROUND

Deep brain stimulation (DBS) surgery is an effective treatment for movement disorders. Introduction of intracranial air following dura opening in DBS surgery can result in targeting inaccuracy and suboptimal outcomes. We develop and evaluate a simple method to minimize pneumocephalus during DBS surgery.

METHODS

A retrospective analysis of prospectively collected data was performed on patients undergoing DBS surgery at our institution from 2014 to 2022. A total of 172 leads placed in 89 patients undergoing awake or asleep DBS surgery were analyzed. Pneumocephalus volume was compared between leads placed with PMT and leads placed with standard dural opening. (112 PMT vs. 60 OPEN). Immediate post-operative high-resolution CT scans were obtained for all leads placed, from which pneumocephalus volume was determined through a semi-automated protocol with ITK-SNAP software. Awake surgery was conducted with the head positioned at 15-30°, asleep surgery was conducted at 0°.

RESULTS

PMT reduced pneumocephalus from 11.2 cm3±9.2 to 0.8 cm3±1.8 (P<0.0001) in the first hemisphere and from 7.6 cm3 ± 8.4 to 0.43 cm3 ± 0.9 (P<0.0001) in the second hemisphere. No differences in adverse events were noted between PMT and control cases. Lower rates of post-operative headache were observed in PMT group.

CONCLUSION

We present and validate a simple yet efficacious technique to reduce pneumocephalus during DBS surgery.

The Effect of Surgical Positioning on Pneumocephalus in Subthalamic Nucleus Deep Brain Stimulation Surgery for Parkinson Disease

OBJECTIVES

This research analyzed the effect of surgical positioning on postoperative pneumocephalus and assessed additional potential risk factors of pneumocephalus in subthalamic nucleus (STN) deep brain stimulation (DBS) for Parkinson disease (PD).

MATERIALS AND METHODS

In this study, 255 consecutive patients with PD who received bilateral STN DBS under general anesthesia were retrospectively included. Of these, 180 patients underwent surgery with their heads in an elevated position, and 75 patients underwent surgery in a supine position. The postoperative pneumocephalus volume was compared between the two groups. Other potential risk factors for pneumocephalus also were analyzed.

RESULTS

The mean pneumocephalus volume for the group with elevated-head positioning (16.76 ± 15.23 cm3) was greater than for the supine group (3.25 ± 8.78 cm3) (p < 0.001). Multivariable analysis indicated that the pneumocephalus volume was related to surgical positioning, lateral trajectory angle, intraoperative mean arterial pressure (MAP), microelectrode recording (MER) passage number, brain atrophy degree, and the anterior trajectory angle. No correlation was found between pneumocephalus and age, sex, duration of PD, surgery length, or intracranial volume. In the subgroup analysis, the pneumocephalus volume exhibited a negative correlation with intraoperative MAP (r = -0.210, p = 0.005) and positive correlations with degree of brain atrophy (r = 0.242, p = 0.001) and MER passage number (r = 0.184, p = 0.014) in the elevated-head group. Specifically, an MER passage number > 3 was a significant risk factor for pneumocephalus in the elevated-head group. A positive correlation was observed between the pneumocephalus volume and the lateral trajectory angle in both groups (elevated-head positioning, r = 0.153, p = 0.041; supine positioning, r = 0.546, p < 0.001).

CONCLUSIONS

In patients with PD who were anesthetized and receiving STN DBS, supine positioning reduced pneumocephalus volume compared with patients with PD receiving STN DBS with their heads elevated. The pneumocephalus volume was negatively correlated with intraoperative MAP and positively correlated with the degree of brain atrophy, the lateral trajectory angle, and the MER passage number.

Complications of deep brain stimulation in Parkinson's disease: a single-center experience of 517 consecutive cases

BACKGROUND

The number of deep brain stimulation (DBS) procedures is rapidly rising as well as the novel indications. Reporting adverse events related to surgery and to the hardware used is essential to define the risk-to-benefit ratio and develop novel strategies to improve it.

OBJECTIVE

To analyze DBS complications (both procedure-related and hardware-related) and further assess potential predictive factors.

METHODS

Five hundred seventeen cases of DBS for Parkinson's disease were performed between 2006 and 2021 in a single center (mean follow-up: 4.68 ± 2.86 years). Spearman's Rho coefficient was calculated to search for a correlation between the occurrence of intracerebral hemorrhage (ICH) and the number of recording tracks. Multiple logistic regression analyzed the probability of developing seizures and ICH given potential risk factors. Kaplan-Meier curves were performed to analyze the cumulative proportions of hardware-related complications.

RESULTS

Mortality rate was 0.2%, while permanent morbidity 0.6%. 2.5% of cases suffered from ICH which were not influenced by the number of tracks used for recordings. 3.3% reported seizures that were significantly affected by perielectrode brain edema and age. The rate of perielectrode brain edema was significantly higher for Medtronic's leads compared to Boston Scientific's (Χ2(1)= 5.927, P= 0.015). 12.2% of implants reported Hardware-related complications, the most common of which were wound revisions (7.2%). Internal pulse generator models with smaller profiles displayed more favorable hardware-related complication survival curves compared to larger designs (X2(1)= 8.139, P= 0.004).

CONCLUSION

Overall DBS has to be considered a safe procedure, but future research is needed to decrease the rate of hardware-related complications which may be related to both the surgical technique and to the specific hardware's design. The increased incidence of perielectrode brain edema associated with certain lead models may likewise deserve future investigation.

MER and increased operative time are not risk factors for the formation of pneumocephalus during DBS

Although only recently directional leads have proven their potential to compensate for sub-optimally placed electrodes, optimal lead positioning remains the most critical factor in determining Deep Brain Stimulation (DBS) outcome. Pneumocephalus is a recognized source of error, but the factors that contribute to its formation are still a matter of debate. Among these, operative time is one of the most controversial. Because cases of DBS performed with Microelectrode Recordings (MER) are affected by an increase in surgical length, it is useful to analyze whether MER places patients at risk for increased intracranial air entry. Data of 94 patients from two different institutes who underwent DBS for different neurologic and psychiatric conditions were analyzed for the presence of postoperative pneumocephalus. Operative time and use of MER, as well as other potential risk factors for pneumocephalus (age, awake vs. asleep surgery, number of MER passages, burr hole size, target and unilateral vs. bilateral implants) were examined. Mann-Whitney U and Kruskal-Wallis tests were utilized to compare intracranial air distributions across groups of categorical variables. Partial correlations were used to assess the association between time and volume. A generalized linear model was created to predict the effects of time and MER on the volume of intracranial air, controlling for other potential risk factors identified: age, number of MER passages, awake vs. asleep surgery, burr hole size, target, unilateral vs. bilateral surgery. Significantly different distributions of air volume were noted between different targets, unilateral vs. bilateral implants, and number of MER trajectories. Patients undergoing DBS with MER did not present a significant increase in pneumocephalus compared to patients operated without (p = 0.067). No significant correlation was found between pneumocephalus and time. Using multivariate analysis, unilateral implants exhibited lower volumes of pneumocephalus (p = 0.002). Two specific targets exhibited significantly different volumes of pneumocephalus: the bed nucleus of the stria terminalis with lower volumes (p < 0.001) and the posterior hypothalamus with higher volumes (p = 0.011). MER, time, and other parameters analyzed failed to reach statistical significance. Operative time and use of intraoperative MER are not significant predictors of pneumocephalus during DBS. Air entry is greater for bilateral surgeries and may be also influenced by the specific stimulated target.

Bilateral deep brain stimulation of the subthalamic nucleus: Targeting differences between the first and second side

INTRODUCTION AND OBJECTIVES

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a recognized treatment for drug-refractory Parkinson's disease (PD). However, the therapeutic success depends on the accuracy of targeting. This study aimed to evaluate potential accuracy differences in the placement of the first and second electrodes implanted, by comparing chosen electrode trajectories, STN activity detected during microelectrode recording (MER), and the mismatch between the initially planned and final electrode positions on each side.

MATERIALS AND METHODS

In this retrospective cohort study, we analyzed data from 30 patients who underwent one-stage bilateral DBS. For most patients, three arrays of microelectrodes were used to determine the physiological location of the STN. Final target location depended also on the results of intraoperative stimulation. The choice of central versus non-central channels was compared. The Euclidean vector deviation was calculated using the initially planned coordinates and the final position of the tip of the electrode according to a CT scan taken at least a month after the surgery.

RESULTS

The central channel was chosen in 70% of cases on the first side and 40% of cases on the second side. The mean length of high-quality STN activity recorded in the central channel was longer on the first side than the second (3.07±1.85mm vs. 2.75±1.94mm), while in the anterior channel there were better MER recordings on the second side (1.59±2.07mm on the first side vs. 2.78±2.14mm on the second). Regarding the mismatch between planned versus final electrode position, electrodes on the first side were placed on average 0.178±0.917mm lateral, 0.126±1.10mm posterior and 1.48±1.64mm inferior to the planned target, while the electrodes placed on the second side were 0.251±1.08mm medial, 0.355±1.29mm anterior and 2.26±1.47mm inferior to the planned target.

CONCLUSION

There was a tendency for the anterior trajectory to be chosen more frequently than the central on the second side. There was also a statistically significant deviation of the second electrodes in the anterior and inferior directions, when compared to the electrodes on the first side, suggesting that another cause other than brain shift may be responsible. We should therefore factor this during planning for the second implanted side. It might be useful to plan the second side more anteriorly, possibly reducing the number of MER trajectories tested and the duration of surgery.

Comparison of dural puncture and dural incision in deep brain stimulation surgery: A simple but worthwhile technique modification

Background

The accuracy of the deep brain stimulation (DBS) electrode placement is influenced by a myriad of factors, among which pneumocephalus and loss of cerebrospinal fluid that occurs with dural opening during the surgery are considered most important. This study aimed to describe an effective method for decreasing pneumocephalus by comparing its clinical efficacy between the two different methods of opening the dura.

Materials and methods

We retrospectively compared two different methods of opening the dura in 108 patients who underwent bilateral DBS surgery in our center. The dural incision group comprised 125 hemispheres (58 bilateral and 9 unilateral) and the dural puncture group comprised 91 (41 bilateral and 9 unilateral). The volume of intracranial air, dural opening time, intraoperative microelectrode recordings (MERs), postoperative electrode displacement, clinical efficacy, and complications were examined. Spearman correlation analysis was employed to identify factors associated with the volume of intracranial air and postoperative electrode displacement.

Results

The volume of intracranial air was significantly lower (0.35 cm³ vs. 5.90 cm³) and dural opening time was significantly shorter (11s vs. 35s) in the dural puncture group. The volume of intracranial air positively correlated with dural opening time. During surgery, the sensorimotor area was longer (2.47 ± 1.36 mm vs. 1.92 ± 1.42 mm) and MERs were more stable (81.82% vs. 47.73%) in the dural puncture group. Length of the sensorimotor area correlated negatively with the volume of intracranial air. As intracranial air was absorbed after surgery, significant anterior, lateral, and ventral electrode displacement occurred; the differences between the two groups were significant (total electrode displacement, 1.0mm vs. 1.4mm). Electrode displacement correlated positively with the volume of intracranial air. Clinical efficacy was better in the dural puncture group than the dural incision group (52.37% ± 16.18% vs. 43.93% ± 24.50%), although the difference was not significant.

Conclusion

Our data support the hypothesis that opening the dura via puncture rather than incision when performing DBS surgery reduces pneumocephalus, shortens dural opening time, enables longer sensorimotor area and more stable MERs, minimizes postoperative electrode displacement, and may permit a better clinical efficacy.

A Modified Dura Puncture Procedure to Reduce Brain Shift in Deep Brain Stimulation Surgery: One Institution's Experience

Objective

The therapeutic effect of deep brain stimulation (DBS) surgery mainly depends on the accuracy of electrode placement and the reduction in brain shift. Among the standard procedures, cerebrospinal fluid (CSF) loss or pneumocephalus caused by dura incision (DI) is thought to be the main reason for brain shift and inaccuracy of electrode placement. In the current study, we described a modified dura puncture (DP) procedure to reduce brain shift and compare it with the general procedure of DBS surgery in terms of electrode placement accuracy.

Materials and Methods

We retrospectively analyzed a series of 132 patients who underwent DBS surgery in Wuhan Union Hospital from December 2015 to April 2021. According to the different surgery procedures, patients were classified into two cohorts: the DI group (DI cohort) had 49 patients who receive the general procedure, and the DP group (DP cohort) had 83 patients who receive the modified procedure. Postoperative pneumocephalus volume (PPV) and CSF loss volume, electrode fusion error (EFE), and trajectory number were calculated. Meanwhile, intraoperative electrophysiological signal length (IESL), electrode implantation duration, and other parameters were analyzed.

Results

In the current study, we introduced an improved electrode implantation procedure for DBS surgery named the DP procedure. Compared with the general DI cohort (n = 49), the modified DP cohort (n = 83) had a shorter electrode implantation duration (p < 0.0001), smaller PPV, lower CSF leakage volume (p < 0.0001), and smaller EFE (p < 0.0001). There was no significant difference in IESL (p > 0.05) or adverse events (perioperative cerebral haematoma, skin erosion, epilepsy, p > 0.05) between the two cohorts.

Conclusion

The DP procedure is a modified procedure that can reduce brain shift and ensure implantation accuracy during DBS surgery without adverse events.

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.

How accurately are subthalamic nucleus electrodes implanted relative to the ideal stimulation location for Parkinson's disease?

INTRODUCTION

The efficacy of subthalamic nucleus (STN) deep brain stimulation (DBS) in Parkinson's disease (PD) depends on how closely electrodes are implanted relative to an individual's ideal stimulation location. Yet, previous studies have assessed how closely electrodes are implanted relative to the planned location, after homogenizing data to a reference. Thus here, we measured how accurately electrodes are implanted relative to an ideal, dorsal STN stimulation location, assessed on each individual's native imaging. This measure captures not only the technical error of stereotactic implantation but also constraints imposed by planning a suitable trajectory.

METHODS

This cross-sectional study assessed 226 electrodes in 113 consecutive PD patients implanted with bilateral STN-DBS by experienced clinicians utilizing awake, microelectrode guided, surgery. The error (Euclidean distance) between the actual electrode trajectory versus a nominated ideal, dorsal STN stimulation location was determined in each hemisphere on native imaging and predictive factors sought.

RESULTS

The median electrode location error was 1.62 mm (IQR = 1.23 mm). This error exceeded 3 mm in 28/226 electrodes (12.4%). Location error did not differ between hemispheres implanted first or second, suggesting brain shift was minimised. Location error did not differ between electrodes positioned with (48/226), or without, a preceding microelectrode trajectory shift (suggesting such shifts were beneficial). There was no relationship between location error and case order, arguing against a learning effect.

DISCUSSION/CONCLUSION

The proximity of STN-DBS electrodes to a nominated ideal, dorsal STN, stimulation location is highly variable, even when implanted by experienced clinicians with brain shift minimized, and without evidence of a learning effect. Using this measure, we found that assessments on awake patients (microelectrode recordings and clinical examination) likely yielded beneficial intraoperative decisions to improve positioning. In many patients the error is likely to have reduced therapeutic efficacy. More accurate methods to implant STN-DBS electrodes relative to the ideal stimulation location are needed.

Targeting of the Subthalamic Nucleus in Patients with Parkinson's Disease Undergoing Deep Brain Stimulation Surgery

Precise stereotactic targeting of the dorsolateral motor part of the subthalamic nucleus (STN) is paramount for maximizing clinical effectiveness and preventing side effects of deep brain stimulation (DBS) in patients with advanced Parkinson's disease. With recent developments in magnetic resonance imaging (MRI) techniques, direct targeting of the dorsolateral part of the STN is now feasible, together with visualization of the motor fibers in the nearby internal capsule. However, clinically relevant discrepancies were reported when comparing STN borders on MRI to electrophysiological STN borders during microelectrode recordings (MER). Also, one should take into account the possibility of a 3D inaccuracy of up to 2 mm of the applied stereotactic technique. Pneumocephalus and image fusion errors may further increase implantation inaccuracy. Even when implantation has been successful, suboptimal lead anchoring on the skull may cause lead migration during follow-up. Meticulous pre- and intraoperative imaging is therefore indispensable, and so is postoperative imaging when the effects of DBS deteriorate during follow-up. Thus far, most DBS centers employ MRI targeting, multichannel MER, and awake test stimulation in STN surgery, but randomized trials comparing surgery under local versus general anesthesia and additional studies comparing MER-STN borders to high-field MRI-STN may change this clinical practice. Further developments in imaging protocols and improvements in image fusion processes are needed to optimize placement of DBS leads in the dorsolateral motor part of the STN in Parkinson's disease.

Pneumocephalus in subthalamic deep brain stimulation for Parkinson's disease: a comparison of two different surgical techniques considering factors conditioning brain shift and target precision

BACKGROUND

Precise placement of electrodes in deep brain stimulation (DBS) may be influenced by brain shift caused by cerebrospinal fluid leaking or air inflow. We compared accuracy and treatment outcomes between a standard technique and one aiming at reducing brain shift.

METHODS

We retrospectively reviewed 46 patients (92 targets) treated with bilateral subthalamic-DBS for Parkinson's disease. The patients were divided into two groups: group A surgery was performed in supine position with standard burr hole, dural opening, fibrin glue and gelfoam plugging. Group B patients were operated in a semi-sitting position with direct dural puncture to reduce CSF loss. We analysed target deviation on head CT performed immediately after surgery and at 1 month merged with preoperative MRI planning. We recorded pneumocephalus volume, brain atrophy and target correction by intraoperative neurophysiology (ION).

RESULTS

In group A, the mean pneumocephalus volume was 10.55 cm³, mean brain volume 1116 cm³, mean target deviation 1.09 mm and ION corrected 70% of targets. In group B, mean pneumocephalus was 7.60 cm³ (p = 0.3048), mean brain volume 1132 cm³ (p = 0.6526), mean target deviation 0.64 mm (p = 0.0074) and ION corrected 50% of targets (p = 0.4886). Most leads' deviations realigned to the planned target after pneumocephalus reabsorbtion suggesting a deviation caused by displacement of anatomical structures due to brain shift. Definitive lead position was always decided with ION.

CONCLUSIONS

The modified DBS technique significantly reduced errors of electrode placement, though such difference was clinically irrelevant. ION corrected a high amount of trajectories in both groups (70% vs 50%). The choice of either strategy is acceptable.

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

INTRODUCTION

The intersection of Bejjani's line with the well-delineated medial subthalamic nucleus (STN) border on MRI has recently been proposed as an individualized reference in subthalamic deep brain stimulation (DBS) surgery for Parkinson's disease (PD). We, therefore, aimed to investigate the applicability across centers of the medial STN border as a patient-specific reference point in STN DBS for PD and explore anatomical variability between left and right mesencephalic area within patients. Furthermore, we aim to evaluate a recently defined theoretic stimulation "hotspot" in a different center.

METHODS

Preoperative 3-Tesla T2 and susceptibility-weighted images (SWI) were used to identify the intersection of Bejjani's line with the medial STN border in left and right mesencephalic area. The average stereotactic coordinates of the center of stimulation relative to the medial STN border were compared with the predefined theoretic stimulation "hotspot."

RESULTS

Fifty-four patients provided 108 stereotactic coordinates of medial STN borders on both sequences. Significant difference in means was found in the Y-(anteroposterior) and Z-(dorsoventral) directions (T2 vs. SWI; p < 0.001). Mean coordinates in the Y-(anteroposterior) direction differed significantly between left and right mesencephalic area (T2: p < 0.001; SWI: p = 0.021). Sixty-six DBS leads were placed in 36 patients that had finished stimulation programming, and the average stereotactic coordinates of the center of stimulation relative to the medial STN border on T2 sequences were 3.1 mm lateral, 0.7 mm anterior, and 1.8 mm superior, in proximity of the predefined theoretic stimulation "hotspot."

CONCLUSION

The medial STN border is applicable across centers as a reference point for STN DBS surgery for PD and seems suitable in order to account for interindividual and intraindividual anatomical variability if one is aware of the discrepancies between T2-weighted imaging and SWI.

Kinesthetic Cells within the Subthalamic Nucleus and Deep Brain Stimulation for Parkinson Disease

OBJECTIVE

We sought to determine the location of kinesthetic cell clusters within the subthalamic nucleus (STN) on magnetic resonance imaging, adjusted for interindividual anatomic variability by employing the medial STN border as a reference point.

METHODS

We retrospectively localized microelectrode recording-defined kinesthetic cells on 3-Tesla T2-weighted and susceptibility-weighted images in patients who underwent STN deep brain stimulation for Parkinson disease and averaged the stereotactic coordinates. These locations were calculated relative to the nonindividualized midcommissural point (MCP) and, in order to account for interindividual anatomic variability, also calculated relative to the patient-specific intersection of Bejjani line with the medial STN border. Two example patients were selected in order to visualize the discrepancies between the adjusted and nonadjusted theoretic kinesthetic cell clusters on magnetic resonance imaging.

RESULTS

Relative to the MCP, average kinesthetic cell coordinates were 12.3 ± 1.2 mm lateral, 1.7 ± 1.4 mm posterior, and 2.3 ± 1.5 mm inferior. Relative to the medial STN border, mean coordinates were 3.4 ± 1.0 mm lateral, 1.0 ± 1.4 mm anterior, and 1.7 ± 1.5 mm superior on T2-sequences, and on susceptibility-weighted images mean coordinates were 3.2 ± 1.1 mm lateral, 0.8 ± 1.5 mm anterior, and 2.1 ± 1.5 mm superior. The theoretic kinesthetic cell clusters may appear outside the sensorimotor STN when using the MCP, whereas these clusters fall well within the sensorimotor STN when employing the medial STN border as a reference point.

CONCLUSIONS

By using the medial STN border as a patient-specific anatomic reference point in STN deep brain stimulation for Parkinson disease, we accounted for interindividual anatomic variability and provided accurate insight in the clustering of kinesthetic cells within the dorsolateral STN.

Techniques for pneumocephalus and brain shift reduction in DBS surgery: a review of the literature

Deep brain stimulation has become an established therapeutic choice to manage the symptoms of medically refractory Parkinson's disease. Its efficacy is highly dependent on the accuracy of electrodes' positioning in the correct anatomical target. During DBS procedure, the opening of the dura mater induces the displacement of neural structures. This effect mainly depends on the loss of the physiological negative intracranial pressure, air inflow, and loss of cerebrospinal fluid. Several studies concentrated on correcting surgical techniques for DBS electrodes' positioning in order to reduce pneumocephalus which may result in therapeutic failure. The authors focused in particular on reducing the brain air window and maintaining the pressure gradient between intra- and extracranial compartments. A significant reduction of pneumocephalus and brain shift was obtained by excluding the opening of the subarachnoid space, by covering the dura mater opening with tissue sealant and by reducing the intracranial pressure in general anesthesia. Smaller burr hole diameters were not statistically relevant for reducing air inflow and displacement of anatomical targets. The review of the literature showed that conserving a physiological intra-extracranial pressure gradient plays a fundamental role in avoiding pneumocephalus and consequent displacement of brain structures, which improves surgical accuracy and DBS long-term results.

Assessment of Deep Brain Stimulation Implantation Surgery: A Practical Scale

BACKGROUND

Patients requiring deep brain stimulation (DBS) will undergo extensive preoperative and postoperative evaluations. However, the field lacks a robust scoring system for quantifying the outcomes of DBS surgery. We sought to determine whether a practical scale could assess the outcomes of DBS surgery and the clinical significance.

METHODS

A retrospective study was performed of the data from 150 patients who had undergone DBS from February 2017 to February 2019. An independence analysis and multivariate testing were used to identify significant independent predictors. The scale scores were computed by summing across the weighted predictors. The correlation between the scale scores and the intraoperative electrophysiological signal length (IESL), DBS power-on voltage, improvement rate in the unified Parkinson disease rating scale (UPDRS) and UPDRS part III (UPDRS III) scores was analyzed. Receiver operating characteristics curve analysis was used to quantify the discriminative capacity of the scale for predicting the prognosis.

RESULTS

Listwise exclusion of patients with incomplete data sets yielded a final sample of 130 patients with Parkinson disease who had undergone bilateral DBS. Multivariate testing identified 3 independent predictors of the prognosis, including electrode implantation duration, postoperative pneumocephalus volume, and electrode fusion error. The scale scores correlated significantly with the subthalamic nucleus DBS power-on voltage (r = -0.4063; P < 0.0001), globus pallidus internus DBS power-on voltage (r = -0.4723; P = 0.0014), and improvement rate of the UPDRS (r = 0.3490; P < 0.0001) and UPDRS III (r = 0.6623; P < 0.0001) scores. However, the scale scores did not significantly correlate with the subthalamic nucleus IESL and globus pallidus internus IESL. Receiver operating characteristics curve analysis revealed impressive outcome discrimination for the UPDRS and UPDRS III scores (UPDRS: area under the curve, 0.62, P = 0.0219; UPDRS III: area under the curve, 0.85, P < 0.0001).

CONCLUSIONS

We have introduced a novel practical scale capable of assessing the outcomes of DBS surgery and predicting the prognosis of patients after DBS surgery.

Brain Shift and Pneumocephalus Assessment During Frame-Based Deep Brain Stimulation Implantation With Intraoperative Magnetic Resonance Imaging

BACKGROUND

Brain shift and pneumocephalus are major concerns regarding deep brain stimulation (DBS).

OBJECTIVE

To report the extent of brain shift in deep structures and pneumocephalus in intraoperative magnetic resonance imaging (MRI).

METHODS

Twenty patients underwent bilateral DBS implantation in an MRI suite. Volume of pneumocephalus, duration of procedure, and 6 anatomic landmarks (anterior commissure, posterior commissure, right fornix [RF], left fornix [LF], right putaminal point, and left putaminal point) were measured.

RESULTS

Pneumocephalus varied from 0 to 32 mL (median = 0.6 mL). Duration of the procedure was on average 195.5 min (118-268 min) and was not correlated with the amount of pneumocephalus. There was a significant posterior displacement of the anterior commissure (mean = -1.1 mm, P < .001), RF (mean = -0.6 mm, P < .001), LF (mean = -0.7 mm, P < .001), right putaminal point (mean = -0.9 mm, P = .001), and left putaminal point (mean = -1.0 mm, P = .001), but not of the posterior commissure (mean = 0.0 mm, P = .85). Both RF (mean = -.7 mm, P < .001) and LF (mean = -0.5 mm, P < .001) were posteriorly displaced after a right-sided burr hole. There was a correlation between anatomic landmarks displacement and pneumocephalus after 2 burr holes (rho = 0.61, P = .007), but not after 1 burr hole (rho = 0.16, P = .60).

CONCLUSION

Better understanding of how pneumocephalus displaces subcortical structures can significantly enhance our intraoperative decision making and overall targeting strategy.

Asleep Deep Brain Stimulation Reduces Incidence of Intracranial Air during Electrode Implantation

BACKGROUND

Asleep deep brain stimulation (aDBS) implantation replaces microelectrode recording for image-guided implantation, shortening the operative time and reducing cerebrospinal fluid egress. This may decrease pneumocephalus, thus decreasing brain shift during implantation.

OBJECTIVE

To compare the incidence and volume of pneumocephalus during awake (wkDBS) and aDBS procedures.

METHODS

A retrospective review of bilateral DBS cases performed at Oregon Health &amp; Science University from 2009 to 2017 was undertaken. Postimplantation imaging was reviewed to determine the presence and volume of intracranial air and measure cortical brain shift.

RESULTS

Among 371 patients, pneumocephalus was noted in 66% of wkDBS and 15.6% of aDBS. The average volume of air was significantly higher in wkDBS than aDBS (8.0 vs. 1.8 mL). Volumes of air greater than 7 mL, which have previously been linked to brain shift, occurred significantly more frequently in wkDBS than aDBS (34 vs 5.6%). wkDBS resulted in significantly larger cortical brain shifts (5.8 vs. 1.2 mm).

CONCLUSIONS

We show that aDBS reduces the incidence of intracranial air, larger air volumes, and cortical brain shift. Large volumes of intracranial air have been correlated to shifting of brain structures during DBS procedures, a variable that could impact accuracy of electrode placement.

Sequence of electrode implantation and outcome of deep brain stimulation for Parkinson's disease

INTRODUCTION

The effect of the variability of electrode placement on outcomes after bilateral deep brain stimulation of subthalamic nucleus has not been sufficiently studied, especially with respect to the sequence of hemisphere implantation.

METHODOLOGY

We retrospectively analysed the clinical and radiographic data of all the consecutive patients with Parkinson's disease who underwent surgery at our centre and completed at least 1 year follow-up. The dispersion in electrode location was calculated by the square of deviation from population mean, and the direction of deviation was analysed by comparing the intended and final implantation coordinates. Linear regression analysis was performed to analyse the predictors of postoperative improvement of the motor condition, also controlling for the sequence of implanted hemisphere.

RESULTS

76 patients (mean age 58±7.2 years) were studied. Compared with the first side, the second side electrode tip had significantly higher dispersion as an overall effect (5.6±21.6 vs 2.2±4.9 mm(2), p=0.04), or along the X-axis (4.1±15.6 vs 1.4±2.4 mm(2), p=0.03) and Z-axis (4.9±11.5 vs 2.9±3.6 mm(2), p=0.02); the second side stimulation was also associated with a lower threshold for side effects (contact 0, p<0.001 and contact 3, p=0.004). In the linear regression analysis, the significant predictors of outcome were baseline activities of daily living (p=0.010) and dispersion of electrode on the second side (p=0.005).

CONCLUSIONS

We observed a higher dispersion for the electrode on the second implanted side, which also resulted to be a significant predictor of motor outcome at 1 year.

Analysis of electrode deformations in deep brain stimulation surgery

PURPOSE

Deep brain stimulation (DBS) surgery is used to reduce motor symptoms when movement disorders are refractory to medical treatment. Post-operative brain morphology can induce electrode deformations as the brain recovers from an intervention. The inverse brain shift has a direct impact on accuracy of the targeting stage, so analysis of electrode deformations is needed to predict final positions.

METHODS

DBS electrode curvature was evaluated in 76 adults with movement disorders who underwent bilateral stimulation, and the key variables that affect electrode deformations were identified. Non-linear modelling of the electrode axis was performed using post-operative computed tomography (CT) images. A mean curvature index was estimated for each patient electrode. Multivariate analysis was performed using a regression decision tree to create a hierarchy of predictive variables. The identification and classification of key variables that determine electrode curvature were validated with statistical analysis.

RESULTS

The principal variables affecting electrode deformations were found to be the date of the post-operative CT scan and the stimulation target location. The main pathology, patient's gender, and disease duration had a smaller although important impact on brain shift.

CONCLUSIONS

The principal determinants of electrode location accuracy during DBS procedures were identified and validated. These results may be useful for improved electrode targeting with the help of mathematical models.

Validity of single tract microelectrode recording in subthalamic nucleus stimulation

In surgery for subthalamic nucleus (STN) deep brain stimulation (DBS), precise implantation of the lead into the STN is essential. Physiological refinement with microelectrode recording (MER) is the gold standard for identifying STN. We studied single tract MER findings and surgical outcomes and verified our surgical method using single tract MER. The number of trajectories in MER and the final position of lead placement were retrospectively analyzed in 440 sides of STN DBS in 221 patients. Bilateral STN DBS yielded marked improvement in the motor score, dyskinesia/fluctuation score, and reduced requirement of dopaminergic medication in this series. The number of trajectories required to obtain sufficient activity of the STN was one in 79.0%, two in 18.2%, and three or more in 2.5% of 440 sides. In 92 sides requiring altered trajectory, the final direction of trajectory movement was posterior in 73.9%, anterior in 13.0%, lateral in 5.4%, and medial in 4.3%. In 18 patients, posterior moves were required due to significant brain shift with intracranial air caused by outflow of CSF during the second side procedure. Sufficient STN activity is obtained with minimum trajectories by proper targeting and precise interpretation of MER findings even in the single tract method. Anterior–posterior moves rather than medial–lateral moves should be attempted first in cases with insufficient recording of STN activity.

A quantitative assessment of the accuracy and reliability of O-arm images for deep brain stimulation surgery

BACKGROUND

Deep brain stimulation (DBS) surgery has an average accuracy of 2 to 3 mm (range, 0-6 mm). Intraoperative detection of track location may be useful in interpreting physiological results and thus limit the number of brain penetrations as well as decrease the incidence of reoperations. The O-arm has been used to identify the DBS lead position; however, early results have indicated a significant discrepancy with lead position on postoperative imaging.

OBJECTIVE

This prospective study was conducted to determine the accuracy and reliability of fiducial and track localization and to assess the accuracy of O-arm image-based registration. The computed tomography (CT) image was considered the gold standard, and so for this study, the locations of all objects on the O-arm image were compared with their CT location.

METHODS

Thirty-three DBS surgeries were performed using the O-arm to image each track with detailed analysis of fiducial and track localization accuracy. Twenty-one subsequent surgeries were performed using O-arm registration. Only the final lead position was assessed in these individuals.

RESULTS

The measurement error of the system was 0.7 mm, with a maximum error of 1.9 mm. Twenty-two percent of the parallel tracks through the BenGun exceeded this error and demonstrated the ability of the O-arm to detect these skewed tracks. The accuracy of final lead position was 2.04 mm in procedures with registration based on an O-arm image. This was not significantly different from CT-based registration at 2.16 mm.

CONCLUSION

The O-arm was able to detect skewed tracks and provide registration accuracy equivalent to a CT scan.

The impact of brain shift in deep brain stimulation surgery: observation and obviation

BACKGROUND

The impact of brain shift on deep brain stimulation surgery is considerable. In DBS surgery, brain shift is mainly caused by CSF loss. CSF loss can be estimated by post-surgical intracranial air. Different approaches and techniques exist to minimize CSF loss and hence brain shift. The aim of this survey was to investigate the extent and dynamics of CSF loss during DBS surgery, analyze its impact on final electrode position, and describe a simple and inexpensive method of burr hole closure.

METHODS

Sixty-six patients being treated with deep brain stimulation were retrospectively analyzed for this treatise. During surgery, CSF loss was minimized using bone wax as a burr hole closure. Intracranial air volume was calculated based on early post-surgery stereotactic 3D CT and correlated with duration of surgery and electrode deviations derived from post-surgery image fusion.

RESULTS

Median early post-surgery intracranial air was 2.1 cm(3) (range 0-35.7 cm(3), SD 8.53 cm(3)). No correlation was found between duration of surgery and CSF-loss (R = 0.078, p = 0.534), indicating that CSF loss mainly occurs early during surgery. Linear regression analysis revealed no significant correlations regarding volume of intracranial air and electrode displacement in any of the three principal axes. No significant difference regarding electrode deviations between first and second side of surgery were observed.

CONCLUSIONS

CSF loss mainly occurs during the early phase of DBS surgery. CSF loss during a later phase of surgery can be effectively averted by burr hole closure. Postoperative intracranial air volumes up to 35 cm(3) did not result in significant electrode displacement in our series. Comparing our results to studies previously published on this subject, burr hole closure using bone wax is highly effective.