Mismatch between electrophysiologically defined and ventriculography based theoretical targets for posteroventral pallidotomy in Parkinson's disease

The Anatomical and Electrophysiological Subthalamic Nucleus Visualized by 3-T Magnetic Resonance Imaging

BACKGROUND:

Accurate localization of the subthalamic nucleus (STN) is critical to the success of deep brain stimulation surgery for Parkinson disease. Recent developments in high-field-strength magnetic resonance imaging (MRI) have made it possible to visualize the STN in greater detail. However, the relationship of the MR-visualized STN to the anatomic, electrophysiological, or atlas-predicted STN remains controversial.

OBJECTIVE:

To evaluate the size of the STN visualized on 3-T MRI compared with anatomic measurements in cadaver studies and to compare the predictions of 3-T MRI and those of the Schaltenbrand-Wahren (SW) atlas for intraoperative STN microelectrode recordings.

METHODS:

We evaluated the STN by 3-T MRI and intraoperative microelectrode recordings in 20 Parkinson disease patients undergoing deep brain stimulation surgery. We compared our findings with anatomic cadaver studies and with the individually scaled SW atlas-based predictions for each patient.

RESULTS:

The dimensions of the 3-T MR-visualized STN were very similar to those of the largest anatomic study (MRI length, width, and height: 9.8 ± 1.6, 11.5 ± 1.6, and 3.7 ± 0.7 mm, respectively; n = 40; cadaver length, width, and height: 9.3 ± 0.7, 10.6 ± 0.9, and 3.1 ± 0.5 mm, respectively; n = 100). The amount of STN traversed during intraoperative microelectrode recordings was better correlated to the 3-T MR-visualized STN than the SW atlas-predicted STN (R = 0.38 vs R = −0.17).

CONCLUSION:

The STN as visualized on 3-T MRI corresponds well with cadaveric anatomic studies and intraoperative electrophysiology. STN visualization with 3-T MRI may be an improvement over SW atlas-based localization for STN deep brain stimulation surgery in Parkinson disease.

IMPLANTATION OF ELECTRODES FORDEEP BRAIN STIMULATION OF THE SUBTHALAMIC NUCLEUS IN ADVANCED PARKINSON'S DISEASE WITH THE AID OF INTRAOPERATIVE MICRORECORDING UNDERGENERAL ANESTHESIA

OBJECTIVE

Deep brain stimulation (DBS) is widely accepted in the treatment of advanced Parkinson's disease (PD) and other movement disorders. The standard implantation procedure is performed under local anesthesia (LA). Certain groups of patients may not be eligible for surgery under LA because of clinical reasons, such as massive fear, reduced cooperativity, or coughing attacks. Microrecording (MER) has been shown to be helpful in DBS surgery. The purpose of this study was to evaluate the feasibility of MERfor DBS surgery under general anesthesia (GA) and to compare the data of intraoperative MERas well as the clinical data with that of the current literature of patients undergoing operation under LA.

CLINICAL PRESENTATION

The data of nine patients with advanced PD (mean Hoehn and Yahr status, 4.2) who were operated with subthalamic nucleus (STN) DBS under GA, owing to certain clinical circumstances ruling out DBS under LA, were retrospectively analyzed. All operations were performed under analgosedation with propofol or remifentanil and intraoperative MER. For MER, remifentanil was ceased completely and propofol was lowered as far as possible.

INTERVENTION

The STN could be identified intraoperatively in all patients with MER. The typical bursting pattern was identified, whereas a widening of the baseline noise could not be as adequately detected as in patients under LA. The daily off phases of the patients were reduced from 50 to 17%, whereas the Unified Parkinson's Disease Rating Scale III score was reduced from 43 (preoperative, medication off) to 19 (stimulation on, medication off) and 12 (stimulation on, medication on). Two patients showed a transient neuropsychological deterioration after surgery, but both also had preexisting episodes of disorientation. One implantable pulse generator infection was noticed. No further significant clinical complications were observed.

CONCLUSION

STN surgery for advanced PD with MERguidance is possible with good clinical results under GA. Intraoperative MERof the STN region can be performed under GA with a special anesthesiological protocol. In this setting, the typical STN bursting pattern can be identified, whereas the typical widening of the background noise baseline while entering the STN region is obviously absent. This technique may enlarge the group of patients eligible for STN surgery. Although the clinical improvements and parameter settings in this study were within the range of the current literature, further randomized controlled studies are necessary to compare the results of STN DBS under GA and LA, respectively.

Reliability of atlas-derived coordinates in deep brain stimulation

BACKGROUND

In deep brain stimulation the way to define and localize the optimal target for the individual patient is still under debate. The objective of our study was to investigate the reliability of atlas derived data by comparing them with direct targeting on MR images.

METHOD

We investigated 28 STN targets in 14 volunteers. The stereotactic coordinates of the dorso-lateral subthalamic nucleus (STN), were determined in 5 different ways for both STNs of each individual volunteer: 1. directly, on axial T2WI spin echo slices, 2. directly, on coronal T2WI spin echo slices and after fusion of data sets: 3. indirectly, on an axial atlas plate, 4. indirectly, on a coronal atlas plate, 5. indirectly, 12 mm lateral, 3 mm posterior and 3 mm inferior to mid-AC-PC.

FINDINGS

The differences between MRI derived targets on axial vs. coronal slices were not statistically significant. After detection of the atlas derived targets the resulting x-coordinates were found more lateral than after direct detection on both, axial and coronal T2-weighted images (p < 0.001). On axial images y-coordinates were located more anterior (p = 0.240) on atlas derived targets and more posterior when target localizations were compared on coronal slices (p < 0.001). z-Coordinates were more superior after atlas targeting compared to MRI targeting (p < 0.001). Differences up to 6.21 mm occurred.

CONCLUSIONS

Despite the limitations concerning image distortions and slice thickness, direct target planning on MRI, regarding our results, is more reliable than targeting solely based on atlas derived data. Only MRI gives us detailed information about the individual configurations of central structures in every single patient. However, targets, which are not detectable on MRI like the nucleus ventralis intermedius have to be planned using stereotactic atlas information. In these cases intra-operative micro-electrode recording might help to better define the target region.

Targeting the subthalamic nucleus for deep brain stimulation: technical approach and fusion of pre- and postoperative MR images to define accuracy of lead placement

OBJECTIVES

To define the role of magnetic resonance imaging (MRI) and intraoperative electrophysiological recording in targeting the subthalamic nucleus (STN) in Parkinson's disease and to determine accuracy of electrode placement.

PATIENTS AND METHODS

We implanted 54 electrodes into the STN in 27 patients. Target planning was done by coordinate guidelines and visualising the STN on MRI and defined in relation to the mid-point of the AC-PC line. Intraoperative microelectrode recording was used. We adjusted electrode positions for placement in the centre of the STN electrical activity and verified this on postoperative MRI in 16 cases, which were fused to the preoperative images to measure actual error in electrode placement in the three axes.

RESULTS

Based on coordinate calculation and MRI localisation, the mean of the target was 11.5 mm lateral, 2.5 mm posterior and 4.1 mm inferior to the mid-point of the AC-PC line. Fifty good electrophysiological recordings of the STN (average length 4.65 mm) were achieved and target point adjusted in 90% of lead placements. The mean of the final target after electrophysiological correction was 11.7 mm lateral, 2.1 mm posterior, and 3.8 mm inferior to the mid-point. The distance from the centre of the electrode artefact to the final target used after electrophysiological recording on the fused images was 0.48 mm, 0.69 mm, and 2.9 mm in the x, y, and z axes, respectively. No postoperative MRI related complication was observed.

CONCLUSION

Both direct visualisation of the STN on MRI and intraoperative electrophysiological recording are important in defining the best target. Individual variations exist in the location of the STN target. Fewer tracks were required to define STN activity on the side operated first. Our current stereotactic method of electrode placement is relatively accurate.

From functional neurosurgery to "interventional" neurology: survey of publications on thalamotomy, pallidotomy, and deep brain stimulation for Parkinson's disease from 1966 to 2001

Articles on surgery for Parkinson's disease (PD), published between 1966 and 2001, were reviewed with respect to whether the first author had a neurosurgical affiliation, and whether the papers appeared in neurosurgical or non-neurosurgical journals. Between 1966 and 1979, neurosurgeons and non-neurosurgeons published almost equally on surgery for PD in both neurosurgical and non-neurosurgical journals; between 1980 and 1995, the majority of publications were by neurosurgeons in neurosurgical journals; and after 1995, non-neurosurgeons were more often first authors of surgical publications and these were more frequent in non-neurosurgical journals. The fact that the first author of surgical publications on PD is often a non-neurosurgeon may have some bearing on the reported results of surgery.

Surgical complications in patients with Parkinson's disease after posteroventral pallidotomy

OBJECTIVE

To investigate the potential operative morbidity in posteroventral pallidotomy (PVP) for patients with Parkinson's disease.

METHODS

We designed a retrospective study that included 796 consecutive patients (mean age, 64.9 yr; male, 559; female, 237) with Parkinson's disease. All PVPs (simultaneous bilateral PVP, n = 272; sequential bilateral PVP, n = 88; unilateral PVP, n = 436) were performed during a 7-year period. The total number of operations was 884, and the number of PVP procedures was 1156. In 108 patients, ventral intermediate nucleus thalamotomy was performed simultaneously.

RESULTS

The overall complication rate, including temporary problems, was 15.3% of 884 operations. Permanent complications occurred in 3.6% of total operations. Intracranial hemorrhage occurred in 24 operations (2.7%). In seven of them, the patients required craniotomy and hematoma evacuation and sustained a disabling motor deficit (0.8%). Intracranial hemorrhage occurred more often in patients who underwent microelectrode recording and had a history of chronic hypertension. Hemiparesis without intracranial hematoma occurred in 12 operations (1.4%). Microelectrode recording was a risk factor for postoperative hemiparesis without hemorrhage. In 19 operations (2.1%), patients developed a partial visual field deficit. Speech disturbance after surgery was observed in 23 operations (2.6%) but resolved in 17 by 1 week after surgery. In 55 operations (6.2%), patients developed postoperative confusion. This occurred more often in elderly patients and those with advanced disease. In 17 operations (1.9%), patients required observation in the intensive care unit because of postoperative hypotension.

CONCLUSION

Complications from stereotactic pallidotomy were not frequent. However, the residual symptoms from complications can be serious in many cases.

Lack of agreement between direct magnetic resonance imaging and statistical determination of a subthalamic target: the role of electrophysiological guidance

OBJECT

The goal of this study was to determine the most suitable procedure(s) to localize the optimal site for high-frequency stimulation of the subthalamic nucleus (STN) for the treatment of advanced Parkinson disease.

METHODS

Stereotactic coordinates of the STN were determined in 14 patients by using three different methods: direct identification of the STN on coronal and axial T2-weighted magnetic resonance (MR) images and indirect targeting in which the STN coordinates are referred to the anterior commissure-posterior commissure (AC-PC) line, which, itself, is determined either by using stereotactic ventriculography or reconstruction from three-dimensional (3D) MR images. During the surgical procedure, electrode implantation was guided by single-unit microrecordings on multiple parallel trajectories and by clinical assessment of stimulations. The site where the optimal functional response was obtained was considered to be the best target. Computerized tomography scanning was performed 3 days later and the scans were combined with preoperative 3D MR images to transfer the position of the best target to the same system of stereotactic coordinates. An algorithm was designed to convert individual stereotactic coordinates into an all-purpose PC-referenced system for comparing the respective accuracy of each method of targeting, according to the position of the best target.

CONCLUSIONS

The target that is directly identified by MR imaging is more remote (mainly in the lateral axis) from the site of the optimal functional response than targets obtained using other procedures, and the variability of this method in the lateral and superoinferior axes is greater. In contrast, the target defined by 3D MR imaging is closest to the target of optimal functional response and the variability of this method is the least great. Thus, 3D reconstruction adjusted to the AC-PC line is the most accurate technique for STN targeting, whereas direct visualization of the STN on MR images is the least effective. Electrophysiological guidance makes it possible to correct the inherent inaccuracy of the imaging and surgical techniques and is not designed to modify the initial targeting.

Stereotactic imaging of the pallidal target

In 48 consecutive patients, we applied a new stereotactic imaging technique to individually visualize the pallidal target before surgery. A turbo spin-echo proton density sequence (acquisition time, 6 minutes 5 seconds) was used for 2-mm-thick contiguous axial scanning. Pallidocapsular border, medial putaminal border, and optic tract were visualized bilaterally in all patients. Boundaries of globus pallidus internus, globus pallidus externus, and lamina medullaris interna were clearly visualised in 71% of the patients. The anatomic target point was chosen in the middle of the visualized posteroventral pallidum, irrespective of the position of this point in relation to commissures. The lateralities of pallidocapsular border, lamina medullaris interna, and medial boundary of putamen were measured bilaterally in each patient, and the width of the posteroventral pallidum was assessed. The laterality of structures (measured from a point 2 mm anterior to midcommissural point and at a level 2-4 mm below anterior commissure-posterior commissure line) showed a wide range. The position of the pallidocapsular border varied by up to almost 1 cm between the most medial and the most lateral one. There were also variations in the position of the pallidal structures between left and right hemispheres in the same patients. The posteroventral pallidum was slightly more wide on the left than the right side. Given the significant inter- and intra-individual variabilities of the position of pallidal structures, it may be hazardous to rely solely on the atlas and the commissures for targeting. A magnetic resonance imaging sequence that enables visualization in each individual patient of the target area and its surroundings may contribute to less electrode passes during intraoperative physiological exploration and to more exact location of the lesion or chronic electrode in the posteroventral pallidum.