Comparison of actual pallidotomy lesion location with expected stereotactic location

Identifying the therapeutic zone in globus pallidus deep brain stimulation for Parkinson's disease

OBJECTIVE

The globus pallidus internus (GPI) has been demonstrated to be an effective surgical target for deep brain stimulation (DBS) treatment in patients with medication-refractory Parkinson's disease (PD). The ability of neurosurgeons to define the area of greatest therapeutic benefit within the globus pallidus (GP) may improve clinical outcomes in these patients. The objective of this study was to determine the best DBS therapeutic implantation site within the GP for effective treatment in PD patients.

METHODS

The authors performed a retrospective review of 56 patients who underwent bilateral GP DBS implantation at their institution during the period from January 2015 to January 2020. Each implanted contact was anatomically localized. Patients were followed for stimulation programming for at least 6 months. The authors reviewed preoperative and 6-month postsurgery clinical outcomes based on data from the Unified Parkinson's Disease Rating Scale Part III (UPDRS III), dyskinesia scores, and levodopa equivalent daily dose (LEDD).

RESULTS

Of the 112 leads implanted, the therapeutic cathode was most frequently located in the lamina between the GPI external segment (GPIe) and the GP externus (GPE) (n = 40). Other common locations included the GPE (n = 24), the GPIe (n = 15), and the lamina between the GPI internal segment (GPIi) and the GPIe (n = 14). In the majority of patients (73%) a monopolar programming configuration was used. At 6 months postsurgery, UPDRS III off medications (OFF) and on stimulation (ON) scores significantly improved (z = -4.02, p < 0.001), as did postsurgery dyskinesia ON scores (z = -4.08, p < 0.001) and postsurgery LEDD (z = -4.7, p < 0.001).

CONCLUSIONS

Though the ventral GP (pallidotomy target) has been a commonly used target for GP DBS, a more dorsolateral target may be more effective for neuromodulation strategies. The assessment of therapeutic contact locations performed in this study showed that the lamina between GPI and GPE used in most patients is the optimal central stimulation target. This information should improve preoperative GP targeting.

Future directions: use of interventional MRI for cell-based therapy of Parkinson disease

Transplantation of neural cells for the treatment of neurologic disorders has garnered much attention and considerable enthusiasm from patients and physicians alike. Cell-based therapies have been proposed for a wide range of central nervous system pathologies ranging from stroke and trauma to demyelinating disorders and neurodegenerative diseases. Notably, cell transplantation for Parkinson disease (PD) has become even more attractive with the rapid advances in derivation of dopaminergic neurons from human embryonic stem cells. This article briefly reviews some of the relevant issues regarding the transplantation of cells for treatment of PD and hypothesizes how interventional MRI may be useful to optimize the surgical delivery of cells for PD and other central nervous system disorders.

MRI guidance improves accuracy of stereotaxic targeting for cell transplantation in parkinsonian monkeys

Accuracy of targeting is critical for the success of cell transplantation in the central nervous system. We compared the accuracy of conventional atlas-guided stereotaxis to magnetic resonance imaging (MRI)-guided stereotaxic targeting in various basal ganglia nuclei in parkinsonian monkeys. 28 monkeys underwent unilateral striatal transplantation. High-resolution 3D MR images of the brain were used in 15 monkeys fitted with a MRI-compatible stereotaxic frame for target localization. This was immediately followed by cranial surgery with the frame "in situ". 13 additional monkeys underwent stereotaxic atlas-guided cranial surgery for placement of cell transplants. Following extensive behavioral testing and microelectrode recordings, all animals were perfused. The brains were sectioned coronally and stained to determine the morphology of needle tracts as an accuracy measure of stereotaxic placements. MRI-guided stereotaxy was completely accurate in 80% as compared to 38.5% in atlas-guided stereotaxis. The chance of missing a target completely was as high as 38.5% in atlas-guided stereotaxis, which was reduced to 6.67% when MRI was used for guidance. Targeting error occurred mostly in the anterior caudate and posterior putamen as against better accuracy in the anterior putamen. These results suggest that accuracy of stereotaxic unilateral cranial targeting into the putamen and the caudate in monkeys can be improved with high-resolution 3D MR imaging.

Verbal fluency declines after pallidotomy: an interaction between task and lesion laterality

Verbal fluency declines are commonly reported after pallidotomy in patients with Parkinson's disease. However, it is not clear whether there is an interaction between side of surgery and task format (lexical vs. semantic) or whether error rates (perseverations, intrusions, rule violations) increase after surgery. This study examined verbal fluency before and approximately 4 months after unilateral pallidotomy. The left and right pallidotomy groups were matched on key demographic, cognitive, and disease variables. Pallidotomy resulted in a decline in lexical but not semantic verbal fluency, and this decline was most evident in the left-sided surgery group. Error rates (perseverations, intrusions, and rule violations) were not affected by pallidotomy. Findings support the role of left frontal-basal ganglionic circuits in word retrieval processes and/or lexical search and access.

Anatomic and neurophysiological methods for the targeting and lesioning of the subthalamic nucleus: Cuban experience and review

OBJECTIVE

To develop a method to place a lesion precisely in the subthalamic nucleus (STN) and evaluate its effectiveness.

METHODS

A retrospective study of targeting data collected during stereotactic planning to lesion the STN in 31 patients with Parkinson's disease and of results in more than 50 procedures was performed. The targeting method was based on computed tomographic imaging together with semimicroelectrode recording digital processing and electrical stimulation. Two statistical methods were used to correlate initial with final target coordinates and assess the efficacy of the targeting procedure.

RESULTS

The anatomic target based on computed tomographic imaging data showed electrical activity in the subthalamus in the first pass in 82% of the procedures. In the remaining 18%, the STN was an average of 1.93 mm away from the nearest trajectory that recorded the STN (range, 1.41-2.24 mm). The average number of trajectories per procedure was 7.2; the location of the first trajectory relative to the center of the nucleus determined by electrical and physiological means (P < 0.01, analysis of variance, Student's t test) was as follows: in the lateral direction, 1.25 +/- 1.15 mm; in the anteroposterior direction, 1.53 +/- 1.31 mm; and in the vertical direction, 0.67 +/- 0.51 mm. The average number of tracts necessary to lesion the STN was two.

CONCLUSION

The combination of computed tomographic imaging, semimicroelectrode recording, and microstimulation provides an effective method to identify the STN lesion in parkinsonian patients. The method used for anatomic localization and electrophysiological mapping of the subthalamus was found to be effective in reaching the sensorimotor region of the nucleus. We carried out an accurate determination of the subthalamus location and its volume in the lesioning.

Declines in switching underlie verbal fluency changes after unilateral pallidal surgery in Parkinson's disease

Declines in verbal fluency are consistently reported in patients with Parkinson's disease (PD) after pallidal surgery. In the present study, the clustering and switching components of semantic or category fluency (oral naming of items obtainable in supermarkets) were examined at baseline and four months after unilateral deep brain stimulation or pallidotomy in 45 patients with PD (30 left, 15 right pallidal surgery). Post-operative declines were observed for supermarket fluency total score and switching, but not for average cluster size. These findings support the proposal that semantic fluency decrements after pallidal surgery reflect a disruption of frontal-basal ganglia circuits mediating efficient shifting between semantic categories, or perhaps efficient access to categories, rather than a degradation of semantic stores.

Magnitude of microelectrode refinement in pallidotomy and thalamotomy

The relative accuracy of starting point algorithms in microelectrode-guided stereotactic pallidotomy and thalamotomy was evaluated using postoperative magnetic resonance imaging (MRI) data. Multiplanar reformations were performed to align postoperative MRI in anterior-posterior, dorsal-ventral and mediolateral planes. Three-dimensional distance and direction from the pallidal and thalamic stereotactic starting points to the respective radiofrequency lesions were measured. Similar magnitude of microelectrode refinement in pallidotomy and thalamotomy suggested similar accuracy of algorithms used to set the stereotactic starting point. Fewer microelectrode-recording tracts were required to identify optimal lesioning sites in thalamotomy compared to pallidotomy. Lesions were consistently localized anterior and superior to the starting point and a refined starting point algorithm may reduce the number of microelectrode recording tracts.