Microelectrode recording and macrostimulation in thalamic and subthalamic MRI guided stereotactic surgery

Randomized, Double-Blind Assessment of LFP Versus SUA Guidance in STN-DBS Lead Implantation: A Pilot Study

Background: The efficacy of deep brain stimulation (DBS) therapy in Parkinson's disease (PD) patients is highly dependent on the precise localization of the target structures such as subthalamic nucleus (STN). Most commonly, microelectrode single unit activity (SUA) recordings are performed to refine the target. This process is heavily experience based and can be technically challenging. Local field potentials (LFPs), representing the activity of a population of neurons, can be obtained from the same microelectrodes used for SUA recordings and allow flexible online processing with less computational complexity due to lower sampling rate requirements. Although LFPs have been shown to contain biomarkers capable of predicting patients' symptoms and differentiating various structures, their use in the localization of the STN in the clinical practice is not prevalent. Methods: Here we present, for the first time, a randomized and double-blinded pilot study with intraoperative online LFP processing in which we compare the clinical benefit from SUA- versus LFP-based implantation. Ten PD patients referred for bilateral STN-DBS were randomly implanted using either SUA or LFP guided targeting in each hemisphere. Although both SUA and LFP were recorded for each STN, the electrophysiologist was blinded to one at a time. Three months postoperatively, the patients were evaluated by a neurologist blinded to the intraoperative recordings to assess the performance of each modality. While SUA-based decisions relied on the visual and auditory inspection of the raw traces, LFP-based decisions were given through an online signal processing and machine learning pipeline. Results: We found a dramatic agreement between LFP- and SUA-based localization (16/20 STNs) providing adequate clinical improvement (51.8% decrease in 3-month contralateral motor assessment scores), with LFP-guided implantation resulting in greater average improvement in the discordant cases (74.9%, n = 3 STNs). The selected tracks were characterized by higher activity in beta (11-32 Hz) and high-frequency (200-400 Hz) bands (p < 0.01) of LFPs and stronger non-linear coupling between these bands (p < 0.05). Conclusion: Our pilot study shows equal or better clinical benefit with LFP-based targeting. Given the robustness of the electrode interface and lower computational cost, more centers can utilize LFP as a strategic feedback modality intraoperatively, in conjunction to the SUA-guided targeting.

MR-guided focused ultrasound cerebellothalamic tractotomy for chronic therapy-resistant essential tremor: anatomical target reappraisal and clinical results

OBJECTIVE

In addition to the well-recognized ventral intermediate nucleus (Vim) thalamotomy for the treatment of chronic therapy-resistant essential tremor (ET), an alternative approach targeting the posterior part of the subthalamus was proposed in the 1960s and early 1970s and then was reactualized as cerebellothalamic tractotomy (CTT) with the advent of MR-guided focused ultrasound (MRgFUS) surgery. The goal of this study was to improve target coverage and thus efficacy (i.e., tremor control and its consistency). The authors undertook a histological reappraisal of the CTT target and proposed a targeting strategy of the MRgFUS CTT based on 1) the MR visualization of the center of the red nucleus and 2) the application of preplanned target subunits realized with short sonications under thermal dose control. This study was aimed at demonstrating the efficacy and risk profile of this approach against chronic therapy-resistant ET.

METHODS

Ten consecutive patients suffering from chronic therapy-resistant ET benefited from a unilateral MRgFUS CTT and were followed over the course of 1 year. Primary endpoints were subjective tremor relief, Clinical Rating Scale for Tremor (CRST) score, activities of daily living (ADL) score, and the hand function (HF) scores HF16 and HF32. Histological reappraisal of the target led the authors to propose a standardized targeting protocol for MRgFUS CTT. Thermal doses for 18 and 240 cumulative equivalent minutes at 43°C were calculated and correlated with intraoperative and 2 days postoperative T2-weighted MR images.

RESULTS

The mean ± SD for the baseline CRST score was 48 ± 12; the score was 16 ± 7 at 3 months, and 17 ± 8 at 1 year. The mean tremor relief rated by the patients for the operated side was 95% after 2 days, 96% at 3 months, and 93% at 1 year. The mean HF16 was 11.0 ± 2.1 at baseline, 0.7 ± 0.7 at 3 months, and 0.8 ± 0.9 at 1 year (93% mean reduction). The minimum reduction for the HF16 at 1 year was 78%. There was a 51% reduction of the mean ADL score at 1 year. There was no bleeding or infection. Gait difficulties, only detectable on tandem gait, were increased in 3 patients and reduced in 2 patients at 1 year. There was no dysarthria.

CONCLUSIONS

The authors' results suggest that MRgFUS CTT is a very effective treatment option for therapy-resistant ET.

Incisionless transcranial MR-guided focused ultrasound in essential tremor: cerebellothalamic tractotomy

Background

Already in the late 1960s and early 1970s, targeting of the “posterior subthalamic area (PSA)” was explored by different functional neurosurgical groups applying the radiofrequency (RF) technique to treat patients suffering from essential tremor (ET). Recent advances in magnetic resonance (MR)-guided focused ultrasound (MRgFUS) technology offer the possibility to perform thermocoagulation of the cerebellothalamic fiber tract in the PSA without brain penetration, allowing a strong reduction of the procedure-related risks and increased accuracy. We describe here the first results of the MRgFUS cerebellothalamic tractotomy (CTT).

Methods

Twenty-one consecutive patients suffering from chronic (mean disease duration 29.9 years), therapy-resistant ET were treated with MRgFUS CTT. Three patients received bilateral treatment with a 1-year interval. Primary relief assessment indicators were the Essential Tremor Rating Scale (Fahn, Tolosa, and Marin) (ETRS) taken at follow-up (3 months to 2 years) with accent on the hand function subscores (HF16 for treated hand and HF32 for both hands) and handwriting. The evolution of seven patients with HF32 above 28 points over 32 (group 1) differentiated itself from the others’ (group 2) and was analyzed separately. Global tremor relief estimations were provided by the patients. Lesion reconstruction and measurement of targeting accuracy were done on 2-day post-treatment MR pictures for each CTT lesion.

Results

The mean ETRS score for all patients was 57.6 ± 13.2 at baseline and 25.8 ± 17.6 at 1 year (n = 10). The HF16 score reduction was 92 % in group 2 at 3 months and stayed stable at 1 year (90 %). Group 1 showed only an improvement of 41 % at 3 months and 40 % at 1 year. Nevertheless, two patients of group 1 treated bilaterally had an HF16 score reduction of 75 and 88 % for the dominant hand at 1 year after the second side. The mean patient estimation of global tremor relief after CTT was 92 % at 2 days and 77 % at 1-year follow-up.

Conclusions

CTT with MRgFUS was shown to be an effective and safe approach for patients with therapy-refractory essential tremor, combining neurological function sparing with precise targeting and the possibility to treat patients bilaterally.

Effects of Cerebellothalamic Tractotomy on Cognitive and Emotional Functioning in Essential Tremor: A Preliminary Study in 5 Essential Tremor Patients

Background: Subthalamic stereotactic interventions have recently caught renewed interest as a treatment for essential tremor (ET). However, it is not clear whether these interventions are associated with neurocognitive, mood or personality changes. Objective: To investigate neurocognition, neuropsychiatric functions and personality variables in patients with ET and to explore the neurocognitive and neuropsychiatric effects of cerebellothalamic tractotomy (CTT), a form of subthalamotomy. Methods: In our study, we investigated cognitive functions, frontal functions, mood and personality variables in 5 patients with intractable ET. Patients were tested before and 3 months after surgery using neuropsychological tests, clinical scales for depression, anxiety, anger regulation and a personality test. Results: Before surgery, ET patients showed normal neurocognitive function, a slightly elevated frontal lobe score in the dimensions mental control and memory, without being indicative of a frontal lesion, and no elevated depression or anxiety scores compared to norm values. After surgery, there was no change in neurocognitive function and no increase in depression or anxiety scores. Conclusion: In this exploratory study on 5 ET patients, CTT was not associated with alterations of mood or neurocognitive functions. © 2015 S. Karger AG, Basel.

Intraoperative image fusion to ascertain adequate lead placement

BACKGROUND

In order to view the position of the deep brain stimulator (DBS) lead in relation to the stereotactic target on 3-tesla magnetic resonance (3T-MR) images prior to the conclusion of the procedure, intraoperative postimplantation computed tomography (CT) images were fused with preoperative 3T-MR images. The method to do this is described and discussed in this paper.

METHODS

Over the last year, this method was used for 8 procedures: 6 for subthalamic nucleus and 2 for ventral-intermediate nucleus of the thalamus. The procedures were done on the CT table in a stereotactic frame. CT and MR images plus coordinates from the Schaltenbrand atlas were used to plan the target. After the lead had been placed at the target, intraoperative CT images were obtained and fused with preoperative 3T-MR images prior to the conclusion of the procedure. If error was detected in the lead position, it was corrected.

RESULTS

Errors in the x-coordinate were detected in 2 patients. These errors were corrected prior to the conclusion of the procedures.

CONCLUSION

This is a simple method to intraoperatively visualize DBS lead position on high-quality 3T-MR images. It gives the surgeon the capability to detect errors and correct them prior to the conclusion of the procedure.

Cross-modal plasticity in the human thalamus: evidence from intraoperative macrostimulations

During stereotactic functional neurosurgery, stimulation procedure to control for proper target localization provides a unique opportunity to investigate pathophysiological phenomena that cannot be addressed in experimental setups. Here we report on the distribution of response modalities to 487 intraoperative thalamic stimulations performed in 24 neurogenic pain (NP), 17 parkinsonian (PD) and 10 neuropsychiatric (Npsy) patients. Threshold responses were subdivided into somatosensory, motor and affective, and compared between medial (central lateral nucleus) and lateral (ventral anterior, ventral lateral and ventral medial) thalamic nuclei and between patients groups. Major findings were as follows: in the medial thalamus, evoked responses were for a large majority (95%) somatosensory in NP patients, 47% were motor in PD patients, and 54% affective in Npsy patients. In the lateral thalamus, a much higher proportion of somatosensory (83%) than motor responses (5%) was evoked in NP patients, while the proportion was reversed in PD patients (69% motor vs. 21% somatosensory). These results provide the first evidence for functional cross-modal changes in lateral and medial thalamic nuclei in response to intraoperative stimulations in different functional disorders. This extensive functional reorganization sheds new light on wide-range plasticity in the adult human thalamocortical system.

Deterministic Dynamics in Neuronal Discharge from Pallidotomy Targets

The non-linear dynamic specificity of the firing pattern discharged from neurons of the internal globus pallidus (GPi) was investigated by recording their spontaneous firing using a microelectrode during posteroventral pallidotomy in eight patients with Parkinson's disease. Raw data from the cells were processed to extract spiking events (discharges above a selected threshold) and the interspike interval was measured. Using the unstable periodic orbits extraction method, significant period-1, −2 and −3 orbits were identified in burst firing discharged from the GPi cells in all eight patients, suggesting that deterministic dynamics exist in the timing of the discharges. As well as providing a useful peri-operative technique for locating posteroventral pallidotomy targets in Parkinson's disease, this method also provides a promising basis for investigating characteristic neuronal discharges in other regions of the brain and for various other neurological disorders.

Human pallidothalamic and cerebellothalamic tracts: anatomical basis for functional stereotactic neurosurgery

Anatomical knowledge of the structures to be targeted and of the circuitry involved is crucial in stereotactic functional neurosurgery. The present study was undertaken in the context of surgical treatment of motor disorders such as essential tremor (ET) and Parkinson's disease (PD) to precisely determine the course and three-dimensional stereotactic localisation of the cerebellothalamic and pallidothalamic tracts in the human brain. The course of the fibre tracts to the thalamus was traced in the subthalamic region using multiple staining procedures and their entrance into the thalamus determined according to our atlas of the human thalamus and basal ganglia [Morel (2007) Stereotactic atlas of the human thalamus and basal ganglia. Informa Healthcare Inc., New York]. Stereotactic three-dimensional coordinates were determined by sectioning thalamic and basal ganglia blocks parallel to stereotactic planes and, in two cases, by correlation with magnetic resonance images (MRI) from the same brains prior to sectioning. The major contributions of this study are to provide: (1) evidence that the bulks of the cerebellothalamic and pallidothalamic tracts are clearly separated up to their thalamic entrance, (2) stereotactic maps of the two tracts in the subthalamic region, (3) the possibility to discriminate between different subthalamic fibre tracts on the basis of immunohistochemical stainings, (4) correlations of histologically identified fibre tracts with high-resolution MRI, and (5) evaluation of the interindividual variability of the fibre systems in the subthalamic region. This study should provide an important basis for accurate stereotactic neurosurgical targeting of the subthalamic region in motor disorders such as PD and ET.

Cicerone: stereotactic neurophysiological recording and deep brain stimulation electrode placement software system

Stereotactic neurosurgery and neurophysiological microelectrode recordings in both humans and monkeys are typically done with conventional 2D atlases and paper records of the stereotactic coordinates. This approach is prone to error because the brain size, shape, and location of subcortical structures can vary between subjects. Furthermore, paper record keeping is inefficient and limits opportunities for data visualization. To address these limitations, we developed a software tool (Cicerone) that enables interactive 3D visualization of co-registered magnetic resonance images (MRI), computed tomography (CT) scans, 3D brain atlases, neurophysiological microelectrode recording (MER) data, and deep brain stimulation (DBS) electrode(s) with the volume of tissue activated (VTA) as a function of the stimulation parameters. The software can be used in pre-operative planning to help select the optimal position on the skull for burr hole (in humans) or chamber (in monkeys) placement to maximize the likelihood of complete microelectrode and DBS coverage of the intended anatomical target. Intra-operatively, Cicerone allows entry of the stereotactic microdrive coordinates and MER data, enabling real-time interactive visualization of the electrode location in 3D relative to the surrounding neuroanatomy and neurophysiology. In addition, the software enables prediction of the VTA generated by DBS for a range of electrode trajectories and tip locations. In turn, the neurosurgeon can use the combination of anatomical (MRI/CT/3D brain atlas), neurophysiological (MER), and electrical (DBS VTA) data to optimize the placement of the DBS electrode prior to permanent implantation.

Microelectrode recording: lead point in STN-DBS surgery

BACKGROUND

Microelectrode recording is an integral part of many surgical procedures for movement disorders. We evaluate the Lead point compared to the NeuroTrek system. We used NeuroTrek in 18 Parkinsonian patients, Lead point-4 in 12 patients, during STN-DBS surgery. We compared MR-Stir image with Microelectrode recording.

METHOD

The MicroGuide system with its integrated screen display provides the user with all the information needed during the surgery on its screen. Microelectrode recordings showed characteristic neuronal discharges on a long trajectory (5-6 mm), intraoperative stimulation induces dramatic improvement of Parkinsonian motor symptoms.

FINDINGS

Microrecording data of the Leadpoint showed high background activity, and firing rate of 14-50 Hz. The discharge pattern is typically chaotic, with frequent irregular bursts and pauses.

DISCUSSION

The microelectrode recording of the neuroTrek and Lead point-4 showed unique results of the typical STN spike. The DBS effect is maximized associated by MER mapping.

Subthalamic nucleus stimulation in Parkinson’s disease

OBJECTIVES

1 - To assess the anatomical localization of the active contacts of deep brain stimulation targeted to the subthalamic nucleus (STN) in Parkinson's disease patients. 2 - To analyze the stereotactic spatial distribution of the active contacts in relation to the dorsal and the ventral electrophysiologically-defined borders of the STN and the stereotactic theoretical target.

METHODS

Twenty-eight patients underwent bilateral high-frequency stimulation of the STN (HFS-STN). An indirect anatomical method based on ventriculography coupled to electrophysiological techniques were used to localize the STN. Clinical improvement was evaluated by Unified Parkinson's Disease Rating Scale motor score (UPDRS III). The normalized stereotactic coordinates of the active contact centres, dorsal and ventral electrophysiologically-defined borders of the STN were obtained from intraoperative X-rays images. These coordinates were represented in a three-dimensional stereotactic space and in the digitalized atlas of the human basal ganglia.

RESULTS

HFS-STN resulted in significant improvement of motor function (62.8%) in off-medication state and levodopa-equivalent dose reduction of 68.7% (p < 0.05). Most of the active contacts (78.6%) were situated close to (+/- 1.6 mm) the dorsal border of the STN (STN-DB), while 16% were dorsal and 5.4% were ventral to it. Similar distribution was observed in the atlas. The euclidean distance between the STN-DB distribution center and the active contacts distribution center was 0.31 mm, while the distance between the active contacts distribution center and the stereotactic theoretical target was 2.15 mm. Most of the space defined by the active contacts distribution (53%) was inside that defined by the STN-DB distribution.

CONCLUSION

In our series, most of the active electrodes were situated near the STN-DB. This suggests that HFS-STN could influence not only STN but also the dorsal adjacent structures (zona incerta and/or Fields of Forel).

The Motor Thalamus in Neurosurgery

THE MOTOR THALAMUS is an important target for the treatment of tremor. It receives afferents from the cerebellum, globus pallidus internus, and substantia nigra and projects mainly to the motor cortex, premotor cortex, and supplementary motor area. Various nomenclatures have been proposed to subdivide the motor thalamus, none of which are universally accepted. Both thalamic lesions and high-frequency stimulation ameliorate tremor in diverse pathological conditions. Modern neurophysiological techniques have allowed the recording of the activity of thalamic neurons in patients with different clinical conditions. This has provided a better understanding of the functions of the motor thalamus in humans. The aim of the present article is to briefly review the major anatomic and physiological aspects of the motor thalamus as well as the electrophysiological findings described in humans undergoing surgical procedures.

Quality index for the quantification of the information recorded along standard microelectrode tracks to the subthalamic nucleus in parkinsonian patients

OBJECTIVE

To quantify the usefulness of the neuronal activity recorded on a standard microelectrode track to the subthalamic nucleus (STN) for the determination of the transition between the thalamus and the STN.

METHODS

The study is based on analysis of 689 extracelullar single units recorded on 70 tracks passing through the thalamus and the STN. Using four neuron parameters that were correlated with electrode depth, a quality index (QI) for each track was computed and compared with the subjective assessment by the electrophysiologist of the track quality.

RESULTS

Subjectively, the transition between the thalamus and the STN was detected in 49 tracks (usual track) and not detected on 21 tracks (unusual tracks). Objectively, spike frequency, cell burst index (BI), signal relative root mean square (RMS) and spike relative amplitude were correlated with electrode depth and used to compute track QI. The average QI index of usual and unusual tracks was 0.25 +/- 0.9 and 0.85 +/- 0.15 (mean +/- confidence interval at P < 0.001), respectively. In 20 patients, QI correlates with post-operative measurement of electrode length in the STN.

CONCLUSION

These results demonstrate that simple statistical analysis taking into account the variation of single-unit characteristics with electrode depth can discriminate between useful and useless tracks for the determination of the STN localisation.