Single neurons in the thalamus and subthalamic nucleus process cardiac and respiratory signals in humans

Visceral signals are constantly processed by our central nervous system, enable homeostatic regulation, and influence perception, emotion, and cognition. While visceral processes at the cortical level have been extensively studied using non-invasive imaging techniques, very few studies have investigated how this information is processed at the single neuron level, both in humans and animals. Subcortical regions, relaying signals from peripheral interoceptors to cortical structures, are particularly understudied and how visceral information is processed in thalamic and subthalamic structures remains largely unknown. Here, we took advantage of intraoperative microelectrode recordings in patients undergoing surgery for deep brain stimulation (DBS) to investigate the activity of single neurons related to cardiac and respiratory functions in three subcortical regions: ventral intermedius nucleus (Vim) and ventral caudalis nucleus (Vc) of the thalamus, and subthalamic nucleus (STN). We report that the activity of a large portion of the recorded neurons (about 70%) was modulated by either the heartbeat, the cardiac inter-beat interval, or the respiration. These cardiac and respiratory response patterns varied largely across neurons both in terms of timing and their kind of modulation. A substantial proportion of these visceral neurons (30%) was responsive to more than one of the tested signals, underlining specialization and integration of cardiac and respiratory signals in STN and thalamic neurons. By extensively describing single unit activity related to cardiorespiratory function in thalamic and subthalamic neurons, our results highlight the major role of these subcortical regions in the processing of visceral signals.

Superficial Vein Thrombosis After Intra-articular Particulate Steroid Injection for Knee Osteoarthritis

ABSTRACT

Intra-articular steroid injections for knee osteoarthritis are a routine procedure in musculoskeletal clinics. While their role in osteoarthritis care is debatable, they serve as an important therapeutic option to relieve osteoarthritis-associated pain. Potential risks are self-limited (increased pain flare, local skin irritation, flushing, insomnia) or severe (septic arthritis, intravascular medication placement, and the deleterious effect on cartilage and bone). In our experience, more serious adverse events are rare. In this case, we present a complication secondary to intra-articular steroid administration that has not previously been reported in the literature: superficial vein thrombosis. This will raise awareness among clinicians, improve the informed consent process, and provide an approach for the management of subsequent injections.

Disease applications of spinal cord stimulation: Chronic nonmalignant pain

Neuropathic pain is a chronic condition representing a significant burden for society. It is estimated 1 out of 10 people over the age of 30 that in the US have been diagnosed with neuropathic pain. Most of the available treatments for neuropathic pain have moderate efficacy over time which limit their use; therefore, other therapeutic approaches are needed for patients. Spinal cord stimulation is an established and cost-effective modality for treating severe chronic pain. In this article we will review the current approved indications for the use of spinal cord stimulation in the US and the novel therapeutic options which are now available using this therapy.

A phase 1 open-label trial evaluating focused ultrasound unilateral anterior thalamotomy for focal onset epilepsy

OBJECTIVE

Focused ultrasound ablation (FUSA) is an emerging treatment for neurological and psychiatric diseases. We describe the initial experience from a pilot, open-label, single-center clinical trial of unilateral anterior nucleus of the thalamus (ANT) FUSA in patients with treatment-refractory epilepsy.

METHODS

Two adult subjects with treatment-refractory, focal onset epilepsy were recruited. The subjects received ANT FUSA using the Exablate Neuro (Insightec) system. We determined the safety and feasibility (primary outcomes), and changes in seizure frequency (secondary outcome) at 3, 6, and 12 months. Safety was assessed by the absence of side effects, that is, new onset neurological deficits or performance deterioration on neuropsychological testing. Feasibility was defined as the ability to create a lesion within the anterior nucleus. The monthly seizure frequency was compared between baseline and postthalamotomy.

RESULTS

The patients tolerated the procedure well, without neurological deficits or serious adverse events. One patient experienced a decline in verbal fluency, attention/working memory, and immediate verbal memory. Seizure frequency reduced significantly in both patients; one patient was seizure-free at 12 months, and in the second patient, the frequency reduced from 90-100 seizures per month to 3-6 seizures per month.

SIGNIFICANCE

This is the first known clinical trial to assess the safety, feasibility, and preliminary efficacy of ANT FUSA in adult patients with treatment-refractory focal onset epilepsy.

Lung Tumor Skin Metastasis: Case Report of a Solitary Cutaneous Ulcerated Lesion as Initial Manifestation of Lung Carcinoma

Lung cancer has the highest cancer incidence, and it is the most common cause of cancer death worldwide. Cutaneous metastases are infrequent compared to hilar nodes, adrenal glands, liver, brain, and bones. However, unusual skin lesions in patients at high risk of lung cancer should be regarded carefully to rule out a metastatic manifestation of an occult primary site tumor. Surgical excision, or incisional biopsy when the former is deemed unfeasible, should be performed to allow histopathological examination in case of occult primary site. In patients affected by advanced lung tumors, surgical excision could be beneficial in terms of pain control and improvement of the quality of life. We report a case of a solitary large skin lesion as an early manifestation of a lung adenocarcinoma.

Polypoid arteriovenous malformation of the rectum: A case report

Background

Intestinal arteriovenous malformation is an abnormal connection between arteries and veins that bypasses the capillary system and may be a cause of significant lower gastrointestinal bleeding. On endoscopy, arteriovenous malformations are usually flat or elevated, bright red lesions. Overall, rectal localization of arteriovenous malformations is rare. The same may be said about polypoid shape arteriovenous malformations. Herein, we present a case of a large rectal polypoid arteriovenous malformations.

Methods

Clinical, diagnostic, and treatment modalities of the patient were reviewed. Pre- and post-operative parameters were collected and analyzed. The clinical English literature is also reviewed and discussed

Results

A 60-year-old female patient was admitted to our emergency department for rectorrhagia and anemia. Rectoscopy revealed a polypoid lesion in the rectum and the biopsy showed fibrosis, necrosis areas, and hyperplastic glands. A total body contrast-enhanced computed tomography (CT) was performed revealing a parietal pseudonodular thickening with concentric growth and contrast enhancement, extending for about 53 mm. The mass wasn't removed endoscopically due to concentric growth, sessile implant, and submucosal nature. The patient underwent an uneventful laparoscopic anterior rectal resection. The postoperative hospitalization was free of complications. Histology showed the presence of a polypoid AVM composed of dilated arteries, veins, capillaries, and lymphatics, engaging the submucosa, muscularis, and subserosa layer.

Conclusion

After a review of the current English literature, we found only one case of rectal polypoid AVM. The scarcity of documented cases encumbers optimal diagnostic and treatment approaches.

Intraoperative lesion characterization after focused ultrasound thalamotomy

OBJECTIVE

Outcomes after focused ultrasound ablation (FUSA) for essential tremor remain heterogeneous, despite therapeutic promise. Clinical outcomes are directly related to the volume and location of the therapeutic lesions, consistent with CNS ablative therapies. Recent data demonstrate that postoperative diffusion MRI, specifically the quantification of intracellular diffusion by restricted diffusion imaging (RDI), can accurately characterize focused ultrasound lesions. However, it is unclear whether RDI can reliably detect focused ultrasound lesions intraoperatively (i.e., within a few minutes of lesioning) and whether the intraoperative lesions predict delayed clinical outcomes.

METHODS

An intraoperative imaging protocol was implemented that included RDI and T2-weighted imaging in addition to intraoperative MR thermography. Lesion characteristics were defined with each sequence and then compared. An imaging-outcomes analysis was performed to determine lesion characteristics associated with delayed clinical outcomes.

RESULTS

Intraoperative RDI accurately identified the volume and location of focused ultrasound lesions. Intraoperative T2-weighted imaging underestimated the lesion volume but accurately identified the location. Intraoperative RDI revealed that lesions of the ventral border of the ventral intermediate nucleus were significantly associated with postoperative tremor improvement. In contrast, the lesions extending into the inferolateral white matter were associated with postoperative ataxia.

CONCLUSIONS

These data support the acquisition of intraoperative RDI to characterize focused ultrasound lesions. Future research should test the histological correlates of intraoperative RDI and test whether it can be developed as feedback to optimize the current technique of FUSA.

Radiological identification of the globus pallidus motor subregion in Parkinson's disease

OBJECTIVE

Globus pallidus (GP) lesioning improves motor symptoms of Parkinson's disease (PD) and is occasionally associated with nonmotor side effects. Although these variable clinical effects were shown to be site-specific within the GP, the motor and nonmotor subregions have not been distinguished radiologically in patients with PD. The GP was recently found to have a distinct radiological signature on diffusion MRI (dMRI), potentially related to its unique cellular content and organization (or tissue architecture). In this study, the authors hypothesize that the magnitude of water diffusivity, a surrogate for tissue architecture, will radiologically distinguish motor from nonmotor GP subregions in patients with PD. They also hypothesize that the therapeutic focused ultrasound pallidotomy lesions will preferentially overlap the motor subregion.

METHODS

Diffusion MRI from healthy subjects (n = 45, test-retest S1200 cohort) and PD patients (n = 33) was parcellated based on the magnitude of water diffusivity in the GP, as measured orientation distribution function (ODF). A clustering algorithm was used to identify GP parcels with distinct ODF magnitude. The individual parcels were used as seeds for tractography to distinguish motor from nonmotor subregions. The locations of focused ultrasound lesions relative to the GP parcels were also analyzed in 11 patients with PD.

RESULTS

Radiologically, three distinct parcels were identified within the GP in healthy controls and PD patients: posterior, central, and anterior. The posterior and central parcels comprised the motor subregion and the anterior parcel was classified as a nonmotor subregion based on their tractography connections. The focused ultrasound lesions preferentially overlapped with the motor subregion (posterior more than central). The hotspots for motor improvement were localized in the posterior GP parcel.

CONCLUSIONS

Using a data-driven approach of ODF-based parcellation, the authors radiologically distinguished GP motor subregions in patients with PD. This method can aid stereotactic targeting in patients with PD undergoing surgical treatments, especially focused ultrasound ablation.

New Frontiers for Deep Brain Stimulation: Directionality, Sensing Technologies, Remote Programming, Robotic Stereotactic Assistance, Asleep Procedures, and Connectomics

Over the last few years, while expanding its clinical indications from movement disorders to epilepsy and psychiatry, the field of deep brain stimulation (DBS) has seen significant innovations. Hardware developments have introduced directional leads to stimulate specific brain targets and sensing electrodes to determine optimal settings via feedback from local field potentials. In addition, variable-frequency stimulation and asynchronous high-frequency pulse trains have introduced new programming paradigms to efficiently desynchronize pathological neural circuitry and regulate dysfunctional brain networks not responsive to conventional settings. Overall, these innovations have provided clinicians with more anatomically accurate programming and closed-looped feedback to identify optimal strategies for neuromodulation. Simultaneously, software developments have simplified programming algorithms, introduced platforms for DBS remote management via telemedicine, and tools for estimating the volume of tissue activated within and outside the DBS targets. Finally, the surgical accuracy has improved thanks to intraoperative magnetic resonance or computerized tomography guidance, network-based imaging for DBS planning and targeting, and robotic-assisted surgery for ultra-accurate, millimetric lead placement. These technological and imaging advances have collectively optimized DBS outcomes and allowed “asleep” DBS procedures. Still, the short- and long-term outcomes of different implantable devices, surgical techniques, and asleep vs. awake procedures remain to be clarified. This expert review summarizes and critically discusses these recent innovations and their potential impact on the DBS field.

Thermal Neuromodulation With Focused Ultrasound: Implications for the Technique of Subthreshold Testing

BACKGROUND

During focused ultrasound ablation (FUSA), the presumed stereotactic target is tested with subthreshold sonications before permanent ablation. This testing relies on ultrasound-induced reversible clinical effects (thermal neuromodulation, TN). However, the thermal dose and spot size thresholds to induce TN are not yet defined.

OBJECTIVE

To define the thermal dose and spot size thresholds associated with TN.

METHODS

We performed a retrospective analysis of intraoperative FUSA data of essential tremor patients. Sonications with a thermal dose of less than 25 cumulative equivalent minutes (CEM) were classified as subthreshold. The intraoperative writing samples were independently rated by 2 raters using the clinical rating scale for tremor. The association between thermal dose and tremor scores was statistically analyzed, and the thermal dose and spot size thresholds for TN were computed using leave-one-out cross-validation analysis.

RESULTS

A total of 331 pairs of sonications and writing samples were analyzed; 97 were classified as subthreshold sonications. TN was observed in 23 (24%) subthreshold sonications. The median tremor improvement during TN was 20% (interquartile range = 41.6). The thermal dose threshold for TN was 0.67 CEM (equivalent to 30 s thermal exposure at 43°C). The spot size threshold for TN was 2.46 mm. Ventral intermediate medial nucleus was exposed to TN thermal dose during subablative and ablative sonications.

CONCLUSION

The TN thermal dose and spot size thresholds are significantly higher than the current FUSA standard of care. We recommend long duration (>30 s), subthreshold sonications for intraoperative testing during FUSA. Future investigations should test whether the thermal dose threshold is tissue-specific and determine the mechanisms underlying focused ultrasound TN.

Functional Neuroimaging During Asleep DBS Surgery: A Proof of Concept Study

Object: A real-time functional magnetic resonance imaging (fMRI) feedback during ventral intermediate nucleus (VIM) deep brain stimulation (DBS) under general anesthesia (or “asleep” DBS) does not exist. We hypothesized that it was feasible to acquire a reliable and responsive fMRI during asleep VIM DBS surgery.

Methods: We prospectively enrolled 10 consecutive patients who underwent asleep DBS for the treatment of medication-refractory essential tremor. Under general anesthesia, we acquired resting-state functional MRI immediately before and after the cannula insertion. Reliability was determined by a temporal signal-to-noise-ratio >100. Responsiveness was determined based on the fMRI signal change upon insertion of the cannula to the VIM.

Results: It was feasible to acquire reliable fMRI during asleep DBS surgery. The fMRI signal was responsive to the brain cannula insertion, revealing a reduction in the tremor network's functional connectivity, which did not reach statistical significance in the group analysis.

Conclusions: It is feasible to acquire a reliable and responsive fMRI signal during asleep DBS. The acquisition steps and the preprocessing pipeline developed in these experiments will be useful for future investigations to develop fMRI-based feedback for asleep DBS surgery.

Acute Abdomen in a 91-Year-Old Male due to Perforated Jejunal Diverticulitis

Non-Meckel small intestine diverticular disease is a rare and mostly asymptomatic condition. However, rare cases of acute and emergent complications bear a high mortality rate. We report a case of a 91-year-old male that presented with an acute abdomen due to perforated jejunal diverticulitis. A review of the literature and key points of the condition are depicted. Although jejunal diverticulosis is rare, it must be considered in the differential diagnosis, especially in the elderly with signs of ambiguous abdominal pain and peritonitis.

Kranion, an open-source environment for planning transcranial focused ultrasound surgery: technical note

Transcranial focused ultrasound (FUS) ablation is an emerging incision-less treatment for neurological disorders. The factors affecting FUS treatment efficiency are not well understood. Kranion is open-source software that allows the user to simulate the planning stages of FUS treatment and to “replay” previous treatments for off-line analysis. This study aimed to investigate the relationship between skull parameters and treatment efficiency and to create a metric to estimate temperature rise during FUS. CT images from 28 patients were analyzed to validate the use of Kranion. For stereotactic targets within each patient, individual transducer element incident angles, skull density ratio, and skull thickness measurements were recorded. A penetration metric (the “beam index”) was calculated by combining the energy loss from incident angles and the skull thickness. Kranion accurately estimated the patient’s skull and treatment parameters. The authors observed significant changes in incident angles with different targets in the brain. Using the beam index as a predictor of temperature rise in a linear-mixed-effects model, they were able to predict the average temperature rise at the focal point during ablation with < 21% error (55°C ± 3.8°C) in 75% of sonications, and with < 44% (55°C ± 7.9°C) in 97% of sonications. This research suggests that the beam index can improve the prediction of temperature rise during FUS. Additional work is required to study the relationship between temperature rise and lesion shape and clinical outcomes.

3-Tesla MRI of deep brain stimulation patients: safety assessment of coils and pulse sequences

OBJECTIVE

Physicians are more frequently encountering patients who are treated with deep brain stimulation (DBS), yet many MRI centers do not routinely perform MRI in this population. This warrants a safety assessment to improve DBS patients’ accessibility to MRI, thereby improving their care while simultaneously providing a new tool for neuromodulation research.

METHODS

A phantom simulating a patient with a DBS neuromodulation device (DBS lead model 3387 and IPG Activa PC model 37601) was constructed and used. Temperature changes at the most ventral DBS electrode contacts, implantable pulse generator (IPG) voltages, specific absorption rate (SAR), and B1+rms were recorded during 3-T MRI scanning. Safety data were acquired with a transmit body multi-array receive and quadrature transmit-receive head coil during various pulse sequences, using numerous DBS configurations from “the worst” to “the most common.”

In addition, 3-T MRI scanning (T1 and fMRI) was performed on 41 patients with fully internalized and active DBS using a quadrature transmit-receive head coil. MR images, neurological examination findings, and stability of the IPG impedances were assessed.

RESULTS

In the phantom study, temperature rises at the DBS electrodes were less than 2°C for both coils during 3D SPGR, EPI, DTI, and SWI. Sequences with intense radiofrequency pulses such as T2-weighted sequences may cause higher heating (due to their higher SAR). The IPG did not power off and kept a constant firing rate, and its average voltage output was unchanged. The 41 DBS patients underwent 3-T MRI with no adverse event.

CONCLUSIONS

Under the experimental conditions used in this study, 3-T MRI scanning of DBS patients with selected pulse sequences appears to be safe. Generally, T2-weighted sequences (using routine protocols) should be avoided in DBS patients. Complementary 3-T MRI phantom safety data suggest that imaging conditions that are less restrictive than those used in the patients in this study, such as using transmit body multi-array receive coils, may also be safe. Given the interplay between the implanted DBS neuromodulation device and the MRI system, these findings are specific to the experimental conditions in this study.

Prospective Tractography-Based Targeting for Improved Safety of Focused Ultrasound Thalamotomy

BACKGROUND

Focused ultrasound thalamotomy (FUS-T) was recently approved for the treatment of refractory essential tremor (ET). Despite its noninvasive approach, FUS-T reinitiated concerns about the adverse effects and long-term efficacy after lesioning.

OBJECTIVE

To prospectively assess the outcomes of FUS-T in 10 ET patients using tractography-based targeting of the ventral intermediate nucleus (VIM).

METHODS

VIM was identified at the intercommissural plane based on its neighboring tracts: the pyramidal tract and medial lemniscus. FUS-T was performed at the center of tractography-defined VIM. Tremor outcomes, at baseline and 3 mo, were assessed independently by the Tremor Research Group. We analyzed targeting coordinates, clinical outcomes, and adverse events. The FUS-T lesion location was analyzed in relation to unbiased thalamic parcellation using probabilisitic tractography. Quantitative diffusion-weighted imaging changes were also studied in fiber tracts of interest.

RESULTS

The tractography coordinates were more anterior than the standard. Intraoperatively, therapeutic sonications at the tractography target improved tremor (>50% improvement) without motor or sensory side effects. Sustained improvement in tremor was observed at 3 mo (tremor score: 18.3 ± 6.9 vs 8.1 ± 4.4, P = .001). No motor weakness and sensory deficits after FUS-T were observed during 6-mo follow-up. Ataxia was observed in 3 patients. FUS-T lesions overlapped with the VIM parcellated with probablisitic tractography. Significant microstructural changes were observed in the white matter connecting VIM with cerebellum and motor cortex.

CONCLUSION

This is the first report of prospective VIM targeting with tractography for FUS-T. These results suggest that tractography-guided targeting is safe and has satisfactory short-term clinical outcomes.

Cognitive Task Performance During Titration Predicts Deep Brain Stimulation Treatment Efficacy: Evidence From a Case Study

Device titration is a major challenge when using deep brain stimulation (DBS) to treat behavioral disorders. Unlike in movement disorders, there is no reliable real-time clinical feedback for changes in complex behaviors resulting from DBS. Here, a female patient receiving DBS of the nucleus accumbens for the treatment of morbid obesity underwent cognitive testing via the flanker task alongside traditional methods of device titration. One set of stimulation parameters administered during titration resulted in acute cognitive improvement (p = 0.033) and increased frontal engagement as measured by electroencephalography (left anterior: p = 0.007, right anterior: p = 0.005) relative to DBS-OFF. The same parameters resulted in the most weight-loss during long-term continuous stimulation (47.8 lbs lost in 129 days) compared to the results of other stimulation settings. Diffusion tensor imaging analyses showed increased connectivity to dorsal attention networks and decreased connectivity to the default mode network for optimal parameters (p < 0.01). Our results provide evidence that targeted cognitive testing is a potentially useful tool for capturing acute effects of DBS stimulation during titration and predicting long-term treatment outcomes.

CLINICAL TRIAL REGISTRATION

www.ClinicalTrials.gov, identifier: NCT01512134.

Reliability of Intraoperative Testing During Deep Brain Stimulation Surgery

INTRODUCTION

Deep brain stimulation (DBS) is an effective treatment for medically refractory Parkinson's disease (PD). During DBS surgery, intraoperative testing is performed to confirm optimal lead placement by determining the stimulation thresholds for symptom improvement and side effects. However, the reliability of intraoperative testing in predicting distant postoperative thresholds is unknown. In this study, we hypothesized that intraoperative testing reliably estimates postoperative thresholds for both symptom improvement and side effects.

METHODS

We retrospectively analyzed a prospective database with intraoperative and postoperative thresholds for symptom improvement and side effects from a cohort of 66 PD patients who underwent STN DBS. We recorded the stimulation locations relative to the mid-commissural point. Within-patient stimulation pairs were generated by clustering the intraoperative stimulation locations closest to the DBS contacts. We computed the distance between stimulation locations and atlas-based pyramidal tract (PT) and medial lemniscus (ML) masks. A leave-one-out cross-validation analysis was performed to determine the reliability of intraoperative testing in predicting postoperative thresholds while controlling for the distance from the relevant tracks.

RESULTS

Intraoperative testing reliably predicted (area under ROC >0.8) postoperative thresholds for tremor and rigidity improvements, as well as stimulation-induced motor contractions and paresthesias. The reliability was poor for improvement in bradykinesia.

CONCLUSION

Intraoperative testing reliably predicts postoperative thresholds. These results are relevant during the informed consent process and patient counseling for DBS surgery. These will also guide the development of future methods for intraoperative feedback, especially during asleep DBS.

Predictors of Outcomes After Focused Ultrasound Thalamotomy

BACKGROUND

Magnetic resonance-guided focused ultrasound thalamotomy (FUS-T) is an emerging treatment for essential tremor (ET).

OBJECTIVE

To determine the predictors of outcomes after FUS-T.

METHODS

Two treatment groups were analyzed: 75 ET patients enrolled in the pivotal trial, between 2013 and 2015; and 114 patients enrolled in the postpivotal trials, between 2015 and 2016. All patients had medication-refractory, disabling ET, and underwent unilateral FUS-T. The primary outcome (hand tremor score, 32-point scale with higher scores indicating worse tremor) and the secondary outcome variables (Clinical Rating Scale for Tremor Part C score: 32-point scale with higher scores indicating more disability) were assessed at baseline and 1, 3, 6, and 12 mo. The operative outcome variables (ie, peak temperature, number of sonications) were analyzed. The results between the 2 treatment groups, pivotal and postpivotal, were compared with repeated measures analysis of variance and adjusted for confounding variables.

RESULTS

A total of 179 patients completed the 12-mo evaluation. The significant predictors of tremor outcomes were patient age, disease duration, peak temperature, and number of sonications. A greater improvement in hand tremor scores was observed in the postpivotal group at all time points, including 12 mo (61.9% ± 24.9% vs 52.1% ± 24.9%, P = .009). In the postpivotal group, higher energy was used, resulting in higher peak temperatures (56.7 ± 2.5 vs 55.6 ± 2.8°C, P = .004). After adjusting for age, years of disease, number of sonications, and maximum temperature, the treatment group was a significant predictor of outcomes (F = 7.9 [1,165], P = .005).

CONCLUSION

We observed an improvement in outcomes in the postpivotal group compared to the pivotal group potentially reflecting a learning curve with FUS-T. The other associations of tremor outcomes included patient age, disease duration, peak temperature, and number of sonications.

Connectivity-based selection of optimal deep brain stimulation contacts: A feasibility study

Background

The selection of optimal deep brain stimulation (DBS) parameters is time‐consuming, experience‐dependent, and best suited when acute effects of stimulation can be observed (e.g., tremor reduction).

Objectives

To test the hypothesis that optimal stimulation location can be estimated based on the cortical connections of DBS contacts.

Methods

We analyzed a cohort of 38 patients with Parkinson's disease (24 training, and 14 test cohort). Using whole‐brain probabilistic tractography, we first mapped the cortical regions associated with stimulation‐induced efficacy (rigidity, bradykinesia, and tremor improvement) and side effects (paresthesia, motor contractions, and visual disturbances). We then trained a support vector machine classifier to categorize DBS contacts into efficacious, defined by a therapeutic window ≥2 V (threshold for side effect minus threshold for efficacy), based on their connections with cortical regions associated with efficacy versus side effects. The connectivity‐based classifications were then compared with actual stimulation contacts using receiver‐operating characteristics (ROC) curves.

Results

Unique cortical clusters were associated with stimulation‐induced efficacy and side effects. In the training dataset, 42 of the 47 stimulation contacts were accurately classified as efficacious, with a therapeutic window of ≥3 V in 31 (66%) and between 2 and 2.9 V in 11 (24%) electrodes. This connectivity‐based estimation was successfully replicated in the test cohort with similar accuracy (area under ROC = 0.83).

Conclusions

Cortical connections can predict the efficacy of DBS contacts and potentially facilitate DBS programming. The clinical utility of this paradigm in optimizing DBS outcomes should be prospectively tested, especially for directional electrodes.

Anatomic Review of the Ventral Capsule/Ventral Striatum and the Nucleus Accumbens to Guide Target Selection for Deep Brain Stimulation for Obsessive-Compulsive Disorder

BACKGROUND

Disturbances in the reward network of the brain underlie addiction, depression, and obsessive-compulsive disorder. The ventral capsule/ventral striatum and nucleus accumbens (NAc) region is a clinically approved target for deep brain stimulation for obsessive-compulsive disorder.

METHODS

We performed a comprehensive literature review to define clinically relevant anatomy and connectivity of the ventral capsule/ventral striatum and NAc region to guide target selection for deep brain stimulation.

RESULTS

Architecturally and functionally, the NAc is divided into the core and the shell, with each area having different connections. The shell primarily receives limbic information, and the core typically receives information from the motor system. In general, afferents from the prefrontal cortex, hippocampus, and amygdala are excitatory. The dopaminergic projections to the NAc from the ventral tegmental area modulate the balance of these excitatory inputs. Several important inputs to the NAc converge at the junction of the internal capsule (IC) and the anterior commissure (AC): the ventral amygdalofugal pathways that run parallel to and underneath the AC, the precommissural fornical fibers that run anterior to the AC, axons from the ventral prefrontal cortex and medial orbitofrontal cortex that occupy the most ventral part of the IC and embedding within the NAc and AC, and the superolateral branch of the medial forebrain bundle located parallel to the anterior thalamic radiation in the IC.

CONCLUSIONS

The caudal part of the NAc passing through the IC-AC junction may be an effective target for deep brain stimulation to improve behavioral symptoms associated with obsessive-compulsive disorder.

Interleaving Stimulation in Parkinson's Disease, Tremor, and Dystonia

BACKGROUND/AIMS

Interleaving stimulation (ILS) in deep brain stimulation (DBS) provides individualized stimulation of 2 contacts delivered in alternating order. Currently, limited information on the utility of ILS exists. The aims of this study were to determine the practical applications and outcomes of ILS DBS in Parkinson's disease (PD), tremor, and dystonia.

METHODS

We performed a single-center, unblinded, retrospective chart review of all patients with DBS attempted on ILS at our referral center assessing for rationale and outcomes.

RESULTS

Fifty patients (PD, n = 27; tremor, n = 7; dystonia, n = 16 patients) tried ILS for 2 rationales: management of adverse effects (n = 29) and to improve clinical efficacy (n = 21). A total of 19 patients demonstrated improvement with ILS for adverse effect management predominately for the treatment of dyskinesias (n = 12). In the vast majority of dyskinetic patients, a contact added into the rostral zona incerta with ILS was performed. Nine out of 21 patients demonstrated improved clinical efficacy with ILS with all 6 PD patients who tried ILS for this rationale demonstrating benefit.

CONCLUSIONS

In PD, ILS provided benefits for dyskinesias and parkinsonism, with minimal improvement of other adverse effects. In tremor and dystonia, marginal effects in terms of mitigation of adverse effects and improvement of clinical outcomes were evident.

Predicting lesion size by accumulated thermal dose in MR-guided focused ultrasound for essential tremor

PURPOSE

To correlate the accumulated thermal dose (ATD) with lesion size in magnetic resonance (MR)-guided focused ultrasound (MRgFUS) thalamotomy to help guide future clinical treatments.

MATERIALS AND METHODS

Thirty-six patients with medication-refractory essential tremor were treated using a commercial MRgFUS brain system (ExAblate 4000, InSightec) in a 3T MR scanner (MR750, GE Healthcare). Intraoperative MR-thermometry was performed to measure the induced temperature and thermal dose distributions (thermal coefficient = -0.00909 ppm/°C). The ATD was calculated over multiple sonications with appropriate corrections for spatial-shifting artifacts. The ATD profile sizes obtained for dose values of 17, 40, 100, 200, and 240 cumulative equivalent minutes at 43°C (CEM) were correlated with the corresponding lesion sizes measured via axial T1- and T2-weighted MR images acquired 1 day post-treatment.

RESULTS

Of a total of 232 included sonications, 83 required corrections for off-resonance-induced spatial-shifting artifacts (correction range = [1.1,2.2] mm). The mean lesion sizes measured on T2-weighted MR images (6.2 ± 1.3 mm, mean ± SD) were 15% larger than those measured on corresponding T1-weighted MR images (5.3 ± 1.2 mm, mean ± SD). The ATD values that provided the best correlations with the measured lesion sizes on T2- and T1-weighted MR images were 100 and 200 CEM, respectively.

CONCLUSION

The ATD was correlated with lesion size measured 1 day following MRgFUS thalamotomy for essential tremor. These data provide useful information for predicting brain lesion size and determining treatment endpoints in future clinical MRgFUS procedures.

Comparison of Diffusion-Weighted MRI Reconstruction Methods for Visualization of Cranial Nerves in Posterior Fossa Surgery

Diffusion-weighted imaging (DWI)-based tractography has gained increasing popularity as a method for detailed visualization of white matter (WM) tracts. Different imaging techniques, and more novel, advanced imaging methods provide significant WM structural detail. While there has been greater focus on improving tract visualization for larger WM pathways, the relative value of each method for cranial nerve reconstruction and how this methodology can assist surgical decision-making is still understudied. Images from 10 patients with posterior fossa tumors (4 male, mean age: 63.5), affecting either the trigeminal nerve (CN V) or the facial/vestibular complex (CN VII/VIII), were employed. Three distinct reconstruction methods [two tensor-based methods: single diffusion tensor tractography (SDT) (3D Slicer), eXtended streamline tractography (XST), and one fiber orientation distribution (FOD)-based method: streamline tractography using constrained spherical deconvolution (CSD)-derived estimates (MRtrix3)], were compared to determine which of these was best suited for use in a neurosurgical setting in terms of processing speed, anatomical accuracy, and accurate depiction of the relationship between the tumor and affected CN. Computation of the tensor map was faster when compared to the implementation of CSD to provide estimates of FOD. Both XST and CSD-based reconstruction methods tended to give more detailed representations of the projections of CN V and CN VII/VIII compared to SDT. These reconstruction methods were able to more accurately delineate the course of CN V and CN VII/VIII, differentiate CN V from the cerebellar peduncle, and delineate compression of CN VII/VIII in situations where SDT could not. However, CSD-based reconstruction methods tended to generate more invalid streamlines. XST offers the best combination of anatomical accuracy and speed of reconstruction of cranial nerves within this patient population. Given the possible anatomical limitations of single tensor models, supplementation with more advanced tensor-based reconstruction methods might be beneficial.

Microelectrode recording findings within the tractography-defined ventral intermediate nucleus

OBJECTIVE

The ventral intermediate nucleus (VIM) of the thalamus is not visible on structural MRI. Therefore, direct VIM targeting methods for stereotactic tremor surgery are desirable. The authors previously described a direct targeting method for visualizing the VIM and its structural connectivity using deterministic tractography. In this combined electrophysiology and imaging study, the authors investigated the electrophysiology within this tractography-defined VIM (T-VIM).

METHODS

Thalamic neurons were classified based on their relative location to the T-VIM: dorsal, within, and ventral to the T-VIM. The authors identified the movement-responsive cells (kinesthetic and tremor cells), performed spike analysis (firing rate and burst index), and local field potential analysis (area under the curve for 13–30 Hz). Tremor efficacy in response to microstimulation along the electrode trajectory was also assessed in relation to the T-VIM.

RESULTS

Seventy-three cells from a total of 9 microelectrode tracks were included for this analysis. Movement-responsive cells (20 kinesthetic cells and 26 tremor cells) were identified throughout the electrode trajectories. The mean firing rate and burst index of cells (n = 27) within the T-VIM are 18.8 ± 9.8 Hz and 4.5 ± 5.4, respectively. Significant local field potential beta power was identified within the T-VIM (area under the curve for 13–30 Hz = 6.6 ± 7.7) with a trend toward higher beta power in the dorsal T-VIM. The most significant reduction in tremor was also observed in the dorsal T-VIM.

CONCLUSIONS

The electrophysiological findings within the VIM thalamus defined by tractography, or T-VIM, correspond with the known microelectrode recording characteristics of the VIM in patients with tremor.

3-Tesla MRI in patients with fully implanted deep brain stimulation devices: a preliminary study in 10 patients

OBJECTIVE The aim of this study was to evaluate the safety of 3-T MRI in patients with implanted deep brain stimulation (DBS) systems. METHODS This study was performed in 2 phases. In an initial phantom study, a Lucite phantom filled with tissue-mimicking gel was assembled. The system was equipped with a single DBS electrode connected to an internal pulse generator. The tip of the electrode was coupled to a fiber optic thermometer with a temperature resolution of 0.1°C. Both anatomical (T1- and T2-weighted) and functional MRI sequences were tested. A temperature change within 2°C from baseline was considered safe. After findings from the phantom study suggested safety, 10 patients with implanted DBS systems targeting various brain areas provided informed consent and underwent 3-T MRI using the same imaging sequences. Detailed neurological evaluations and internal pulse generator interrogations were performed before and after imaging. RESULTS During phantom testing, the maximum temperature increase was registered using the T2-weighted sequence. The maximal temperature changes at the tip of the DBS electrode were < 1°C for all sequences tested. In all patients, adequate images were obtained with structural imaging, although a significant artifact from lead connectors interfered with functional imaging quality. No heating, warmth, or adverse neurological effects were observed. CONCLUSIONS To the authors' knowledge, this was the first study to assess the clinical safety of 3-T MRI in patients with a fully implanted DBS system (electrodes, extensions, and pulse generator). It provided preliminary data that will allow further examination and assessment of the safety of 3-T imaging studies in patients with implanted DBS systems. The authors cannot advocate widespread use of this type of imaging in patients with DBS implants until more safety data are obtained.

Prediction and detection of seizures from simultaneous thalamic and scalp electroencephalography recordings

OBJECTIVE The authors explored the feasibility of seizure detection and prediction using signals recorded from the anterior thalamic nucleus, a major target for deep brain stimulation (DBS) in the treatment of epilepsy. METHODS Using data from 5 patients (13 seizures in total), the authors performed a feasibility study and analyzed the performance of a seizure prediction and detection algorithm applied to simultaneously acquired scalp and thalamic electroencephalography (EEG). The thalamic signal was obtained from DBS electrodes. The applied algorithm used the similarity index as a nonlinear measure for seizure identification, with patient-specific channel and threshold selection. Receiver operating characteristic (ROC) curves were calculated using data from all patients and channels to compare the performance between DBS and EEG recordings. RESULTS Thalamic DBS recordings were associated with a mean prediction rate of 84%, detection rate of 97%, and false-alarm rate of 0.79/hr. In comparison, scalp EEG recordings were associated with a mean prediction rate of 71%, detection rate of 100%, and false-alarm rate of 1.01/hr. From the ROC curves, when considering all channels, DBS outperformed EEG for both detection and prediction of seizures. CONCLUSIONS This is the first study to compare automated seizure detection and prediction from simultaneous thalamic and scalp EEG recordings. The authors have demonstrated that signals recorded from DBS leads are more robust than EEG recordings and can be used to predict and detect seizures. These results indicate feasibility for future designs of closed-loop anterior nucleus DBS systems for the treatment of epilepsy.

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.

Aspiration of parafalcine empyemas with flexible scope

PURPOSE

Subdural empyemas are considered neurosurgical emergencies, and the parafalcine location is particularly insidious. We revised the experience of general surgeons who are used to manage chronic pleural purulent collections with video-assisted thoracoscopy.

METHODS

With a similar technique, we successfully aspirated a parafalcine empyema using a flexible scope avoiding a more invasive craniotomy. A review of the treatment options of empyematous collections is also provided, focusing particularly on the hazardous parafalcine location.

RESULTS

The management of subdural empyemas poses different decision-making problems compared to common brain abscesses, urging a more rapid and holistic surgical treatment with minimally invasive approach. Endoscopic aspiration of parafalcine empyema was followed by complete recovery in our patient.

CONCLUSIONS

Flexible endoscopy is a promising method to obtain complete pus removal even from loculated collections through a bur hole, avoiding large craniotomies and consequent potential complications.

Tractography-Based Ventral Intermediate Nucleus Targeting: Novel Methodology and Intraoperative Validation

Background

The ventral intermediate nucleus of the thalamus is not readily visible on structural magnetic resonance imaging. Therefore, a method for its visualization for stereotactic targeting is desirable.

Objective

The objective of this study was to define a tractography‐based methodology for the stereotactic targeting of the ventral intermediate nucleus.

Methods

The lateral and posterior borders of the ventral intermediate nucleus were defined by tracking the pyramidal tract and medial lemniscus, respectively. A thalamic seed was then created 3 mm medial and anterior to these borders, and its structural connections were analyzed. The application of this method was assessed in an imaging cohort of 14 tremor patients and 15 healthy controls, in which we compared the tractography‐based targeting to conventional targeting. In a separate surgical cohort (3 tremor and 3 tremor‐dominant Parkinson's disease patients), we analyzed the accuracy of this method by correlating it with intraoperative neurophysiology.

Results

Tractography of the thalamic seed revealed the tracts corresponding to cerebellar input and motor cortical output fibers. The tractography‐based target was more lateral (12.5 [1.2] mm vs 11.5 mm for conventional targeting) and anterior (8.5 [1.1] mm vs 6.7 [0.3] mm, anterior to the posterior commissure). In the surgical cohort, the Euclidian distance between the ventral intermediate nucleus identified by tractography and the surgical target was 1.6 [1.1] mm. The locations of the sensory thalamus, lemniscus, and pyramidal tracts were concordant within <1 mm between tractography and neurophysiology.

Interpretation

The tractography‐based methodology for identification of the ventral intermediate nucleus is accurate and useful. This method may be used to improve stereotactic targeting in functional neurosurgery procedures. © 2016 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society

Advances in surgery for movement disorders

Movement disorder surgery has evolved throughout history as our knowledge of motor circuits and ways in which to manipulate them have expanded. Today, the positive impact on patient quality of life for a growing number of movement disorders such as Parkinson's disease is now well accepted and confirmed through several decades of randomized, controlled trials. Nevertheless, residual motor symptoms after movement disorder surgery such as deep brain stimulation and lack of a definitive cure for these conditions demand that advances continue to push the boundaries of the field and maximize its therapeutic potential. Similarly, advances in related fields - wireless technology, artificial intelligence, stem cell and gene therapy, neuroimaging, nanoscience, and minimally invasive surgery - mean that movement disorder surgery stands at a crossroads to benefit from unique combinations of all these developments. In this minireview, we outline some of these developments as well as evidence supporting topics of recent discussion and controversy in our field. Moving forward, expectations remain high that these improvements will come to encompass an even broader range of patients who might benefit from this therapy and decrease the burden of disease associated with these conditions. © 2016 International Parkinson and Movement Disorder Society.

Low-frequency Subthalamic Stimulation in Parkinson's Disease: Long-term Outcome and Predictors

BACKGROUND

Parkinson's disease patients undergoing subthalamic nucleus deep brain stimulation (STN DBS) at standard frequency (>100 Hz) often develop gait impairment, postural instability and speech difficulties. Low frequency stimulation (<100 Hz, LFS) can improve such axial symptoms, but there are concerns that improvement may be transient.

OBJECTIVE

To identify long-term outcome and predictors of low-frequency subthalamic stimulation in Parkinson's disease.

METHODS

Through a chart review we identified 85 out of 324 STN DBS patients who received a trial of LFS and describe their characteristics and outcome predictors.

RESULTS

Patients were switched to LFS (<100 Hz) 3.8 ± 3.3 years after surgery. Most patients (64%) attained a subjective improvement of gait, speech or balance for 2.0 ± 1.9 years. Motor scores improved within the first year after the stimulation change and showed a slower progression over time when compared to patients switched back to high frequency stimulation. UPDRS III axial score on medication before surgery and the y-axis coordinate of the active contact were independent predictors of LFS retention.

CONCLUSIONS

This report provides evidence that the use of LFS yields an enduring benefit in a considerable percentage of patients who develop axial motor symptoms during conventional stimulation.

Diffusion tensor imaging assessment of microstructural brainstem integrity in Chiari malformation Type I

OBJECTIVE The diagnosis of Chiari malformation Type I (CM-I) is primarily based on the degree of cerebellar tonsillar herniation even though it does not always correlate with symptoms. Neurological dysfunction in CM-I presumably results from brainstem compression. With the premise that conventional MRI does not reveal brain microstructural changes, this study examined both structural and microstructural neuroimaging metrics to distinguish patients with CM-I from age- and sex-matched healthy control subjects. METHODS Eight patients with CM-I and 16 controls were analyzed. Image postprocessing involved coregistration of anatomical T1-weighted with diffusion tensor images using 3D Slicer software. The structural parameters included volumes of the posterior fossa, fourth ventricle, and tentorial angle. Fractional anisotropy (FA) was calculated separately in the anterior and posterior compartments of the lower brainstem. RESULTS The mean age of patients in the CM-I cohort was 42.6 ± 10.4 years with mean tonsillar herniation of 12 mm (SD 0.7 mm). There were no significant differences in the posterior fossa volume (p = 0.06) or fourth ventricular volume between the 2 groups (p = 0.11). However, the FA in the anterior brainstem compartment was significantly higher in patients with CM-I preoperatively (p = 0.001). The FA values normalized after Chiari decompression except for persistently elevated FA in the posterior brainstem compartment in patients with CM-I and syrinx. CONCLUSIONS In this case-control study, microstructural alterations appear to be reliably associated with the diagnosis of CM-I, with a significantly elevated FA in the lower brainstem in patients with CM-I compared with controls. More importantly, the FA values normalized after decompressive surgery. These findings should be validated in future studies to determine the significance of diffusion tensor imaging-based assessment of brainstem microstructural integrity as an adjunct to the clinical assessment in patients with CM-I.

Anterior Nucleus Deep Brain Stimulation for Refractory Epilepsy

BACKGROUND:

Anterior nucleus (AN) deep brain stimulation (DBS) is a palliative treatment for medically refractory epilepsy. The long-term efficacy and the optimal target localization for AN DBS are not well understood.

OBJECTIVE:

To analyze the long-term efficacy of AN DBS and its predictors.

METHODS:

We performed a retrospective review of 16 patients who underwent AN DBS. We selected only patients with reliable seizure frequency data and at least a 1-year follow-up. We studied the duration of the seizure reduction after DBS insertion and before stimulation (the insertional effect) and its association with long-term outcome. We modeled the volume of activation using the active contacts, stimulation parameters, and postoperative imaging. The overlap of this volume was plotted in Montreal Neurological Institute 152 space in 7 patients with significant clinical efficacy.

RESULTS:

Nine patients reported a decrease in seizure frequency immediately after electrode insertion (insertional or microthalamotomy effect). The duration of insertional effect varied from 2 to 4 months. However, 1 patient had a long-term insertional effect of 36 months. Altogether, 11 patients reported &gt;50% decrease in seizure frequency with long-term stimulation. The most common pattern of seizure control was immediate and sustained stimulation benefit (n = 8). In patients with long-term stimulation benefit, the efficacious target was localized in the anteroventral AN in close proximity to the mammillothalamic tract.

CONCLUSION:

AN DBS is efficacious in the control of seizure frequency in selected patients. An insertional effect is commonly observed (56%). The most efficacious site of stimulation appears to be the anteroventral AN.

Neuromodulation for Epilepsy

Several palliative neuromodulation treatment modalities are currently available for adjunctive use in the treatment of medically intractable epilepsy. Over the past decades, a variety of different central and peripheral nervous system sites have been identified, clinically and experimentally, as potential targets for chronic, nonresponsive therapeutic neurostimulation. Currently, the main modalities in clinical use, from most invasive to least invasive, are anterior thalamus deep brain stimulation, vagus nerve stimulation, and trigeminal nerve stimulation. Significant reductions in seizure frequency have been demonstrated in clinical trials using each of these neuromodulation therapies.