Techniques, Indications, and Outcomes in Magnetic Resonance-guided Focused Ultrasound Thalamotomy for Tremor

Abstract

Magnetic resonance (MR)-guided focused ultrasound surgery (MRgFUS) is the latest minimally invasive stereotactic procedure, and thalamotomy using this novel modality has demonstrated its effectiveness and safety, especially for patients with essential tremor (ET) and Parkinson's disease (PD). In Japan, the application of MRgFUS to treat ET and PD has recently been covered by health insurance. Technically, the transducer with 1024 elements emits ultrasound beams, which are then focused on the target with a phase control, resulting in optimal ablation by thermal coagulation. The technical advantages of MRgFUS are continuous intraoperative monitoring of clinical symptoms and MR images and fine adjustment of the target by the steering function. Postoperative tremor control is compatible with other modalities, although long-term follow-up is necessary. The adverse effects are usually transient and acceptable. Prognostic factors for good tremor control include high temperature and large lesion size. A high skull density ratio is a factor to achieve high temperature and large lesioning, but it may not be necessary and sufficient for clinical outcomes. For patients with advanced symptoms such as bilateral tremor or head/neck tremor, deep brain stimulation may be recommended because of the adjustability of stimulation and the possibility of bilateral treatment. Patients have high expectations of MRgFUS because of its non-invasiveness. To perform this treatment safely and effectively, physicians need to understand the technological aspects, the physiological principles. To choose the appropriate modality, physicians also should recognize the clinical advantages and disadvantages of MRgFUS compared to other modalities.

Surgical Therapies for Parkinson Disease

“…4 The tip of the lesioning probe is heated to create an irreversible lesion by coagulating brain tissue at the target site. 4,19 With this intervention, contralateral motor UPDRS score was improved by 41% and dyskinesias by 57% at 1 year following unilateral pallidotomy. 23 Alternatively, unilateral subthalamotomy showed a 31% motor improvement on the Unified Parkinson's Disease Rating Scale at 2 years.…”

“…21 Additionally, the Bilateral Essential Tremor Treatment with FUS (BEST-FUS) study sponsored by University Health Network, Toronto, Canada, aims to perform contralateral MRIgFUS treatment on study participants who have previously undergone successful unilateral MRIgFUS, with an estimated study date completion in October 2024. 19,22 OTHER LESIONAL THERAPIES Surgical therapies for PD began in the early 1900s with lesioning techniques, such as cryothalamotomy and chemothalamotomy. 4 Following the introduction of levodopa in 1968, which revolutionized the patient's ability to treat clinical symptoms, ablative surgery for this indication decreased.…”

“…A single-arm clinical trial is assessing early safety and efficacy of bilateral treatment of medication-refractory essential tremor with MRIgFUS, with estimated study completion date in March 2026 21 . Additionally, the Bilateral Essential Tremor Treatment with FUS (BEST-FUS) study sponsored by University Health Network, Toronto, Canada, aims to perform contralateral MRIgFUS treatment on study participants who have previously undergone successful unilateral MRIgFUS, with an estimated study date completion in October 2024 19,22 …”

“…A skilled operator is needed to balance the potential side effects versus efficacy of the procedure as large lesions are expected to be more effective, although this increases the risk of side effects 16 . case 3-2 presents a typical case, and figure 3-2 illustrates a schematic of the MRIgFUS device 19 …”

“…The transducer elements emit ultrasound beams, which result in ablation by thermal coagulation when focused on a target 18 . For these patients with clinically probable PD, MRIgFUS can be used as another method to address symptoms poorly controlled with levodopa without a craniotomy, electrode penetration, anesthesia, or ionizing radiation 1,19 . Patients may consider MRIgFUS when restrictions to DBS are present, such as surgical risks, concerns about multiple clinic visits for stimulator setting optimization, or a patient’s reluctance to undergo brain surgery or have an implanted device 4,5 .…”