Enhancing precision in MRgFUS for tremor treatment: a systematic review of tractography-based VIM targeting approaches.

Background: Magnetic resonance guided focused ultrasound (MRgFUS) thalamotomy has been an effective treatment option in the management of various tremor etiologies. The process of targeting the VIM thalamic location relies on indirect atlas/coordinate-based systems using anatomic reference points. With advancing imaging modalities, thalamic structures can be better visualized resulting in additional targeting techniques and improved accuracy.

Objectives: To identify and evaluate MRgFUS thalamotomy targeting techniques for tremor beyond atlas/coordinate-based systems.

Methods: A systematic review was conducted in Embase, Cochrane, and PubMed. Studies including MRgFUS for tremor, targeting methods, and tremor outcomes were included. After review of 297 studies, 13 met inclusion criteria.

Results: All 13 studies used tractography to visualize various combinations of white matter tracts to guide target acquisition. These tracts include the medial lemniscus (ML), corticospinal tract (CST), and the dentatorubrothalamic tracts (DRTT) which was further delineated into the non-decussating (ndDRTT) and a decussating components (dDRTT) by some studies. At least 50% reduction was reported by all studies with paresthesia and gait instability being the most common side effects, although mostly mild and transient.

Conclusions: Advanced targeting via tractography may lead to better outcomes and could broaden the eligibility criteria for MRgFUS. Individualized targeting allows for more precise sonication, potentially reducing the number of sonications needed, improving patient tolerance, making sedation a viable option, and boosting effectiveness, especially in cases of atypical anatomy. To confirm these potential benefits in MRgFUS thalamotomy, standardized trials are definitely needed.