Cavitations During Mrgfus Thalamotomy for Tremor Do Not Prevent Satisfactory Tremor Outcomes

Introduction: Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is increasingly utilized to treat refractory essential tremor (ET) and tremor dominant Parkinson’s disease (TdPD). Cavitations are microscopic rapidly expanding and violently collapsing pockets of water vapor created by low pressure regions of the ultrasonic waves. Cavitations typically occur at higher treatment energies, disrupt sonication, and can prevent the delivery of intended energy. Several techniques exist to manage cavitations, including slight adjustments to the target or using lower energies, however it is unclear whether adequate tremor results can be achieved reliably.

Methods: We retrospectively evaluated 275 cases of MRgFUS thalamotomy performed from 2020 to 2024 at a tertiary academic hospital. For patients with and without cavitations, we compared skull density ratio (SDR), maximum sonication energy delivered, and tremor outcomes via the Clinical Rating Scale for Tremor Part B (CRST-B).

Results: Among 275 treated patients, 92 (33.5%) experienced cavitations. The average SDR was 0.51 for those with cavitations versus 0.55 for those without (p = 0.001). Mean maximum sonication energies were 20.6 kJ for patients with cavitations compared with 14.8 kJ for patients without (p < 0.001). Higher sonication energies were associated with cavitation occurrence (OR = 1.06, 95% CI 1.03 – 1.09, p < 0.001). The lowest sonication energy at which a cavitation occurred was 6.5 kJ. Half of cavitations occurred with maximum energies below 19 kJ. Patients with and without cavitations experienced similar improvements in tremor, with mean CRST-B for those with cavitations decreased from baseline 10.5 to 2.7 post-procedurally, and for those without decreased from baseline 12.3 to 4.0 post-procedurally (p = 0.09).

Conclusion : While cavitations are commonly experienced during MRgFUS thalamotomy for tremor, in general, they can be managed to achieve tremor outcomes comparable with patients who did not experience cavitations. As anticipated, cavitations were associated with higher maximum sonication energies.