Safety of Staged Bilateral MRgFUS Thalamotomy: Associations Between Lesion Characteristics, Stereotactic Coordinates, and Adverse Events

Staged bilateral magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is increasingly performed for medication-refractory essential tremor, yet the relationship between lesion characteristics and profiles of adverse events (AE) across sessions remains poorly characterized. We sought to examine how lesion volume, stereotactic coordinates, and session order relate to AE profiles in staged bilateral MRgFUS thalamotomy.

Retrospective analysis of 50 patients who underwent staged bilateral MRgFUS thalamotomy at a single center. AE were assessed at postoperative day 1 and 3-month follow-up. Lesion volumes were categorized into tertiles from the pooled distribution. Stereotactic coordinates were normalized to anterior commissure-posterior commissure distance. Linear regression assessed associations between coordinates and AE.

The second session was characterized by fewer sonications (6.0 ± 1.9 vs 6.5 ± 1.4, P = .013), lower peak temperatures (56.4 ± 2.9°C vs 57.3 ± 2.3°C, P = .044), and smaller lesion volumes (168.5 ± 107.7 mm3 vs 198.7 ± 85.1 mm3, P = .007), consistent with a conservative approach that maintained comparable tremor outcomes. At 3 months, AE rates were higher after the second session for gait/balance disturbance (44.0% vs 18.0%, P = .016) and sensory abnormalities (24.0% vs 8.0%, P = .033), despite similar immediate postoperative profiles. This divergence was volume-dependent, small lesions (126.8 mm3 or less) showed comparable rates between sessions, whereas medium and large lesions demonstrated substantially higher second-session rates. More posterior positioning was independently associated with speech deficits (P = .001) and mouth numbness (P = .014).

AE persistence after the second session was volume-dependent, with rates comparable to the first session at smaller lesion volumes but elevated at larger volumes. Posterior lesion positioning was independently associated with mouth numbness and speech deficits, supporting anterior targeting adjustments for contralateral procedures. These findings suggest that lesion volume constraint combined with anterior positioning may optimize the safety profile of staged bilateral MRgFUS thalamotomy, although prospective validation is needed to establish definitive volume thresholds.