• Artur Vetkas, Alexandre Boutet, Can Sarica, Jurgen Germann, Dave Gwun, Kazuaki Yamamoto, Hyun Ho Jung, Afnan Alkhotani, Nardin Samuel, Stefan Lang, Christopher R Conner, Gavin J B Elias, Cletus Cheyuo, Clement Chow, Brendan Santyr, Christian Iorio-Morin, Andrew Z Yang, Carolina Candeias da Silva, Alfonso Fasano, Suneil K Kalia, and Andres M Lozano.
• 1Department of Surgery, Division of Neurosurgery, University Health Network and University of Toronto.
• J. Neurosurg. 2024 Mar 1; 140 (3): 639647639-647.

ObjectiveThe use of magnetic resonance-guided focused ultrasound (MRgFUS) for the treatment of tremor-related disorders and other novel indications has been limited by guidelines advocating treatment of patients with a skull density ratio (SDR) above 0.45 ± 0.05 despite reports of successful outcomes in patients with a low SDR (LSDR). The authors' goal was to retrospectively analyze the sonication strategies, adverse effects, and clinical and imaging outcomes in patients with SDR ≤ 0.4 treated for tremor using MRgFUS.MethodsClinical outcomes and adverse effects were assessed at 3 and 12 months after MRgFUS. Outcomes and lesion location, volume, and shape characteristics (elongation and eccentricity) were compared between the SDR groups.ResultsA total of 102 consecutive patients were included in the analysis, of whom 39 had SDRs ≤ 0.4. No patient was excluded from treatment because of an LSDR, with the lowest being 0.22. Lesioning temperatures (> 52°C) and therapeutic ablations were achieved in all patients. There were no significant differences in clinical outcome, adverse effects, lesion location, and volume between the high SDR group and the LSDR group. SDR was significantly associated with total energy (rho = -0.459, p < 0.001), heating efficiency (rho = 0.605, p < 0.001), and peak temperature (rho = 0.222, p = 0.025).ConclusionsThe authors' results show that treatment of tremor in patients with an LSDR using MRgFUS is technically possible, leading to a safe and lasting therapeutic effect. Limiting the number of sonications and adjusting the energy and duration to achieve the required temperature early during the treatment are suitable strategies in LSDR patients.

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