Safety and accuracy of incisionless transcranial MR-guided focused ultrasound functional neurosurgery: single-center experience with 253 targets in 180 treatments

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Since the first clinical application of the incisionless magnetic resonance–guided focused ultrasound (MRgFUS) technology only small series of patients have been reported, and thus only extrapolations of the procedure-related risks could be offered. In this study, the authors analyze side-effects and targeting accuracy in 180 consecutive treatments with MRgFUS for chronic therapy-resistant idiopathic Parkinson’s disease (PD), essential tremor (ET), cerebellar tremor (CT), and neuropathic pain (NP), all performed in their dedicated center.


A total of 180 treatments with MRgFUS for chronic therapy-resistant idiopathic PD, ET, CT, and NP were prospectively assessed for side-effects and targeting accuracy. Monitoring for later side-effects was continued for at least 3 months after the procedure in all but 1 case (0.6%); in that single case, the patient was lost to follow-up after an uneventful early postoperative course. The surgical targets were the pallidothalamic tract (pallidothalamic tractotomy, n = 105), the cerebellothalamic tract (cerebellothalamic tractotomy, n = 50), the central lateral nucleus (central lateral thalamotomy, n = 84), the centrum medianum (centrum medianum thalamotomy, n = 12), and the globus pallidus (pallidotomy, n = 2). Cognitive testing was performed before, 1–2 days after, and 1 year after the procedure. The Mini–Mental State Examination (MMSE) was used for the first 29 cases and was then replaced by the Montreal Cognitive Assessment (MoCA). Lesion reconstruction and measurement of targeting accuracy were done on 2-day posttreatment MR images for each performed target. To determine targeting accuracy measurement, 234 out of the 253 lesions depicted in the 2-day postoperative MR examination could be 3D-reconstructed.


The mean MoCA score was slightly improved 2 days postoperatively (p = 0.002) and remained stable at 1-year follow-up (p = 0.03). The mean MMSE score was also slightly improved 2 days postoperatively and at 1-year follow-up, but the improvement was not statistically significant (p = 0.06 and p = 0.2, respectively). The mean (± SD) accuracy was 0.32 ± 0.29 mm, 0.29 ± 0.28 mm, and 0.44 ± 0.39 mm for the mediolateral, anteroposterior, and dorsoventral dimensions, respectively. The mean 3D accuracy was 0.73 ± 0.39 mm. As to side-effects, 14 events over 180 treatments were documented. They were classified into procedure-related (n = 4, 2.2%), effect on neighboring structures (n = 3, 1.7%), and disease-related (n = 7, 3.9%). There was no bleeding.


The incisionless transcranial MRgFUS technology demonstrates a higher targeting accuracy and a lower side-effect profile than techniques requiring cerebral penetration. In the absence of penetration brain shift, this technique avoids the placement of a thermolesion away from the chosen target, thus suppressing the need for reversible therapeutic energy application. With the use of proper physiopathology-based targets, definitive therapeutic effects can be coupled with sparing of sensory, motor, and paralimbic/multimodal thalamocortical functions. Clinical efficacy, not analyzed in this investigation, will ultimately rest in proper target selection and optimized thermolesional coverage of the target.

ABBREVIATIONS AC = anterior commissure; AP = anteroposterior; CLT = central lateral thalamotomy; CMT = centrum medianum thalamotomy; CT = cerebellar tremor; CTT = cerebellothalamic tractotomy; DBS = deep brain stimulation; DV = dorsoventral; ET = essential tremor; MoCA = Montreal Cognitive Assessment; ML = mediolateral; MMSE = Mini–Mental State Examination; MRgFUS = MR-guided focused ultrasound; NP = neuropathic pain; PC = posterior commissure; PD = Parkinson’s disease; PTT = pallidothalamic tractotomy; RF = radiofrequency.

Article Information

Correspondence Marc Gallay: Center for Ultrasound Functional Neurosurgery, Solothurn, Switzerland.

INCLUDE WHEN CITING Published online May 25, 2018; DOI: 10.3171/2017.12.JNS172054.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.



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    Measurement of targeting accuracy on T2-weighted MR images obtained on postoperative day 2. Upper: Screenshot of the mediolateral (ML) and anteroposterior (AP) accuracy measurements on a T2-weighted axial image, using PACS viewer software (Synedra). The intercommissural line (ICL, red line) is drawn first, and then the anterior commissure (AC) and posterior commissure (PC) lines are drawn perpendicular to that line. Finally, the midcommissural line (MCL) is drawn at an equal distance from the AC and PC. The geometrical center of the lesion is then estimated by drawing 2 diameters (omitted for clarity). The ML coordinate (blue line) is measured from the border of the ventricle to that center and the AP coordinate from the MCL to that center. Lower: Screenshot of dorsoventral (DV) accuracy measurement on a sagittal T2-weighted scan. The ICL is drawn on the midsagittal scan and then reported to the sagittal slice where the lesion is the largest. The height (positive direction, blue line) and depth (negative direction, white line) of the lesion are measured and added, and the result is halved: this gives the DV coordinate of the center of the lesion. B = lesion extension above the ICL; C = lesion extension below ICL; E = AC-PC distance; F = midcommissural distance; H = distance of the center of the lesion to the thalamic border. Figure is available in color online only.

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    The 4 main targets displayed on axial T2-weighted MR images obtained 2 days after treatment. A: For central lateral thalamotomy—the posterior part of the central lateral nucleus (CLp) 6 mm dorsal to the intercommissural plane (D6). B: For pallidothalamic tractotomy—the pallidothalamic tract (indicated in this image by PTT) at DV0 (intercommissural plane). C: For centrum medianum thalamotomy—the centrum medianum (CM, centromedian nucleus) at D2. D: For cerebellothalamic tractotomy—the cerebellothalamic tract (indicated in this image by CTT) 4 mm below DV0 (V4). Figure is available in color online only.

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    Measured accuracy. We obtained a mean (± SD) accuracy of 0.32 ± 0.29 mm, 0.29 ± 0.28 mm, and 0.44 ± 0.39 mm for ML, AP, and DV dimensions, respectively. The mean 3D accuracy was 0.73 ± 0.39 mm. Figure is available in color online only.

  • View in gallery

    Dimensions of the 234 reconstructed lesions (depicted in black) in the axial, coronal, and sagittal planes. All of the reconstructed lesions are located inside the ellipsoid (red) of 4 mm diameter and 6 mm height, representing the average volume of our targets as determined from the stereotactic atlas of Morel.30,32 Nine measurements in ML (3.8%), 5 in AP (2.1%), and 19 in DV (7.9%) were 1 mm or greater, and 12 3D measurements were 1.5 mm or greater. Figure is available in color online only.



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