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

OBJECTIVE 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. METHODS 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. RESULTS 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. CONCLUSIONS 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.