Volumetric analysis of magnetic resonance–guided focused ultrasound thalamotomy lesions

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>Magnetic resonance–guided focused ultrasound (MRgFUS) thalamotomy was recently approved for use in the treatment of medication-refractory essential tremor (ET). Previous work has described lesion appearance and volume on MRI up to 6 months after treatment. Here, the authors report on the volumetric segmentation of the thalamotomy lesion and associated edema in the immediate postoperative period and 1 year following treatment, and relate these radiographic characteristics with clinical outcome.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>Seven patients with medication-refractory ET underwent MRgFUS thalamotomy at Brigham and Women’s Hospital and were monitored clinically for 1 year posttreatment. Treatment effect was measured using the Clinical Rating Scale for Tremor (CRST). MRI was performed immediately postoperatively, 24 hours posttreatment, and at 1 year. Lesion location and the volumes of the necrotic core (zone I) and surrounding edema (cytotoxic, zone II; vasogenic, zone III) were measured on thin-slice T2-weighted images using Slicer 3D software.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>Patients had significant improvement in overall CRST scores (baseline 51.4 ± 10.8 to 24.9 ± 11.0 at 1 year, p = 0.001). The most common adverse events (AEs) in the 1-month posttreatment period were transient gait disturbance (6 patients) and paresthesia (3 patients). The center of zone I immediately posttreatment was 5.61 ± 0.9 mm anterior to the posterior commissure, 14.6 ± 0.8 mm lateral to midline, and 11.0 ± 0.5 mm lateral to the border of the third ventricle on the anterior commissure–posterior commissure plane. Zone I, II, and III volumes immediately posttreatment were 0.01 ± 0.01, 0.05 ± 0.02, and 0.33 ± 0.21 cm<jats:sup>3</jats:sup>, respectively. These volumes increased significantly over the first 24 hours following surgery. The edema did not spread evenly, with more notable expansion in the superoinferior and lateral directions. The spread of edema inferiorly was associated with the incidence of gait disturbance. At 1 year, the remaining lesion location and size were comparable to those of zone I immediately posttreatment. Zone volumes were not associated with clinical efficacy in a statistically significant way.</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>MRgFUS thalamotomy demonstrates sustained clinical efficacy at 1 year for the treatment of medication-refractory ET. This technology can create accurate, predictable, and small-volume lesions that are stable over time. Instances of AEs are transient and are associated with the pattern of perilesional edema expansion. Additional analysis of a larger MRgFUS thalamotomy cohort could provide more information to maximize clinical effect and reduce the rate of long-lasting AEs.</jats:p></jats:sec>

Magnetic resonance–guided focused ultrasound thalamotomy for treatment of essential tremor: A 2‐year outcome study

“…Lesion size is associated with clinical efficacy postradiofrequency ablation for movement disorders, but the same relationship is less clear for MRgFUS thalamotomy . Our model based on this relatively large cohort provides evidence to support the importance of larger initial lesion size to sustained clinical benefit.…”

“…These observations may be explained by the expected evolution of a thermocoagulative lesion, which has been described in both MRgFUS and radiofrequency literature. Lesion size decreases rapidly within the first 3 months after MRgFUS thermoablation . Similarly, the relapse in tremor may be the result of a combination of lesion shrinkage, reduction in perilesional edema, or inaccurate targeting.…”

Improved Vim targeting for focused ultrasound ablation treatment of essential tremor: A probabilistic and patient‐specific approach

“…There have been conflicting results from the literature showing both that ablation volume correlates (Federau et al, 2018; Pineda‐Pardo et al, 2020) or does not correlate (Atkinson et al, 2002; Goodman et al, 1998; Harary et al, 2018; Hariz & Hirabayashi, 1997) with clinical outcome. However, Pineda‐Pardo et al, as well as Boutet et al (2018), did find that larger lesions were also associated with more adverse effects and note that reliable control over the lesion volume is important.…”

“…The 1‐month clinical timepoint was chosen based on the availability of a complete set of clinical outcome measurements for all 14 patients in our study. In addition, the 1‐month timepoint is an intermediate timepoint that is sufficiently close in time to the MRgFUS procedure to show strong therapeutic effects (the therapeutic effect has been observed to decrease over time in some patients), but sufficiently far in time from the procedure that edema and adverse events are reduced (Chang et al, 2015; Harary et al, 2018; Jung et al, 2015; Wintermark et al, 2014). Evaluation with clinical outcomes at later timepoints will be critical for assessing the ability of our probabilistic target region to predict longer term therapeutic effects.…”

“…We investigated whether a proximity‐to‐target metric, defined as the overlap of each patient's ablation core with this probabilistic target region, correlated with clinical outcome at 1 month. The 1‐month timepoint was selected for assessing clinical outcome based on the availability of a complete set of clinical outcome measurements for all patients, as well as being a timepoint that is both sufficiently close in time to the MRgFUS procedure to show strong therapeutic effects, but sufficiently delayed to allow for decreased edema and reduced adverse events (Chang et al, 2015; Harary, Essayed, Valdes, McDannold, & Cosgrove, 2018; Jung et al, 2015). Lastly, we tested to see if this proximity‐to‐probabilistic‐target metric was a better predictor of clinical outcome than the corresponding proximity metric computed between the ablation core and the standard initial target.…”