Lesions of the cerebello-thalamic tract rather than the ventral intermediate nucleus determine the outcome of focused ultrasound therapy in essential tremor: A 3T and 7T MRI-study.

INTRODUCTION: The ventral intermediate nucleus of the thalamus (VIM) is an important relay station receiving cerebellar and pallidal fiber tracts. Data on structural visualization of the VIM however is limited and uncertainty prevails to what extent lesional approaches to treat tremor affect the VIM itself or passing tracts. The aim of the study was to analyze the localization of individual lesions with respect to the VIM and the cerebello-thalamic tract (CTT). METHODS: We employed ultrahigh resolution (7 Tesla) MRI to delineate the VIM and performed 3 T-DTI-imaging pre- and post-interventional in seven ET patients undergoing transcranial magnetic resonance guided focused ultrasound (tcMRgFUS). Tremor improvement was measured using a modified subscore of the Clinical Rating Scale for Tremor. RESULTS: All subjects showed substantial tremor improvement (88.5%, range 80.7%-94,8%) after tcMRgFUS. We found only a minor overlap of the lesions with the VIM (4%, range 1%-7%) but a larger overlap with the CTT (43%, range 23%-60%) in all subjects. CONCLUSIONS: Lesions within the CTT rather than the VIM seem to drive the tremorlytic response and clinical improvement in tcMRgFUS.

Temperature distribution during radiofrequency ablation of spinal metastases in a human cadaver model: Comparison of three electrodes.

BACKGROUND: Radiofrequency ablation (RFA) temperatures reaching 45°C in adjacent tissues are cytotoxic to the spinal cord, nerves and surrounding tissues. OBJECTIVE: This study compares different RFA electrodes with regard to the temperature distribution during ablation of spinal metastases. METHODS: In vitro experimental study in isolated lumbar vertebrae of a human cadaveric spine. The temperature distribution of RFA electrodes was measured during ablation in human cadaveric lumbar vertebrae containing a simulated vertebral body lesion. The analysis compared a novel bipolar RFA electrode with two conventional monopolar RFA electrodes. A vertebral metastasis model was prepared in eight lumbar vertebrae for each electrode. Differences between the electrodes were evaluated with a one-way ANOVA. RESULTS: The lowest temperature at the thermocouples adjacent to the simulated lesion was achieved when using the bipolar RFA electrode (46.4 ± 3.3°C), but temperature difference to the monopolar RFA electrodes was not significant. In the neural foramen and epidural space of lumbar vertebrae the maximal temperature measured when using the bipolar RFA electrode was 37.0 ± 0°C and 37.3 ± 0.7°C, which was significantly lower than during ablation via either of the monopolar RFA electrodes (p ≤ 0.001). CONCLUSIONS: Temperatures in areas of adjacent tissue during RFA using a specific for spinal ablation designed electrode with integrated thermocouples were significantly lower compared to other electrodes, potentially reducing temperature related risks during ablation.