Skull Lesions after MR-Guided High-Intensity Focused Ultrasound: A Case Series

Transcranial MR-guided high-intensity focused ultrasound (HIFUS) ablation is a therapeutic technique for essential tremor and tremor-dominant Parkinson disease. Skull marrow lesions may occur posttreatment and mimic metastatic disease. In this retrospective study of 10 patients receiving a delayed posttreatment MRI, 4 patients developed skull lesions. There were no lesions on immediate posttreatment MR scans obtained within 24 hours. Skull lesions on delayed scans weeks to months after HIFUS consisted of multiple heterogeneous regions, prompting 1 patient to undergo a complete metastatic work-up that was negative for primary neoplasm. Another patient with prolonged headaches had ring-enhancing lesions on MRI obtained 23 days after treatment. Patients with skull lesions received significantly greater maximum energy (40 [9] versus 12 [3] kJ, mean [SD]; P < .01), total energy (113 [45] versus 44 [13] kJ; P < .01), and had a lower skull density ratio (0.41 [0.03] versus 0.56 [0.08]; P < .01) compared with those without lesions. While there do not appear to be harmful effects of these presumed thermal lesions, the long-term clinical significance is not known. In summary, skull lesions after transcranial MR-guided HIFUS ablation are typically asymptomatic and associated with higher acoustic energies. It is critical that radiologists recognize this entity to avoid unnecessary workups for metastatic disease. Further research is needed to minimize skull heating in patients requiring high acoustic energy for ablation, to understand the time course of skull lesions, and determine the long-term clinical significance.