Magnetic Resonance-guided Focused Ultrasound Surgery (MRgFUS) for ablation of osteoid osteoma: Long-term results from 10 years of experience.

Osteoid Osteoma (OO) is a benign but extremely painful bone lesion, mostly treated using Radiofrequency Ablation with needle (RFA). Magnetic Resonance-guided Focused Ultrasound Surgery (MRgFUS) is an alternative technique able to ablate without using needles or skin incisions. Given the scarcity of literature in this field, the purpose of this paper is to retrospectively analyze long-term results of MRgFUS treatments of OO and to investigate technical limits. This is a retrospective analysis of all the MRgFUS procedures performed in our institution to treat OOs. Demographic, clinical data, and morphological features were analyzed, looking for correlation between the clinical results and the morphological features. Sixty-seven procedures were analyzed. The success rate - intended as complete pain relief - was 91 %. Almost all the patients (60 out of 67) were followed up to 4 years. A thick bone cortex above the nidus (p.014) and a short distance between the nidus and the ultrasound source (p.002) were statistically linked to failure. No complications were recorded. This is the largest series of OO treated using MRgFUS even reported. The main strength of this study lies in its large sample size and the extended follow-up period for nearly all patients (4 years for 90 % of patients) which allow us to clearly confirm the safety and efficacy of this ablative technique. Moreover, exclusion criteria for this treatment modality are proposed, based on two causes of treatment failure identified during our procedures.