Factors influencing magnetic resonance imaging changes associated with pelvic bone injury after high-intensity focused ultrasound ablation of uterine fibroids: a retrospective case-control study

Background: The application of high-intensity focused ultrasound (HIFU) in the treatment of uterine fibroids is becoming increasingly widespread, and postoperative collateral thermal damage to adjacent tissue has become a prominent subject of discussion. However, there is limited research related to bone injury. Therefore, the aim of this study was to investigate the potential factors influencing unintentional pelvic bone injury after HIFU ablation of uterine fibroids with magnetic resonance imaging (MRI). Methods: A total of 635 patients with fibroids treated with HIFU in the First Affiliated Hospital of Chongqing Medical University were enrolled. All patients underwent contrast-enhanced MRI (CE-MRI) pre-and post-HIFU. Based on the post-treatment MRI, the patients were divided into two groups: pelvic bone injury group and non-injury group, while the specific site of pelvic bone injury of each patient was recorded. The univariate and multivariate analyses were used to assess the correlations between the factors of fibroid features and treatment parameters and pelvic bone injury, and to further analyze the factors influencing the site of injury. Results: Signal changes in the pelvis were observed on CE-MRI in 51% (324/635) of patients after HIFU. Among them, 269 (42.4%) patients developed sacral injuries and 135 (21.3%) had pubic bone injuries. Multivariate analyses showed that patients with higher age [P=0.003; odds ratio (OR), 1.692; 95% confidence interval (CI): 1.191-2.404], large anterior side-to-skin distance of fibroid (P<0.001; OR, 2.297; 95% CI: 1.567-3.365), posterior wall fibroid (P=0.006; OR, 1.897; 95% CI: 1.204-2.989), hyperintensity on T2 weighted imaging (T2WI, P=0.003; OR, 2.125; 95% CI: 1.283-3.518), and large therapeutic dose (TD, P<0.001; OR, 3.007; 95% CI: 2.093-4.319) were at higher risk of postoperative pelvic bone injury. Further analysis of the factors influencing the site of the pelvic bone injury showed that some of the fibroid features and treatment parameters were associated with it. Moreover, some postoperative pain-related adverse events were associated with the pelvic bone injury. Conclusions: Post-HIFU treatment, patients may experience pelvic injuries to the sacrum, pubis, or a combination of both, and some of them experienced adverse events. Some fibroid features and treatment parameters are associated with the injury. Taking its influencing factors into full consideration preoperatively, slowing down treatment, and prolonging intraoperative cooling phase can help optimize treatment decisions for HIFU.