Treatment-related alterations of imaging findings in osteoid osteoma after percutaneous radiofrequency ablation.

Objectives: We aimed to report the long-term outcomes of osteoid osteoma patients and to determine CT and dynamic contrast-enhanced MR imaging characteristics of radiofrequency ablation (RFA) treatment related changes of osteoid osteoma between follow-up periods.
Materials and Methods: Thirty patients (seven female, 23 male) who underwent CT-guided RFA of osteoid osteoma were included. Follow-up imaging examinations were divided into two subgroups; first (1-3 months) and second (> 6 months) periods. Nidus size, calcification, cortical thickening, maximum signal intensity (SImax), time of SImax (Tmax), slope of signal intensity-time (SIT) curves were noted. CT and dynamic MR imaging findings were compared between follow-up periods.
Results: Clinical success rate was 100%. The mean of OO nidi size was 5.85 ± 1.98 mm before treatment. There was a significant difference for OO nidi sizes between pretreatment and second follow-up period examinations (p = 0.002). SImax and slope of SIT curves of all patients (100%) showed decrease on follow-up MRIs. There was a significant decrease for SImax values between pretreatment and second follow-up period. There was a significant decrease for slope of SIT curves between pretreatment and both follow-up periods.
Conclusions: RFA is an effective and safe treatment choice for osteoid osteomas. On follow-up imaging, slope of SIT curve and Tmax have the most important positive predictive value for long-term outcomes and single dynamic contrast-enhanced MRI within first 3 months after treatment may be sufficient for symptom-free patients.