Radiofrequency vs. Microwave Ablation in Osteoid Osteoma: Comparative Outcomes and Prognostic Factors.

Background: Osteoid osteoma (OO) is a benign osteogenic tumor that causes severe pain despite its small size. Minimally invasive image-guided thermal ablation has replaced surgery as the treatment of choice. While radiofrequency ablation (RFA) is considered the gold standard, microwave ablation (MWA) offers faster and more homogeneous heating, though comparative evidence remains limited. Methods: We retrospectively analyzed 53 patients with OO treated with RFA (n = 27) or MWA (n = 26) between 2014 and 2023. All procedures were CT-guided. Technical success, clinical success, recurrence, complications, and prognostic factors-including the nidus diameter and eccentricity index-were evaluated over a minimum 24-month follow-up period. Results: Technical success was achieved in all cases. Overall clinical success was 94.3% (96.2% MWA vs. 92.6% RFA, p = 1.000). Two recurrences (4%) occurred, unrelated to device type. One major complication (1.9%, third-degree skin burn after MWA) was noted. Median nidus diameter was 7 mm; lesions ≥10 mm were significantly linked to failure (p = 0.009). Logistic regression identified nidus size as the strongest outcome predictor, with the eccentricity index showing a borderline effect. Conclusions: Both RFA and MWA are safe and effective for OO, with comparable outcomes and low recurrence rates. Treatment selection should prioritize lesion-specific factors-particularly nidus size ≥ 10 mm and geometry-rather than device type. Lesion size (≥10 mm) and geometry-not ablation modality-were the principal determinants of treatment success. Individualized modality selection based on these features may optimize outcomes.