Factors associated with treatment response to microwave ablation of benign thyroid nodules: a retrospective single-center study of nodule composition and vascularity

Background This study aimed to evaluate radiological and procedural factors associated with treatment response in benign thyroid nodules treated with microwave ablation (MWA). Methods Of 90 consecutive patients who underwent MWA for cytologically benign (Bethesda II) thyroid nodules, 80 who completed 12 months of follow-up were retrospectively analyzed. Pre-procedural ultrasonography was used to assess nodule volume, composition, and Doppler vascularity. All ablations were performed under ultrasound guidance using the moving-shot technique, and volume reduction ratio (VRR) was calculated during follow-up at 1, 3, 6, and 12 months. The primary outcome, treatment success, was defined as a VRR ≥75% at 12 months. Pearson correlation and multivariable logistic regression (forced-entry method) analyses were performed to determine factors influencing response. Results The mean patient age was 46.7 ± 16.6 years, and 66.3% were female. Mean baseline nodule volume was 11.75 ± 3.31 mL. Nodules were predominantly cystic in 38.8%, solid in 35%, and mixed in 26.3%. Mean VRR increased progressively during follow-up, from 26.2 ± 8.1% at 1 month to 72.5 ± 5.9% at 12 months, and treatment success (VRR ≥75%) was achieved in 35.0% of patients (28/80), whereas all nodules (100%) achieved a VRR ≥50%. Regrowth (any volume increase from the smallest recorded volume) occurred in 25.0% of patients, repeat ablation was required in 13.8%, and the complication rate was 5.0%. No significant correlation was found between baseline volume and VRR (r = 0.102, p = 0.367). Logistic regression identified nodule composition (p = 0.009) and vascularity (p = 0.017) as factors independently associated with treatment success. Predominantly cystic nodules and nodules with lower vascularity were more likely to achieve treatment success. Conclusion MWA was associated with substantial volume reduction and a low complication rate in benign thyroid nodules. Within the studied volume range, treatment response was associated with nodule composition and vascularity rather than initial size. Pre-procedural evaluation of nodule morphology and perfusion may help optimize patient selection.