Mid-Term Outcomes and Outcome Predictors after Radiofrequency Ablation for Indeterminate Thyroid Nodules Following Functional Imaging Screening: A Retrospective Cohort Study

Abstract

Objective: Current guidelines recommend surveillance or diagnostic lobectomy for indeterminate thyroid nodules. Although radiofrequency ablation (RFA) has emerged as a potential alternative, its role remains controversial. Functional imaging modalities, including 99mTc-methoxyisobutylisonitrile scintigraphy and ¹⁸F-fluorodeoxyglucose positron emission tomography, have been used to support risk stratification. This study evaluated the mid-term outcomes of RFA and their predictors in a functionally screened cohort of patients with indeterminate thyroid nodules.

Materials and methods: This retrospective cohort study included 109 patients with Bethesda category III or IV thyroid nodules who underwent RFA after functional imaging-based evaluation between January 2018 and November 2024. The primary outcome was local treatment failure (LTF), defined as the first occurrence of nodule regrowth, an increase in vital volume, or repeated indeterminate cytology. The secondary outcome was complete disappearance of the nodule. Supplementary outcomes included the volume reduction rate, symptom and cosmetic scores, and biochemical markers.

Results: During a median follow-up of 2.2 years (range, 0.7-6.8 years), LTF occurred in 15 of 109 patients (13.8%), whereas complete disappearance was observed in 9 (8.3%) patients. The 3-year LTF-free probability and cumulative incidence of complete disappearance were 85.4% and 6.5%, respectively. Significant reductions were observed in the nodule volume, symptom scores, cosmetic scores, and free T4 and thyroglobulin levels. A greater initial maximum nodule diameter was independently associated with a higher likelihood of LTF (hazard ratio [HR] per 1-cm increase, 2.35; 95% confidence interval [CI], 1.23-4.48; P = 0.010) and a lower likelihood of complete disappearance (HR, 0.16; 95% CI, 0.04-0.60; P = 0.006). At 3 years, 93% of the tumors with an initial diameter <3.0 cm remained free of LTF, whereas no tumors >2.1 cm achieved complete disappearance.

Conclusion: In this functionally screened cohort of patients with indeterminate thyroid nodules, RFA demonstrated acceptable outcomes with volume reduction and symptom relief, particularly in patients with nodules <3 cm.

Keywords: 99mTc-MIBI scintigraphy; Complete regression; FDG-PET/CT; Indeterminate thyroid nodules; Local treatment failure; Outcome; Prediction; Predictor; Radiofrequency ablation.