ACR TI-RADS Risk Score Escalation Observed in Benign Thyroid Nodules Following Radiofrequency Ablation.

Background and purpose: Radiofrequency ablation (RFA) has emerged as an effective non-surgical treatment for symptomatic benign thyroid nodules and toxic adenomas. While post-RFA ultrasonographic changes are expected, they may inadvertently evoke alarm and prompt unnecessary interventions when risk stratification models such as the American College of Radiology Thyroid Imaging Reporting & Data System (ACR TI-RADS) are applied. This study aims to quantify the ultrasound imaging changes using TIRADS scoring of thyroid nodules before and after RFA, and we highlight that these changes should not be used as a basis for clinical action.

Materials and methods: This retrospective study analyzed patients who underwent RFA for symptomatic thyroid nodules at a quaternary care academic medical center between May 2021 and May 2024. All nodules were assessed using the ACR TI-RADS calculator and underwent fine-needle aspiration (FNA) biopsy prior to treatment. Following RFA, ultrasonography was conducted at 3-month intervals and TI-RADS scores were reassessed. The primary endpoint was the change in TI-RADS classification following RFA.

Results: A total of 28 nodules from 25 patients were monitored after RFA for a median follow-up duration of 419 days. The majority (92.9%) were benign (Bethesda II) on FNA. The mean volume reduction ratio (VRR) was 66.7% (range 33.0% to 91.6%), with therapeutic success (VRR > 50%) achieved in 86% of patients. Post-RFA risk stratification increased following RFA, with the mean TI-RADS score increasing from 3.04 to 4.25 (p-value < 0.001), predominantly driven by increased hypo-echogenicity and new echogenic foci/calcifications.

Conclusions: Thyroid nodules frequently undergo post RFA structural changes which result in misleading upstaging on the ACR TIRADS stratification system. These changes are expected and require cautious interpretation to avoid overdiagnosis, patient anxiety, and mismanagement.

Abbreviations: RFA = radiofrequency ablation; ACR TI-RADS = American College of Radiology Thyroid Imaging Reporting & Data System; FNA = fine-needle aspiration; VRR = volume reduction ratio.