Long-Term Outcomes of Thermal Ablation for Benign Thyroid Nodules: The Issue of Regrowth

Abstract

Thermal ablation (TA) for benign thyroid nodules (BTNs) is widely accepted as an effective and safe alternative to surgery. However, studies on the long-term outcomes of TA have reported problems with nodule regrowth and symptom recurrence, which have raised the need for adequate control of regrowth. Therefore, a more complete TA with a longer-lasting treatment effect may be required. In this study, we review and discuss long-term outcomes and regrowth of BTNs following TA and evaluate factors affecting the long-term outcomes. We also discuss the management of regrowth based on long-term outcomes.

Figure 1

A benign symptomatic thyroid nodule in a 36-year-old female treated with three sessions of radiofrequency ablation (RFA). (a) The nodule was in the patient's left lower lobe. The longest diameter was 4.7 cm, and the volume was 20.6 mL. There was no vascularity in and around the nodule. (b) Longitudinal image of the RFA-treated nodule 1 month after the procedure. The total nodule volume (Vt) was reduced to 14.5 mL and the longest diameter to 3.8 cm. The volume reduction ratio was 30%. Ablated tissue located in the central portion of the treated nodule (Va) is surrounded by the peripherally located small amount of remaining viable tissue (arrows). The dotted lines indicate the measurements for Va, which best represent the volume of the complex and irregularly shaped ablated area. There was no vascularity. At this time, Va was 11.2 mL, the viable volume (Vv) was 3.2 mL, and the initial ablation ratio was 84%. (c) Color Doppler image of the treated nodule 19 months after the procedure shows the development of vascularity in the nodule. Vt had decreased to 6.8 mL, but Va (arrow) had regressed to 1.1 mL and Vv had increased to 5.7 mL. Such a Vv increase is an early sign that can predict regrowth, even while Vt is decreasing. As regrowth was expected, the patient received a second RFA in the following month. (d) Thirty-four months after the second RFA, the nodule showed a Vv increase again, and a third RFA was performed. Five percent dextrose injected for hydrodissection can be seen as an anechoic area between the nodule margin and carotid sheath (^∗). The tip of the electrode (long arrow) is located near the veins of the nodule margin to achieve venous ablation. Air bubbles formed by ablation are compactly filling the venous lumen (arrows). (e) Ten months after the third RFA, the nodule had turned into a small scar-like region of tissue without vascularity. The Vt was 0.4 mL with no demonstrable Vv.