Radiofrequency ablation of benign thyroid nodules: evaluation of the treatment efficacy using ultrasonography

Abstract

Purpose: The aim of this study was to evaluate the efficacy of radiofrequency (RF) ablation for benign thyroid nodules and assess the usefulness of internal factors (ultrasonographic findings) and external factors (treatment-related findings) in prediction of treatment efficacy.

Methods: We evaluated 22 benign thyroid nodules from 19 patients treated with RF ablation between March 2010 and January 2013. The internal and external factors of these nodules were retrospectively reviewed and correlated with the therapeutic success and the volume reduction ratio (VRR). The volume and size of the nodules were determined before treatment, and the VRR was calculated at 6-month and 1-year follow-up examinations after RF ablation. Therapeutic success was defined as a >50% volume reduction.

Results: The mean VRRs were 66.1±18.7% at 6 months and 74.3±16.7% at 1 year. The therapeutic success rate after 6 months and 1 year was 81.8% and 90.9%, respectively. At the 1-year follow-up, the margin of the nodule correlated with therapeutic success. Most of the successfully ablated nodules showed well-defined margins on initial ultrasonography (18/20, 90%) (P=0.026). In addition, nodules with ill-defined margins showed a tendency toward having a low VRR at the 6-month and 1-year follow-up examinations.

Conclusion: RF ablation was effective in decreasing the volume of benign thyroid nodules. Thyroid nodules with well-defined margins tended to show successful outcomes at the 1-year follow-up examination after RF ablation.

Keywords: Ablation techniques; Thyroid nodule; Ultrasonography.

Fig. 1.. Changes in the volume of the thyroid nodules and volume reduction ratio (VRR).

Graph shows that the mean volume of benign thyroid nodules is markedly decreased after radiofrequency ablation on the 6-month and 1-year follow-up ultrasonography.

Fig. 2.. A 60-year-old woman with two conglomerated solid nodules in the left thyroid.

A. Initial ultrasonogram shows a predominantly solid nodule (arrows) in the superficial area and a pure solid nodule (arrowheads) in the deep portion of the left thyroid abutting each other, with the deep nodule showing a relatively ill-defined margin in the lateral and posterior aspects in comparison with the superficial nodule. B. During the radiofrequency ablation, an internally cooled electrode (arrows) is inserted into the nodules and multiple echogenic micro-bubbles (arrowheads) were noted within the nodules after the procedure. C. On 1-month follow-up ultrasonography after the ablation, the nodules are slightly decreased in volume and size, with the volume reduction ratio of the superficial nodule being 36% and that of the deep nodule being 23%; thus a second session of radiofrequency ablation was performed for these nodules. D. On 1-year follow-up ultrasonography after the ablation, superficial and deep nodules show a greater decrease in volume (43% and 25%, respectively), but they do not achieve a volume reduction ratio of more than 50%; thus the therapeutic success criteria are not satisfied in this patient.