Long-Term Results of Ultrasound-Guided Radiofrequency Ablation of Benign Thyroid Nodules: State of the Art and Future Perspectives-A Systematic Review

Abstract

Background: Nearly 20 years after the first feasibility study, minimally invasive ultrasound (US)-guided therapeutic techniques are now considered as a safe and effective alternative to surgery for symptomatic benign thyroid nodules. Radiofrequency ablation (RFA) is one of the most widely used treatment in specialized thyroid centers but, due to the relatively recent introduction into clinical practice, there are limited long-term follow-up studies. Aim of our work was to review the outcomes of RFA on solid nonfunctioning and on autonomous thyroid nodules (AFTN) on a long-time period for assessing the results in term of efficacy, complications, and costs and to compare them to the current indications of RFA.

Methods: A systematic review was performed using EMBASE and Medline library data between 2008 and 2021. Seventeen studies evaluated RFA for the treatment of benign solid (nonfunctioning or autonomous) thyroid nodules, with an at least 18 months of follow-up. Data extraction and quality assessment were performed by two endocrinologist according to PRISMA guidelines. Anthropometric data, safety and efficacy parameters were collected.

Results: The majority of the studies was retrospective study and reported 933 nodules, mostly solid. Baseline volume ranged between 6.1 ± 9.6 and 36.3 ± 59.8 ml. Local analgesia was used and the time duration of the treatment was between 5 ± 2 and 22.1 ± 10.9 min. The volume reduction rate at 12 months ranged from 67% to 75% for the nodule treated with a single procedure and reached to 93.6 ± 9.7% for nodules treated with repeat ablations. The regrowth rate at 12 months ranged from 0% to 34%.

Conclusion: All the studies under examination consistently validated the long-term clinical efficacy and the substantial safety of RFA for the treatment of benign thyroid nodules. Thermal ablation, however, is an operator-dependent technique and should be performed in centers with specific expertise. The selection of the patients should be rigorous because the nodule size and the structural and functional characteristics influence the appropriateness and the outcomes of the treatment. Future perspectives as the treatment of micro-papillary thyroid cancer or cervical recurrence need further investigations.

Keywords: benign thyroid nodule; minimally invasive treatment; non-functioning thyroid nodule; thermal ablation; ultrasound-guided radiofrequency ablation.

Figure 1

Flowchart of the study selection process.

Figure 2

Algorithm for the treatment of symptomatic benign thyroid nodules, based on the 2020 European Thyroid Association (ETA) guidelines. FNAC, fine-needle aspiration cytology; CNB, core needle biopsy; RFA, radiofrequency ablation. TSH expressed as µUI/ml.

Figure 3

Radiofrequency ablation (RFA): physiology, equipment and ablation. Ionic agitation (A) and formation of frictional heat. Monopolar: Using a 40W RF power, and an active-tip of 10 mm, the diameter of the action zone is 13 mm. Bipolar RFA electrode with two tips (D). Internally cooled electrode (active-tip 5 and 10 mm) receives cold fluid (B) perfusing by a peristaltic pump (E). The generator (F) supplies RF power through the active-tip of the electrode. Grounding pads (C) act to disperse electricity in the RF circuit. Using ultrasound guidance (G), the electrode is inserted into the nodule. A trans-isthmic approach (H) and a moving shot technique are recommended. A cloudy effect (I) and an increase of the impedance (red circle) indicate the moment to change ablation zone. CEUS confirms (J) the complete treatment of the nodule (“vascular desert”).