Purpose: To obtain the treatment parameters of internally cooled microwave antenna and to evaluate the feasibility of ultrasound-guided percutaneous microwave ablation (MWA) for benign thyroid nodules. Materials and methods: MWAs were performed by microwave antenna (16G) in ex vivo porcine liver. The lesion diameters achieved in different groups (20, 25, and 30 W for 3, 5, 7, 10, and 12 min) were compared. The clinical study was approved by the ethics committee. Written informed consent was obtained from all patients. MWA was performed in 11 patients (male to female ratioZ1:10; mean age, 50G7 years) with 11 benign thyroid nodules. Ultrasound scan, laboratory data, and clinical symptoms were evaluated before and 1 day and 1, 3, 6, 9, and 12 months after the procedure. Results: In ex vivo study, the ablation lesion at 30 W 12 min tended to have appropriate scope and spherical shape. In clinical study, the follow-up periods ranged from 1 to 9 months. At the last followup, the largest diameter decreased from 2.9G1.0 (range, 1.6-4.1) to 1.9G0.7 (range, 0.4-3.0) cm (P!0.01), and the volume decreased from 5.30G4.88 (range, 0.89-14.81) to 2.40G2.06 (range, 0.02-6.35) ml (P!0.01). The volume reduction ratio was 45. 99G29.90 (range, 10.56-98.15) %. The cosmetic grading score was reduced from 3.20G0.79 to 2.30G0.95 (P!0.05). One patient experienced temporary nerve palsy and was recovered within 2 months after treatment. Conclusion: The internally cooled microwave antenna can yield ideal ablation lesions, and ultrasoundguided percutaneous MWA is a feasible technique for benign thyroid nodules.

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Compared with microwave ablation (MWA), percutaneous radiofrequency ablation (RFA) and laser ablation (LA) have been recommended as minimally invasive treatments for patients with symptomatic benign thyroid nodules (BTNs) because of the large number of clinical applications. This prospective multicenter study sought to evaluate the clinical outcomes of RFA and MWA for BTNs. In eight participating institutions, the total number of 1252 patients treated by RFA and MWA were 649 ones with 687 BTNs and 603 ones with 664 BTNs, respectively. The clinical outcomes including the nodular maximal diameter reduction ratio (MDRR), the nodular volume reduction ratio (VRR), and the incidence of complications were compared to evaluate the efficacy and safety of the two techniques. The results for the nodular MDRR and VRR in the RFA group were significantly better than those in the MWA group at 6 months and later follow-up, and the major complication rates of 4.78% and 6.63% in RFA and MWA groups showed no statistically significant differences. In conclusion, both RFA and MWA are safe and effective techniques for selected patients with symptomatic BTNs. The achieved MDRR and VRR in the RFA group were greater than those in the MWA group at 6 months and later follow-up.

The US-guided MWA results in a satisfactory long-term outcome of the patients with a benign solitary thyroid nodule. We identified three risk factors for recurrence: initial volume, vascularity and the energy per 1 ml reduction in nodular volume.