To evaluate the feasibility of ablating the cystic component of cystic-solid nodules of the thyroid (CSNT) using radiofrequency ablation (RFA) and microwave ablation (MWA) in vitro.

The fluid simulation of CSNT cystic components in the body, like distilled water, normal saline, blood, puncture fluid of liver cyst, and the puncture fluid of CSNT, were ablated with the currently commonly used thermal ablation instruments. RFA and MWA were utilized in this study, and the ablation output power was 35 W and 50 W, respectively, which were commonly used in clinical practice. The temperature value was recorded every 30 seconds, and continuously for 10 minutes. The time temperature curve (TTC) was drawn for every test. The tip of the ablation needle was observed after the ablation, and the size, shape, and internal structure of the solidification around the needle tip were recorded. Pathological examination of the solidification around the needle tip was performed if necessary. The time of RFA and MWA to reach the target temperature (60 ℃) with the same power was compared, and the TTC was analyzed by variance analysis.

Distilled water can only be ablated by MWA, but not by RFA. The target temperature of RFA in normal saline and liver cyst puncture fluid was reached earlier than that of MWA [(171.4±3.9) s vs (343.6±5.7) s, F=228.311, P＜0.001; (170.2±4.8) s vs (444.5±7.2) s, F=193.632, P＜0.001] at the output power of 35 W, while at the power of 50 W, MWA had better thermal efficiency in TTC [(127.3±3.1) s vs (165.7±3.4) s, F=47.429, P＜0.001). In contrast, the target temperature in blood and the fluid punctured from CSNT was not reached. MWA at 50 W achieved the target ablation temperature in all the simulated liquids, and the thermal efficiency in blood and the fluid punctured from CSNT were obviously better than that of RFA (F=47.429 and 22.859, both P＜0.001).

MWA can be used to ablate the simulated fluid of CSNT, and the performance is relatively stable. RFA has a high thermal efficiency, but it fails to ablate distilled water. RFA has a poor effect on blood and the fluid punctured from CSNT because the tip of the needle is easy to form carbon deposit.