The thermal ablation (TA) procedure, proposed as a minimally invasive treatment method, has received increasing attention in recent years (1–4). TA methods include radiofrequency ablation (RFA), microwave ablation (MWA), laser ablation (LA), and high-frequency focused ultrasound (HIFU) (5). The principle of these methods involves the induction of tissue coagulation necrosis under extreme hyperthermic conditions (6). TA is a suitable treatment for benign thyroid nodules with ≥ 10% solid components (7). Compared with surgery, the advantages of thyroid TA include safety, efficacy, low cost, good tolerability and preservation of thyroid function (8, 9). The 2022 international multidisciplinary consensus explicitly stated that TA can be considered for symptomatic thyroid nodules (6). Furthermore, multiple other global follow-up studies have confirmed the effectiveness of TA for benign nodules and papillary thyroid microcarcinoma (PTMC) (10–14); however, the status of complications of TA is unclear. In this study, data regarding the complications of thyroid TA at our hospital were combined with those in different countries to analyze the range of complications associated with thyroid TA.

The study was approved by the Ethics Committee of Shanghai Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine (SH9H-2021-MT6-1) and informed consent for each procedure was obtained from all patients prior to the procedure.

TA is widely used, though the indications for TA remain unclear. The existing guidelines are mostly for RFA and can be used for the treatment of benign thyroid nodules, PTMCs, and recurrent thyroid cancers (RTCs). Thermal ablation of thyroid cancer is only indicated for single low-risk PTMCs, the low degree of invasiveness should be verified prior to ablation. For patients with RTC, curative-intent RFA should be considered when complete removal of the tumor is possible in patients with RTC and a limited number (≤ 3) of small tumors (size ≤ 2 cm). RFA can be performed with curative or palliative intent for RTCs at the thyroidectomy bed, neck dissection site, or metastatic cervical lymph nodes for patients who refuse surgery or are at high surgical risk (15, 16).

Some studies have reported the use of RFA for other types of PTC, including PTC larger than 1 cm, and palliative treatment for recurrent and metastatic PTC. The results are encouraging and provide a safe and effective treatment option for patients with PTC who cannot undergo or refuse surgery. However, further research is needed (17).

The management of indeterminate nodules with TA is not recommended as it is difficult to achieve diagnostic needs and TA cannot prevent metastasis. In the 2023 Bethesda System for Reporting Thyroid Cytopathology, Bethesda category III is simplified as atypia of undetermined significance (AUS), which is subdivided into “AUS nuclear” and “AUS other” (18). AUSs with nuclear atypia have significantly greater ROMs and require more cautious clinical management, corresponding to research results since the publication of the second edition of the classification (19–21).

In the current study, all patients who received TA treatment at SHNH underwent biopsy to confirm the pathological diagnosis of benign nodule or PTMC, with no history of lymph node metastasis or previous thyroid surgery. TA was used as a minimally invasive initial treatment to alleviate patient pain, reduce costs, and improve safety and aesthetics. However, the probability of serious postoperative complications, such as tracheal injury, remains. Therefore, the indications for TA must be further clarified. Moreover, considering that the probability of serious complications still occurs, strict inclusion criteria for TAs are very important.

There are several reports and reviews involving TA complications. The 2022 international multidisciplinary consensus concluded that the two most common postoperative complications are recurrent laryngeal nerve injury and thyroid nodule rupture (6). These two situations can be separately treated by injection of a cold irrigant into the region of suspected thermal injury (22) and by conservative management (23). A meta-analysis of the incidence of common complications was conducted (24) and reported values of 1.0%-2.0%, 0.2%-0.5%, 1.0%-100%, 0.0%-17.0%, and 0.27%-3.7% for nerve injury, nodule rupture, pain, hematoma, and skin burns, respectively. However, comparisons across countries are lacking. In the present study, we compared the complications of thyroid TA across different countries with our own data for further statistical analysis. We found that TAs have been widely applied in China (25, 26), South Korea (27, 28) and Italy (29, 30). Common complications include pain, vocal changes, edema, hematoma, fever, etc. (31–33). Uncommon complications are tracheal injury and esophageal injury. Fu Q reported in 2021 that esophageal injury, which was located in the esophageal serosa, was caused by insufficient observation during the procedure. The patient experienced foreign body sensations while swallowing after ablation and recovered one month after the ablation procedure (34). Two case reports were analysed in the previously published literature. Patients experienced intense pain and difficulty breathing one to two weeks after the ablation procedure; possible contributing factors were an excessive thyroid nodule volume, a prolonged ablation time, and deep sedation anesthesia (35, 36). We also reported a case of airway fistula after MWA. The patient developed neck pain, fever, cough and increased sputum after surgery. CT revealed small air bubbles on the right side of the airway with inflammation of the neck tissue. The patient’s symptoms disappeared one month after anti-infective treatment.

Our study is the first to compare complications regionally. This retrospective study revealed that the region with the highest incidence rate of complications after ablation was Europe, including France (14, 37, 38) and the Netherlands (32, 39). France has the highest incidence rate of complications (46.42%). A total of 321 patients were included in three studies conducted in France; the incidence rates of TA complications were 15.6% (14), 6.2% (37) and 78.9% (38). The incidence in the Netherlands ranks second (21.45%). There are two reasons for the high incidence rates of TA complications in France and the Netherlands. One reason is that the number of thyroid TA procedures in these two countries was limited (France reported 321 cases, and the Netherlands reported 124 cases), and the proficiency of the operator was thus affected. The other reason is that most of the complications reported in France and the Netherlands involved pain, and this factor increased the proportion of complications. For example, Ben Hamou reported that 92 out of 166 patients experienced pain, leading to an incidence of up to 78.9% (39). In some countries, pain was not included in the reported complications.

In addition, we compared the complication data of various countries in the previous literature with those of our single centre, SHNH. There are significant differences in the incidence of certain single complications, but there is no significant difference in the incidence of overall complications.

This study has several limitations. The determination of some complications is subjective, which affects the results involving pain. In addition, the follow-up time of previous studies varied from six months to five years, and most of them were retrospective studies. Furthermore, there are very few cases reported in some countries, such as Singapore and Bulgaria. Further attention and research are needed in this area.

The incidence rate of complications associated with thyroid TA is approximately 10% to 15%. However, the proportions and types of complications vary reionally.