The Universidad San Francisco de Quito approved the institutional review board (IRB). This study followed the STROBE guidelines for observational studies [10]. All the patients signed the informed consent before the RFA procedure.

This single-center, cross-sectional study was conducted at the Instituto de la tiroides y Enfermedades de Cabeza y Cuello (ITECC), a private reference center for patients with thyroid nodules and thyroid cancer in Quito, Ecuador. From July 2019 to May 2022, we included a convenience sample of 44 patients who underwent RFA for benign non-functional TN and PTMC performed by a head and neck surgeon (C.G.).

Thyroid nodules were considered benign if (i) two separate fine-needle aspirations (FNA) cytology biopsies reported benign features or (ii) one FNA reported benign features with ultrasonographic (US) characteristics highly specific for benignity (e.g., spongiform). Similarly, unifocal PTMCs were confirmed by fine-needle aspiration cytology biopsies (Bethesda 5 and 6). To be included, patients with PTMC needed to fulfill the following criteria: (i) a maximum diameter no larger than 10 mm; (ii) absence of capsular infiltration and extrathyroidal invasion in the US; and (iii) no cervical lymph node metastasis in the US. Patients who received thyroid treatments within the year before the study period, those without follow-up information, and patients or caregivers who refused to participate were excluded from the study.

Before treatment, patients had complete blood count, thyroid function tests, coagulation tests, and imaging evaluation. The US collected features including size, location, margin, shape, echogenicity, calcification, and vascularity. The nodule volume was calculated according to the American Thyroid Association (ATA) calculator [11] (formula: V = πabc/6 - where V is the volume, a is the largest diameter in the US, and b and c are the other two perpendicular diameters).

Nodules were categorized based on the ratio of cystic to solid portion into solid (no apparent cystic content), predominantly solid (cystic amount ≤ 50% of nodule), predominantly cystic (cystic part > 50% of nodule), and cystic (no apparent solid content) [12]. Also, we defined mixed TN when the solid component was less than 70% and greater than 30%.

We employed a classification system, described in a previous consensus statement, to assess the severity of symptoms and the impact on cosmetic appearance [13]. Patients were asked to rate their pressure symptoms on a 10-cm visual analog scale, with a range of 0 to 10 cm, at the initiation of the study (same day of RFA) and during subsequent visits (1, 3, 6, and 12 months). The cosmetic score was evaluated using a 4-point scale, which included the following categories: (1) absence of a palpable mass; (2) palpable mass with no cosmetic impact; (3) cosmetic impact only during swallowing; and (4) easily visible mass.

RFA was performed by a head and neck surgeon using local anesthesia (2% lidocaine without epinephrine). The technical feasibility assessment focused on an easily accessible microprocessor, Mygen M-3004, with an internally cooled electrode (18-gauge, 5 mm, or 7 mm active tip) according to the nodule’s size and nature (benign or malignant). Ultrasound guidance linear transducer L6-12 RS / GE with a trans-isthmic approach and moving shot technique with 20 to 40 W of power was applied [14]. Ablation termination was determined when all visual fields of the nodule had changed to transient hyperechoic zones. For those TN felt to be hugely fulfilled of cystic liquid, aspiration with a G18 syringe was performed before RFA. This equipment is available in our institution for all our patients. Moreover, our patients stay in our clinic for a couple of hours post-RFA and then go home the same day.

Patients were followed up at 1, 3, 6, and 12 months after index RFA. During these appointments, we evaluated the cosmetic and symptomatic scores. Also, US and laboratory tests were required at each follow-up visit. The (VRR), which was applied to assess the extent of nodule volume reduction, was determined using the ATA calculator. Effective treatment was defined as a volume reduction > 50% of the initial nodule volume on a follow-up US examination.

Statistical analysis was performed by using the R program. The normality of distribution was assessed visually and using the Kolmogorov-Smirnov test. For continuous variables, we calculated the median and interquartile range. Categorical variables were presented by frequency (percentage). We used a paired t-test to assess the pre-and post-RFA VRR changes, laboratory values of stimulating thyroid hormone (TSH), and free thyroxine (fT4). The Wilcoxon signed-rank test compares the pre-and post-RFA cosmetic score changes. We used pairwise deletion to address missing data during the statistical analysis.