Cytomorphological changes in thyroid nodules induced by radiofrequency ablation therapy: Emphasis on recurrent papillary thyroid carcinoma

Radiofrequency ablation (RFA) therapy is a minimally invasive treatment option for benign thyroid nodules and metastatic papillary thyroid carcinoma (PTC). This study investigated the cytomorphological changes induced by RFA in thyroid nodules. The study included patients who received RFA for benign thyroid nodules (n = 6) or recurrent PTC (n = 14), in the thyroid bed or lymph nodes following thyroidectomy. Patients underwent fine-needle aspiration (FNA) or core needle biopsy (CNB) to evaluate therapeutic responses. Most benign thyroid nodules showed acellular or hypocellular cellularity and coagulative necrosis. Thermal artifacts, fibrosis, and foreign body reactions were also noted. All cases were successfully treated, showing reduced nodule size with no recurrence during follow-up. In patients with recurrent PTC, post-RFA biopsies diagnosed 12 out of 14 samples as PTC, with most displaying degenerated tumor cells. Cytomorphological changes included acellular necrosis, nuclear pyknosis, or karyorrhexis. The second biopsy group showed lower cellularity, fewer degenerated cells, and fewer viable PTC cells than the first biopsy group. Two patients with persistent viable PTC cells after repeated RFA underwent surgical treatment. FNA and CNB effectively evaluate the response to RFA and detect residual tumors. Acellular specimens, total necrosis, and severely degenerated tumor cells indicate successful RFA, while viable cells with preserved PTC features suggest incomplete treatment.