Endocrine Abstracts

Background: Some regrowing nodules after radiofrequency ablation (RFA) of symptomatic large benign thyroid nodules are revealed as malignancies in surgery. The aim of the study was to assess the ultrasound (US) characteristic of thyroid nodules diagnosed as cancer later, the predictive factors for cancer after RFA, and the prevention methods for these cancers to avoid RFA.

Materials and Methods: The medical records of 22 thyroid nodules with 18 patients who underwent RFA for debulking symptomatic benign thyroid nodules between 2008 and 2016 and followed by surgery were reviewed. We investigated pre-RFA characteristics of thyroid nodules and change in follow-up after RFA and final surgical pathology.

Results: Final malignancies were confirmed in seven of 22 RFA-treated nodules. Pre-RFA mean maximal diameter was significantly greater in malignant nodules than benign nodules (3.89±0.98 cm vs 5.23±1.52 cm, P = 0.04). There was no difference in regrowth interval between benign and malignant nodules (56.00±36.00 months vs 47.14±33.66 months, P = 0.48). Volume reduction rate at 12-month was lower in malignant nodules than benign nodules (51.16±13.81% vs 73.68±20.15%, P = 0.08). Pre-RFA benign confirmation of all seven malignant nodules were used with two US-guided fine needle aspirations (FNA) except for one using US-guided core needle biopsy (CNB). Using CNB, all regrowing ablated nodules confirmed as malignancy after RFA were diagnosed as suspicious for follicular neoplasm. The histology of the malignant nodules in surgery after RFA was follicular thyroid carcinoma except for one follicular variant of papillary thyroid carcinoma.

Conclusion: Symptomatic large thyroid nodules confirmed as benign before RFA should be considered for false negative FNA, and the possibility of regrowth after RFA is high. When considering retreatment of regrowing nodules, reconfirmation with CNB prevents the diagnosis of cancer from being delayed.