Diagnostic Algorithm for Metastatic Lymph Nodes of Differentiated Thyroid Carcinoma

Simple Summary Fine-needle aspiration cytology (FNAC) with measurement of thyroglobulin concentrations obtained through aspiration (FNA-Tg) is routinely used for the diagnosis of metastatic lymph nodes (LNs) from differentiated thyroid carcinomas. However, some areas of uncertainty remain, including the optimal FNA-Tg cutoff and its interpretation based on ultrasound (US) features. In this study, we evaluated the appropriate strategies for interpreting FNAC and FNA-Tg results based on the sonographic features of LNs. We confirmed that the malignancy rate of LNs found to be malignant by FNAC or elevated FNA-Tg was sufficiently high to be diagnosed as metastasis, regardless of the sonographic features. The malignancy rate of LNs with indeterminate or benign FNAC findings and low FNA-Tg were stratified according to their sonographic features. We propose a diagnostic algorithm, based on combined FNAC, FNA-Tg, and US features of LNs, for diagnosing metastatic LNs of differentiated thyroid carcinomas. We aimed to evaluate appropriate strategies for interpreting fine-needle aspiration cytology (FNAC) and thyroglobulin concentrations obtained through aspiration (FNA-Tg) results based on the sonographic features of lymph nodes (LNs). Consecutive patients who underwent ultrasound-guided FNAC and FNA-Tg for metastatic LNs from differentiated thyroid carcinomas (DTCs) from January 2014 to December 2018 were reviewed retrospectively. LNs were categorized sonographically as suspicious, indeterminate, or benign. The optimal FNA-Tg cutoff for metastatic LNs was evaluated preoperatively, after lobectomy, and after total thyroidectomy. The diagnostic performances of FNA-Tg, FNAC, and their combination were analyzed based on the sonographic features of LNs. The malignancy rates of LNs were analyzed based on the sonographic features, FNAC, and FNA-Tg results. Of the 1543 LNs analyzed, 528 were benign, whereas 1015 were malignant. FNA-Tg increased the sensitivity and accuracy of FNAC for LNs. The malignancy rate of LNs found to be malignant by FNAC or elevated FNA-Tg ranged from 82% to 100%, regardless of the sonographic features. The malignancy rate of LNs with indeterminate or benign FNAC findings and low FNA-Tg were stratified according to their sonographic features. We propose a diagnostic algorithm, based on combined FNAC, FNA-Tg, and ultrasound features of LNs, for diagnosing metastatic LNs of DTCs.