Comparison of cytological results obtained by repeated US-guided fine-needle aspiration biopsies of thyroid nodules: Focus on the rate of malignancy and diagnostic concordance

The debate still continues on the repeated fine-needle aspiration biopsies (FNABs) for thyroid nodule in clinical practice. In this study, we determined the rate of cytological change to malignancy and the diagnostic concordance of repeated FNABs when the same nodules were targeted under US-guidance. We retrospectively reviewed data for 187 thyroid nodules (173: twice, 14: three times) from 160 patients who underwent repeated USguided FNABs, which were performed by one skilful radiologist targeting for the same nodules at a mean interval of 7.5 months. Their initial cytological findings were compared with second or third results and histopathologic follow-up. The initial FNABs findings of 187 nodules were unsatisfactory, benign, and indeterminate in 56, 52, and 79 cases, respectively. The rate of a second cytological diagnosis changed to malignancy was significantly higher in the unsatisfactory aspirates (10.7%; 6/56), when compared with those of the benign (0.0%; 0/52) or of indeterminate aspirates (3.8%; 3/79) (P = 0.022). However, there was no change to malignancy at third cytological findings of all 14 nodules. After the second US-guided FNABs, 30.8% (16/52) of the initially diagnosed as benign aspirates were reclassified as indeterminate, while 26.6% (21/79) of the initially diagnosed as indeterminate were reclassified as benign. In conclusion, to identify malignancies, repeated US-guided FNABs are recommended for thyroid nodules initially classified as unsatisfactory aspirates. However, although US-guidance is applied, a discrepancy might be unavoidable in the cytological interpretation of the nodules classified as benign or as indeterminate aspirates because of overlapping cytological criteria.