Cystic thyroid nodules after aspiration mimicking malignancy sonographic characteristics

Objective. The purpose of our study was to provide sonographic findings of cystic nodules, which can mimic malignancies, after fine-needle aspiration (FNA) and to determine the differential points from malignancies. Methods. We retrospectively reviewed the sonographic findings of 33 lesions in 32 patients who had FNA for predominantly cystic nodules or cysts and showed suspicious findings during sonographic follow-up, as well as findings of 47 surgically confirmed papillary thyroid carcinomas (PTCs) in 45 consecutive patients. We evaluated the size, shape, presence of shadowing and a halo, margin, echogenicity, and presence of echogenic dots for each nodule. The final diagnosis of cystic nodules was confirmed by FNA, surgery, or follow-up sonography. Results. Of the 33 cystic lesions, 31 (94%) were adequate with benign results, and 2 (6%) were inadequate specimens at the initial FNA. There were no malignancies in the cystic nodules at follow-up. The average interval between the initial FNA and suspicious sonographic findings was 26 months (range, 1-92 months). The average size of the suspicious nodules was 0.8 cm (range, 0.3-1.8 cm). Cystic nodules after aspiration were similar to PTCs in their sonographic findings, but the former frequently showed shadowing and a halo (85% versus 21%; P < .0001). With further follow-up, 29 lesions (88%) showed additional decreases in size. Conclusions. Benign cystic nodules after aspiration can have suspicious malignant features. However shadowing and a halo associated with malignant features are characteristic findings of cystic nodule shrinkage. Awareness of these findings and correlation with the FNA history can aid in preventing unnecessary FNA.