Fine‐needle aspiration cytology of unsuspected metastatic thyroid carcinoma initially presenting in bone: Report of three cases and a review of the literature

We present a series of three cases of unsuspected thyroid carcinoma presenting as bony lesions and initially studied by fine-needle aspiration (FNA). This series consists of two cases of follicular carcinoma and a third case of Hurthle cell carcinoma. FNA was performed on all three lesions. In two of these cases, a definitive diagnosis of metastatic thyroid carcinoma was made based on the FNA material. FNA smears of both follicular carcinomas displayed cohesive clusters of atypical round cells with nuclear overlapping and positive immunoperoxidase staining for thyroglobulin. The aspirates of the Hurthle cell carcinoma were composed of sheets and individually scattered oval oncocytic cells with prominent nucleoli. All three cases demonstrated the presence of marginal vacuoles consistent with flame cells. To the best of our knowledge, this is the first series discussing the cytologic features and differential diagnosis of unsuspected thyroid carcinoma initially presentin as metastatic bone lesions.