FNA diagnosis of a metastatic papillary thyroid carcinoma arising from a previously unknown follicular variant of papillary thyroid microcarcinoma

Abstract

While metastatic tumors to bone or lymph nodes from previously known primaries are often successfully diagnosed via fine-needle aspiration (FNA), a metastatic deposit in a patient with no previously known cancer may pose a diagnostic dilemma. Here, we present a case of metastatic papillary thyroid carcinoma that presented initially as a large pelvic bone mass. FNA was performed on this mass. The diagnosis was challenging due the fact that the tumor did not display the classic nuclear features associated with papillary thyroid carcinoma, instead the nuclear morphology was in keeping with a follicular thyroid carcinoma. Given the patient's concurrent, unremarkable thyroid imaging studies the final diagnosis required an extensive immunohistochemical work-up.

Keywords: follicular variant; metastasis; papillary thyroid microcarcinoma.