Microinvasive follicular thyroid carcinoma detected by fine needle aspiration skeletal metastases. A case report

Fine needle aspiration biopsy (FNAB) for the cytologic diagnosis of bone metastatic lesions is often useful for locating the primary tumor and choosing treatment. The cytologic picture of follicular carcinoma most commonly resembles normal thyroid but may exhibit variable anaplasia. Marginal vacuoles, also known as fire flare-like vacuoles and "flame cells," have been found mainly in toxic goiter but also in some non-toxic goiter. The presence of marginal vacuoles of FNAB of metastatic follicular carcinoma was first reported by Pitts et al in 1988.

A 77-year-old male presented with multiple lytic lesions involving the vertebral bones and ribbons. FNAB of vertebral bone showed tumor cell clusters in a follicular pattern with peripherically situated, pink-stained vacuoles on May-Grünwald-Giemsa stain.

FNAB is useful in the diagnosis of metastatic thyroid neoplasms. The recognition of marginal vacuoles, along with the appropriate cytologic findings, should provide morphologic clues leading to a suspicion of thyroid neoplasm metastasis in FNAB.