Megakaryocytes detected in fine-needle aspiration cytology of the thyroid

—A potential diagnostic pitfall—

Abstract

We present a case of goiter with ectopic bone formation and extramedullary hematopoiesis in the thyroid, diagnosed by fine-needle aspiration cytology (FNAC). A 43-year-old female patient with a calcified thyroid nodule underwent ultrasound (US) -guided FNAC. Microscopic examination showed mature megakaryocytes with multilobulated nuclei and abundant granular cytoplasm, and myeloid and erythroid cells in various stages of development in a background of benign thyroid follicular epithelial cells. Adipose tissue and fragmented bone materials were also found. Presence of hematopoietic cells in the thyroid gland is an unusual finding ; moreover, detection of giant cells in FNAC of the thyroid could lead to the mistaken diagnosis of thyroid anaplastic carcinoma.