Extramedullary hematopoiesis of the thyroid gland diagnosed by FNA cytology - A case report

BACKGROUND: Extramedullary hematopoiesis (EMH) is the production of element s of erythroid and myeloid series at ectopic sites; when concomitant with a gnogenic myeloid metaplasia, it is invariably seen in advanced disease. In EMH, involvement of the thyroid gland is extremely rare. CASE: An 82-year-old male with thyroid enlargement underwent fine needle as piration (FNA) cytology with a diagnosis of malignancy. A month later anoth er FNA cytology was performed and was consistent with Eh IH. A complete hem atologic workup subsequently allowed the diagnosis of agnogenic myeloid met aplasia. CONCLUSION: The presence of EMH in the thyroid gland is an unusual finding, and, due to the presence of numerous giant cells, the cytologic presentati on might be mistaken for anaplastic thyroid carcinoma. The differential dia gnosis is based on the recognition of giant cells as megakaryocytes.