Mass-forming extramedullary hematopoiesis diagnosed by fine-needle aspiration cytology.

Extramedullary hematopoiesis (EMH) is usually a microscopic finding. However, it may present as a mass-forming lesion making it amenable to fine-needle aspiration biopsy (FNAB). When mass-forming EMH occurs, it can simulate a neoplasm clinically and radiologically. Additionally, the megakaryocytes can mimic malignant neoplastic cells, particularly if EMH is not a considered diagnosis. We report six cases of mass-forming EMH diagnosed by FNAB and evaluate the utility of FNAB in diagnosing EMH. Four patients had prior diagnoses of hematologic disorders, one patient had malignant mastocytosis who presented with lymphadenopathy and one patient had a history of carcinoma. The patients' ages ranged from 46 to 78 yr with an equal sex distribution. Aspirate smears showed trilineage hematopoiesis. The cytomorphologic differential diagnosis included metastatic carcinoma, Hodgkin lymphoma and myeloid sarcoma. No special stains were necessary due to the classic cytologic findings and prior hematologic history.