Pleural fluid extramedullary hematopoiesis case report with review of the literature.

Extramedullary hematopoiesis (EMH) is the trilineage formation of normal blood cells outside of the bone marrow. While predominantly seen in the spleen and liver, EMH rarely occurs in serous effusions. Accurate diagnosis requires recognition of megakaryocytes and other precursor hematopoietic elements. We present a case of pleural fluid EMH in a patient with primary myelofibrosis and developing leukemia, with a review of the literature, prognostic implications and diagnostic challenges.