Fibrous hematopoietic tumors arising in agnogenic myeloid metaplasia

Tumors of extramedullary hematopoiesis occasionally occur in long-standing cases of agnogenic myeloid metaplasia (AMM) and resemble hypercellular marrow in a connective tissue stroma. Rarely, this type of tumor mass is markedly fibrous and may pose diagnostic difficulty, especially when there is only limited knowledge of a patient's clinical history. The authors report two cases of AMM with such a fibrous hematopoietic tumor, occurring in one patient as a pelvic mass and in another as lymphadenopathy and skin nodules. A review of the literature revealed that fibrous hematopoietic tumors associated with AMM arise predominantly in the retroperitoneum, pelvis, mesentery, and pleura. Features helpful in establishing the diagnosis include long-standing AMM, megakaryocytes and other hematopoietic cells within the fibrous tissue, and lack of atypia in the fibrous tissue. Current evidence suggests that the fibrous component of the masses is reactive and possibly related to stimulation of fibro-blasts by a humoral substance released from platelets