Sclerosing extramedullary hematopoietic tumor in chronic myeloproliferative disorders

Sclerosing extramedullary hematopoietic tumor (SEMHT) occasionally may aris e in patients with chronic myeloproliferative disorders (CMPDs). Morphologi cally, these tumors may be mistaken for sarcomas or other neoplasms, especi ally if the clinical history is unknown. We analyzed four cases to identify features to aid in this differential diagnosis. Clinically, there were fou r men (mean age, 64.5 years), each with a history of CMPD. Grossly, the SEM HTs formed solitary renal or perirenal masses or multiple mesenteric or ome ntal nodules. Morphologically, each SEMHT had a sclerotic to myxoid backgro und with thick collagen strands and trapped fat. Atypical megakaryocytes, m aturing granulocytic and erythroid precursors, and few to no blasts were id entified in all cases. The megakaryocytes, granulocytic precursors, and ery throid precursors reacted strongly with antibodies to factor Vm, myeloperox idase, and hemoglobin, respectively, in immunohistochemical studies perform ed in selected cases. SEMHT is a rare manifestation of CMPD that may be mis taken for a sarcoma, especially sclerosing liposarcoma, Hodgkin's disease, especially lymphocyte depletion type, or a myelolipoma. In a myxoid tumor w ith trapped fat and atypical cells, morphologic and immunohistochemical ide ntification of maturing hematopoietic precursors helps distinguish SEMHT fr om sarcoma or Hodgkin's disease. The presence of sclerosis and atypical meg akaryocytes helps distinguish SEMHT from myelolipoma.