Sclerosing Extramedullary Hematopoietic Tumor

Comments:
Sclerosing extramedullary hematopoietic tumor (SEMHT) is a rare tumor-like process seen in patients with chronic myeloproliferative disorders. It usually forms solitary or multiple retroperitoneal (often perirenal) or peritoneal masses (mesenteric or omental), but has been reported in other sites such as breast, axillary lymph nodes, lung, and skin.

Morphologically, it shows sclerotic stroma with thick collagen strands, admixed with variable amounts of mature adipose tissue. Trilineage hematopoietic elements (megakaryocytes, granulocytic and erythroid precursors) are present within the sclerotic matrix. Blasts are rare or entirely absent. The megakaryocytes are markedly dysplastic and consist of both giant as well as micromegakaryocytes with nucleus-cytoplasm asynchrony.

If pertinent clinical history is not available, SEMHT may be mistaken for carcinoma, sarcoma (especially sclerosing liposarcoma), myelolipoma, or Hodgkin lymphoma (lymphocyte depleted).

This photomicrograph is from an axillary lymph node excised from a patient with myelofibrosis. The nodal architecture is completely effaced by dense collagen sclerosis. A few residual follicles are seen.