Sclerosing extramedullary hematopoietic tumor: emphasis on diagnosis by renal biopsy.

Sclerosing extramedullary hematopoietic tumor (SEMHT) is a rare lesion that typically arises in patients with chronic myeloproliferative disorders. Morphologically, it exhibits atypical megakaryocytes, granulocytic precursors, and erythroid precursors set in a background of dense collagen sclerosis. Sclerosing extramedullary hematopoietic tumor may be easily mistaken for other neoplasms, such as sarcoma, carcinoma, or Hodgkin lymphoma, particularly if pertinent clinical history is not provided. Misdiagnosis may occur because of the difficulty in recognizing the megakaryocytic lineage of the atypical cells and because of the paucity of other hematopoietic elements. We report a case of a 72-year-old man with proteinuria and renal insufficiency who underwent renal biopsy to determine the etiology of the proteinuria. The kidney biopsy demonstrated an unusual tumor in which the initial morphological impression that of sclerosing liposarcoma. However, upon learning of the patient's previous history of chronic idiopathic myelofibrosis and with the aid of immunohistochemistry, the correct diagnosis of sclerosing extramedullary hematopoietic tumor was made. Sclerosing extramedullary hematopoietic tumor should be considered in the differential diagnosis when percutaneous renal biopsy or other intra-abdominal biopsy reveals a sclerotic lesion with interspersed large atypical cells, especially in a patient with a history of chronic myeloproliferative disorder.