AJR 2002; 179:1239-1243.
Georgiades CS, Neyman EG, Francis IR, Sneider MB, Fishman EK.
Hemopoiesis is the formation and maturation of blood elements. Hemopoiesis normally occurs in the marrow of long bones, the ribs, and the vertebrae of the adult, in contradistinction to the fetus, in which the principal sites of hemopoiesis are the yolk sac, spleen, and liver [1, 2] (Fig. 1). When the primary sites of hemopoiesis in the adult fail, as in myelofibrosis (of many causes) and in hemoglobinopathies (especially thalassemia and sickle cell disease), various extramedullary sites take on the role of blood formation. Extramedullary hemopoiesis favors
certain sites such as the liver, the spleen, and the paraspinal regions of the thorax. However, in addition to these common sites of extramedullary hemopoiesis, the process can involve virtually any organ or tissue and can often manifest as a mass mimicking a neoplasm. Symptoms are usually caused by the mass effect. Recognizing the imaging findings that may be compatible with extramedullary hemopoiesis is important, because biopsy will exclude a neoplasm and alter management and prognosis. Equally important is knowledge of the patient's clinical history, hi this article, we present patients with a variety of imaging manifestations of biopsy-proven extramedullary hemopoiesis.