Extramedullary hemopoiesis.

Various chronic hematologic disorders that lead to ineffective hemopoiesis or inadequate bone marrow function (ie, chronic hemolytic anemias, thalassemia, sickle cell anemia, myelofibrosis of many causes, lymphoma, and leukemia) can potentially precipitate extramarrow new blood element creation. Extramarrow soft tissue that produces blood elements is called extramedullary hemopoietic tissue and the process extramedullary hemopoiesis (EMH). Sites commonly involved by EMH include the liver, spleen, lymph nodes, and most commonly, paravertebral regions, although other sites can sometimes be involved. Physicians rarely consider EMH in their differential diagnosis even in cases where it is warranted (diseases of ineffective erythropoiesis). This is likely because of the rarity of the condition and because imaging findings are nonspecific. We present here a systematic review of the imaging findings in EMH.