Extramedullary Hematopoiesis

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Hematopoiesis, the making of blood, can happen outside of the medulla of the bone in organs such as the liver and spleen. There can be two different reasons for this. The fetus in the uterus will make blood this way prior to a formed skeleton. Pathological causes such as myelofibrosis can cause fibrotic changes to the bone marrow, “crowding” out the normal hematopoietic cells. These cells will then migrate back to the spleen and liver where they take up the blood making process. Removal of the spleen in this case, for instance, would remove the hematopoietic cells possibly leading to non-regenerative anemia.

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