Extramedullary hematopoiesis occurs when certain blood cells form outside of the medulla (bone marrow).
In extramedullary hematopoiesis, a type of blood cell that normally only exists in the medulla of the bone (bone marrow) forms in other areas of the body. Extramedullary hematopoiesis typically forms as a mass or pseudotumor. The most common areas for this are the spleen or liver, but it can also occur in the skin, lungs, kidneys or other organs.
There are two main types of extramedullary hematopoiesis:
Pathologic extramedullary hematopoiesis – occurs due to an abnormal reaction of the body’s immune system
Physiologic extramedullary hematopoiesis – occurs during fetal development
This condition can occur during fetal development (physiologic), or it can be caused as a reaction of the body’s immune system (pathologic) in one of the following situations:
Bone marrow that is no longer functional
Infection in the bone marrow
Infection or inflammation in an organ
Signs and symptoms of extramedullary hematopoiesis can include: