Hematopoiesis is the process by which the body produces blood cells, including red blood cells, white blood cells, and platelets. In adults, hematopoiesis occurs primarily in the bone marrow, but during fetal development, the liver and spleen serve as the main sites of blood cell production. This is relevant to sonography because in certain conditions, such as severe anemia, myelofibrosis, or fetal hemolytic disease, the liver and spleen can resume blood cell production in a process called extramedullary hematopoiesis, which causes these organs to enlarge. On ultrasound, hepatosplenomegaly from extramedullary hematopoiesis may appear as diffuse enlargement of the organs with changes in their echogenicity.
Sonography Term