Ultrasound appearance of extramedullary hematopoiesis.

Extramedullary hematopoiesis accompanies a wide variety of diseases and is defined as the abnormal production of blood outside the normal confines of the bone marrow. Most of the time, extramedullary hematopoiesis is found as microscopic foci in soft tissues; however, on occasion this process may reach a size that is detectable with ultrasound. Two forms are possible: "paraosseous"--in which the normal medullary tissue of the bone marrow ruptures through the bone to present as a paraosseous soft tissue mass,--and "extraosseous"--in which extramedullary hematopoiesis occurs within soft tissue. These "masses" of hematopoietic tissue can appear almost anywhere in the abdomen and pelvis and can mimic a wide variety of more serious diseases.