Extramedullary

Extramedullary describes processes or tissues located outside the bone marrow. In medical use, the term often refers to hematopoietic activity or malignant infiltration occurring outside the medullary cavity of bones.

Extramedullary hematopoiesis refers to the production of blood cells outside the bone marrow. It typically arises in response to marrow failure or increased demand, such as in severe chronic hemolytic anemias, myelofibrosis, and some thalassemias. Common sites include the liver and spleen, with other possible locations being lymph nodes, thymus, skin, lungs, and the retroperitoneum. Patients may experience organ enlargement or mass effects from these hematopoietic tissues. Diagnosis relies on imaging and, when feasible, tissue biopsy demonstrating hematopoietic elements outside the marrow. Management targets the underlying cause and may include supportive transfusions, iron chelation as needed, and, for focal EMH masses, radiotherapy or surgical debulking. In some cases, disease-modifying therapies are used.

Extramedullary disease in hematologic malignancies refers to infiltration of malignant cells outside the bone marrow. This can occur in conditions such as multiple myeloma with plasmacytomas outside bone structures, leukemia, or lymphoma involving various organs. It often signals disease progression or relapse and may require systemic therapy, with local treatments reserved for symptomatic lesions.

Etymology and implications: extramedullary literally means outside the medulla. Recognizing extramedullary involvement has diagnostic and therapeutic implications, distinguishing marrow-based processes from those occurring elsewhere in the body.