Extramedullary means “outside the bone marrow.” The bone marrow is the soft tissue inside bones where blood cells are made, and “medulla” is the Latin word for marrow. Pathologists use extramedullary to describe blood cells, or tumors made of blood-forming cells, that are found somewhere other than the bone marrow.
Extramedullary is a description of where something is located, not a diagnosis on its own. It appears in reports for both noncancerous conditions and blood cancers. This article explains the common ways the term is used and what it means in your pathology report.
What does extramedullary hematopoiesis mean?
Hematopoiesis is the process of making new blood cells. After birth, it normally happens only in the bone marrow. Extramedullary hematopoiesis means blood cells are being made in another organ, most often the spleen or liver.
This happens when the bone marrow cannot make enough blood cells, or when the body needs more blood cells than the marrow can supply. Common causes include primary myelofibrosis, in which scar tissue replaces the marrow, and thalassemia and other types of severe anemia. Extramedullary hematopoiesis is not cancer itself, but it is a sign that the marrow is under strain.
What is extramedullary disease in blood cancers?
Blood cancers usually start in the bone marrow. When the cancer cells form a tumor or collect in tissue outside the marrow, it is called extramedullary disease. Examples include:
- Extramedullary plasmacytoma. A plasmacytoma is a tumor made of abnormal plasma cells. An extramedullary plasmacytoma develops in soft tissue rather than in bone, most often in the nose, sinuses, or throat.
- Extramedullary myeloma. In multiple myeloma, plasma cells sometimes form tumors in soft tissue or organs outside the bone. Your doctor will consider this when planning treatment.
- Myeloid sarcoma. A myeloid sarcoma is a tumor made of leukemia cells that forms outside the bone marrow. It is closely related to acute myeloid leukemia.
- Leukemia in other organs. Leukemia cells can also be found in the skin, the fluid around the brain and spinal cord, the testes, and other organs.
Does extramedullary have other meanings?
In reports about the spine, “extramedullary” has a different meaning. Here, “medulla” refers to the spinal cord itself. A spinal tumor described as “intradural extramedullary” is inside the protective covering of the spinal cord but outside the cord. Common examples are meningioma and schwannoma. The context of your report will make clear which meaning applies.
How is an extramedullary finding identified?
Extramedullary findings are identified when a pathologist examines tissue from outside the bone marrow under the microscope. In extramedullary hematopoiesis, the pathologist sees young red blood cells, white blood cells, and large platelet-making cells in an organ where they do not normally belong. For a tumor, the pathologist uses stains such as immunohistochemistry to identify the cell type.
Questions to ask your doctor
- What does extramedullary mean in my report?
- Is my finding extramedullary hematopoiesis or a tumor?
- What is causing my bone marrow to be under strain?
- If I have a blood cancer, has it spread outside the bone marrow?
- Do I need a bone marrow biopsy?
- Does this finding change my treatment plan?
- Do I need any further imaging or follow-up?
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