Bone marrow edema (BME) is an accumulation of fluid within the spongy tissue inside bones, known as bone marrow, visible on medical imaging. While it can indicate serious conditions like cancer, BME is a sign of an underlying process, not a diagnosis itself. It stems from various causes, both benign and malignant.
Understanding Bone Marrow Edema
Bone marrow edema (BME) describes increased fluid signals within the bone marrow, typically identified through magnetic resonance imaging (MRI). This fluid buildup indicates a reaction to an underlying condition or injury affecting the bone. On an MRI, BME appears as areas with high signal intensity on specific fat-suppressed sequences, differentiating it from normal bone marrow. It is often referred to as a “bone marrow lesion” or “bone bruise” in less severe contexts.
This fluid can cause symptoms such as deep, dull pain in the affected area, which may worsen with activity. Swelling, tenderness, and restricted movement in an associated joint are also possible. However, some individuals with BME experience no symptoms, with the finding discovered incidentally during an MRI for another condition.
When Bone Marrow Edema Indicates Cancer
Bone marrow edema can be a manifestation of cancer, particularly when malignant cells infiltrate the bone marrow or tumors grow within or near bone. Cancers originating in the bone marrow, such as leukemias, lymphomas, and multiple myeloma, can directly cause fluid accumulation as cancer cells proliferate and disrupt normal marrow structure. Acute myeloid leukemia (AML) is one type of cancer that causes BME.
Metastatic cancer, which has spread from another part of the body to the bones, is another significant cause. Primary cancers that commonly metastasize to bone and cause BME include breast, prostate, lung, kidney, and thyroid cancers. Additionally, primary malignant bone tumors like osteosarcoma, Ewing’s sarcoma, and chondrosarcoma can present with BME surrounding the tumor. This edema can result from the tumor’s direct presence or be a reactive inflammatory change in the surrounding marrow tissue.
Non-Cancerous Causes of Bone Marrow Edema
While cancer is a concern, bone marrow edema more frequently stems from benign conditions. Injuries are a common culprit, ranging from acute trauma like fractures and bone bruises to chronic issues such as stress injuries. Stress fractures, often seen in athletes due to repetitive physical activity, result from microtrauma and present with BME. Overuse syndromes and ligamentous injuries, including ACL tears, can also lead to fluid accumulation.
Inflammation and infection are frequent causes of BME. Osteomyelitis, a bone infection, causes swelling as the body fights the infection, leading to fluid buildup in the bone marrow. Various forms of arthritis, both inflammatory and non-inflammatory, can trigger BME, including osteoarthritis, rheumatoid arthritis, psoriatic arthritis, and gout. In osteoarthritis, BME often accompanies cartilage loss as the disease progresses.
Other non-cancerous conditions that can cause BME include avascular necrosis (AVN), where a lack of blood supply to the bone leads to bone tissue death. Metabolic disorders such as osteoporosis, which weakens bones and makes them prone to microfractures, can also result in BME. Benign bone tumors, although not cancerous, can also cause edema by placing stress on the bone marrow as they grow.
Diagnosing Bone Marrow Edema and Determining Its Cause
The diagnostic process for bone marrow edema begins with a thorough medical history and physical examination. Magnetic resonance imaging (MRI) is the primary tool for detecting BME, as it precisely visualizes fluid accumulation within the bone marrow. Unlike X-rays or CT scans, MRI is highly sensitive to changes in fluid content, making it invaluable for BME detection.
Once BME is identified, determining its underlying cause requires further investigation. Blood tests are performed to check for signs of inflammation or specific markers that might indicate an infection or certain medical conditions. Depending on the suspected cause, additional imaging such as ultrasound may be used. If cancer is suspected, a bone marrow biopsy or aspiration is performed to obtain tissue samples for microscopic examination. This procedure is often definitive in confirming or ruling out malignancy.