An edema is a buildup of fluid. A bone marrow edema — often referred to as bone marrow lesion — occurs when fluid builds up in the bone marrow. Bone marrow edema is typically a response to an injury such as a fracture or conditions such as osteoarthritis. Bone marrow edema usually resolves itself with rest and physical therapy.Bone marrow edemas are typically found with an MRI or ultrasound. They can’t be seen on X-rays or CT scans. They’re typically diagnosed when a patient has another condition or pain in or around the bone.Bone marrow is made up of bony, fatty, and blood cell–producing material. Bone marrow edema is an area of increased fluid inside the bone.The detection of bone marrow edema is important, especially in managing symptoms of arthritis, stress fracture, cancer, or infection. Edema can indicate where pain started and how strong your bones are, which can affect treatment.