Bone marrow edema is the term given to abnormal fluid signals seen within the bone marrow on MRI. It is a non-specific yet important imaging finding, usually indicating the presence of underlying pathology.
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Terminology
The term edema was coined on MRI as the signal in abnormal bone marrow is similar to that seen with excess water; low T1, high T2. The term is, however, misleading as "edema" implies that there is only excess fluid, whereas in reality, within areas of so-called bone marrow edema, a wide variety of processes can exist, including infarction, hemorrhage, inflammatory cell infiltration, fibrosis, and hypervascularity 6.
Pathology
Etiology
There is a long (long) list of possible causes of this finding:
primary: bone marrow edema syndrome (no cause found)
trauma: fractures, bone contusion, ligamentous injury, etc.
arthropathy: e.g. degenerative joint disease, rheumatoid arthritis, etc.
hypoperfusion: e.g. sickle cell disease
infective: e.g. osteomyelitis, diskitis, septic arthritis
iatrogenic: e.g. chemotherapy, postoperative, chronic corticosteroid therapy
neurological: neuropathic arthropathy
neoplastic: malignancies e.g. bone metastases, and benign e.g. giant cell tumor, chondroblastoma, osteoid osteoma
miscellaneous: e.g. chronic renal failure
Radiographic features
CT
Dual-energy CT may demonstrate bone marrow edema using fluid-sensitive "edema maps", however, its sensitivity and specificity are poorer than MRI 5,6.
MRI
Bone marrow edema is generally primarily identified on MRI and is best investigated using fat-suppressed T2W sequences.
There will be intermediate T1 signal, with a high T2 signal in the fat of the bone marrow (usually fat-suppressed sequences required to see the increased T2 signal).
However other imaging modalities may have a role in investigating the underlying cause.
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