Bone marrow edema

Bone marrow oedema is the term given to abnormal fluid signalsignals seen within the bone marrow on MRI. It is a non-specific yet important imaging finding, usually indicating the presence of underlying pathology.

Terminology

The term oedema was coined on MRI as the signal in abnormal bone marrow is similar to that which would be seen with the presence of excess water; low T1, high T2. The term is, however, misleading as "oedema" implies that there is only excess fluid, whereas in reality, within areas of so-called bone marrow oedema, a wide variety of processes can exist, including infarction, haemorrhage, inflammatory cell infiltration, fibrosis, and hypervascularity ⁶.

Pathology

Aetiology

There is a long (long) list of possible causes of this finding:

• primary:bone marrow oedema 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 tumour, chondroblastoma, osteoid osteoma

• miscellaneous: e.g. chronic renal failure

Radiographic features

CT

Dual-energy CT may demonstrate bone marrow oedema using fluid-sensitive "oedema maps", however, its sensitivity and specificity isare poorer than that of MRI ^5,6.

MRI

Bone marrow oedema 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 then have a role in investigating the underlying cause.