There was a H/O right hip joint pain. Previously the patient had left hip joint pain.
There are diffuse areas of hypointensity on the T1W images that turn hyperintense on the T2W and STIR images within the head and neck of the right femur. Also seen is a small effusion in the right hip joint. Fatty marrow changes are seen in the left femoral head and neck. Similar signal changes were seen in the left femoral head and neck on a previous MRI, eight months ago (have resolved, as seen on the current MRI).
Bone marrow edema (BME) is usually seen as nonspecific MR signal intensity changes that are hypointense on the T1-weighted images and hyperintense on T2-weighted images or STIR sequences. BME includes transient osteoporosis of the hip, transient bone marrow edema and osteonecrosis. A nonspecific BME pattern can also be observed in cases of occult osseous trauma, infection, and neoplasms (however, these can usually be distinguished from the aforementioned entities). BME may enhance with gadolinium.
Transient BME is a reversible BME pattern and is self-limited (may represent a form of transient osteoporosis of the hip). Osteonecrosis may also present with a diffuse BME pattern that may obscure a poorly defined subchondral focal lesion or precede the development of a discrete well-demarcated focus of osteonecrosis. Patients with BME and subchondral changes usually proceed to avascular necrosis (AVN). Histologically, transient osteoporosis of the hip, transient BME and AVN may show similar findings of edema, necrosis and a fibrovascular reaction.
BME usually involves the femoral head and neck. Extension of marrow involvement to the epiphysis and lack of soft tissue involvement are characteristic on MR imaging. Radiographs are usually positive within eight weeks after the onset of symptoms. If there is no osteopenia, further follow-up with MRI is indicated. There is usually resolution of clinical and MR abnormalities within 2 to 10 months. These transient entities may be migratory.
Differential Diagnosis:
| Features | Transient Osteoporosis | Bone Marrow Edema | Avascular Necrosis |
| Onset: | Acute | Usually insidious | Gradual or insidious |
| Symptoms: | Pain with weight bearing, limp | Pain at rest, limp later on | Pain at rest, limp later on |
| Etiology: | Not known | Not known | Interruption of circulation |
| M:F Ratio | 3:1 | Equal | Equal |
| Incidence: | Rare | Uncommon | Common |
| Risk factors for AVN: | Absent | May be present | Present |
| Bilateral: | No | No | 50-80% |
| Radiographic features: | Osteopenia 4-6 weeks after onset | +/- Osteopenia | Sclerosis, lucency, subchondral collapse |
| Bone Scan: | Diffuse uptake of tracer in head, neck and trochanteric region | Diffuse uptake of tracer in head and neck region | Localized uptake of tracer or photopenia. |
| MRI: | T1W-Hypointense | T1W-Hypointense | Focal subchondral defect |
| MRI: | T2W/STIR-Hyperintense | T2W/STIR-Hyperintense | +/- Marrow edema |
| MRI: | Head, neck and trochanteric region | Head and neck region | |
| Prognosis: | Resolves in 2-10 months | Resolves in 2-10 months | 70-80% Progress |
| Treatment: | Conservative, non-weight bearing | Conservative, core decompression | Core decompression, vascularized graft, arthroplasty |
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