MRI of AVN of Femoral Head - Wheeless' Textbook of Orthopaedics

- See:
- MRI of Hip:
- Johns Hopkins - MRI Evaluation of AVN

- Discussion:
- magnetic resonance imaging is probably the most accurate imaging modality for dx of AVN of femoral head;
- MRI imaging is also used to outline the area of involvement;
- it can show the revascularization front and provide objective evidence of changes in the tissue in response to treatment;
- it allows sequential evaluation of asymptomatic lesions that are not yet detectable on plain radiographs;

- Classic Findings:
- look for focal lesion in the anterosuperior portion of femoral
head that is well demarcated but is inhomogeneous;
- T1 images:
- will show low signal intensity;
- T2 images:
- double line sign:
- classic sign of AVN;
- made up of 2 concentric low and high signal bands;
- the high-signal-intensity line may represent hypervascular granulation tissue;

- Diff Dx:
- bone marrow edema syndrome:
- ref: Bone marrow edema syndrome and transient osteoporosis of the hip.
S Hofmann et al. JBJS Vol 75-B. 1993 p 210-216.
- transient regional osteoporosis:
- T1 images: pattern of diffusely decreased signal intensity;
- T2 images: high signal intensity which matches the T1 changes;

- False Negative Results:
- on rare occasions, investigators have found AVN on histological exam
of specimens of bone when magnetic resonance imaging was negative;
- Koo et al reported on a group of patients who had several risk factors for avascular necrosis;
- of 136 biopsy specimens that were consistent w/ avascular necrosis,
ten were assoc w/ negative magnetic resonance images;