What is the role of MRI in the diagnosis of femoral head avascular necrosis (AVN)?

Updated: Oct 22, 2018
  • Author: John D Kelly, IV, MD; Chief Editor: Craig C Young, MD  more...
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Answer

MRI

  • MRI is the study of choice in patients who demonstrate signs and symptoms that are suggestive of AVN but whose radiographs are normal.

  • MRI is the most sensitive and specific means of diagnosing AVN. MRI may detect disease as early as 5 days subsequent to an ischemic insult.

  • Characteristic MRI findings for AVN of the hip include a low signal intensity band (seen on T1 and T2 images) that demarcates a necrotic anterosuperior femoral head segment. The extent and location of femoral head necrosis on MRIs have been studied as predictors of femoral head collapse. Smaller lesions (less than one fourth the diameter of the femoral head) and more medial lesions (away from primary weight-bearing areas) predict a better outcome. [10]

Bone scanning

  • Abnormalities may show up on a bone scan before they do on plain radiographs. Bone scan findings should be supplemented with MRI findings.

  • The presence of a photopenic area that is surrounded by increased tracer uptake is the typical scintigraphic picture for radionuclide imaging.

  • Bone scans are considerably less sensitive and less specific than MRI, but the images may be useful if the use of MRI is contraindicated.

Computed tomography (CT) scanning

  • CT scans confer significant radiation exposure to the patient and are less sensitive than MRI in diagnosing AVN.

  • CT scanning may help delineate early subchondral collapse because the resolution of bony architecture with this modality is unsurpassed.

Angiography is an invasive mean of diagnostic confirmation of AVN; it is most useful as an investigational modality.


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