Should an MRI of the hip for ischemic necrosis be done with or without contrast?

MRI Without Contrast is the Recommended Imaging Modality for Evaluating Ischemic Necrosis of the Hip

MRI without IV contrast is the most appropriate imaging modality for evaluating ischemic necrosis (avascular necrosis) of the hip, with sensitivity and specificity approaching 100%. 1, 2

Diagnostic Imaging Algorithm for Ischemic Necrosis

1. Initial Imaging: Plain Radiographs

   • Start with anteroposterior and lateral (frog-leg) views of the hip
   • Radiographs help exclude other causes of hip pain (fracture, arthritis, tumor)
   • Limited sensitivity for early ischemic necrosis 1

2. When Radiographs are Normal or Inconclusive:

   • Proceed directly to MRI without contrast
   • MRI without contrast is explicitly recommended by the American College of Radiology as the next appropriate imaging study 1, 2

Why MRI Without Contrast is Superior

• Highest Sensitivity and Specificity:

  • Nearly 100% sensitivity and specificity for detecting ischemic necrosis 1, 2
  • Can detect changes immediately after onset, before radiographic changes appear 2, 3
  • Significantly more sensitive than bone scintigraphy and CT 1, 3

• Detailed Characterization:

  • Shows exact location and extent of necrosis 3
  • Allows assessment of lesion volume, which is critical for prognosis 1
  • Can detect associated findings like bone marrow edema or joint effusion 1

• Differential Diagnosis:

  • Helps differentiate ischemic necrosis from other conditions with similar presentations:
    • Transient osteoporosis of the hip
    • Subchondral insufficiency fracture
    • Epiphyseal tumors 1, 2

When Is Contrast-Enhanced MRI Indicated?

• Standard Cases:

  • Contrast is generally NOT needed for routine diagnosis of ischemic necrosis 1, 2
  • The ACR Appropriateness Criteria specifically recommends MRI without IV contrast 1

• Special Circumstances:

  • Dynamic contrast enhancement may help differentiate between:
    • Osteonecrosis
    • Transient bone marrow edema syndrome
    • Subchondral insufficiency fracture 1
  • However, this is not routinely necessary for initial diagnosis 1

Comparison with Other Imaging Modalities

• CT Scanning:

  • Less sensitive than MRI for early detection 1
  • Better for showing location and extent of articular collapse in advanced cases 1
  • Should be reserved for preoperative planning after diagnosis is established 1

• Bone Scintigraphy:

  • Poor spatial resolution and lower specificity compared to MRI 1
  • Cannot quantify size of necrotic lesion accurately 1
  • Has been largely replaced by MRI for detection of ischemic necrosis 1

Clinical Implications

• Early detection with MRI without contrast allows for timely intervention before femoral head collapse occurs 3, 4
• MRI findings can predict risk of progression - for example, humeral heads with a necrotic angle <90° typically don't collapse within 24 months 1
• Asymptomatic lesions detected on MRI may not always progress to bone collapse 4

Conclusion

Based on the highest quality and most recent evidence from the American College of Radiology Appropriateness Criteria, MRI without IV contrast is the gold standard for evaluating ischemic necrosis of the hip 1, 2. This approach provides optimal diagnostic accuracy while avoiding unnecessary contrast administration.