Is MRI with or without contrast preferred for diagnosing avascular necrosis (AVN)?

MRI for Avascular Necrosis: With or Without Contrast

MRI without contrast is the preferred imaging modality for diagnosing avascular necrosis (AVN) with nearly 100% sensitivity, and contrast administration is generally not necessary for initial diagnosis. 1

Diagnostic Accuracy of Non-Contrast MRI

Non-contrast MRI offers several advantages for AVN diagnosis:

• Nearly 100% sensitivity for detecting occult femur fractures and AVN 1
• Superior to standard radiographs (15-35% sensitivity) and CT scans (69-87% sensitivity) 1
• Allows for early detection before radiographic changes appear 2
• Provides assessment of lesion size and location, which relates to prognosis 2

MRI Findings in AVN Without Contrast

Non-contrast MRI typically shows:

• Well-demarcated epiphyseal areas of variable signal intensity 3
• Characteristic patterns including:
  • Linear or patchy low signal areas in the superoanterior portion of the femoral head (early stage) 4
  • Band or ring of low signal intensity surrounding central areas of high signal intensity on T1WI 4
  • Focal subchondral regions with intermediate signal on T1WI and high signal on T2WI 4

When Contrast May Be Considered

While non-contrast MRI is typically sufficient, contrast-enhanced MRI may be beneficial in specific scenarios:

• When there is diagnostic uncertainty between AVN and transient bone marrow edema 3
• In cases where increased diagnostic confidence is needed to distinguish:
  • Homogeneous hypervascularization in bone marrow edema lesions
  • Hypovascular marrow areas in AVN lesions 3

Practical Approach to MRI for AVN

1. Initial Evaluation: Order non-contrast MRI with T1 and T2-weighted sequences
2. Protocol: Include both coronal and axial views of the affected hip
3. Consider Rapid MRI Protocols: For screening purposes, rapidly acquired MR sequences (<1 minute) can reliably reveal the presence or absence of AVN 5
4. Reserve Contrast: Only add contrast if initial non-contrast images are equivocal or if differentiation from other pathologies is needed

Common Pitfalls to Avoid

• Relying solely on radiographs for early AVN detection (low sensitivity)
• Unnecessary use of contrast, which increases cost, procedure time, and potential for adverse reactions
• Failure to recognize that MRI can distinguish AVN from other hip diseases with high sensitivity (85%) and specificity (98%) even without contrast 6

MRI without contrast remains the gold standard for AVN diagnosis, providing excellent visualization of bone marrow changes and characteristic patterns that define this condition.