Is X-ray (radiograph) better than CT (computed tomography) scan for ruling out osteomyelitis?

MRI is Superior to X-ray and CT for Ruling Out Osteomyelitis

MRI is significantly superior to both X-ray and CT for ruling out osteomyelitis due to its exceptional sensitivity (82-100%) and specificity (75-96%) 1. Neither X-ray nor CT offers comparable diagnostic accuracy for this condition.

Diagnostic Imaging Algorithm for Suspected Osteomyelitis

Initial Imaging

• Plain radiographs (X-rays) should be the first imaging test performed, but they have significant limitations:
  • Early acute osteomyelitis (<14 days) may show normal radiographs or only mild soft tissue swelling 1
  • X-rays primarily provide anatomic evaluation and can only reveal changes of chronic osteomyelitis, gas, or foreign bodies

Secondary Imaging

• MRI with contrast enhancement is the preferred imaging modality after initial radiographs because:

  • Superior sensitivity (82-100%) and specificity (75-96%) for detecting bone marrow changes 1
  • Excellent ability to detect early manifestations of osteomyelitis 2
  • Superior soft tissue resolution for evaluating surrounding infection 3
  • Ability to detect abscesses, fistulas, and sinus tracts 1

• CT has significant limitations for osteomyelitis diagnosis:

  • No relevant literature supports CT as the next imaging study for evaluation of osteomyelitis in children under 5 years of age 2
  • CT is useful primarily for detecting sequestra, foreign bodies, or gas formation but is generally less sensitive than other modalities 4
  • CT should only be considered when MRI is contraindicated (rated 7/9 by ACR compared to MRI's 9/9) 1

Key MRI Protocol Elements

• Optimal MRI sequences should include:
  • T1-weighted imaging
  • Fluid-sensitive sequences
  • Post-contrast T1-weighted fat-suppressed images 1
• In uncomplicated cases, particularly in children, fluid-sensitive sequences alone may be sufficient for diagnosis 2

Special Considerations

Pediatric Patients

• MRI is preferred over nuclear medicine studies due to radiation concerns 1
• Multifocal osteomyelitis is more common in children <6 years, making whole-body evaluation important 1
• Consider imaging both extremities as 11% of pediatric patients with osteomyelitis had contralateral extremity findings 1

When MRI is Contraindicated

• Alternative options include:
  • CT with IV contrast (rated 7/9 by ACR) 1
  • Nuclear medicine studies (3-phase bone scan with labeled leukocyte scan) 1
  • Nuclear medicine is particularly useful for identifying multifocal involvement in children 4

Common Pitfalls to Avoid

• Relying solely on X-rays for diagnosis can lead to missed cases, as radiographic changes may not be apparent until days or weeks after onset 5
• CT may underestimate lesion size by up to 37% compared to actual extent of disease 6
• Challenges in diagnosis include:
  • Distinguishing infection from reactive inflammation
  • Differentiating osteomyelitis from bone infarction in sickle cell disease
  • Potential confusion between osteomyelitis and Ewing sarcoma 1

In conclusion, while X-rays should be the initial imaging test for suspected osteomyelitis, they are insufficient for ruling out the condition. MRI is vastly superior to both X-ray and CT for this purpose, with CT playing a limited role primarily when MRI is contraindicated.