Is plain computed tomography (CT) preferred to contrast computed tomography (CT) for diagnosing spondylodiscitis?

Plain CT vs Contrast CT for Diagnosing Spondylodiscitis

Plain CT without contrast is preferred over contrast-enhanced CT for diagnosing spondylodiscitis, as contrast has not been shown to provide significant additional diagnostic value for this specific condition. 1

Imaging Modality Selection for Spondylodiscitis

Initial Imaging Approach

• Radiography is recommended as the first imaging modality for evaluation of suspected spondylodiscitis, though it has low sensitivity for early disease 1
• MRI without and with IV contrast is the imaging modality of choice for suspected spondylodiscitis due to its high sensitivity and specificity 1, 2
• CT is indicated when MRI cannot be performed or when there are equivocal radiographic findings 1

Role of CT in Spondylodiscitis

• CT without contrast provides excellent delineation of osseous detail with greater sensitivity than radiography 1
• CT without contrast is particularly useful for identifying:
  • Subtle bone erosions and reparative changes 1
  • Soft tissue ossification 1
  • Complex anatomy of the affected vertebral segments 1
• CT without contrast receives a high appropriateness rating (7/9) for evaluation of suspected axial spondyloarthropathy when MRI cannot be performed 1

Why Plain CT is Preferred Over Contrast CT

• According to the ACR Appropriateness Criteria, "CT with contrast should be considered only when MRI is contraindicated or not feasible" 1
• The addition of IV contrast to CT has not been shown to significantly increase diagnostic accuracy for spondylodiscitis 1
• CT spine with contrast receives the lowest appropriateness rating (1/9) for evaluation of suspected axial spondyloarthropathy 1
• There is "no literature to support a benefit to contrast use" in CT for spine infections 1

Important Clinical Considerations

Advantages of Plain CT

• Lower risk profile by avoiding potential contrast-related complications such as:
  • Nephrotoxicity 1
  • Contrast reactions 1
  • Nephrogenic systemic fibrosis in at-risk patients 1
• Lower cost compared to contrast-enhanced studies 1
• No need for IV access 1
• Excellent visualization of bony details which is crucial for identifying erosions and structural changes in spondylodiscitis 1

Limitations of CT in General

• CT (both with and without contrast) lacks sensitivity for direct inflammatory changes of early infection 1
• CT has low sensitivity (6%) for the identification of epidural abscess 1
• CT cannot reliably differentiate between infectious and degenerative changes in some cases 2

Best Practices for Imaging Spondylodiscitis

• When spondylodiscitis is suspected, the optimal imaging algorithm is:
  1. Start with plain radiographs 1
  2. If radiographs are negative or equivocal but clinical suspicion remains high, proceed to MRI without and with contrast 1, 2
  3. If MRI is contraindicated or unavailable, use plain CT without contrast 1
• For follow-up imaging to monitor treatment response, plain CT may be useful to assess bony healing, though MRI remains superior for evaluating ongoing inflammation 2, 3

Pitfalls to Avoid

• Relying solely on CT (with or without contrast) for early diagnosis of spondylodiscitis may lead to false negatives due to its limited sensitivity for early inflammatory changes 1
• Performing both non-contrast and contrast-enhanced CT unnecessarily increases radiation exposure without adding significant diagnostic value 1
• Assuming that contrast enhancement will significantly improve diagnostic accuracy for spondylodiscitis when evidence suggests otherwise 1