Should a CT (Computed Tomography) scan of the elbow for suspected cellulitis be done with or without contrast?

CT of the Elbow for Suspected Cellulitis Should Be Done With IV Contrast

For suspected cellulitis of the elbow, CT should be performed with intravenous (IV) contrast to maximize diagnostic accuracy and detection of complications. 1

Rationale for Contrast-Enhanced CT

CT with IV contrast offers several advantages when evaluating soft tissue infections:

• Enhanced visualization of infection extent: Contrast-enhanced CT improves detection of synovitis, inflammation, fistulas, abscesses, and vascular complications 1
• Better tissue differentiation: IV contrast helps differentiate cellulitis from other soft tissue pathologies such as myositis, tenosynovitis, and abscess formation 1
• Complication assessment: Contrast is essential for evaluating vascular complications that may accompany severe infections 1

The American College of Radiology (ACR) Appropriateness Criteria specifically rates CT with IV contrast as a 6/9 ("may be appropriate") for suspected soft tissue infections following initial radiographs, while non-contrast CT receives only a 4/9 rating 1.

Clinical Decision Algorithm

1. Initial evaluation: Plain radiographs should be the first imaging study to exclude alternative diagnoses and identify any radiodense foreign bodies 2

2. When to order CT:

   • When deeper tissue involvement is suspected
   • When ultrasound findings are equivocal
   • When there is concern for abscess formation not adequately visualized by ultrasound
   • When necrotizing infection is suspected

3. CT protocol selection:

   • WITH contrast: For most cases of suspected cellulitis
   • WITHOUT contrast: Only in specific scenarios:
     • Patient has severe contrast allergy
     • Significant renal dysfunction
     • When specifically looking for a foreign body (contrast may obscure identification) 1

Evidence-Based Considerations

The 2022 ACR Appropriateness Criteria update emphasizes that "contrast-enhanced CT can assess soft tissue and the extent of infection, which can guide aspiration or surgical debridement" 1. This is particularly important as cellulitis can sometimes be difficult to distinguish from deeper infections that require more aggressive intervention.

A recent retrospective analysis found that CT examination for extremity cellulitis has a low yield for detecting deep infection (5.5%), suggesting that CT should be used selectively rather than routinely 3. However, when CT is indicated, contrast enhancement significantly improves diagnostic accuracy.

Important Caveats and Pitfalls

• Don't delay treatment: Never delay antimicrobial therapy while waiting for imaging if there is high clinical suspicion of severe infection 2
• Consider ultrasound first: For suspected abscess formation requiring drainage, ultrasound may be more appropriate as the initial advanced imaging modality 2
• Recognize CT limitations: CT is less sensitive than MRI for detecting early bone marrow changes that might indicate osteomyelitis 1
• Avoid unnecessary radiation: CT should not be routinely ordered for uncomplicated cellulitis 3
• Consider MRI alternative: MRI provides superior soft tissue contrast and may be preferred when available and not contraindicated, especially when concerned about early osteomyelitis 1, 2

By following these evidence-based guidelines, the appropriate use of contrast-enhanced CT can significantly improve diagnostic accuracy and guide management decisions in cases of suspected elbow cellulitis.