Should a CT scan be performed with or without contrast to diagnose necrotizing fasciitis?

CT with Contrast is Recommended for Diagnosing Necrotizing Fasciitis

CT with intravenous contrast is the preferred imaging modality for diagnosing necrotizing fasciitis as it allows visualization of both fascial thickening and lack of fascial enhancement, which are highly specific findings for necrotizing fasciitis. 1

Diagnostic Value of CT in Necrotizing Fasciitis

CT with Contrast

• Contrast-enhanced CT allows detection of fascial fluid, thickening, and critically, the lack of enhancement of the fascia, which is highly specific for necrotizing fasciitis 1
• Contrast enhancement improves assessment of tissue necrosis, abscess formation, and vascular complications 1
• A retrospective study demonstrated that absence of fascial enhancement on contrast CT was highly associated with surgically confirmed necrotizing fasciitis compared to other musculoskeletal infections 1

CT without Contrast

• Non-contrast CT is still highly accurate for detecting soft tissue gas, with a sensitivity of 89% and specificity of 93% 1
• Gas within fascial planes is a hallmark of necrotizing fasciitis, though it may be absent in early disease or with aerobic infections 1
• CT findings of necrotizing fasciitis include fat stranding, fluid collections along fascial planes, and fascial thickening 1

Important Considerations

Clinical Context

• Necrotizing fasciitis is primarily a clinical diagnosis, with imaging serving as an adjunct when diagnosis is uncertain 1
• Imaging studies should never delay surgical consultation and intervention when clinical suspicion is high 1, 2
• CT has demonstrated 100% sensitivity and 81% specificity for identifying necrotizing fasciitis in one case series 1

Alternative Imaging Modalities

• MRI has the highest sensitivity (93%) for detecting fascial fluid and edema but may be impractical in emergency situations 1
• Ultrasound can be useful in unstable patients with a sensitivity of 88.2% and specificity of 93.3%, but has limitations in deeper tissues 1, 2
• Plain radiographs have limited value and should not be used to rule out necrotizing infection 1

Diagnostic Algorithm for Suspected Necrotizing Fasciitis

1. Begin with clinical assessment for signs of necrotizing fasciitis 2
2. For stable patients with uncertain diagnosis:
   • CT with IV contrast is the preferred initial imaging study 1
   • Look for fascial thickening, fluid collections, and lack of fascial enhancement 1
   • Presence of soft tissue gas strongly supports the diagnosis 1
3. For unstable patients:
   • Bedside ultrasound may be helpful to differentiate simple cellulitis from necrotizing fasciitis 1
4. If clinical suspicion remains high despite negative or equivocal imaging:
   • Proceed to surgical exploration, which remains the gold standard for diagnosis 2
   • Consider frozen section biopsy in equivocal cases 1

Pitfalls to Avoid

• Relying solely on the presence of gas, as it may be absent in early disease or with aerobic infections 1
• Delaying surgical intervention for imaging when clinical suspicion is high 1, 2
• Using plain radiographs to rule out necrotizing fasciitis due to their low sensitivity 1
• Waiting for MRI when CT is more readily available in emergency settings 1