From the Guidelines
Necrotizing fasciitis on point-of-care ultrasound is characterized by fascial thickening greater than 4mm, fascial fluid accumulation, and subcutaneous gas appearing as hyperechoic foci with dirty shadowing or reverberation artifacts, as identified in a prospective observational study of 62 patients with clinically suspected necrotizing fasciitis 1.
Key Ultrasound Findings
- Fascial thickening greater than 4mm
- Fascial fluid accumulation
- Subcutaneous gas appearing as hyperechoic foci with dirty shadowing or reverberation artifacts
- Fascial irregularity
- Subcutaneous edema appearing as cobblestoning
- Increased fluid in the deep soft tissue layers
- Hyperemia in surrounding tissues on Power Doppler These findings are consistent with the pathophysiology of necrotizing fasciitis, where bacterial toxins cause tissue necrosis, edema, and gas formation along fascial planes.
Diagnostic Accuracy
The study found that ultrasound had a sensitivity of 88.2%, specificity of 93.3%, positive predictive value of 95.4%, and negative predictive value of 95.4% for diagnosing necrotizing fasciitis 1.
Clinical Implications
When these findings are identified, immediate surgical consultation is warranted as necrotizing fasciitis is a surgical emergency requiring prompt debridement alongside appropriate antibiotic therapy. Point-of-care ultrasound serves as a rapid bedside tool that can raise early suspicion for this life-threatening condition.
Comparison with Other Imaging Modalities
While other imaging modalities such as CT and MRI may be useful in diagnosing necrotizing fasciitis, ultrasound has the advantage of being rapidly performed at bedside and can help differentiate necrotizing fasciitis from cellulitis 1.
Limitations
It is essential to note that the presence of subcutaneous gas is highly specific but not always present, especially in early disease. Therefore, a high index of suspicion and clinical correlation are necessary when interpreting ultrasound findings.
From the Research
Ultrasound Findings of Necrotizing Fasciitis
The ultrasound findings of necrotizing fasciitis on point-of-care (POC) ultrasound include:
- Thickening of the subcutaneous tissue 2
- Hypoechoic and hyperechoic zones with a "cobblestone" appearance 3, 2
- "Cobblestone separation" on two layers 2
- Presence of fluid above the fascia 2
- Thickening of the fascia 2
- Indistinctness of the fascia edges 2
- Loss of fascial homogeneity 2
- Dissection of thickened fascia with a strip of fluid 2
- Accumulation of fluid under the fascia 2
- Reverberation artifacts due to hyperechoic outbreaks, defined as "snow globes" 3
- "Dirty shadowing" due to the foggy shadow created by the gas 3
Diagnostic Accuracy
The diagnostic accuracy of POC ultrasound in diagnosing necrotizing fasciitis is promising, but more studies are required to investigate its diagnostic accuracy and potential to reduce time delay before surgical intervention, morbidity, and mortality 4.
Clinical Utility
POC ultrasound is a useful adjunct tool for clinical evaluation and assessment in diagnosing early critically ill patients with life-threatening necrotizing infections 5, 6, 2. It allows visualization of soft tissue changes that may be hidden in the initial stages of necrotizing fasciitis and should be recommended for implementation as a mandatory method of examination in patients with suspected surgical soft tissue infection 2.