From the Guidelines
Magnetic Resonance Imaging (MRI) is the best imaging modality for diagnosing necrotizing fasciitis when available and if the patient is stable enough for the study. This is based on the most recent and highest quality study, which reported that MRI has the highest sensitivity of 93% for the diagnosis of necrotizing fasciitis due to its ability to detect fluid signal on T2 fat suppressed or short tau inversion recovery (STIR) sequences 1. The study also noted that the absence of fluid signal along the fascia essentially excludes the diagnosis of necrotizing fasciitis.
Some key points to consider when using MRI for diagnosing necrotizing fasciitis include:
- Thickening of the deep intermuscular fascia of 3 mm or more on fluid-sensitive MR sequences is a strong predictor of necrotizing fasciitis 1
- Significant involvement of the deep fascia with 3 or more muscular compartments involved in one extremity is also a strong predictor of necrotizing fasciitis 1
- Low signal intensity foci or collections on all MRI sequences representing soft tissue gas are highly associated with necrotizing fasciitis 1
- Noncontrast MRI is still an important examination and can detect soft tissue findings of fascial edema/fluid signal, deep fascial/intermuscular edema, soft tissue gas, and fluid collections 1
While other imaging modalities such as CT and ultrasound may be used in certain situations, MRI remains the gold standard for diagnosing necrotizing fasciitis due to its high sensitivity and ability to detect subtle changes in the deep soft tissues. It's also important to note that imaging should never delay surgical intervention when necrotizing fasciitis is strongly suspected clinically, as early surgical exploration and debridement remain the definitive diagnostic and therapeutic approach for this life-threatening condition 1.
From the Research
Imaging Modalities for Necrotizing Fasciitis
The best imaging modality for diagnosing necrotizing fasciitis is a crucial aspect of its management. Several studies have compared the effectiveness of different imaging modalities in diagnosing this condition.
- Magnetic Resonance Imaging (MRI) is considered the gold standard for evaluating necrotizing fasciitis due to its high sensitivity, specificity, and soft tissue contrast 2.
- Computed Tomography (CT) imaging is also useful, with a sensitivity of 80%, but it is less specific than MRI 3.
- Ultrasound can provide useful clues, but it is not recommended in adults due to the infiltration of the hypodermis blocking ultrasound transmission 4.
- Plain radiography is the least sensitive and specific modality, but it can still provide useful information, such as the presence of subcutaneous gas 5, 3.
Key Imaging Findings
The key imaging findings in necrotizing fasciitis include:
- Asymmetric thickening of fascia
- Soft tissue air
- Blurring of fascial planes
- Inflammatory fat stranding
- Reactive lymphadenopathy
- Nonenhancement of muscular fascia 5, 3, 4
- Fascial thickening with potential fat stranding, edema, subcutaneous gas, and abscess formation 3, 4
Limitations of Imaging
While imaging is a powerful adjunct to clinical diagnosis, it should not delay surgical consultation or treatment. The diagnosis of necrotizing fasciitis remains a clinical one, and imaging should be used to support the diagnosis, rather than replace it 3, 4.