Discussion of Necrotizing fasciitis
- Necrotizing fasciitis is a rapidly progressive and often fatal infection of the soft-tissue fascia deep to the skin but superficial to the muscles.
- Elderly patients and those with impaired immunity are at increased risk.
- Predisposing factors include underlying infections such as diverticulitis, furuncles, minor trauma, surgery, or insect bites.
- Factors associated with a poor outcome include diabetes mellitus, alcoholism, peripheral vascular disease, obesity, and old age.
- Mortality rate may be as high as 30%–70%, with death being due to sepsis, respiratory failure, kidney failure, or multi–organ system failure.
- The most common type of necrotizing fasciitis is a polymicrobial infection with both aerobic and anaerobic organisms. This form of the disease is often seeded from underlying infections such as diverticulitis.
- A second form of the disease is caused by group A streptococci, the "flesh-eating bacteria," and is seen in approximately 10% of cases.
- Lack of a walled-off boundary accounts for both the rapid spread of disease and the difficulty in clinical diagnosis.
- Crepitus due to superficial fascial emphysema is only rarely palpable.
- Extreme pain followed by anesthesia suggests the diagnosis.
- The treatment for necrotizing fasciitis is prompt surgical fasciotomy and debridement of the necrotic tissue.
- Broad-spectrum antibiotic coverage should be maintained until the causative organisms have been identified.
 Imaging Findings for Necrotizing fasciitis
 Plain film
- Increased soft-tissue thickness and opacity.
- Characteristic finding of gas in the soft tissues is seen in only a minority of cases.
- The CT hallmark of necrotizing fasciitis is soft-tissue air associated with fluid collections within the deep fascia, although this finding is inconstant.
- Also evident at CT are thickening and enhancement of one or both of the superficial and deep fascial layers.
- Liquefactive tissue necrosis and inflammatory edema both create fascial fluid that is detected with MR imaging as abnormally increased signal intensity on T2-weighted images and variably increased signal intensity on T1-weighted images along thickened deep fascial planes.
- In general, fat-suppressed T2-weighted imaging has been found to display inflammatory changes better than fat-suppressed gadolinium-enhanced T1-weighted imaging.
- Gas bubbles, if present, appear as focal signal voids on both T1- and T2-weighted images.
- The subcutaneous tissues may have reticular increased signal intensity, similar to cellulitis. Unlike cellulitis, however, the deep fascia is also involved.
- Useful in the pediatric age group.
- Distorted and thickened fascial planes with turbid fluid accumulation in the fascial layers and subcutaneous edema.
- Examination may be limited by soft-tissue gas, although this finding may be of diagnostic benefit.
 See Also
 External Links
 References for Necrotizing fasciitis
- J. Brett Fugitt, Michael L. Puckett, Michael M. Quigley, and Stewart M. Kerr. Necrotizing Fasciitis. RadioGraphics 2004 24: 1472-1476.