Surgical Emergency
Gas tracking along fascial planes is pathognomonic on CT. Do not delay surgical debridement for additional imaging if clinical suspicion is high.
CT Findings
- Gas in fascia (linear/bubbly hypodensities along fascial planes) — pathognomonic
- Asymmetric fascial thickening
- Fluid tracking along fascial planes
- Absent or diminished fascial enhancement
- Skin thickening
Report any gas in soft tissue planes with urgency. Mortality 20–40% — increases significantly with operative delay beyond 12–24 hours.
Imaging Limitations
CT sensitivity 88–90%, specificity ~93%. Negative CT does NOT exclude necrotizing fasciitis. If clinical suspicion is high (pain out of proportion, rapid progression, skin changes, toxicity, crepitus), operate regardless of CT findings. LRINEC score (Laboratory Risk Indicator for Necrotizing Fasciitis) can aid but does not replace clinical judgment.
Classification
| Type | Organisms | Location / Population |
|---|---|---|
| Type I — polymicrobial | Mixed aerobic and anaerobic organisms (E. coli, Klebsiella, Bacteroides, Peptostreptococcus, Clostridium); synergistic infection | Most common type (~80%); trunk, perineum, lower extremities; diabetics, immunocompromised, post-operative, elderly; gas production common from anaerobes |
| Type II — monomicrobial (Group A Strep) | Group A Streptococcus pyogenes (±S. aureus); potent exotoxins; toxic shock syndrome | Extremities; previously healthy adults; minor trauma or no entry point; rapidly progressive; toxic shock syndrome (fever, hypotension, multiorgan failure); less gas than Type I |
| Fournier's gangrene | Polymicrobial (Type I); E. coli, Klebsiella, Bacteroides, Clostridium | Perineum, scrotum, perianal region; males >> females; diabetics; CT: gas in scrotal/perineal soft tissues, fascial thickening, abscess; can spread to thigh and abdominal wall via fascial planes; wide surgical debridement ± orchiectomy |
Reference
Malghem J et al. Necrotizing fasciitis: contribution and limitations of diagnostic imaging. Joint Bone Spine. 2013;80(2):146–54.