= progressive rapidly spreading infection of deep fascia → secondary necrosis of SQ tissue

N.B.: life-threatening surgical emergency!

Prevalence: 500 cases in literature

Age: 58 ± 14 years; M>F

Cause: deep internal infection / malignancy (perforated duodenal ulcer / retroperitoneal appendix, retroperitoneal / perirectal infection, infiltrating rectal / sigmoid carcinoma

Predisposed: immunocompromised patients (with diabetes, cancer, alcohol / drug abuse, vascular insufficiency, organ transplant), poor nutrition, foreign body in surgical wound

Organism: often gas-forming anaerobic bacteria in combination with aerobic gram-negative organisms: Staphylococcus, E. coli, Bacteroides, Streptococcus, Peptostreptococcus, Klebsiella, Proteus, C. perfringens (5–15%); multiple organisms in 75%

Histo: necrotic superficial fascia, leukocytic infiltration of deep fascial layers; fibrinoid thrombosis of arterioles + venules with vessel wall necrosis; microbial infiltration of destroyed fascia

• indolent: 1–21 days delay before diagnosis
• nonspecific symptoms: severe pain, fever, leukocytosis, shock, altered mental status
• crepitus (50%), overlying skin may be completely intact

Location: lower extremity, arm, neck, back, male perineum / scrotum (= Fournier gangrene)

• image findings similar to cellulitis but more severe with involvement of deeper structures
• asymmetric fascial thickening with fat stranding (80%) ← fluid
• fluid collections along deep fascial sheaths
• gas in soft-tissues dissecting along fascial planes ← gas-forming organisms (in 55%)
• associated deep abscess (35%)
• ± secondary muscle involvement:
  • extension of edema into intermuscular septa and muscles
  • NO demonstrable enhancement of fascia ← necrosis

Prognosis: poor with delay in diagnosis ← progresses rapidly; morbidity and mortality rate of 70–80%

Rx: extensive surgical débridement + antibiotics

DDx:

1. Myonecrosis (= infection originating in muscle)
2. Fasciitis-panniculitis syndromes (chronic swelling of skin + underlying soft tissues + fascial planes in arm + calf)
3. Soft-tissue edema of CHF / cirrhosis (symmetrical diffuse fat stranding)
4. cellulitis (less severe, without involvement of deeper structures)