Necrotizing Fasciitis

 General Considerations

• A rapidly progressive, infection of fascia which leads to subsequent necrosis of the subcutaneous tissue; muscles are frequently spared
• It may be caused by several organisms of groups of organisms
• Type 1: Polymicrobial
• Bacteroides, Clostridium, or Peptostreptococcus) in combination with streptococci other than group A and E. coli, Enterobacter, Klebsiella or Proteus
• Type 2: Group A beta-hemolytic streptococcus
• Clostridial infections (gas gangrene)
• Frequency may be increasing because of immunocompromised patients
• Organisms spread from subcutaneous tissue along both superficial and deep fascial planes
• Spread may be aided by bacterial enzymes and toxins.
• Carbon dioxide, hydrogen, nitrogen, hydrogen sulfide, and methane are produced from aerobic and anaerobic metabolism and lead to the presence of gas in the soft tissues

Clinical Findings

• Intense pain, sometimes out of proportion to the physical findings, and tenderness over involved area
• After a few days, nerve necrosis may produce anesthesia in the area, a clue to the presence of necrotizing fasciitis
• Edema, skin vesicular eruptions and crepitus
• Lymphangitis and lymphadenitis are infrequent
• Fever, malaise
•  Surgical exploration is the only way to definitively establish the diagnosis of necrotizing infection and distinguish it from other entities

Imaging Findings

• Plain films are insensitive to the presence of gas in the soft tissues so that a negative conventional radiograph should not rule out the diagnosis
• Non-enhanced CT is the study of choice and may show thickening of fascial planes and gas in the subcutaneous tissue
• Gas is seen most often in Type 1 and that caused by Clostridium
• CT is specific but not highly sensitive
• In the absence of gas, surgical exploration is necessary
• MRI can be sensitive in determining the presence of necrosis and need for surgical debridement, combined with clinical evaluation
• Ultrasound may reveal subcutaneous collections of air and fluid not otherwise seen

Differential Diagnosis

• Cellulitis

Complications

• Of all patients with necrotizing fasciitis about 20-40% are diabetic
• May be seen in association with cardiac catheterization
• Vein sclerotherapy
• Diagnostic laparoscopy
• Possible association with non-steroidal anti-inflammatory drugs
• May be idiopathic, as in scrotal or penile necrotizing fasciitis (Fournier Gangrene)

Treatment

• Surgical emergency involving debridement of the affected areas
• Aggressive antibiotic therapy
• Hyperbaric oxygen treatment may be helpful

Prognosis

• Mortality rates from 20% to 80% have been reported
• Factors which affect prognosis include
• Pathogens
• Complicating diseases
• Infection site
• Rapidity with which treatment is instituted

Necrotizing Fasciitis. Axial CT scans taken through the upper thighs show gas in the soft tissue fascial planes (white circle and white arrows) in a patient with extreme tenderness in this region.
For this same photo without the arrows, click here and here
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Necrotizing Fasciitis. eMedicine. Richard F Edlich 

Necrotizing Soft Tissue Infections. Up-to-Date. Dennis L Stevens, and Larry M Baddou