Necrotizing fasciitis

Necrotising fasciitis refers to a rapidly progressive and often fatal soft tissue infection of soft-tissue fasciaprimarily involving the superficial and often deep to the skin but superficial to the musclesfascia.

Epidemiology

Necrotising fasciitis is relatively rare, although its prevalence is thought to be rising.

Risk factors

The most common risk factor is diabetes mellitus, especially in combination with peripheral arterial disease. Other predisposing factors include immunocompromise due to HIV infection, diabetes mellitus, cancer, alcoholism, vascular insufficiency, and organ transplants. ItHowever, infections can also occur afterin otherwise healthy individuals following surgery, penetrating trauma, minor wounds such as insect bites or abrasions, or even blunt trauma or around foreign bodies inwith no clear portal of entry ^7,15.

Clinical presentation

The most common clinical findings overlap with that of nonnecrotizing soft tissue infection, including local edema and erythema ¹⁵. Findings that are more concerning for necrotizing infection include acute onset severe pain, crepitus, and fever and other signs of systemic toxicity indicating sepsis ¹⁵. Necrotizing fasciitis is ultimately a surgical woundsdiagnosis, based on direct inspection of friable superficial fascia and foul grey "dishwater" exudate ⁷¹⁵.

Pathology

ThereMicrobiologically, there are at least twotwo major recognised forms:

• thepolymicrobial (type I): most common type is a polymicrobial infection with; involves both aerobicanaerobic and anaerobicaerobic organisms, such as Clostridium, Proteus, Escherichia coli,Bacteroides, and Peptostreptococcus in the former group, and Enterobacteriaceae: this form is often seeded from underlying infections such as diverticulitisfamily members and Staphylococcus aureus in the latter group ¹⁴
• the second form of the disease is caused by a single organism: monomicrobial (type II): less common (10-15%); most commonly involves group A streptococci, the “flesh-eating bacteria,” and is seen in approximately 10-15% of cases ^3,4; may be complicated by toxic shock syndrome may complicate this latter form^3,4; less commonly due to Staphylococcus aureus

Location

While it can affect any part of the body, 50% of cases involve the lower extremities, other. Other common areas include the upper extremities, the perineum, truncal areas (Fournier gangrene), and the submandibularhead and neck region ^4,12.

Subtypes

• Fournier gangrene: necrotising fasciitis of In neonates, the perineum

Radiographic features

It should always be noted that noImaging is more sensitive than physical exam for detecting the hallmark feature of soft tissue gas (subcutaneous emphysema) and can also identify findings contributing to infection such as foreign bodies ¹². However, no imaging modality can reliably exclude underlying necrotising fasciitis in the absencediagnosis with certainty and a study with only nonspecific evidence of soft tissue gas and negative studyinflammation should not preclude obtaining a tissue biopsy. Also,or delay surgical exploration and intervention in cases with very high clinical suspicion imaging should not delay surgical interventionfor necrotizing infection. Hence, imaging plays a very limited role in the diagnosis and management of necrotising fasciitis.  

Plain film

The common plain radiographic findings non-specific an often similar to those of cellulitis, with increased soft-tissue thickness and opacity. Radiographs can be normal until the advanced stages of infection and necrosis. The characteristic finding Early findings are nonspecific, similar to those of cellulitis, such as increased soft-tissue thickness and opacity. Soft tissue gas in the soft tissues isis seen in only a minority of cases.

CT

CT is the most commonly used imaging modality for evaluation of suspected necrotizing fasciitis ¹². The sensitivity of CT is 80%, but the specificity is low given overlapping features with nonnecrotizing fasciitis ¹². CT classically tends to show soft-tissue gas associated with Gas within fluid collections withintracking along fascial planes is the deep fascia, although thismost specific finding but is inconstantnot always present ¹².

Other non-specific, nonspecific findings include:

• asymmetrical fascial thickening associated with fat stranding
• oedema extending into the inter-muscular septa and the muscle
• thickening of one or both of the superficial and deep fascial layers

Although fascial fluid collections are typically non-focal, abscesses may be seen. 

Postcontrast

On contrast enhanced CT

Some authors describe the

Ultrasound

Ultrasound may be more useful in children ^3,4 (with a rising incidence after primary varicella infection ¹¹). Sonographic findings include distorted and thickened fascial planes with turbid fluid accumulation in the fascial layers and subcutaneous oedema. Sonographic assessment may, however, be limited by soft-tissueSoft tissue gas, although if identified, this finding may be appears as a layer of diagnostic benefitechogenic foci with posterior dirty shadowing ¹².

MRI

MRI is considered thethe gold standard imaging modality of choice infor the investigation of necrotising fasciitis with a sensitivity of 93% ¹². T1 and T2 sequences are imperative to assess both the anatomy involved and detect fascial thickeningFindings include ^1210,12.:

• T1:T2 FS usually has subtle abnormalityor STIR
  • fascial thickening ≥3 mm and hyperintensity, starting in the superficial fascia and often involving deep intramuscular fascia in multiple compartments
  • subfascial and interfascial fluid collections
  • low signal foci of gas
  • subcutaneous edema, although commonly seen with cellulitis as well
• T1
  • subtle loss of muscle texture and may showpossible high signal intensity compatible with intramuscular haemorrhage¹⁰
  • low signal foci of gas
• T2T1 C+
  • ​variable fascial contrast enhancement: usually shows subcutaneous and intramuscular oedema in a reticulated pattern as well as subfascial and interfascial crescentic fluid collections ¹⁰ increased early due to capillary permeability but absent later due to necrosis

Treatment and prognosis

Mortality rates can range between 25-75% ⁵. TreatmentNecrotizing fasciitis is usually with aa surgical emergency. Definitive diagnosis and treatment involves prompt surgical fasciotomy with aggressive debridement of the necrotic tissue. Antibiotics are started with broad spectrum coverage, including anaerobes, and tailored when culture data are available. Subsequent repeat (second look) surgery is necessary until no necrotic tissue is found. Amputation may be required to preempt further spread of infection. Mortality rates can range between 9-25% ¹⁷.

Differential diagnosis

Necrotising fasciitis is rareFor soft tissue inflammatory findings, consider ^12,13:

• nonnecrotizing fasciitis, cellulitis, and/or myositis
• ischemic myonecrosis
• dermatomyositis
• graft vsversus host disease

For gas within soft tissues, consider:

• gas gangrene (clostridial myonecrosis)
subcutaneous emphysema
• penetrating trauma or percutaneous/surgical procedure
• communication from the aerodigestive tract (e.g. pneumomediastinum from a non-infective cause: has an entirely different clinical presentation, esophageal perforation)

History and etymology

ItThe entity was first described by Hippocrates in the 5th century BC as a complication of erysipelas, termed hospital gangrene in a large series byJoseph Jones, an(an American army surgeon during the American civil war Civil War), and finally called "necrotizing fasciitis" in 1952 in an article by B. Wilson³¹⁸.

See also

• subcutaneous abscess