Necrotising fasciitis refers to a rapidly progressive and often fatal infection of soft-tissue fascia deep to the skin but superficial to the muscles.
Necrotising fasciitis is relatively rare, although its prevalence is thought to be rising due an increase in the number of immunocompromised patients with HIV infection, diabetes mellitus, cancer, alcoholism, vascular insufficiency, and organ transplants. It can also occur after trauma or around foreign bodies in surgical wounds 7.
There are at least two recognised forms:
- the most common type is a polymicrobial infection with both aerobic and anaerobic organisms such as Clostridium, Proteus, Escherichia coli, Bacteroides, and Enterobacteriaceae: this form is often seeded from underlying infections such as diverticulitis
- the second form of the disease is caused by a single organism: most commonly group A streptococci, the “flesh-eating bacteria,” and is seen in approximately 10-15% of cases 3-4; toxic shock syndrome may complicate this latter form
While it can affect any part of the body, the extremities, the perineum, and the truncal areas are the most commonly involved 4.
It should always be noted that no imaging modality can reliably exclude underlying necrotising fasciitis in the absence of soft tissue gas and negative study should not preclude obtaining tissue biopsy. Also, in cases with very high clinical suspicion imaging should not delay surgical intervention. Hence, imaging plays a very limited role in diagnosis and management of necrotising fasciitis.
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 of gas in the soft tissues is seen in only a minority of cases.
CT classically tends to show soft-tissue gas associated with fluid collections within the deep fascia, although this finding is inconstant.
Other non specific findings include:
- asymmetrical fascial thickening associated with fat stranding
- edema 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.
Post contrast CT
Some authors describe diffuse enhancement of fascia with contrast 3,8. If there is no enhancement of the fascia, this can be a finding that can help differentiate from a non-necrotising fasciitis 7.
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-tissue gas, although if identified, this finding may be of diagnostic benefit.
- T1: usually has subtle abnormality with loss of muscle texture and may show high signal intensity compatible with intramuscular haemorrhage 10
- T2: usually shows subcutaneous and intramuscular oedema in a reticulated pattern as well as subfascial and interfascial crescentic fluid collections 10
Treatment and prognosis
Mortality rates can range between 25-75% 5. Treatment is usually with a prompt surgical fasciotomy with debridement of the necrotic tissue.
For gas within soft tissues consider
- subcutaneous emphysema from a non infective cause: has an entirely different clinical presentation
History and etymology
It was first described by Joseph Jones, an American army surgeon during the American civil war 3.
- 1. Wysoki MG, Santora TA, Shah RM et-al. Necrotizing fasciitis: CT characteristics. Radiology. 1997;203 (3): 859-63. Radiology (abstract) - Pubmed citation
- 2. Kim KT, Kim YJ, Won lee J et-al. Can necrotizing infectious fasciitis be differentiated from nonnecrotizing infectious fasciitis with MR imaging? Radiology. 2011;259 (3): 816-24. doi:10.1148/radiol.11101164 - Pubmed citation
- 3. Fugitt JB, Puckett ML, Quigley MM et-al. Necrotizing fasciitis. Radiographics. 24 (5): 1472-6. doi:10.1148/rg.245035169 - Pubmed citation
- 4. Mulcahy H, Richardson ML. Imaging of necrotizing fasciitis: self-assessment module. AJR Am J Roentgenol. 2010;195 (6): S66-9. doi:10.2214/AJR.09.7156 - Pubmed citation
- 5. Zacharias N, Velmahos GC, Salama A et-al. Diagnosis of necrotizing soft tissue infections by computed tomography. Arch Surg. 2010;145 (5): 452-5. doi:10.1001/archsurg.2010.50 - Pubmed citation
- 6. Schmid MR, Kossmann T, Duewell S. Differentiation of necrotizing fasciitis and cellulitis using MR imaging. AJR Am J Roentgenol. 1998;170 (3): 615-20. AJR Am J Roentgenol (abstract) - Pubmed citation
- 7. Fayad LM, Carrino JA, Fishman EK. Musculoskeletal infection: role of CT in the emergency department. Radiographics. 27 (6): 1723-36. doi:10.1148/rg.276075033 - Pubmed citation
- 8. Becker M, Zbären P, Hermans R et-al. Necrotizing fasciitis of the head and neck: role of CT in diagnosis and management. Radiology. 1997;202 (2): 471-6. Radiology (abstract) - Pubmed citation
- 9. Mchenry CR, Brandt CP, Piotrowski JJ et-al. Idiopathic necrotizing fasciitis: recognition, incidence, and outcome of therapy. Am Surg. 1994;60 (7): 490-4. - Pubmed citation
- 10. Fugitt JB, Puckett ML, Quigley MM et-al. Necrotizing fasciitis. Radiographics. 2004;24 (5): 1472-6. Radiographics (full text) - doi:10.1148/rg.245035169 - Pubmed citation
- 11. Zerr DM, Alexander ER, Duchin JS et-al. A case-control study of necrotizing fasciitis during primary varicella. Pediatrics. 1999;103 (4 Pt 1): 783-90. Pubmed citation