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Necrotizing Fasciitis


Sergio Alvarez, MD
Emergency and Sports Medicine Physician
Kaiser Santa Clara Medical Center
Clinical Assistant Professor (Affiliate) of Emergency Medicine
Stanford University, School of Medicine


  • Prompt diagnosis and surgical debridement are the most important prognostic factors for survival
  • The most sensitive and specific ultrasound findings are subcutaneous edema and a layer of fluid along the deep fascial layer (Sen. 88%, Spec. 93%)
  • Look for combinations of subcutaneous edema (cobblestoning), thickened fascia, fluid along the fascial layer, and gas
Illustration of Necrotizing Fasciitis[1]Helman A, CCFP(EM), FCFP. Necrotizing fasciitis diagnoses and therapy – ACEP Now. Published July 15, 2018. Accessed October 2, 2021. … Continue reading
Sonographic evaluation of soft tissue with obvious necrotizing fasciitis. Note the cobblestoning, hypoechoic gas with posterior acoustic shadowing.
Sonographic evaluation of the testes with obvious necrotizing fasciitis (Fournier’s Gangrene). Note the cobblestoning, hyperechoic fluid, hypoechoic gas with posterior acoustic shadowing.


  • Necrotizing fasciitis is a soft-tissue infection and surgical emergency that can involve multiple layers from the epidermis to the deep musculature. Defining features are a friable fascia and a dishwater-grey exudate.
  • Necrotizing fasciitis is part of a larger collection of necrotizing soft-tissue infections (NSTI) which are often divided into two main types; polymicrobial (Type I) which is most common and monomicrobial (Type II). These infections include; necrotizing cellulitis, streptococcal gangrene, gas gangrene, and non-clostridial gangrene, etc.[2]Stevens DL, Bryant AE. Necrotizing soft-tissue infections. N Engl J Med. 2017;377(23):2253-2265.
  • The most common clinical features include rapid progression, edema, erythema, and severe pain which can be seen in roughly 75% of cases. Fever and skin bullae or necrosis are less common but often considered classic manifestations.[3]McHenry CR, Piotrowski JJ, Petrinic D. Malangoni MA Determinants of mortality for necrotizing soft-tissue infections. Ann Surg. 1995;221:558–563.
  • The initial diagnosis and management is very similar between all subgroups with early surgical consultation, empiric antibiotics, and advanced imaging such as computed tomography scan (CT), magnetic resonance imaging (MRI), or ultrasound.[4]Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin … Continue reading
  • Although lacking sensitivity, plain radiographs can be used to aid in the diagnosis of necrotizing infections when gas is present and when patients are too hemodynamically unstable for CT scan or MRI.[5]Bonne SL, Kadri SS. Evaluation and Management of Necrotizing Soft Tissue Infections. Infect Dis Clin North Am. 1016;2017;31(3):497-511:05 011.
  • The most important prognostic factor for survival is time to surgical debridement and thus prompt diagnosis is essential.[6]McHenry CR, Piotrowski JJ, Petrinic D, Malangoni MA. Determinants of mortality for necrotizing soft-tissue infections. Ann Surg. 1995;221(5):558-563; discussion 563-5.[7]Voros D, Pissiotic C, Georgantas D, Katsaragakis S, Antoniou S, Papadimitriou J. Role of early and extensive surgery in the treatment of severe necrotizing soft tissue infections. Br J Surg. … Continue reading
  • CT and MRI have shown to have sensitivities between 80% and 100% and are generally considered the most efficacious studies for the diagnosis.[8]Wysoki MG, Santora TA, Shah RM, Friedman AC. Necrotizing fasciitis: CT characteristics. Radiology. 1997;203(3):859-863.[9]Schmid MR, Kossmann T, Duewell S. Differentiation of necrotizing fasciitis and cellulitis using MR imaging. AJR Am J Roentgenol. 1998;170(3):615-620.
  • Ultrasound with the presence of diffuse thickening of the subcutaneous tissue when compared to the contralateral side or limb, and a layer of fluid seen more than 4 mm deep along the deep fascial layer (Figure 4.) has been shown to have a sensitivity of 88% and specificity of 93% in the diagnosis of necrotizing fasciitis.[10]Yen Z-S. Ultrasonographic Screening of Clinically-suspected Necrotizing Fasciitis. Acad Emerg Med. 2002;9(12):1448-1451. Other classic features on ultrasound are thickened fascia, fascial irregularities, and subcutaneous air.
  • Given that prompt diagnosis and time to surgical debridement are strong prognostic factors for survival, point-of-care ultrasound should be used as an adjunct when necrotizing infections are clinically suspected and when a delay in CT or MRI is present.[11]Shyy W, Knight RS, Goldstein R, Isaacs ED, Teismann NA. Sonographic findings in necrotizing fasciitis: Two ends of the spectrum: Two ends of the spectrum. J Ultrasound Med. 2016;35(10):2273-2277.

Ultrasound Evaluation

  • Probe choice: high-frequency linear array transducer should be used (10-5Mhz).
    • This frequency range is optimal for evaluating superficial structures that may require higher resolution.
    • In larger patients where increased depth is desired the curvilinear probe with frequency 5-2Mhz can be utilized but will provide poor soft tissue resolution.
  • Normal
    • Layers of the skin include epidermis, dermis, and hypodermis.
    • Subcutaneous fat and connective tissue are deep to epidermis/dermis (hypodermis is above fascial layer)[12]Lindsay Biga SD, ed. 5.1 Layers of the Skin. In: Anatomy and Physiology. Pressbooks; 2020.
    • On ultrasound the epidermis/dermis layer is hyperechoic, the subcutaneous tissue is relatively hypoechoic, and the muscle fascia and muscle are again hyperechoic.
Long-Axis view of soft-tissue. Notice epidermis/dermis layer, subcutaneous fat layer, superficial fascia, organized striations of muscle, and bone deep to muscle striations.[13]Dawson M, Mallin M. Introduction to bedside ultrasound. In: Vol 1. Emergency Ultrasound Solutions; 2012.


  • Clinically suspicious areas may be erythematous, may have regional lymphadenopathy, and may be warm to touch. Crepitus may be felt on palpation.
  • Begin scanning the affected area and scan the interface between normal and affected skin. Scan the majority of affected areas to avoid missing fluid collections or gas.
  • Ensure adequate depth and should include the superficial soft-tissue, muscle fascial layer and down to bone if possible -this can help make diagnoses such as necrotizing fasciitis and pyomyositis.
Cobblestoning of soft-tissue (#) and a small amount of fluid superficial to a thickened deep fascial layer (arrow).[14]Shih J, RDMS. Ultrasound for the win! – 63M with an erythematous abdomen #US4TW. Published June 20, 2016. Accessed October 2, 2021. … Continue reading
  • Evaluate for cobblestoning, diffuse thickening of the subcutaneous tissues (when compared to contralateral side) subcutaneous gas, thickened fascia, and fluid along the deep fascial layer.[15]Yen Z-S. Ultrasonographic Screening of Clinically-suspected Necrotizing Fasciitis. Acad Emerg Med. 2002;9(12):1448-1451.
  • Necrotizing infections have a characteristic appearance on ultrasound and can present with subcutaneous edema (cobblestoning), fluid collection, fascia thickening and gas. Gas formation is a defining characteristic and will present as hyperechoic “comma” shaped structures with posterior shadowing.
Radiograph showing soft tissue swelling and subcutaneus air. Ultrasound over the air shows hypoechoic fluid containing tiny echogenic foci with dirty shadowing in the perifascial region.[16]Effron D, Richards CR, Emerman C, et al. Catching necrotizing fasciitis on ultrasound. Published December 28, 2013. Accessed October 2, 2021. … Continue reading
Ultrasound revealing marked subcutaneous and glandular edema, intraglandular fluid collection, brighter echo (A), and decreased superficial blood flow in Doppler sonogram (B) compared to that in the contralateral normal breast (C, D).[17]Lee J, Lee KJ, Sun WY. Necrotizing fasciitis of the breast in a pregnant woman successfully treated using negative-pressure wound therapy. Ann Surg Treat Res. 2015;89(2):102-106.
Subcutaneous gas in the scrotum consistent with Fournier’s Gangrene (Necrotizing Fasciitis of the Scrotum)[18]Vy PPAM. Bedside ultrasound for the rapid diagnosis of Fournier’s gangrene. Journal of Education and Teaching in Emergency Medicine. Published online March 20, 2019. doi:10.21980/J8CP99
Soft tissue gas in the surrounding perineum, appearing as multiple hyperechoic foci with reverberation artifact and ”dirty” shadowing (arrowheads).[19]Kim DJ, Kendall JL. Fournier’s gangrene and its characteristic ultrasound findings. J Emerg Med. 2013;44(1):e99-101.

Pearls and Pitfalls

  • Use linear probe first
  • Scan entire area under evaluation and surrounding tissue
  • Surgical emergency, so involve consultant early, administer antibiotics and consider advanced imaging if sonographic evaluation is equivocal