Necrotizing fasciitis is a rare but life-threatening infection of the soft tissue characterized by inflammation that rapidly spreads, especially through the fascia and surrounding tissue.8–10 The soft tissue covering of the body is composed of several different layers. The skin, composed of the epidermis and dermis, is the outermost superficial layer. Beneath this is the subcutaneous tissue, which is composed of connective tissue and lobules of fat and superficial fascia. The superficial fascia is a network of blood vessels and nerves just beneath the skin that promotes movement and communication between the skin and underlying structures. The deep fascia is a form of connective tissue that covers skeletal muscle throughout the body.11
Local inflammation of soft tissue often marks the beginning of NF. It can progress to the underlying fascia, which can elicit systemic sepsis.8,10 The most common initial differential diagnosis is cellulitis, which can be coexistent.8,20 Diagnostic imaging such as magnetic resonance imaging (MRI), CT, and sonography can provide tissue characterization and multimodality information that should be correlated with the patient’s clinical presentation and laboratory test results for a diagnosis of NF.
Magnetic resonance imaging has a sensitivity of 93% in detecting necrotizing fasciitis.8 It is considered the gold standard for diagnosing NF and is considered superior to other imaging modalities because of its exceptional soft tissue imaging capabilities.21 An MRI typically demonstrates thickening of greater than 3 mm in the deep fascia in addition to extensive multicompartment involvement of the deep fascia.21,22
Computed tomography has an estimated sensitivity of 80% in detecting necrotizing fasciitis.18,23 The cross-sectional imaging capabilities offered by CT can reveal intermuscular fluid collections and fascial plane thickening with variable contrast enhancement.21,24 A CT also demonstrates increased attenuation of the subcutaneous fat and shows gas and edema within the soft tissue layers.8,9 However, these findings lack specificity in both MRI and CT as they can often still be seen in cases of non-NF and even noninflammatory conditions.25
In one study, sonography revealed a sensitivity of 88.2%, specificity of 93.3%, positive predictive value of 83.3%, negative predictive value of 95.4%, and accuracy of 91.9% in the diagnosis of NF.26 With the use of sonography on unaffected patients, the skin generally appears as a single superficial echogenic layer at the top of the screen. Beneath the skin is the subcutaneous layer, which generally appears hypoechoic with randomly distributed hyperechoic fibrous septa, between the fat globules. The fascial planes are hyperechoic, and the muscle appears hypoechoic with brightly echogenic striations throughout.27 Conversely, in cases of NF, sonography typically demonstrates distorted and thickened fascial planes with fluid accumulation in the fascial and subcutaneous layers.28 Sonographic assessment may be limited by soft tissue gas, although if it can be identified, this finding may be diagnostically beneficial.28 Sonography is often used as the imaging method of choice in pediatric cases of NF to limit radiation exposure. Sonography offers rapid, dynamic assessment of soft tissue, which is helpful in identifying fluid above the fascia (an indirect sign of NF).8,9 . . . . The sonographic appearance of abscess typically appears more complex and irregular, while NF will often appear as subcutaneous thickening with the presence of air and fascial fluid.30 The depth of tissue involvement shown by sonography can help to distinguish from cellulitis.
Cellulitis is defined as inflammation affecting only the dermal and subdermal layers of soft tissue, while NF has deeper involvement affecting the superficial fascia and subcutaneous tissue.31,32
The sonographic features that should raise the most suspicion for NF rather than a more common pathology are: irregularities of the fascia, thickening of the fascia, and abnormal fluid collections along the fascial plane. Early detection, diagnosis, and treatment are all keys to improving the patient outcome to prevent further tissue damage, amputation, and/or death.
(1) Ultrasound Of Skin And Soft Tissue Infections
Posted on November 26, 2018 by Tom Wade MD
(2) Diagnosis of Necrotizing Faciitis with Bedside Ultrasound: the STAFF Exam. [PubMed Abstract] [Full Text HTML] [Full Text PubReader—With this version of the article, the two brief teaching videos are available within the text.] [Full Text PDF] West J Emerg Med. 2014 Feb;15(1):111-3. doi: 10.5811/westjem.2013.8.18303.
The early diagnosis of necrotizing fasciitis is often ambiguous. Computed tomography and magnetic resonance imaging, while sensitive and specific modalities, are often time consuming or unavailable. We present a case of necrotizing fasciitis that was rapidly diagnosed using bedside ultrasound evaluating for subcutaneous thickening, air, and fascial fluid (STAFF). We propose the STAFF ultrasound exam may be beneficial in the rapid evaluation of unstable patients with consideration of necrotizing fasciitis, in a similar fashion to the current use of a focused assessment with sonography for trauma exam in the setting of trauma.
PMID: 24578776 [PubMed – in process] PMCID: PMC3935782 Free PMC Article.
(3) Point-of-Care Ultrasound Diagnosis of Necrotizing Fasciitis Missed By Computed Tomography and Magnetic Resonance Imaging. [PubMed Abstract]
Necrotizing fasciitis (NF) is a rare but deadly disease. Diagnosis of necrotizing soft tissue infections can be challenging for a variety of reasons. Point-of-care (POC) ultrasound (US) has been described as a diagnostic tool to help the acute care clinician make the early diagnosis that is imperative to optimize outcomes.
To report a case of Group A Streptococcus NF recognized with POC US, and subsequent negative findings on computed tomography (CT) and magnetic resonance imaging (MRI).
A 54-year-old diabetic woman presented to the Emergency Department with atraumatic right foot and lower leg pain associated with fever. Examination was concerning for NF, and a POC US was performed, which showed thickened deep fascia and fluid tracking along the deep fascial plane, with fluid pockets measuring 6 mm in depth, consistent with NF. Surgical consultation was obtained. Per request, CT and MRI of the patient’s lower extremity were performed; both were interpreted by the radiologist as showing changes consistent with cellulitis. Septic shock and multisystem organ failure ensued; the patient was eventually taken to the operating room, where operative findings were consistent with NF. Operative cultures grew Streptococcus pyogenes.
NF is a surgical emergency. Early and accurate diagnosis is critical to ensure the necessary aggressive management needed to optimize outcomes. This case illustrates the utility of POC US to make the prompt diagnosis of NF, particularly in light of subsequently negative CT and MRI.
Copyright © 2014 Elsevier Inc. All rights reserved.
necrotizing fasciitis; point-of-care; ultrasound
PMID: 24560016 [PubMed – indexed for MEDLINE]
(4) Necrotizing Fasciitis: Let’s scare you into using POCUS shall we?
Greg Hall • December 13, 2014 • 0 Comments from the EDE Blog [This is a blog on Point of Care Ultrasound.
Warning: Scary article ahead.
It’s one of those diagnoses that scares us. Hard to figure out clinically in many cases at initial presentation. Adjunctive tests can be false negative. How can we increase our sensitivity? Use your POCUS skills of course!
This article reminds me of two of my own cases. The first was in a homeless male patient in his 60’s who was a smoker and had untreated diabetes. He presented with a minimally painful, erythematous left foot with early skin ulcerations on the dorsum. Simple answer right? Diabetic ulcer, perhaps some cellulitis and/or stasis changes related to peripheral vascular disease. However, being the POCUS keener I applied my trusty probe to that foot and found this:
Lots of air artifact within the tissue layers. Cobblestoning of the superficial tissues consistent with edema or cellulitis but the air indicates a gas forming pathology. This guy was getting debrided in the O.R. a few hours later for his necrotizing fasciitis. Nice pick up!
Second case involved a gentleman in his early 40’s who again liked to smoke and not make optimum use of his pancreas (DM II). He had just got off a plane from a tropical vacation and had a hot, painful right leg. Hmmm, probably a DVT right? If it’s after hours, give him some empiric anticoagulation and arrange a doppler ultrasound within the next 24 hours or so. Except for one problem: the POCUS showed no sign of DVT, but a large pocket of fluid extending from groin to popliteal fossa. What the heck? Asked for an urgent ultrasound from the radiologists. The report stated no DVT. And that’s it. No mention of the fluid pocket. I wasn’t happy about that so a quick talk with I.D. doc and surgeon led to an immediate aspiration in the ED which revealed purulent material. The patient went to the O.R. within the next hour for a large necrotizing fasciitis. Life and limb saved!
Bottom line: no single test is going to rule out necrotizing fasciitis. But POCUS can be used to enhance your clinical skills and help RULE IN a few cases or discover an alternate diagnosis. I really don’t think it will be defensible in the future to not use this modality on the front lines for the undifferentiated soft tissue infection. The stakes are too high.
Some more quick reads:
Emergency ultrasonography for the early diagnosis of necrotizing fasciitis: a case series from the ED. [This link is to the abstract]. American Journal of Emergency Medicine, March 2013Volume 31, Issue 3, Pages 632.e5–632.e7
Necrotizing fasciitis: early sonographic diagnosis. [This link is to the full text]. Journal of Clinical Ultrasound, Wiley-Blackwell, 2010, 39 (4), pp.236.