Editing Necrotizing fasciitis (section)

=== Medical imaging ===
[[File:CT scan of right thigh, showing inflammatory stranding and low attenuation in vastus latralis (arrow).webp|thumb|CT scan of right thigh, showing inflammatory stranding and low attenuation in vastus lateralis muscle (arrow)]]
Necrotizing fasciitis is ideally a clinical diagnosis based on symptoms. Due to the need for rapid surgical treatment, the time delay in performing imaging is a major concern.<ref name=":0" />  Hence, imaging may not be needed if signs of a necrotizing infection are clear.  However, due to the vague symptoms associated with the earlier stages of this disease, imaging is often useful in clarifying or confirming the diagnosis.<ref name=":0" />

Both CT scan and MRI are used to diagnose NF, but neither are sensitive enough to rule out necrotizing changes completely.<ref name="Hak2014" />

==== Computed tomography (CT) ====
[[File:Pnecrotisingfasc.png|thumb|Necrotizing fasciitis producing gas in the soft tissues as seen on CT scan]]
If available, [[CT scan|computed tomography]] (CT) is the most convenient tool in diagnosing NF due to its speed and resolution (detects about 80% of NF cases).<ref>{{cite journal |last1=Puvanendran |first1=R |last2=Huey |first2=JC |last3=Pasupathy |first3=S |date=October 2009 |title=Necrotizing fasciitis |journal=Canadian Family Physician |volume=55 |issue=10 |pages=981–987 |pmc=2762295 |pmid=19826154}}</ref> CT scan may show fascial thickening, edema, or abscess formation.<ref name="Hak2014" /><ref name=":0" /> CT is able to pick up on [[Subcutaneous emphysema|gas within tissues]] better than MRI, but it is not unusual for NF to present without gas on imaging.<ref name=":0" /> In addition, CT is helpful in evaluating complications due to NF and finding possible sources of infections.<ref name=":0" /> Its use may be limited in pregnant patients and patients with kidney issues.<ref name=":0" />

==== Magnetic resonance imaging (MRI) ====
[[File:Necrotizing fasciitis MRI.png|thumb|Axial T2 weighted MRI (a) and contrast-enhanced MRI (b) of left wrist showing necrotizing fasciitis. There is diffuse hyperintensity with irregular enhancement of the deep fascia (asterisks). The arrows indicate a lobulating abscess, and the triangle a skin bulla.]]
[[Magnetic resonance imaging]] (MRI) is considered superior to [[CT scan|computed tomography]] (CT) in the visualization of soft tissues and is able to detect about 93% of NF cases.<ref name=":0" /> It is especially useful in finding fluid in the deep fascia, which can distinguish between NF and cellulitis.<ref name=":0" />  When fluid collects in the deep fascia, or thickening or enhancement with [[Contrast medium|contrast]], necrotizing fasciitis should be strongly suspected. However, MRI is much slower than CT and not as widely available.<ref name=":0" />  There may also be limitations on its use in patients with kidney problems.<ref name=":0" />

==== Point-of-care ultrasonography (POCUS) ====
[[File:UOTW 58 - Ultrasound of the Week 1.webm|thumb|Necrotizing fasciitis as seen on ultrasound<ref>{{cite web |date=7 September 2015 |title=UOTW#58 – Ultrasound of the Week |url=https://www.ultrasoundoftheweek.com/uotw-58/ |url-status=live |archive-url=https://web.archive.org/web/20160718055845/http://www.ultrasoundoftheweek.com/uotw-58/ |archive-date=18 July 2016 |access-date=27 May 2017 |website=Ultrasound of the Week}}</ref>]]
[[File:Necrotizing fasciitis with soft tissue gas NF.webp|thumb|Necrotizing fasciitis with soft tissue gas seen on (b) plain radiography and (c) ultrasound]]
[[Emergency ultrasound|Point-of-care ultrasound]] (POCUS) may be useful in the diagnosis of NF if MRI and CT are not available.<ref name=":1">{{Cite journal |last1=Gan |first1=Rick Kye |last2=Sanchez Martinez |first2=Antoni |last3=Abu Hasan |first3=Muhammad Abdus-Syakur |last4=Castro Delgado |first4=Rafael |last5=Arcos González |first5=Pedro |date=2023-06-01 |title=Point-of-care ultrasonography in diagnosing necrotizing fasciitis—a literature review |journal=Journal of Ultrasound |language=en |volume=26 |issue=2 |pages=343–353 |doi=10.1007/s40477-022-00761-5 |issn=1876-7931 |pmc=10247625 |pmid=36694072}}</ref> It can also help rule out diagnoses that mimic earlier stages of NF, including [[Deep vein thrombosis|deep vein thrombosis (DVT)]], superficial abscesses, and [[venous stasis]].<ref name=":1" /> Linear probes are generally preferred for the assessment, especially in the extremities.<ref name=":1" />

Findings characteristic of NF include abnormal thickening, air, or fluid in the [[subcutaneous tissue]].<ref name=":1" /> This can be summarized as the mnemonic "STAFF" (Subcutaneous irregularity or Thickening, Air, and Fascial Fluid).<ref name=":1" /> The official diagnosis of NF using ultrasound requires "the presence of BOTH diffuse subcutaneous thickening AND fascial fluid more than 2 mm."<ref name=":1" /> Gas in the subcutaneous tissue may show "dirty acoustic shadowing."<ref name=":0" /> However, similar to other imaging modalities, the absence of subcutaneous free air does not definitively rule out a diagnosis of NF, because this is a finding that often emerges later in the disease process.<ref name=":1" />

Of note, the quality and accuracy of POCUS is highly user-dependent.  It may also be difficult to visualize NF over larger areas, or if there are many intervening layers of fat or muscle.  It is still unclear whether POCUS improves the speed of diagnosis of NF, or if it reduces the time to surgical intervention as a whole.<ref name=":1" />

==== Plain radiography (X-ray) ====
It is difficult to distinguish NF from cellulitis in earlier stages of the disease using plain radiography.<ref name=":0" /> X-rays can detect subcutaneous emphysema (gas in the [[subcutaneous tissue]]), which is strongly suggestive of necrotizing changes. However, air is often a late-stage finding, and not all necrotizing skin infections create subcutaneous emphysema. Hence, radiography is not recommended for the initial diagnosis of NF.<ref name=":0" /> However, it may be able to identify the source of infection, such as foreign bodies or fractures, and thus aid in subsequent treatment.<ref name=":0" />