: Elsevier Health Sciences, 2013;633-644. 2017 Jun;31(2):299-324. doi: 10.1016/j.idc.2017.01.004. Skeletal Radiol. CT without contrast in a patient with a history of interstitial lung disease and right lung transplant shows the patent but partially narrowed anastomotic site of the right bronchus (A) (red arrow). 2021;50(12):2319-47. Skeletal Radiol. Iodinated contrast should be avoided for two months before administration of iodine 131. Signs of cellulitis are easy to appreciate on CT and MRI and include thickening of the fat, best appreciated on the preseptal space, fat infiltration, and contrast enhancement. At the time the article was last revised David Carroll had 1 0 obj Thank you for your interest in spreading the word on Cleveland Clinic Journal of Medicine. Ultrasound is usually the first investigation to evaluate a clinical suspicion of cellulitis. IV contrast may be used to visualize vasculature as well as the internal organs of the abdomen and pelvis. % HHS Vulnerability Disclosure, Help These agents for enhancing the image created on CT may be delivered by a number of different routes, the most common of which are oral and intravenous. In B, the native left lung is small, with evidence of bronchiectasis, bronchiolectasis, and areas of honeycombing (black arrow). Disclaimer. Fascial thickening and involvement of multiple compartments is a sensitive finding on MRI. Careers, Unable to load your collection due to an error. www.acr.org/~/media/ACR/Documents/PGTS/guidelines/CT_Thoracic.pdf, www.acr.org/~/media/37D84428BF1D4E1B9A3A2918DA9E27A3.pdf, EVALUATION OF PULMONARY PARENCHYMAL DISEASE, EVALUATION OF STERNAL AND MEDIASTINAL INFECTIONS, Cleveland Clinic Center for Continuing Education. 2009;39(10):957-71. Ultrasound is helpful to rule out deep venous thrombosis, assess for possible foreign bodies, and guide potential diagnostic fluid aspiration.8, 13 Sensitivity of ultrasound for the diagnosis of necrotizing fasciitis is 88.2%, with a specificity of 93.3%.20, CT is the primary imaging modality in the work-up of necrotizing fasciitis given its wide availability and high spatial resolution compared to radiography or ultrasound.3 Soft-tissue gas is a pertinent CT finding, but absence of it should not exclude the diagnosis of necrotizing fasciitis if clinically suspected.1, 2,11,17 Gas within fluid collections along subfascial planes is the hallmark of necrotizing fasciitis (Figures 5 and 6).11, 21 The lack of soft-tissue gas on CT may be due to early disease, aerobic infections, or if the patient is diabetic.1, 16 The sensitivity of CT in diagnosing necrotizing fasciitis is 80%, but it lacks specificity as findings can also be seen in nonnecrotizing fasciitis.21, 22 Thickening and nonenhancement of the fascia on contrast-enhanced CT may be helpful to distinguish from nonnecrotizing fasciitis.2 Subfascial and intermuscular fluid accumulation can also be seen on CT, and may represent early findings of necrotizing fasciitis (Figure 7).21. endstream The concentration of barium used for fluoroscopy is more than 20 times that of the typical oral contrast suspension for CT. For example, the barium concentration from an upper gastrointestinal series or an enema will produce an artifact on abdominal CT because it is significantly more concentrated than bowel contrast agents used for CT. Barium enemas are also given after abdominal CT to allow time for the less-dense barium to leave the colon. The parapharyngeal space was the most commonly involved space. In pleural effusion, CT assessment for the presence, location, and extent of the effusion does not require contrast. Cellulitis. Follow-up of a solitary pulmonary nodule also typically does not require contrast enhancement, though some investigators have reported high sensitivity with dynamic contrast enhancement of pulmonary nodules.4 This rep resents a rare clinical application of chest CT with and without contrast. MRI Nomenclature for Musculoskeletal Infection. Preparation: Please have only a clear liquid diet for 4 hours prior to exam. Compared to plain radiography, ultrasound, CT and MR provide higher sensitivity and specificity for the diagnosis of necrotizing fasciitis. myriad of non-infective erythematous rashes, Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys. The US Preventive Services Task Force currently recommends low-dose CT without contrast, along with appropriate patient counseling, for patients with a history of smoking and an age range as detailed in the Task Force statement. Hayeri MR, Ziai P, Shehata ML, Teytelboym OM, Huang BK. A paranasal sinus pathology is . Imaging of Musculoskeletal Soft Tissue Infections. Imaging of Musculoskeletal Soft-Tissue Infections in Clinical Practice: A Comprehensive Updated Review. Although a very uncommon soft-tissue infection, it has significant mortality up to 7080% and constitutes a life-threatening surgical emergency.1, 2 The most important predictor of mortality is a delay in diagnosis, thus it is essential to make a prompt diagnosis.2 Clinically, the findings of necrotizing fasciitis can overlap with other soft-tissue infections including cellulitis, abscess or even compartment syndrome, but pain out of proportion to the degree of skin involvement and signs of systemic shock should alert the clinician to the possibility of necrotizing fasciitis.46 Other red flag clinical findings are listed in Table 1. Oral contrast can be administered through a nasogastric tube to minimize the risk of aspiration. Reinert CP, Pfannenberg C, Dittmann H, Gckel B, la Fougre C, Nikolaou K, Hoefert S. J Clin Med. Shortness of breath Abdomen andPelvis Without IV contrast 1. Some centers use oral contrast to evaluate for appendicitis; some do not use bowel contrast,3 and others use rectal contrast to avoid the delay associated with oral administration.4, Iodine-based intravenous (IV) contrast agents are used for opacification of vascular structures and solid abdominal and pelvic organs. CT is the most sensitive modality for soft-tissue gas detection, and compared with radiography, CT is superior to evaluate the extent of tissue or osseous involvement, show an underlying (and potentially more remote) infectious source, and reveal serious complications such as vascular rupture complicating tissue necrosis [ 10, 13 - 20 ]. endobj Case 1: orbital and periorbital cellulitis, see full revision history and disclosures. This risk is significantly increased in patients with chronic renal disease, diabetes, heart failure, and anemia. sonographic hallmarks of cellulitis include abnormal echogenicity and increased thickness of the dermis with indistinct "haziness" and increased echogenicity of the subcutaneous tissue, it is often helpful to compare the area in question to the (presumably normal)contralateral side, progressive accumulation of edema in the subcutaneous tissue appears as branching, anechoic striations which impart a lobulated ("cobble-stone" appearance), presence of thickened and abnormally echogenic overlying skin will favor cellulitis over edema, linear anechoic bands of fluid deep to the subcutaneous layer favor lymphedema, ultrasound is more sensitive than MRI for the detection of a retained foreign body as the causative agent, especially if small and wooden 4,5. Cellulitis(rare plural: cellulitides) is an acute infection of the dermis and subcutaneous tissues without deep fascial or muscular involvement. 2009;16(4):267-76. Author disclosure: No relevant financial affiliations. A 45-year-old male with necrotizing fasciitis of the right thigh. DOI: https://doi.org/10.3949/ccjm.83a.15037, Computed tomography: revolutionizing the practice of medicine for 40 years, ACR-SCBT-MR-SPR practice parameter for the performance of thoracic computed tomography (CT), Screening for lung cancer: US Preventive Services Task Force recommendation statement, Solitary pulmonary nodules: dynamic enhanced multi-detector row CT study and comparison with vascular endothelial growth factor and microvessel density, High-pitch ECG-synchronized pulmonary CT angiography versus standard CT pulmonary angiography: a prospective randomized study, Intravenous contrast medium administration and scan timing at CT: considerations and approaches, Emergency imaging assessment of acute, nontraumatic conditions of the head and neck, Iodinated contrast media and their adverse reactions, ACR Committee on Drugs and Contrast Media, ACR Manual on Contrast Media. Skeletal Radiol. 2. The most common contrast agents used with CT imaging are barium- and iodine-based. Different imaging modalities require different concentrations of contrast for optimal detection of pathology. One study showed similar increases in serum creatinine levels between inpatient populations who received IV iodinated contrast and those who did not.16, Noncontrast-enhanced CT is used in patients with head trauma and acute stroke. ADVERTISEMENT: Radiopaedia is free thanks to our supporters and advertisers. CT is commonly used to diagnose, stage, and plan treatment for lung cancer, other primary neoplastic processes involving the chest, and metastatic disease.2 The need for contrast varies on a case-by-case basis, and the benefits of contrast should be weighed against the potential risks in each patient. The PubMed wordmark and PubMed logo are registered trademarks of the U.S. Department of Health and Human Services (HHS). Swartz M. Clinical Practice. 9. Schmid M, Kossmann T, Duewell S. Differentiation of Necrotizing Fasciitis and Cellulitis Using MR Imaging. 70470 Metastases/Known cancer HIV Intracranial infection Note: CT can be used if there are contraindications for MRI. Order "HAND" if entire wrist and hand. doi: 10.5114/pjr.2022.113825. Jamal K, Mandel L, Jamal L, Gilani S. 'Out of hours' adult CT head interpretation by senior emergency department staff following an intensive teaching session: a prospective blinded pilot study of 405 patients. [ 16, 17, 18] On CT scans, a preseptal cellulitis may appear as. 2022 Mar 5;87:e141-e162. However, IV radiologic contrast may cause transient alteration in renal function, which could impair metformin clearance, leading to a higher risk of metabolic acidosis. Contrast-related nephrotoxicity has been reported,11 although this has been challenged more recently.12 Suspected risk factors for this complication include advanced age, cardiovascular disease, treatment with chemotherapy, elevated serum creatinine level, dehydration, diabetes, use of nonsteroidal anti-inflammatory medications, myeloma,13 renal disease, and kidney transplant. On MRI, the signal on T2-WI is variable depending on the etiology. Detailed protocols for premedication and management of contrast adverse reactions are beyond the scope of this review and the reader is advised to refer to dedicated manuals.10. Chaudhry AA, Baker KS, Gould ES, Gupta R. Necrotizing fasciitis and its mimics: what radiologists need to know, Musculoskeletal infection: role of CT in the emergency department. A 39-year-old-male with necrotizing fasciitis of the right thigh. 2 0 obj ADVERTISEMENT: Supporters see fewer/no ads. Muscular fascia lies deep to the subcutaneous layer. Your email address will not be published. Uncomplicated cellulitis is usually treated conservatively with antibiotics and locally supportive measures. Pulmonary fibrosis 3. 1. . T2 weighted images with fat saturation demonstrates extensive high signal within the intermuscular septa surrounding the gastrocnemius and soleus muscle bellies suggestive of subfascial fluid (white arrows). We do not capture any email address. In uncomplicated cellulitis, CT demonstrates skin thickening, septation of the subcutaneous fat, and thickening of the underlying superficial fascia. Special consideration should be given to geriatric patients, in whom cellulitis of the lower extremities is more likely to develop into thrombophlebitis. JAMES V. RAWSON, MD, AND ALLEN L. PELLETIER, MD. The need for enhancement with intravenous (IV) contrast depends on the specific clinical indication (Table 1). Possible contraindications for using intravenous contrast agents during computed tomography include a history of reactions to contrast agents, pregnancy, radioactive iodine treatment for thyroid disease, metformin use, and chronic or acutely worsening renal disease. the contents by NLM or the National Institutes of Health. Cellulitis. Other CT findings include increase soft-tissue attenuation, subcutaneous edema and inflammatory fat stranding, which can also be seen in cellulitis.2,2123 In a study by Wysoki et al. CT scanning is often the first imaging modality that is used because of its ease and availability at most medical institutions. They are used for bowel opacification and are not nephrotoxic. Computed tomography (CT scan or CAT scan) is a noninvasive diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce horizontal, or axial, images (often called slices) of the body. This site needs JavaScript to work properly. Next imaging study. Patients with a mild allergy may be pre-medicated with an antihistamine or steroids before imaging. That said, it is seldom required for diagnosing cellulitis and is therefore usually ordered for suspected complications or to rule out alternative diagnoses in cases of an atypical presentation. National Library of Medicine Concerns for using IV contrast during CT include a history of reactions to contrast agents, pregnancy, treatment of thyroid disease with radioactive iodine, use of metformin (Glucophage), and chronic or acutely worsening renal disease. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, organs, and blood vessels. FOIA Weaver JS, Omar IM, Mar WA, Klauser AS, Winegar BA, Mlady GW, McCurdy WE, Taljanovic MS. Pol J Radiol. In uncomplicated cellulitis, CT demonstrates skin thickening, septation of the subcutaneous fat, and thickening of the underlying superficial fascia. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted In a 79-year-old patient with chronic thromboembolic pulmonary hypertension, CT angiography of the pulmonary artery (A) shows weblike (red arrow) and partially calcified filling defects (yellow arrow), as well as diffuse mild mosaic attenuation of lung parenchyma (B). Answer (1 of 4): You asked: Are CT scans without contrast always done before CT scans with contrast? The U.S. Food and Drug Administration advises that metformin should be withheld at the time of IV contrast administration and for 48 hours afterward, and resumed only after reevaluation of renal status (i.e., return to baseline serum creatinine level).13. It results in pain, erythema, oedema, and warmth. This content is owned by the AAFP. Intrathecal iodinated contrast is given during myelography to evaluate spinal or basal cisternal disease and cerebrospinal fluid leaks.11 Plain radiography of the spine is then obtained under fluoroscopic guidance. This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. Radiology. endobj 1998 Aug;6(3):537-59. 30 0 obj MRI's visualization of the bone marrow allows for the sensitive detection of osteomyelitis, although specificity for the diagnosis of osteomyelitis is aided by other findings, including cortical destruction. 3. Contrast agents can be further classified as high or low osmolality, based on the iodine concentration. These agents are not used for imaging of the abdomen and/or pelvis if bowel pathology is not suspected, or if doing so will delay scanning as in the case of acute trauma. Recent estimates place the number of computed tomography (CT) scans performed annually in the United States at approximately 70 million.1 Given the cost and radiation exposure, it is critical that CT is appropriate and performed with optimal technique. 7 0 obj Oral contrast is generally used for visualization of the abdomen and/or pelvis when there is suspicion of bowel pathology. Large volume of gas seen within the scrotum wall and scrotum sac on the scout image (curved black arrow), consistent with Fourniers gangrene. Additionally, systemic features such as fevers and rigors may also be present. Department of Radiology Department of Radiology Outpatients requiring oral contrast for a CT scan require a prescription for Readi-Cat 2, 2 bottles of 450ml, take as directed. Patients with peripheral vascular disease or diabetes mellitusare particularly susceptible to cellulitis since minor injuries to the skin or cracked skin in the feet or toes can serve as a point of entry for infection. 3 In general, oral contrast is used for most abdominal and pelvic CT scans unless there is no suspicion of bowel pathology (e.g., noncontrast CT to detect kidney stones) or when administration would delay a diagnosis in the trauma setting. Version 10.1.2015, Intravenous contrast material exposure is not an independent risk factor for dialysis or mortality. Signs of cellulitis are easy to appreciate on CT and MRI and include thickening of the fat, best appreciated on the preseptal space, fat infiltration, and contrast enhancement. . The overall PPV for the prediction of deep neck abscess with contrast-enhanced CT was 79.6%. Wronski M, Slodkowski M, Cebulski W, Karkocha D, Krasnodebski IW. 6. CT Head or brain with and without contrast Note: MRI Brain with/without contrast is preferred. Miller TT, Randolph DA, Staron RB, Feldman F, Cushin S. Fat-suppressed MRI of musculoskeletal infection: fast T2-weighted techniques versus gadolinium-enhanced T1-weighted images, Necrotizing fasciitis: unreliable MRI findings in the preoperative diagnosis, Differentiation of necrotizing fasciitis and cellulitis using MR imaging. 8. Copyright 2023 The Cleveland Clinic Foundation. However, CT scanning with contrast involves exposure to ionizing radiation, which may increase the risk of malignancy and eye lens damage. If the infection spreads to deeper tissues, soft-tissue abscess, infectious myositis, necrotizing fasciitis, and osteomyelitis can all be detected with CT. MRI is sensitive for distinguishing cellulitis alone from necrotizing fasciitis and infectious myositis and for showing subcutaneous fluid collections and abscesses. T2 weighted image with fat saturation of the left thigh demonstrates a large area of myonecrosis within the proximal rectus femoris muscle, with extensive muscular, fascial, and subcutaneous enhancement and edema, with crescentic fascial fluid collections, predominantly around the rectus femoris and sartorius, suggestive of necrotizing fasciitis. A 47-year-old male with necrotizing fasciitis of the left thigh. A neck mass or adenopathy also may be investigated, particularly when it results in airway or vascular compromise. official website and that any information you provide is encrypted Cross-sectional imaging findings include asymmetric thickening of the fascia, soft-tissue air, blurring of fascial planes, inflammatory fat stranding, reactive lymphadenopathy, and nonenhancement of the muscular fascia. With respect to employing CT as an imaging modality, first one should be aware of the different ty. Marked preseptal edema and discrete contrast enhancement in the area of the affected left upper eyelid. Careers. Cross-sectional schematic diagram through the right thigh demonstrating the various findings of necrotizing fasciitis. Soft-tissue infections and their imaging mimics: from cellulitis to necrotizing fasciitis, Necrotizing soft-tissue infection: diagnosis and management, Red flags for necrotizing fasciitis: a case control study, Sonographic detection of necrotizing fasciitis, Necrotizing soft tissue infections: a primary care review. In particular, the evaluation of soft tissue infections, including cellulitus, myositis, fasciitis, abscess, and septic arthritis are often best evaluated by MRI or CT due to their excellent anatomic resolution and soft tissue contrast. Assessment of interstitial lung disease does not require use of IV contrast; rather, a tailored protocol with thinner slices and non-contiguous expiratory images can be used to evaluate for air-trapping and dynamic airway compromise (Figure 4). Additionally, systemic features such as fevers and rigors may also be present. Renal function should be assessed with a baseline creatinine level before administration as patients with impaired renal function are at risk for complications associated with IV contrast. Prior to contrast administration, patients should be asked about previous allergy to CT contrast. Necrotizing fasciitis: CT characteristics. The extent of enhancement depends on the amount and rate of contrast material administered, as well as on patient factors (eg, tissue vascularity, permeability, interstitial space) and the energy (tube voltage) of the incident x-rays.8. Ultrasonographic screening of clinically-suspected necrotizing fasciitis. 1Department of Radiology, Massachusetts General Hospital, Boston, MA, USA. Almost always, CTs should be ordered with or without contrast, not both. Necrotizing fasciitis is a rapidly spreading soft tissue infection involving the deep fascial layers, which can cause secondary necrosis leading to significant morbidity and mortality.13 It most commonly affects the lower extremities accounting for approximately 50% of cases, and can affect different body parts including the perineum (as in Fourniers gangrene), and submandibular region (as in Ludwig angina). Fugitt JB, Puckett ML, Quigley MM, Kerr SM. no financial relationships to ineligible companies to disclose. and transmitted securely. A person viewing it online may make one printout of the material and may use that printout only for his or her personal, non-commercial reference. Data Sources: We used the term radiologic contrast to search the following: PubMed Clinical Queries (systematic reviews); the OVID database (all evidence-based medicine reviews; Cochrane Database of Systematic Reviews, ACP Journal Club, Database of Abstracts of Reviews of Effects, Cochrane Central Trial Registry, Cochrane Methodology Register, Health Technology Assessment, and NHS Economic Effectiveness Database); Dynamed; and the U.S. Preventive Services Task Force and Agency for Healthcare Research and Quality clinical guidelines and evidence reports. See permissionsforcopyrightquestions and/or permission requests. It is also not used in patients with suspected acute stroke. Contrast-enhanced CT demonstrates crescentic subfascial fluid (arrow) with fluid also seen superficial to the fascia (arrow head) and between muscle planes (a). Epidemiology Risk factors trauma foreign bodies Special consideration should be given to geriatric patients, in whom cellulitis of the lower extremities is more likely to develop into thrombophlebitis. Even in osseous infection, CT and MRI can give better anatomic delineation of the extent of infection. A baseline serum creatinine level should be obtained up to one month before administration of intravenous contrast agents in patients with suspected renal insufficiency. Become a Gold Supporter and see no third-party ads. One of these questions that came up frequently related to CT scans was Do I need contrast?. {"url":"/signup-modal-props.json?lang=us"}, Radswiki T, Carroll D, Knipe H, et al. During the injection you may feel flushed and get a metallic taste in your mouth. BMJ. Working in the emergency department as a nurse practitioner, I order CT scans in my evaluation of patients every day. MR imaging of pediatric musculoskeletal inflammatory and infectious disorders. The soft-tissue air deep to the fascia is seen as multiple echogenic foci (arrows) on ultrasound study (b). Since the epidermis is not involved, cellulitis is not transmitted by person-to-person contact. Paz Maya S, Dualde Beltrn D, Lemercier P, Leiva-Salinas C. Necrotizing fasciitis: an urgent diagnosis. A 35-year-old male with necrotizing fasciitis of the right calf. The most common are baruim and iodine based. AJR Am J Roentgenol. Wong CH, Khin LW, Heng KS, Tan KC, Low CO. Search dates: November 2009 and April 27, 2010. The .gov means its official. In patients with elevated creatinine, withholding IV dye may be necessary. A ct urogram uses IV contrast (dye) to better evaluate the renal pelvis and ureter (the "tube" connecting your kidneys t. Read More. Compared to plain radiography, ultrasound, CT and MR provide higher sensitivity and specificity for the diagnosis of necrotizing fasciitis. N.p. Although many radiology departments screen for shellfish allergy, there is no cross-reactivity between shellfish and iodinated contrast. no financial relationships to ineligible companies to disclose. During the injection you may feel flushed and get a metallic taste in your mouth. Disease processes that involve calcifications may benefit from noncontrast-enhanced images because contrast may mask the appearance of calcifications. Most centers use nonionic contrast agents (which are generally low osmolality) for IV contrast studies.5 The rate of major reactions (e.g., anaphylaxis, death) is the same for ionic and nonionic IV contrast agentsan estimated one in 170,000 administrationsbut nonionic contrast has a lower rate of minor reactions.6 Approximately 5% to 12% of patients who receive high-osmolality contrast have adverse reactions, most of which are mild or moderate.7 Use of low-osmolality contrast has been associated with a reduction in adverse effects. If youre a nurse practitioner who struggles with the same question, check out the following guide to contrast and CT scans. CT area of interest without IV contrast Usually Appropriate Varies Variant 7: Suspected soft tissue infection. government site. There is subcutaneous emphysema (arrows) overlying the right ankle with plate and screw fixation seen (a). The risk of developing metabolic acidosis with metformin use is rare, but is higher in persons with chronic renal disease or transient impairment of renal function. PMC Below is an overview of the following CTA studies and their indications: Regardless of the pathology youre looking for, contrast isnt right for everyone. Adams, James, and Erik D. Barton. Copyright2022 ThriveAP Inc., All Rights Reserved, Key Advice for NPs & PAs with Angela Golden, DNP, FNP-C, FAANP, FOMA, Evidence-Based Wound Care for Advanced Practice Providers, Featured ThriveAP Faculty: Benjamin Smith, DMSc, PA-C, DFAAPA, Finding Your Why with ThriveAP Speaker Steven Wei, EdD, MPH, MS, PA-C, DFAAPA. endobj A 53-year-old male with necrotizing fasciitis of the left knee. N/A No CT WRIST LEFT WO CONTRAST (IMG3906) CT WRIST RIGHT WO CONTRAST(IMG3909) CT HAND LEFT WO CONTRAST (IMG3794) CT HAND RIGHT WO CONTRAST (IMG3797) 73200 Hydration can decrease these risks. 2007 Nov-Dec;27(6):1723-36. doi: 10.1148/rg.276075033. Contrast enhancement is also used to evaluate superior vena cava syndrome. MR Imaging in Acute Infectious Cellulitis. This absorption and scattering in turn results in higher CT attenuation values, or enhancement on CT images. 7. Here is a summary of the indications for non-contrasted CT: Contrast helps enhance certain body structures. In later stages, nonenhancement of the fascia may be seen due to necrosis, which can be helpful to differentiate from nonnecrotizing fasciitis.3, 28,29, Although more apparent on CT, gas in the soft tissues is represented by punctate or curvilinear T1 and T2 low signal with corresponding blooming artifact on gradient echo sequences.1, 18,25,30 Although a highly specific finding, the absence of soft-tissue gas does not exclude the diagnosis of necrotizing fasciitis.3, 11. 8600 Rockville Pike Sign In to Email Alerts with your Email Address. 1. Despite its limitations, radiographs can be more sensitive than physical exam for the detection of soft-tissue gas, with radiographic findings present before clinical crepitus is detected.17 Radiographs can also be helpful in identifying other causes of infection including the presence of a foreign body or underlying fracture.3, 13, The role of ultrasound is limited in the work-up of necrotizing fasciitis given that the lack of resolution of deeper structures.8 The presence of soft-tissue gas can be more apparent on ultrasound compared to radiographs.17, 18 Findings include an echogenic layer of gas above the deep fascia with posterior dirty acoustic shadowing (Figure 4).19 Other nonspecific findings include hyperechogenicity of the overlying fat, with cobblestone appearance indicating subcutaneous edema, but these findings can also be seen in cellulitis or anasarca.8, 19 Color Doppler evaluation may not reveal hypervascularity.8 Specific signs that are helpful to differentiate necrotizing fasciitis from cellulitis include irregularity of the fascia, abnormal fluid collection along fascial planes, and diffuse fascia thickening when compared to the contralateral unaffected side.8.

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