Necrotizing fasciitis and its mimics: what radiologists need to know.

M u s c u l o s k e l e t a l I m a g i n g • R ev i ew Chaudhry et al. Imaging of Necrotizing Fasciitis and Its Mimics

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Musculoskeletal Imaging Review

Necrotizing Fasciitis and Its Mimics: What Radiologists Need to Know Ammar A. Chaudhry 1 Kevin S. Baker 1 Elaine S. Gould1 Rajarsi Gupta2 Chaudhry AA, Baker KS, Gould ES, Gupta R

OBJECTIVE. The purpose of this article is to review the imaging features of necrotizing fasciitis and its potential mimics. Key imaging features are emphasized to enable accurate and efficient interpretation of variables that are essential in appropriate management. CONCLUSION. Necrotizing fasciitis is a medical emergency with potential lethal outcome. Dissecting gas along fascial planes in the absence of penetrating trauma (including iatrogenic) is essentially pathognomonic. However, the lack of soft-tissue emphysema does not exclude the diagnosis. Mimics of necrotizing fasciitis include nonnecrotizing fasciitis (eosinophilic, paraneoplastic, inflammatory (lupus myofasciitis, Churg-Strauss, nodular, or proliferative), myositis, neoplasm, myonecrosis, inflammatory myopathy, and compartment syndrome. Necrotizing fasciitis is a clinical diagnosis, and imaging can reveal nonspecific or negative findings (particularly during the early course of disease). One should be familiar with salient clinical and imaging findings of necrotizing fasciitis to facilitate a more rapid and accurate diagnosis and be aware that its diagnosis necessitates immediate discussion with the referring physician.

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Keywords: Churg-Strauss fasciitis, eosinophilic fasciitis, lupus myofasciitis, necrotizing fasciitis, nodular fasciitis, paraneoplastic fasciitis DOI:10.2214/AJR.14.12676 Received February 1, 2014; accepted after revision April 26, 2014. 1 Department of Radiology, Stony Brook University Medical Center, HSC Level 4, Rm 120, East Loop Rd, Stony Brook, NY 11794. Address correspondence to A. A. Chaudhry ([email protected]). 2

Department of Pathology, Stony Brook University Medical Center, Stony Brook, NY. This article is available for credit. AJR 2015; 204:128–139 0361–803X/15/2041–128 © American Roentgen Ray Society

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ecrotizing fasciitis and its differential diagnoses are often encountered in the emergency department and inpatient settings. Although a clinical diagnosis, cross-sectional imaging is nonetheless frequently performed for evaluation of disease extent and complications. Therefore, radiologists should be familiar with the entity and its mimics. This article will describe the clinical features, imaging findings, pathophysiology, treatment options, and prognosis of necrotizing fasciitis and other soft-tissue processes (nonnecrotizing fasciitis, myositis, myonecrosis, and cellulitis) resulting from infection, inflammation, injury, or malignancy. The representative imaging examples are predominately from extremities, with the exception of Fournier gangrene and dermatomyositis. Necrotizing Fasciitis Necrotizing fasciitis is a rapidly progressive often fatal soft-tissue infection most commonly resulting from polymicrobial infection. The process initially begins in the superficial fascial planes and progresses into the deep fascial layers causing necrosis by microvascular occlusion. Causative infectious agents tend to be both aerobic and

anaerobic organisms such as Clostridium species, Proteus species, Escherichia coli, Bacteroides species, Enterobacteriaceae species, and others [1–8]. The entity is a medical emergency with reported mortality rates as high as 70–80%, with common causes of death including sepsis or respiratory, renal, or multisystem organ failure [2, 6–8]. Necrotizing fasciitis is divided into types I and II by the Society of Infectious Disease according to bacteriology profile [6–9]. Type I involves a mixed infection with aerobic and anaerobic bacteria and is most commonly seen in patients with diabetes mellitus, peripheral vascular disease, alcoholism, malignancy (especially leukemia and lymphoma), immunocompromise, and postsurgical status (especially transplantations) [1–6]. Fournier gangrene refers to necrotizing fasciitis of the perineum and is usually of the type I variety [6, 7, 10]. Type II necrotizing fasciitis is caused by group A Streptococcus (GAS, S. pyogenes) or Staphylococcus aureus and results in gangrenous myofasciitis with the potential complication of toxic shock syndrome (primarily through release of exotoxins A, B, and C) [6, 7, 9]. M-protein is a key molecular virulent factor in GAS organisms and has antiphagocytic properties which allow the in-

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Imaging of Necrotizing Fasciitis and Its Mimics fectious agent to evade host immune response. M-protein is more prevalent in cases of necrotizing fasciitis caused by GAS. Approximately 50% of cases of necrotizing fasciitis caused by GAS are positive for M-protein [3, 6, 9]. There are many different isolates of the M-protein, with types I and type III the most common [3, 6, 9]. Type II necrotizing fasciitis can be seen in any patient age group and in those without significant medical history. Reported risk factors for type II necrotizing fasciitis include history of blunt trauma, penetrating injuries, Varicella zoster, IV drug abuse, recent surgical procedures, childbirth, burns, and nonsteroidal antiinflammatory drugs (NSAIDs) [6–9]. The increased risk from NSAID use has been shown in several retrospective studies and is thought to result from blunting and delaying of local and systemic immune responses. No specific NSAID has been reported to predispose to necrotizing fasciitis more than others in the same medication class [6, 11, 12]. Kim and colleagues [13] divided necrotizing fasciitis into three stages on the basis of the sequential presence of clinical features reported by Wong and associates [7]. In stage I (early stage), the overlying skin is warm, erythematous, and indurated, producing “wooden skin.” In stage II (intermediate stage), blisters and bullae form, and in stage III (late stage), the bullae become hemorrhagic, crepitus can be noted on physical examination, and skin necrosis (which can progress to overt gangrene) ensues. Involved areas in necrotizing fasciitis tend to be extremely painful in early stages and painless in more advanced stages [7, 14]. Histopathologic evaluation of necrotizing fasciitis reveals edematous expansion of interand intrafascicular fibrous septa surrounding skeletal muscle bundles, infiltration of inflammatory cells (plasma cells, lymphocytes, neutrophils, and rarely eosinophils), and early fibroblastic proliferation [6, 15, 16]. Necrotizing fasciitis remains a clinical diagnosis, and although the utility of imaging is limited, it can be useful to map disease extent to aid in planning the surgical approach and margins and to exclude other processes. Importantly, in patients whose cases are severely toxic, treatment should not be delayed for the performance of imaging. Radiographic findings in the early stage of necrotizing fasciitis are similar to those of cellulitis and include increased soft-tissue opacity and thickness. However, radiographs can also be normal until the infection and ne-

crosis are advanced and manifest as soft-tissue emphysema tracking along fascial planes (Fig. 1) [14, 16]. CT characteristics correlate with pathologic findings of soft-tissue inflammation or liquefactive necrosis and thus may feature dermal thickening, increased soft-tissue attenuation, inflammatory fat stranding, and possible superficial or deep crescentic fluid or air in the subfascial planes [5, 16–20] (Figs. 1, and 2). The CT hallmark of soft-tissue air with deep fascial fluid collections is not always seen, and its absence should not prompt exclusion of necrotizing fasciitis from the differential diagnosis because the patient may have early disease in which gas has not yet formed or reached detectable levels [20]. 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]. Similarly, the rapidity of CT compared with MRI may be advantageous for an emergent necrotizing fasciitis evaluation. MRI is the modality of choice for detailed evaluation of soft-tissue infection but is often not performed for necrotizing fasciitis evaluation because its acquisition is time consuming and will delay treatment [10, 20]. MRI of necrotizing fasciitis shows circumferential dermal and soft-tissue thickening that have variable signal intensity on T1-weighted sequences and increased signal intensity on fluid-sensitive sequences [10, 12, 20]. Subcutaneous edema in necrotizing fasciitis is typically a less-prominent feature than in patients with cellulitis. Fascial thickening is also hyperintense on fluid-sensitive sequences (Figs. 3 and 4) and typically begins in superficial fascia, extends along the length of the involved muscle compartment, and is smooth or fusiform. Because this finding is nonspecific and difficult to distinguish from nonnecrotizing fasciitis, clinical correlation is crucial. Patients with negative or nonspecific imaging findings and a high clinical suspicion of necrotizing fasciitis should be promptly treated. Follow-up imaging can be performed in relatively stable patients who have changing clinical status and equivocal initial imaging findings to assess for possible progression to necrosis. Late-stage gas collections dissecting superficial or deep fascia are seen as punctate or curvilinear T1- and T2-hypointense foci. IV gadolinium con-

trast material increases sensitivity for tissue necrosis and can be used for more detailed evaluation of soft-tissue involvement. On contrast-enhanced images, the abnormal fascia generally enhances and may be surrounded by nonenhancing islands of tissue. Occasionally, associated rim-enhancing abscess may also be seen [13, 16, 20–26]. However, patients with necrotizing fasciitis may also present with renal failure, and thus administration of IV gadolinium may not be possible. Nonnecrotizing Fasciitis As its name implies, nonnecrotizing fasciitis features soft-tissue inflammation and fascial thickening or enhancement without evidence of necrosis and encompasses paraneoplastic fasciitis, eosinophilic fasciitis, nodular fasciitis, and proliferative fasciitis. Paraneoplastic Fasciitis Paraneoplastic fasciitis falls under the spectrum of acute febrile neutrophilic dermatosis (Sweet syndrome), in which myofascial inflammation can be seen with or without dermal involvement [27, 28]. The condition is most often associated with hematologic malignancies, especially leukemias, with acute myeloid leukemia the most common [27, 28]. Paraneoplastic fasciitis can precede diagnosis of malignancy, occur concomitantly, or even herald malignancy recurrence after treatment [27, 28]. Histopathologic evaluation is characterized by infiltration of the dermis and endomysial connective tissue with mature neutrophils with or without vessel wall destruction [27, 28]. Skin (especially of the extremities, face, and neck) is the most common site of involvement, which initially presents as single or multiple painful red or purple-red papules or nodules. Myositis, fasciitis, myalgia, or tendinitis-tenosynovitis can be seen but are less common [27, 28]. Laboratory findings may reveal peripheral leukocytosis with neutrophilia and elevated erythrocyte sedimentation rate (ESR) [27, 28]. Imaging findings are nonspecific and require clinicopathologic correlation. Radiographic findings include dermal thickening and increased opacity of involved areas. CT shows dermal thickening, increased soft-tissue edema, fat infiltration, and fascial thickening (which may be patchy depending on the areas involved). MRI will show dermal and fascial thickening along with fascial edema, which is seen as increased signal intensity on fluid-sensitive sequences (Fig. 5). Concomi-

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Chaudhry et al. tant myositis may or may not be seen. Because paraneoplastic fasciitis is a result of a systemic process, multiple sites are often involved [27]. Treatment includes high-dose steroids and treatment of underlying malignancy [27]. Eosinophilic Fasciitis Eosinophilic fasciitis (Shulman syndrome) is a rare inflammatory condition in which superficial muscle fascia collagen is infiltrated by lymphocytes, plasma cells, and eosinophils. It usually presents in the extremity and trunk with scleroderma-like dermal induration and swelling. Laboratory findings include increased ESR, hyperglobulinemia, and peripheral eosinophilia. Patients may also have mild elevation in WBC count, antinuclear antibodies (ANAs), and rheumatoid factor. Creatine phosphokinase and other blood chemistry values are usually within normal limits. Imaging findings of eosinophilic fasciitis resemble those of paraneoplastic fasciitis and almost always require clinicopathologic correlation to confirm the diagnosis. Thus, radiography will show dermal thickening and increased softtissue opacity. CT will also show these findings and may show thickening or edema of myofascial structures. T1-weighted MR images show thickening of the superficial muscle fasciae and fluid-sensitive sequences will show increased fascial signal intensity relative to muscle (Fig. 6). Contrast-enhanced enhancement is variable depending on the stage of the disease. There is usually no evidence of myositis. Treatment usually involves administration of glucocorticoids and other immunosuppressants and usually leads to rapid correction of peripheral blood eosinophilia and normalization of the ESR. Imaging findings will also rapidly resolve after appropriate therapy [29, 30]. Nodular and Proliferative Fasciitis Nodular and proliferative fasciitis are benign reactive processes of uncertain cause that are thought to result from local stress reactions resulting in fibrous proliferation [31– 34]. Nodular fasciitis, also known as infiltrative fasciitis, pseudosarcomatous fasciitis, and pseudosarcomatous fibromatosis, is most commonly seen in young adults, with 85% of patients younger than 50 years and only 5% over 70 years [33]. Lesions typically involve the extremities and trunk and are usually less than 2 cm in size (70%) [33]. Lesions can be subcutaneous, intrafascial, intramuscular, and rarely intradermal and intervascu-

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lar [35]. The most common presentation of nodular fasciitis is a rapidly growing fibrous mass (occasionally multiple) that grows over a period of 1 to 2 weeks and is painful in about half of cases [33]. Imaging and histopathologic characteristics of nodular fasciitis depend on whether the lesion is predominantly fibrous, cellular, or myxoid. Hypercellularity and the amount of collagen will also vary. Fibroblasts are generally organized in short bundles and fascicles in a background of myxoid stroma. In some cases, there is increased fibrosis with decreased cellularity [28, 29]. Imaging correlates with histology and can be highly variable. Hypercellular lesions are isointense to skeletal muscle on T1-weighted MR images and hyperintense to fat on T2-weighted images. Highly fibrous lesions are hypointense on all sequences (Fig. 7). There is generally homogeneous contrast enhancement; however, rim or irregular enhancement can occur depending on the cellularity of the lesion [31–36]. Imaging and histopathologic characteristics of nodular fasciitis can result in confusion for sarcoma. Thus, follow-up imaging may be warranted to document lesion stability or resolution after treatment. When the diagnosis of nodular fasciitis is confirmed, treatment usually involves complete surgical excision. Recurrence rates are extremely low (1–2%) and most commonly occur shortly after excision [31–36]. Proliferative fasciitis is a benign pseudosarcomatous lesion and is thought to be a reactive process resulting from mechanical trauma, similar to nodular fasciitis. It occurs most commonly in adults between the ages of 40 and 70 years. Lesions most commonly occur in the extremities, especially in the forearm and thigh, and clinically present as a palpable, mobile, and firm subcutaneous nodule with rapid initial growth that lasts a few weeks. Histopathologic evaluation reveals “active proliferation of immature-appearing cells” [37] that can be seen in sarcoma and other pseudosarcomatous lesions, and thus sarcoma may be incorrectly diagnosed. Imaging findings are nonspecific and similar to nodular fasciitis, in which the appearance depends on the fasciitis stage. Thus, clinicopathologic correlation is often required, and followup imaging is often useful to document absence of lesion growth, radiologically aggressive behavior (such as tissue infiltration or invasion, necrosis, neovascularity, and so on), or recurrence [37].

Cellulitis Cellulitis is a soft-tissue infection with an inflammatory response that results in dermal thickening, swelling, erythema, and pain. Although often localized to the dermis, if left untreated, cellulitis may progress to necrotizing fasciitis, sepsis, septic arthritis, tenosynovitis, and osteomyelitis depending on its location. Although commonly caused by Staphylococcus and Streptococcus bacteria, cellulitis can be caused by a multitude of microorganisms. Risk factors include recent trauma, IV drug abuse, diabetes mellitus, end-stage renal disease, and other immunocompromised states. Histologic evaluation, although rarely performed, reveals infiltration of subcutaneous tissue with leukocytes (primarily neutrophils) and capillary dilatation. CT shows soft-tissue thickening and swelling, fat stranding, and enhancement or hyperemia on contrast-enhanced imaging. The presence of soft-tissue gas in the absence of penetrating trauma suggests progression to necrotizing fasciitis [6]. Rim-enhancing collections in the setting of cellulitis suggest abscess formation. MRI reveals irregular dermal and soft-tissue thickening with heterogeneous T2 hyperintensity and variable contrast enhancement of the involved soft-tissue. MR is a good modality to exclude progression of cellulitis into fasciitis or osteomyelitis in high-risk patients [5, 13]. Cellulitis remains a clinical diagnosis, with imaging studies used to evaluate the extent of disease and associated complications. Uncomplicated cellulitis usually resolves with appropriate antibiotic therapy [5, 38]. Dermatomyositis Dermatomyositis is an idiopathic autoinflammatory myopathy characterized by symmetric bilateral proximal muscle weakness (Fig. 8). The most common age of onset is early adulthood with a 2:1 female to male predominance. The lower extremities are more commonly involved than the upper extremities. There are five major diagnostic criteria, initially developed by Bohan and Peter [39], accepted by the American College of Rheumatology [40], and later revised by Tanimoto and colleagues [41]: symmetric proximal muscle weakness, muscle biopsy of myositis, increase in serum skeletal muscle enzymes, characteristic electromyographic pattern, and typical rash (including Gottron papules, heliotrope rash, photodistributed erythema [“shawl sign”], poikiloderma, and calcinosis cutis). Antibody ti-



Imaging of Necrotizing Fasciitis and Its Mimics ters are also often used for diagnosis (ANA, rheumatoid factor, anti tRNA synthetase [antijo and antimi2]) [42]. In the acute setting, nonspecific soft-tissue thickening may be seen on radiography. Radiographic findings of chronic dermatomyositis are more apparent and include persistent soft-tissue prominence, subcutaneous and intramuscular calcifications, or muscle atrophy [39, 42–45]. In the acute stages of the disease, CT may show subcutaneous perimuscular and intramuscular edema with surrounding fat infiltration and diffuse heterogeneous intramuscular contrast-enhanced enhancement. In the advanced and chronic stages of the disease, CT may show intramuscular fatty replacement with punctate or “sheetlike” soft-tissue calcifications [44, 45]. MRI of dermatomyositis is preferred because it can detect the disease early, even before clinical skin manifestations are visible. In the acute stage of dermatomyositis, MRI will show symmetric bilateral diffuse subcutaneous, perimuscular, and intramuscular edema suggested by hyperintensity on fluid-sensitive sequences. Heterogeneous intramuscular enhancement on contrastenhanced sequences will indicate areas of acute myositis. Fatty replacement and muscle atrophy resulting from chronic dermatomyositis appear hyperintense on T1-weighted images, and punctate or sheetlike T1- and T2-hypointense foci indicating calcification may be seen [44, 45]. Glucocorticoids are the first-line treatment of dermatomyositis, with methotrexate or azathioprine used for nonresponsive cases. Early diagnosis is critical because early treatment enables muscles to return to full strength and function, whereas delayed treatment can result in irreversible muscle damage [42, 43]. Churg-Strauss Vasculitis Churg-Strauss vasculitis, also known as eosinophilic granulomatosis with polyangiitis, is a medium- and small-vessel vasculitis characterized by asthma, chronic rhinosinusitis, and prominent peripheral blood eosinophilia. It primarily affects the lungs causing pulmonary capillaritis but can involve other organs, such as the skin, kidneys, heart, CNS, and musculoskeletal system. Laboratory tests show elevated ESR, elevated C-reactive protein, peripheral eosinophilia, and positive perinuclear antineutrophil cytoplasmic antibody (pANCA) titers [46, 47]. Histopathologic evaluation of muscle reveals eosinophilic infiltrate with eosinophilic giant cells, nec-

rotizing vasculitis (primarily arterioles and venules), and extravascular granulomas. Although there is little information in the literature on the musculoskeletal manifestations of Churg-Strauss vasculitis, in our experience, CT findings are nonspecific and include increased soft-tissue thickness with fat stranding and edema without soft-tissue emphysema or fluid collections. On MRI, smooth fascial thickening with heterogeneous T2 hyperintensity and relatively homogeneous contrast enhancement are seen (Fig. 9). Biopsy with histologic staining for pANCA is confirmatory for Churg-Strauss vasculitis, and the treatments of choice are glucocorticoids and immunosuppressant agents [46, 47]. Lupus Myofasciitis Systemic lupus erythematous (SLE) is an autoimmune disease with multiorgan involvement. Lupus myofasciitis occurs rarely and can present at any stage of the disease (although usually several years after the onset of SLE). Clinical findings include myalgias, arthralgias, and tendinopathy (which can rarely progress to tendon rupture). Histopathologic evaluation shows immune complex deposition resulting in small-vessel vasculitis with diffuse lymphocyte infiltration. Laboratory studies are typical for lupus patients, including elevated acute-phase reactants, elevated antibody titers (including ANA, anti-Smith, and anti–double-stranded DNA), and elevated creatine kinase. CT and MRI reveal circumferential deep perifascial subcutaneous edema with or without intramuscular edema (Fig. 10). MRI is the more sensitive study because it provides better compartmental detail and improves evaluation of associated complications, such as osteonecrosis and septic joints. Treatment of lupus myofasciitis includes NSAIDs, corticosteroids, and hydroxychloroquine [48, 49]. Compartment Syndrome Compartment syndrome occurs when compartmental pressure increases and arterial pressure decreases, resulting in insufficient blood supply to muscles and nerves. Predisposing factors include fracture, muscle injury, crush injuries, acute hemorrhage, burns, splints or casts, androgen abuse, IV drug abuse (especially cocaine), snake venom, and rarely deep venous thrombosis. Clinically, compartment syndrome has been divided into acute and chronic stages by the American College of Orthopedic Surgeons [50–53]. The acute stage is defined as rest-

ing compartmental pressures of greater than 30 mm Hg and is a surgical emergency. In the acute stage, the pain is usually out of proportion to the sustained injury and is worsened when the involved muscle is passively stretched. Chronic compartment syndrome is defined as resting compartmental pressure ≥ 15 mm Hg, 1-minute postexercise intracompartmental pressure ≥ 30 mm Hg, and 5-minute postexercise intracompartmental pressure ≥ 20 mm Hg. It is not emergent and usually occurs gradually after repetitive motion or exercise. Patients usually present with pain on exertion that is relieved after activity cessation (often referred to as “chronic exertional compartment syndrome”) [50–53]. Laboratory findings show markedly increased creatine kinase and myoglobinuria. Radiographs are usually unremarkable, excluding the sequela of any sustained trauma. CT images may reveal intramuscular hypoattenuation from edema (Fig. 11). In more acute and subacute stages, MR images show decreased T1 signal intensity and increased T2 signal intensity within edematous muscle, loss of normal muscle striations, enlargement of the affected muscle group, and variable signal intensity of any compartmental hemorrhage (depending on the age). Diffuse heterogeneous hypointense T1 and T2 signal intensity is seen in chronic compartment syndrome and with muscle necrosis. Contrast enhancement is variable depending on the degree of myonecrosis and soft-tissue ischemia. Fasciotomy and decompression are the treatments of choice [50–53]. Graft-Versus-Host Disease Graft-versus-host disease (GVHD) is a complication of allogeneic transplantation, blood transfusion, or thymic transplantation. Donor T-lymphocytes cause damage to epithelial cells lining the recipient target organ. Acute versus chronic onset of GVHD is determined by whether the symptoms begin before or after 100 days, respectively. The presentation of GVHD resembles connective tissue disorders. Histopathologic examination shows vacuolization of the epidermis basal layer and lymphocytic infiltration of the superficial dermis. Imaging findings are usually identical to those of dermatomyositis, and thus clinical correlation is required. On CT, acute GVHD usually features subcutaneous perimuscular or intramuscular edema and diffuse contrast enhancement, whereas chronic GVHD features intramuscular fatty infiltration (Fig. 12). MRI most commonly shows in-



Chaudhry et al. tramuscular T2 hyperintensity and may also show subcutaneous and perimuscular T2 hyperintensity with diffuse heterogeneous contrast enhancement. Immunosuppressants are the treatment of choice [54–56]. Diabetic Myonecrosis Myonecrosis is one of the many complications of diabetes. The exact mechanism of action is not known, but it is thought to occur secondary to muscle infarction, possibly from arteriosclerosis obliterans. Myonecrosis presents as an acute onset of muscle pain without a history of trauma. Tissue biopsy may be required for diagnosis; however, imaging is often characteristic in the chronic stage. Histopathologically, there are infarcted patches of myocytes, eosinophilic infiltrates, and necrotic muscle fibers that lack striation and nuclei. Thickening of small-vessel walls with hyalinization and luminal narrowing or complete occlusion can also be seen. CT shows muscular edema with or without surrounding fat infiltration with diffuse, heterogeneous contrast enhancement. In the acute setting, MRI can show diffuse subcutaneous edema, perifascial fluid, marked muscle swelling, diffuse muscle contrast enhancement, and possible rim-enhancing foci indicating areas of necrosis (Fig. 13). Chronic diabetic myonecrosis will show muscle atrophy and loss of prior muscular T2 hyperintensity, with or without calcification. The treatment of diabetic myonecrosis is supportive care and antiinflammatory agents [45, 56–58]. Conclusion Necrotizing fasciitis can be a devastating disease process and should be suspected clinically. In the absence of penetrating trauma or iatrogenic causes, gas tracking along fascial planes in a septic patient is virtually pathognomonic. Although imaging is often not required because it may delay treatment (especially MRI), it may be used for problem solving and surgical planning. CT is used to search for gas and obtain an estimate of softtissue involvement. Contrast-enhanced MRI is more sensitive and can aid in evaluation of the extent of disease although its time-consuming nature often makes acquisition not clinically feasible. Other entities that may be in the differential diagnosis of necrotizing fasciitis include nonnecrotizing fasciitis, cellulitis, dermatomyositis, vasculitis (lupus myofasciitis, Churg-Strauss vasculitis, and others), GVHD, diabetic myonecrosis, and compartment syndrome. Although these entities are not surgi-

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of Rheumatology website. www.rheumatology.org/ Practice/Clinical/Patients/Diseases_And_Conditions/ Dermatomyositis_%28Juvenile%29/. Published July 2012. Accessed April 7, 2014 41. Tanimoto K, Nakano K, Kano S, et al. Classification criteria for polymyositis and dermatomyositis. J Rheumatol 1995; 22:668–674 42. Mammen AL. Dermatomyositis and polymyositis: clinical presentation, autoantibodies and pathogenesis. Ann N Y Acad Sci 2010; 1184:134–153 43. Sanner H, Kirkhus E, Merckoll E, et al. Longterm muscular outcome and predisposing and prognostic factors in juvenile dermatomyositis: a case-control study. Arthritis Care Res (Hoboken) 2010; 62:1103–1111 44. Tzaribachev N, Well C, Schedel J, Horger M. Whole-body MRI: a helpful diagnostic tool for juvenile dermatomyositis case report and review of the literature. Rheumatol Int 2009; 29:1511–1514 45. May DA, Disler DG, Jones EA, et al. Abnormal signal intensity in skeletal muscle at MR imaging: patterns, pearls and pitfalls. RadioGraphics 2000; 20(spec no):S295–S315 46. Solans R, Bosch JA, Perez-Bocanegra C, et al. Churg-Strauss syndrome: outcome and long term follow-up of 32 patients. Rheumatology (Oxford) 2001; 40:763–771 47. Katzenstein AL. Diagnostic features and differential diagnosis of Churg-Strauss syndrome in the lung. Am J Clin Pathol 2000; 114:767–772 48. Nakamura J, Saisu T, Yamashita K, et al. Age at time of corticosteroid administration is a risk factor for osteonecrosis in pediatric patients with systemic lupus erythematosus: a prospective magnetic resonance imaging study. Arthritis Rheum 2010; 62:609–

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Fig. 1—52-year-old woman with necrotizing fasciitis. A–C, Lateral radiograph (A) and axial CT images (B and C) of lower extremity show dermal thickening, fascial edema (arrowheads, B and C) and gas (arrows) tracking along superficial and deep fascial planes, consistent with necrotizing fasciitis.



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B Fig. 2—43-year-old man with Fournier gangrene. A–D, Axial (A and B) and coronal (C and D) CT images of poorly controlled diabetic patient show air tracking into deep soft tissues of perineum, representing Fournier gangrene.

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Fig. 3—19-year-old man with early necrotizing fasciitis. A, Axial T2-weighted fat-suppressed spectral presaturation with inversion recovery (SPIR) image with TR/TE, 2600/70; flip angle, of 90° shows edema (increased T2 signal intensity) of soft tissues and superficial fascia (arrowheads) of proximal right lower leg. B, Gadolinium-enhanced fat-suppressed T1weighted image with TR/TE, 618/10; flip angle, 90° shows enhancement (arrowheads). No definitive muscle edema or enhancement is yet appreciated. No T1- or T2-hypointense air locules are appreciated.



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B Fig. 4—47-year-old man with necrotizing fasciitis. A and B, T2-weighted fat-suppressed spectral presaturation with inversion recovery (SPIR) with TR/TE, 3000/70; inversion time, 0; and flip angle, 90° in coronal (A) and axial (B) planes show marked diffuse edema (increased T2 signal intensity) of superficial and deep fascia involving right pectoralis major and minor muscles (arrows). C, Axial contrast-enhanced T1-weighted high-resolution isotropic volume examination (THRIVE, Philips Healthcare) with TR/TE, 4.1/2.0; inversion time, 0; and flip angle, 10° shows diffusely enlarged pectoralis major and minor with mild fascial contrast enhancement (arrowheads).

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Fig 5—68-year-old man with paraneoplastic fasciitis. A–C, Axial T2-weighted fat-suppressed (A) with TR/ TE, 5000/105 and flip angle, 90°, unenhanced T1weighted (B) with TR/TE, 650/14 and flip angle, 90°, and contrast-enhanced fat-suppressed T1-weighted (C) with TR/TE, 600/14 and flip angle, 90° images show diffuse edema of right hand represented by dermal, perifascial, and perimyseal increased T2 signal intensity and heterogeneous T1 signal intensity with variable contrast enhancement. There is 3.0 × 1.5 × 0.4 cm nonenhancing cystic dermal lesion (white arrows), which is magnified on images on right. Biopsy of right hand and cyst aspiration were performed and revealed diffuse soft-tissue and fascial neutrophilic infiltrate, confirming diagnosis of paraneoplastic fasciitis.


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Fig. 6—26-year-old man with eosinophilic fasciitis. A and B, Coronal fat-suppressed T2-weighted images with TR/TE, 3934/70 and flip angle, 90° show increased T2 signal intensity of anterior and lateral deltoid muscles representing edema. Muscle biopsy was consistent with eosinophilic fasciitis.

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Fig. 7—73-year-old woman with nodular fasciitis and history of remote chest and shoulder trauma and breast cancer after mastectomy, radiation, and chemotherapy. A–D, Sagittal T1-weighted turbo spin-echo (TSE) (A) with TR/TE, 650/8 and flip angle, 90°; sagittal contrast-enhanced fat-suppressed T1-weighted (B) with TR/TE, 626/8 and flip angle, 90°; coronal T2weighted TSE fat-suppressed spectral presaturation with inversion recovery (SPIR) (C); and coronal PET CT (D) obtained for breast cancer restaging images show well-circumscribed T1-isointense (to muscle) lesion arising from fascia of supraspinatus muscle (arrowheads, A). Lesion shows avid gadolinium contrast enhancement (asterisk, B) and T2 hyperintensity (arrowheads, C) as well as significant 18 F-FDG uptake on PET (arrows, D). Biopsy of lesion confirmed diagnosis of nodular fasciitis.



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Fig. 8—8-year-old girl with dermatomyositis. A–C, Axial (A and B) and coronal (C) CT images show significant fat stranding and inflammation around bilateral psoas major (arrows), iliacus (asterisks), quadratus lumborum (arrowheads), and posterior spinal muscles.

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C Fig. 9—68-year-old woman with Churg-Strauss myofasciitis who presented with history of asthma, hemoptysis, and worsening left lower extremity pain. A, Coronal T2-weighted fat-suppressed spectral presaturation with inversion recovery (SPIR) with TR/TE, 2600/70 and flip angle, 90° shows ill-defined T2-hyperintense lesion along ulnar forearm (asterisk). B, Axial T2-weighted fat-suppressed SPIR with TR/ TE, 3572/70 and flip angle, 90° shows lesion to be heterogeneous and involve flexor carpi ulnaris. C, Axial unenhanced turbo spin-echo (TSE) T1weighted with TR/TE, 642/10 and flip angle, 90° shows that lesion is isointense to muscle. D, Lesion has subtle enhancement on fat-suppressed contrast-enhanced T1-weighted TSE image with TR/ TE, 717/10 and flip angle, 90°. Muscle biopsy stained positive for perinuclear antineutrophil cytoplasmic antibody, confirming diagnosis of Churg-Strauss myofasciitis.


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Fig. 10—9-year-old girl with lupus myofasciitis. A and B, Coronal T2-weighted fat-suppressed spectral presaturation with inversion recovery (SPIR) with TR/ TE, 3684/70 and flip angle, 90° in left calf at anterior (A) and posterior (B) levels show diffuse marked T2 hyperintensity of dermis, muscles, and fascialperifascial soft tissues. C, Marked muscle edema is also shown in left foot on axial T2-weighted fat-suppressed SPIR image with TR/TE, 1935/70 and flip angle, 90°. Muscle biopsy confirmed immune-complex deposition consistent with lupus myofasciitis.

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Fig. 11—64-year-old man with compartment syndrome. Axial unenhanced CT image of right thigh shows loss of striations and hypodensity in semitendinosus muscle (arrows), indicating diffuse edema secondary to muscle ischemia and necrosis.

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Fig. 12—50-year-old woman after renal transplantation with graft versus host disease. A and B, Unenhanced (A) and T2-weighted spectral presaturation with inversion recovery (SPIR) (B) CT images with TR/TE, 3885/70 and flip angle, 90° show subcutaneous (asterisks) and perimuscular (arrowheads) edema. (Fig. 12 continues on next page)



Imaging of Necrotizing Fasciitis and Its Mimics Fig. 12 (continued)—50-year-old woman after renal transplantation with graft versus host disease. C and D, Unenhanced (C) and contrast-enhanced (D) T1-weighted images with TR/TE, 703/10 and flip angle, 90° show mild intramuscular contrast enhancement (arrows, D).

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Fig. 13—67-year-old man with diabetic myonecrosis of right calf. A, Coronal fast spin-echo T2-weighted image with fat suppression with TR/TE, 4800/54.6; inversion time, 0; and flip angle, 90° shows heterogeneous masslike lesion in tibialis anterior. B and C, Unenhanced (B) and contrast-enhanced (C) images with TR/TE, 550/40; inversion time, 0; and flip angle, 90° show mass is heterogeneously hypointense (B), and features heterogeneous enhancement after IV administration of gadolinium (C). Tissue biopsy was performed and was consistent with diabetic myonecrosis.

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