Infection, inflammation, and edema of the lung parenchyma are usually well depicted on CT without contrast enhancement. Bakleh M, Wold LE, Mandrekar JN, Harmsen WS, Dimashkieh HH, Baddour LM. Cellulitis (rare plural: cellulitides) is an acute infection of the dermis and subcutaneous tissues without deep fascial or muscular involvement. Schmid M, Kossmann T, Duewell S. Differentiation of Necrotizing Fasciitis and Cellulitis Using MR Imaging. government site. Nurse practitioners must be familiar with the contraindications for CT contrast administration. Since the epidermis is not involved, cellulitis is not transmitted by person-to-person contact. The decision to order contrast-enhanced CT is based on the clinical question being asked. 2007 Nov-Dec;27(6):1723-36. doi: 10.1148/rg.276075033. Magnetic resonance imaging of musculoskeletal infections. 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. Contrast-enhanced CT demonstrates crescentic subfascial fluid (arrow) with fluid also seen superficial to the fascia (arrow head) and between muscle planes (a). of 20 consecutive patients with necrotizing fasciitis, CT revealed fascial thickening and fat stranding in 80%, soft tissue gas in 55%, and abscesses in 35%.22, CT is helpful in guiding surgical debridement and drainage by evaluating the extent of soft tissue and osseous involvement, identifying the potential infectious source and identifying potential complications including vascular rupture or tissue necrosis.1, 2,13,22, MRI is the gold-standard for soft-tissue infections as it provides excellent soft-tissue contrast resolution with a sensitivity of 93% for the diagnosis for necrotizing fasciitis.1, 24 Essential sequences include T1 weighted imaging to assess anatomy, and T2 fat saturated or short tauinversion-recovery sequences to look for fascial thickening and edema.3, 25 Post gadolinium sequences are helpful to delineate the extent of infection, identify abscesses and areas of necrosis, but may not be feasible in patients with acute renal failure, which is common in this patient population.3, 26, Deep fascial thickening and subfascial fluid accumulation can be seen as high signal on fluid sensitive sequences (Figures 8 and 9).21 The deep intramuscular fascia is usually protected in the setting of cellulitis, but is involved in necrotizing fasciitis.1 Fascial thickening begins in the superficial fascia and extends along the deep intermuscular fascia, not just in areas contiguous to the deep peripheral fascia.1, 18 Hyperintensity and thickness of the fascia greater than or equal to 3 mm on fat saturated T2 weighted or short tauinversion-recovery images with involvement of three or more compartments is a sensitive finding to suggest necrotizing fasciitis.3, 8,13,25,27 The absence of T2 hyperintensity within the deep fascia can essentially exclude a diagnosis necrotizing fasciitis.3, 18,21. Pulmonary fibrosis 3. 1994;192(2):493-6. 7. 2022 Jul 10;11(14):3998. doi: 10.3390/jcm11143998. [ 16, 17, 18] On CT scans, a preseptal cellulitis may appear as. 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. Radiol Clin North Am. Axial CT with contrast enhancement obtained subsequently (B and C) shows that this abnormality corresponds to right hilar lymphadenopathy partially encasing the right pulmonary artery (arrows). Water-soluble, iodine-based contrast agents can also be given orally. Unenhanced CT is also used in patients with spine and extremity trauma. 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. 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. 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. The choice of contrast agent depends on route of administration, desired tissue differentiation, and suspected diagnosis. Initial radiographs show soft tissue gas (without puncture wound) or are normal with high clinical suspicion of necrotizing fasciitis. : Elsevier Health Sciences, 2013;633-644. Insights Imaging. Peri-orbital cellulitis is of concern in children because it may be secondary to occult underlying bacterial sinusitis or, rarely, due . Laryngeal edema (severe or rapidly progressing), Methylprednisolone (Medrol), 32 mg orally 12 and 2 hours before contrast administration; plus diphenhydramine (Benadryl), 50 mg intravenously, intramuscularly, or orally 1 hour before contrast administration, Prednisone, 50 mg orally 13, 7, and 1 hour before contrast administration; plus diphenhydramine, 50 mg intravenously, intramuscularly, or orally 1 hour before contrast administration, Normal renal function and no comorbid disorder, Metformin (Glucophage) can be continued when contrast is administered; serum creatinine does not need to be measured, Normal renal function and at least one comorbid disorder, Metformin should be discontinued when contrast is administered; if the patient remains clinically stable and has no new intercurrent risk factors for renal impairment, metformin may be resumed in 48 hours without repeating serum creatinine measurement, Metformin should be discontinued when contrast is administered; resume only after careful reevaluation and monitoring of renal status, Noncontrast-enhanced CT of the head is the preferred initial study if performed within three hours of acute symptom onset; contrast-enhanced CT should be obtained for patients with symptoms lasting longer than three hours; contrast-enhanced CT combined with CT angiography of the neck may be needed for follow-up, Thin section high-resolution CT without contrast, Extremity soft tissue swelling, infection, or trauma, Contrast is necessary if vascular involvement or injury is suspected, Scan suspected area of trauma in cervical, thoracic, or lumbar spine, Abdominal and pelvic CT; oral or rectal contrast agent based on institutional preference, Protocols vary depending on cancer type and stage, Diverticulitis; suspected complications of inflammatory bowel disease, Intravenous contrast agent for diverticulitis; oral and/or rectal contrast agent can be administered to visualize bowel, Noncontrast-enhanced CT is sensitive for calcifications (chronic pancreatitis); contrast-enhanced CT is best for evolving pancreatitis or pancreatic pseudocyst, Many centers now include venous phase CT of the pelvis and lower extremities in combination with CT angiography of the lung. A 39-year-old-male with necrotizing fasciitis of the right thigh. Recent studies suggest that a combination of hydration, sodium bicarbonate, N-acetylcysteine, and decreased contrast volume may reduce this risk in high-risk populations.14,15, The question of whether this risk has been overstated has been raised in the medical literature. These reactions are relatively rare and are usually mild but occasionally can be severe.9 Anaphylactoid reactions have an unclear etiology but mimic allergic reactions, and they are more likely to occur in patients with a previous reaction to contrast and in patients with asthma or cardiovascular or renal disease. In cases of suspected arteriovenous malformation, a protocol similar to that used for suspected pulmonary embolus is used (Figure 3), although in some instances, the imaging features of arteriovenous malformation may be detectable without IV contrast. Reference article, Radiopaedia.org (Accessed on 01 May 2023) https://doi.org/10.53347/rID-15554. no financial relationships to ineligible companies to disclose. 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%. In uncomplicated cellulitis, CT demonstrates skin thickening, septation of the subcutaneous fat, and thickening of the underlying superficial fascia. Axial non-contrast. Correlation of histopathologic findings with clinical outcome in necrotizing fasciitis. Clipboard, Search History, and several other advanced features are temporarily unavailable. 3 Oral contrast agents are barium- or iodine-based and are used for bowel opacification. 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.

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