Necrotizing fasciitis: unreliable MRI findings in the preoperative diagnosis
Introduction
Necrotizing fasciitis (NF) is a relatively rare soft-tissue infection characterized by rapidly spreading, progressive necrosis of the subcutaneous fat and fasciae. It is frequently accompanied by moderate to severe systemic toxicity. Septic complications may develop within hours with fatal outcome unless prompt diagnosis and aggressive surgical treatment are applied [1], [2]. The mortality rate of patients with NF varies with the interval from the onset of disease to its treatment [1]. Overall mortality rates of 33–73% have been reported [1], [3], [4]. The mortality rate can be reduced by 10% by aggressive early management which consists of adequate surgical debridement, extensive fasciotomy or amputation [5], [6], [7]. Nonnecrotizing soft-tissue infections such as cellulitis which involves only subcutaneous tissue, can be treated in most cases with antibiotics alone [6] and noninfectious causes simulating NF can be treated conservatively [6], [7]. Definitive diagnosis is made only at surgery. The ability to probe a blunt instrument between the suppurative fasciae without resistance has been considered a surgical finding that differentiates necrotizing soft tissue infections from nonsurgical cellulitis [3], [6], [7]. Because of the possibility of subsequent reconstruction problems [3] and unnecessary surgery, accurate presurgical diagnosis is preferable.
Magnetic resonance imaging (MRI) is frequently used in the differential diagnosis of soft tissue diseases. Schmid et al. [6] reported that when no deep fascial involvement was revealed with MRI, NF could be excluded. However, our experience reveals that the MRI findings are non-specific and not reliable in differentiating NF from other non-necrotizing infections and non-infectious diseases. We present similar MRI findings in two cases with NF, one case of dermatomyositis and one case of posttaumatic muscle injury.
Section snippets
Case 1
A 7-year-old immunocompromised girl, with the complaints of high fever and gradually increasing pain in the left leg during the previous week, was admitted with the suspicion of necrotizing fasciitis. She had undergone chemotherapy for acute myeloblastic leukemia 1 year before. Physical examination revealed a temperature of 39.9°C, and swelling and erythema in the lower half of the left leg which was tender on palpation. Blood tests showed low hemoglobin, low thrombocyte count, high white blood
Discussion
NF may at first appear to be a benign, low-grade cellulitis [1]. Diagnosis is often difficult in the early stages when the skin is spared. The infection spreads rapidly, and eventually ischemia from the thrombosis of nutrient subcutaneous blood vessels leads to gangrene of the skin [1], [8].
There is a high incidence of associated chronic disease such as diabetes mellitus, chronic renal failure, leukemia, HIV infection, immunosuppression, malnutrition and alcohol abuse which may contribute to
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