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Findings: T2 weighted axial images of the upper (A), mid (B) and lower (C) thigh are presented. In the upper thigh extensive deep fascial edema is seen between the sartorius muscle and the adjacent vastus medialis and intermedius muscles. The deep fascial edema surrounds the neurovascular bundle and bright signal is seen tracking along the deep surface of the sartorius muscle. The most extreme changes are present in the mid thigh where a large amount of fluid surrounds the sartorius muscle. Fluid is also present deep to the gracilis muscle and deep fascial edema is identified between the adductor magnus muscle and the hamstring muscles. Extensive edema is present within the vastus intermedius and medialis muscles and throughout the adductor magnus muscle. Inflammatory but not necrotic muscle was identified at surgery. Cultures were positive for Group A streptococci.

Diagnosis: Necrotizing fasciitis.

Discussion: Necrotizing fasciitis is a life threatening infection of the deep fascia with rapid progression and a high incidence of mortality. Early diagnosis is essential. Hyperintense signal of the deep fascia on T2-weighted images with or without associated changes in the adjacent muscle is considered diagnostic for necrotizing fasciitis in the appropriate clinical scenario. However, these findings are not specific for the diagnosis. Necrotizing fasciitis is typically a clinical diagnosis. MR may be useful in questionable cases and may be useful for preoperative planning, especially when there is extensive chest or abdominal wall involvement.

References:
Rahmouni A, Chosidow O, Mathieu D, et al. MR Imaging in Acute
Infectious Cellulitis. Radiology. 1994;192:493-496.

Loh N, Ch'en IY, Ch'en LP, Li KC. Deep Fascial Hyperintensity in
Soft-Tissue Abnormalities. Radiology. 1995;197:296.

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