MRI in necrotizing fasciitis of the extremities.

[pyomyositis]

Necrotizing fasciitis is a life-threatening soft -tissue infection of bacterial origin , which involves mainly the deep fascia . Early recognition of this condition may be hampered by the uncommon nature of the disease and non-specificity of initial clinical signs and symptoms in less fulminant cases , making the role of imaging important . MRI is the most useful imaging modality in the diagnosis of necrotizing fasciitis . The presence of thick (>3 mm ) hyperintense signal in the deep fascia (particularly intermuscular fascia ) on fat-suppressed T 2 weighted or short tau inversion-recovery images is an important marker for necrotizing fasciitis . Contrast enhancement of the thickened necrotic fascia can be variable , with a mixed -pattern of enhancement being more commonly encountered . Involvement of multiple musculofascial compartments increases the likelihood of necrotizing fasciitis . It is important to remember that T 2 -hyperintense signal in the deep fascia is not specific to necrotizing fasciitis and can also be seen in cases such as non-infective inflammatory fasciitis or muscle tear . In this pictorial essay , we aim to review the MRI findings in necrotizing fasciitis , discuss its limitations and pitfalls and identify differentiating features from non-necrotizing soft -tissue infections , such as cellulitis and infective myositis /pyomyositis , conditions which may clinically mimic necrotizing fasciitis .