[Pyomyositis].

A 49 year old man with a palpable femoral tumor was examined by ultrasonography, CT and MRI within five days. Ultrasonography and CT indicated a solid malignant tumor, whereas MRI showed high signal intensity throughout the medial vastus muscle on T2-weighted images and centrally localized areas with low signal intensity on T1-weighted images indicative of pyomyositis. This diagnosis was immediately confirmed at surgery. Prompt diagnosis of pyomyositis is of utmost importance since it can rapidly develop into a life-threatening condition. The present case demonstrates the superiority of MRI in this clinical entity, whereas ultrasonography and CT may be misleading in the early stage.