Iliopsoas myositis mimicking appendicitis: MRI diagnosis.

Myositis of the truncal muscles can closely mimic acute appendicitis. Myositis is the early stage of muscular infection. It is characterized by diffuse muscular pain and swelling without a distinct mass. Early diagnosis of myositis improves the outcome and surgical debridement is usually avoided. Pyomyositis, the advanced stage of the disease, can be diagnosed by MRI examination. We present a case of early bacterial myositis that was diagnosed by MRI.