[MR imaging of fatigue fractures: characteristics and value for differential diagnosis]

The magnetic resonance (MR) appearance of five fatigue fractures was analyzed in an attempt to isolate characteristic MR findings which would facilitate the differentiation of this entity from bone neoplasms and osteomyelitis. The bone lesions reviewed for comparison included three osteoid osteomas, eight osteosarcomas, two malignant lymphomas and four osteomyelitis. Four characteristics useful for differentiation were found: 1) All fatigue fractures showed a smooth and continuous periosteal reaction with a superficial layer of high signal intensity on T 2-weighted images, while all malignant bone tumors and osteomyelitis showed irregular, interrupted or undetectable periosteal reaction, and osteoid osteomas showed no superficial high signal on periosteal reactions. 2) In all fatigue fractures and osteoid osteomas, abnormal signals in the bone marrow were ill defined, whereas they were well defined in all bone neoplasms and one of four osteomyelitis. 3) None of the fatigue fractures or osteoid osteomas was associated with extraosseous components. 4) Fatigue fractures showed little signal change in the surrounding soft tissues, while most of the bone tumors and osteomyelitis were accompanied by high signal in the adjacent soft tissues on T 2-weighted images. These MR characteristics are helpful in differentiating fatigue fracture from bone neoplasms and osteomyelitis, enabling unnecessary surgical procedures to be avoided.