[Fatigue fracture as a tumor-simulating lesion. Differential diagnostic delimitation using proton spin tomography]

Fatigue (stress) fractures are due to increased repetitive stresses. The onset of clinical symptoms and the pain characteristic usually are vague; furthermore the radiographic picture shows lesions of different age and therefore may mimic a pattern typical of bone tumors. While for malignant bone tumors early diagnosis, biopsy and initiation of the appropriate treatment is of importance, the biopsy of a fatigue fracture is not only unnecessary, but also may interfere with the healing process. The value of magnetic resonance imaging in the differential diagnosis between tumors and fatigue fractures has therefore been analysed. Five consecutive cases of fatigue fractures have been evaluated from the onset of symptoms for a mean of 19 month (range 3-45 month) of follow-up. The signal pattern with low intensity in the area of the lesion in T1- and T2-weighted images seen in 2 cases has lead to observe the process under immobilization of the affected limb, while because of an increase of the signal intensity from T1- to T2-weighted images as seen in almost all malignant bone tumors biopsy has been performed in 2 cases. In 1 cases no biopsy but close-meshed clinical examinations were performed although there was an increase of the signal. From these observations we conclude that the MRI in fatigue fractures may either show a 'chronic' type of reaction with low signal intensity allowing for the caution observation while in cases with the rather 'acute' reaction with increased signal biopsy usually cannot be avoided in order not to miss a malignant tumor.