Misleading aggressive MR imaging appearance of some benign musculoskeletal lesions.

After plain radiography has been performed, magnetic resonance (MR) imaging is considered the modality of choice for the evaluation of suspected musculoskeletal lesions because of its exquisite sensitivity to changes in the signal intensity of marrow and soft tissue. That sensitivity, however, may lead to an overestimation of the aggressiveness and extent of some benign bone lesions, particularly in children. Such lesions include chondroblastoma, osteoid osteoma, eosinophilic granuloma, and stress fractures. Potentially misleading MR features commonly seen include prominent marrow edema, soft-tissue edema, and apparent mass effect adjacent to the bone lesion. Features that these lesions have in common that may explain the MR findings include associated inflammatory reactions caused by the lesions and their occurrence in childhood, when the periosteum is more loosely attached. Knowledge of the potential pitfalls encountered with MR imaging may help explain the discrepancy between the radiographic and MR appearances of these benign lesions and avoid misplaced reliance on MR imaging for a diagnosis. Radiography remains the single most valuable modality in determining a differential diagnosis for bone lesions.