Differentiation of benign and malignant musculoskeletal tumors: potential pitfalls with MR imaging.

Magnetic resonance (MR) imaging is the most sensitive and accurate imaging technique for evaluation of musculoskeletal tumors. With increasing clinical experience, however, an overlap between the classic characteristics of benign and malignant tumors is frequently observed. In a prospective analysis of 87 consecutive cases of musculoskeletal tumors, the malignancy of skeletal lesions was correctly assessed with MR imaging in 55% of the cases. In 39% of the cases, the malignancy of skeletal lesions was overestimated with MR imaging. Correlation with plain radiography is extremely important in such cases and would have resulted in correct assessment of 73% of the skeletal lesions. For soft-tissue lesions, a large variability is found in the benign versus malignant appearances of lesions on MR images, with poor correlation between classic benign characteristics and the benignity of the lesion (17% of cases). The exceptions are hemangiomas and lipomas, which have characteristic appearances on MR images. Knowledge of potentially misleading appearances of musculoskeletal tumors on MR images allows more accurate diagnosis of such tumors.