MR imaging of the musculoskeletal soft tissue mass: is heterogeneity a sign of malignancy?

BACKGROUND Magnetic resonance (MR) is considered the imaging modality of choice to evaluate soft tissue lesions. Whether MR imaging can be used to differentiate benign from malignant soft tissue lesions is still controversial. To elucidate this controversy, MR images of 37 patients with soft tissue masses of the musculoskeletal system were reviewed at Christchurch Hospital, New Zealand. METHODS There were 19 benign and 18 malignant lesions. MR images were evaluated with regard to lesion size, border definition, homogeneity, changes in pattern of homogeneity, signal characteristic (signal intensity on T1-weighted, T2-weighted), and demonstration of relation to neurovascular bundle and bone as well as edema in or around the lesion. RESULTS Statistically significant imaging features favoring a diagnosis of malignancy included inhomogeneity at T2-weighted images (p = 0.002) and a change in pattern from homogeneity on T1-weighted images to inhomogeneity at T2-weighted images (p = 0.003). Malignant tumors also had neurovascular or bone involvement in 28% of cases, which was not seen in their benign counterparts. Size, border definition, and edema of surrounding tissues were generally not helpful in distinguishing benign from malignant soft tissue masses. CONCLUSIONS The inhomogeneity of lesions on T2, the change from homogeneity on T1 to inhomogeneity on T2 sequence, and involvement of bone or neurovascular structures are features that may be helpful in differentiating benign from malignant soft tissue masses.