MR imaging of malignant soft-tissue tumors.

Nearly 6000 cases of soft-tissue sarcoma are diagnosed annually. Many are evaluated with MR imaging, which, because of its superior tissue contrast, has become the most important tool for detecting, staging, and monitoring treatment of the primary tumor. Although irregular margins, invasion of bone, and vascular encasement are indicators of soft-tissue malignancy, sarcomas may also be localized and well-circumscribed. Regardless of their histology, most soft-tissue sarcomas are similar in intensity to muscle on T1-weighted images and intermediate to high signal relative to fat on T2-weighted images. The addition of paramagnetic contrast agents can help differentiate between recurrent primary tumor and postoperative fluid collections.