THE ROLE OF MR IMAGING FOR FOLLOWING AGGRESSIVE AND MALIGNANT SOFT TISSUE TUMORS AFTER RESECTION, RADIATION THERAPY, AND CHEMOTHERAPY

Shapeero LG ^1,2, Vanel D.³, (1.Uniformed Services University, Bethesda, MD 20814, 2.Walter Reed Army Medical Center, Washington D.C., 3. Institut Gustave Roussy, Villejuif, France)

Objective: To develop a magnetic resonance (MR) imaging algorithm for evaluating aggressive and malignant soft tissue tumors after surgery, radiation therapy, and chemotherapy.

Methods and Materials: MR studies were evaluated on 302 patients with soft tissue sarcomas or aggressive fibromatosis after surgery, external beam radiation therapy, brachytherapy, and chemotherapy. MR studies included T l and T-2 weighted MR sequences with fat saturation, standard contrast-enhanced T1- weighted sequence, and dynamic contrast-enhanced MR sequences with subtraction and color-encoding. All patients had either surgical confirmation or 2-5 year follow-up.

Results: The T2-weighted sequence was the most useful initial sequence for excluding recurrence. Low signal intensity at the site of the surgical resection, external beam radiation and brachytherapy signified fibrosis without recurrence. Although the pristine malignant fibrous histiocytoma or aggressive fibromatosis may present as a homogeneous or heterogeneous low signal intensity mass on T2-weighted sequence because of collagen content, all recurrences demonstrated heterogeneity with areas of high signal intensity. Diffuse high signal intensity without mass represented postoperative or post-irradiation changes. High signal intensity masses on T2- weighted MR imaging were not specific. Standard static contrast-enhanced MR imaging distinguished the non-enhancing hygroma or hematoma from the recurrent tumor and inflammatory pseudotumors but could not differentiate recurrences from the less common inflammatory pseudomass. Our new technique, dynamic contrast-enhanced MR imaging, because of its temporal resolution and post-processing techniques of subtraction, parametric color-encoding, and time intensity curves, allowed separation of enhancement kinetics of MR contrast media in tumors from those in postsurgical, post-irradiation, and postchemotherapeutic changes. Dynamic contrast-enhanced MR imaging differentiated the early enhancing recurrence from the late-enhancing pseudotumor and inflammation and distinguished the early-enhancing viable tumor in the poor responder from the late-enhancing nonviable tumor in the good responder after chemotherapy.

Conclusions: An organized algorithmic MR imaging approach is important for consistent imaging follow-up evaluation of patients with aggressive and malignant soft tissue tumors. When the T2-weighted sequence shows low signal intensity or diffuse high signal intensity, the study is negative and complete. However, a high signal intensity mass needs further study. Dynamic contrast-enhanced MR imaging, which can demonstrate early contrast kinetics, should be the final step to distinguish the rapidly enhancing recurrence from the slowly enhancing pseudomass after resection and radiation therapy and the poor responder from the good responder after chemotherapy.