Design and patients. Five patients who developed postradiation sarcomas in the pelvic bones following radiation therapy for carcinoma of the uterine cervix within the irradiated field were evaluated. Pelvic radiographs, computed tomography (CT) and magnetic resonance (MR) imaging were undertaken in all patients. Histologic confirmation of the tumor type was obtained.

Results. Three patients whose tumors were characterized as an osteosarcoma, an angiosarcoma and a malignant fibrous histiocytoma (MFH) showed a large round or oval mass mainly in the sacroiliac joint which extended into the posterior gluteal soft tissues. In a fourth patient an osteosarcoma developed in the central ilium extending widely into the soft tissues both anteriorly and posteriorly, with calcified areas within the extraosseous mass. The fifth patient had a MFH which showed osteolytic destruction of the cortex of the acetabulum, and minimal soft tissue extension. There were no specific features or signal intensity changes on MR imaging to differentiate these cases from primary sarcomas.

Conclusion. Postradiation sarcoma must be considered in patients with uterine carcinoma when a soft tissue mass is seen in the previously irradiated field, especially if the mass is posterior to the sacroiliac joint and the latent period is more than 5 years.