ABSTRACT
Objective To summarize the CT and MRI features of radiation-induced sarcoma (RIS) after radiotherapy in patients with nasopharyngeal carcinoma (NPC).Methods From January 1997 to October 2012,a total of 73 NPC patients with RIS after radiotherapy were confirmed by pathology.The clinical data and imaging findings (CT and MRI findings) were retrospectively reviewed.Of the 73 patients,43 underwent CT examination,24 underwent MRI,and the remaining 6 underwent both CT and MRI scans.Results Fibrosarcoma [45.3％ (33/73)] was the most frequently histologic type,followed by osteosarcoma[31.5％ (23/73)] and malignant fibrous histiocytoma [9.6％ (7/73)].The top three common sites were maxillary sinus [26.7％ (20/73)],followed by the neck soft tissue [17.8％ (13/73)] and mandible[13.7％ (10/73)].The main characteristics of the RIS on CT and MRI were soft tissue masses[78.1％ (57/73)] with an irregular shape and ill-defined margin,or rounded masses with welldefined margin [21.9％ (16/73)].CT of 49 patients showed masses with isodensity or mixed density on precontrast CT.MRI of 30 patients showed lesions with isointensity signal on T1WI and intermediate signal intensity on T2WI.On post-contrast images,65.8％ (48/73) tumors showed markedly homogeneous or inhomogeneous enhancement,23.2％ (17/73) lesions showed moderate enhancement,and 11.0％ (8/73) masses showed mild enhancement.Among the 23 patients with radiation-induced osteosarcomas,78.3％ (18/23) presented tumor bone formation.Conclusions RIS has a characteristic imaging features.Clinical history,tumor sites and serial imaging follow-up are necessary for early detection of RIS in patients with NPC.