Radiation-induced sarcoma in a patient with nasopharyngeal carcinoma (NPC). A 25-year-old man (patient 23) had undergone irradiation with a total dose of 70 Gy for undifferentiated NPC (arrow in a: computed tomography (CT) scan). Approximately 10 years after radiotherapy, he presented with pain in the right temporal region and exophthalmus of his right eye. Magnetic resonance (MR) imaging demonstrated a contrast-enhanced lesion in the right temporal region with intracranial and orbital invasion (arrow in b: axial contrast-enhanced MR image).One month later, the preoperative CT scan revealed significant enlargement of the lesion (arrow in c). Subtotal resection was performed and postoperative histological examination showed nests and sheets of pleomorphic malignant tumor cells with scattered osteoid formation, consistent with an osteosarcoma (d: hematoxylin and eosin staining, ×100).