Secondary Peripheral Dedifferentiated Chondrosarcoma

Abstract

Case: In a 54-year-old man, imaging findings suggested a malignant bone tumor having 2 distinct components of the left ilium. Histopathologically, the resected tumor was diagnosed as dedifferentiated chondrosarcoma (CS) arising in secondary peripheral CS. Conclusion: Dedifferentiated CS consists of a high-grade noncartilaginous sarcoma adjacent to a preexisting low-grade CS, among which the peripheral type is extremely rare. Because the bimorphic imaging findings reflected the dedifferentiated area and the CS area, they were considered useful for diagnosis. In addition, the dedifferentiated area was localized to the tumor’s edge, suggesting that the dedifferentiation originated from the cartilage cap.