Dedifferentiated liposarcoma of the retroperitoneum with osteosarcomatous component: report of two cases

We describe two cases of ossified soft tissue tumors of the retroperitoneum. Computed tomographic and magnetic resonance imaging both revealed retroperitoneal masses consisting of two components—densely ossified and lipid-rich components. In one case, a 50-year-old man, a histological diagnosis of dedifferentiated liposarcoma with osteosarcoma was made based on the needle biopsy of the two components. In another case, a 54-year-old man, surgical resection of the complex perirenal mass was performed and the same diagnosis was made. Although an ossified component represent high-grade lesion, the fatty component is an important clue to the diagnosis of dedifferentiated liposarcoma. The imaging features may be similar to those of malignant mesenchymoma, which is not a currently used term.