Dedifferentiated liposarcoma of the lower extremity with low-grade dedifferentiation and low-grade osteosarcomatous component.

Dedifferentiated liposarcoma can arise de novo or as a complication of a preexisting well-differentiated liposarcoma. We describe the radiologic and pathologic features of a long-standing liposarcoma with multiple recurrences in a 59-year-old male. Imaging demonstrated a heterogeneous fat-containing mass in the anterior thigh. The adjacent proximal femur showed irregular cortical new bone, eventually followed by intramedullary osteoblastic involvement and pathologic fracture. Histologic assessment at resection revealed dedifferentiated liposarcoma with low-grade osteosarcomatous component. The patient subsequently developed metastatic lesions in the lungs containing osteoid and osteoblastic bone metastases. We discuss the radiologic and pathologic features of this rare entity that, to our knowledge, has previously been reported to directly involve osseous structures in only one other case and discuss the potential pitfalls in diagnosis.