Dedifferentiated liposarcoma of the extremities: imaging findings in four patients

Abstract

Objective: The term "dedifferentiated" liposarcoma is used to describe a distinctive lesion in which a well-differentiated liposarcoma is juxtaposed with a high-grade nonlipogenic sarcoma. Dedifferentiated liposarcoma is probably the most common of all the dedifferentiated sarcomas, occurring almost exclusively in the mediastinum, the retroperitoneum, and the inguinal/paratesticular regions. We report the imaging findings in four cases of dedifferentiated liposarcoma of the lower extremities.

Materials and methods: The radiologic images and clinical histories of four patients with histologically verified dedifferentiated liposarcoma were retrospectively studied. The mean age of the patients was 61 years (range, 33-79 years). All lesions occurred in the thigh. Spin-echo MR images were available for review in two cases and CT scans in the two remaining cases. Plain radiographs were available in all cases.

Results: All lesions were large, with a mean maximum size of 24 cm (range, 12-30 cm), and had a significant fatty component radiologically. Both MR and CT showed a well-delineated fatty component of the lesions and a closely apposed nonfatty region. Radiographs showed well-defined bone within one lesion, bone and amorphous calcification in another, and a single punctate calcification in a third. Two patients had a history of excision of a lipomatous lesion in the region of the mass. One patient had pulmonary metastases.

Conclusion: The potential for deep well-differentiated fatty tumors of the extremities to dedifferentiate is not generally recognized. Although the different types of liposarcoma cannot be reliably distinguished with imaging studies, a well-defined nonlipomatous mass juxtaposed with a predominantly fatty tumor is suggestive of a dedifferentiated liposarcoma.