CT findings of retroperitoneal malignant mesenchymoma.

Malignant mesenchymoma (MM) is a rare mesenchymal neoplasm which, by definition, demonstrates at least two distinct types of malignant mesenchymal differentiation. We present the computed tomographic (CT) findings of a 42-year-old female with a pathologically proven retroperitoneal MM consisting of osteoid production combined with foci of liposarcoma and Kaposi sarcoma. MM should be considered along with extraosseous osteosarcoma and teratoma in the differential diagnosis for unusual large heterogeneous retroperitoneal masses with massive calcification.