A rare lesion of the retroperitoneum, liposarcomas are usually very large at presentation and tend to displace adjacent structures as in the above image (bowel is displaced to the right abdomen). The lesions demonstrate fat attenuation on CT, high signal on T1WI, low signal on T2WI, and dark signal on fat suppression sequences. Calcification or ossification within the lesion usually indicates poor prognosis. Since lipomas generally do not occur in the retroperitoneum, liposarcoma should be considered when a retroperitoneal fat containing lesion is seen.
Craig WD, Fanburg-Smith JC, Henry LR, et al. Fat-containing lesions of the retroperitoneum: radiologic-pathologic correlation. Radiographics 2009;29:261-90.