Challenging differential diagnosis between lipoma and well-differentiated liposarcoma in the retroperitoneum. A case report.

: Liposarcomas are the most common type of sarcomas arising in the retroperitoneum. Retroperitoneal lipomas are extremely rare. They should be distinguished from well-differentiated liposarcomas in order to provide the appropriate treatment. A 53-years-old male was admitted with the presence of a palpable mass in the upper abdomen. Contrast enhanced computerized tomography (CT) of the abdomen and pelvis showed a 20x12 cm mass arising in the retroperitoneum and inglobing the celiac and superior mesenteric trunks. Because of unresectability an open surgical biopsy was performed. Histological examination showed the presence of adipose tissue with diffuse liponecrosis without definitive features of neoplasia. At six-month follow-up a CT documented an increase of the tumor to 22x13 cm. The mass was stable at the CT, performed at 1-year follow-up. Given the impossibility to distinguish well-differentiated liposarcomas from lipomas and the in the present case of unresectable retroperitoneal mass, an observational follow-up was a justified.