The kidney is completely surrounded by tumor, in this case a liposarcoma. The gross features of liposarcoma and normal adipose tissue are at times indistinquishable, as in this case. Usually diagnosed in the fifth to seventh decade of life. Uncommon in children. Tumors are usually large, especially those occuring in the retroperitoneum.
Tumors are usually well-circumscribed, encapsulated and lobulated.
The cut surface is variable depending on the histologic type. Tumors may resemble adipose tissue, may have a gelatinous appearance or may be fleshy and solid with variable areas of necrosis and hemorrhage. Well-differentiated liposarcomas closely resemble adipose tissue with varying degrees of atypical features. Round cell liposarcomas are cellular neoplasms with varying degrees of lipoblastic differentiation. Pleomorphic liposarcomas are cellular neoplasms composed of pleomorphic tumor cells.