Are these tumours usually large or small at presentation?
Typically large ( > 10 cm ) as presentation only occurs when a palpable mass is identified or when symptoms develop from the mass effect of the large retroperitoneal mass.
What are the characteristic imaging appearances?
Appearances can vary, but a retroperitoneal mass, with variable amounts of fat and soft tissue ( can be only small nodules ).
Huge right-sided retroperitoneal mass - largely composed of fat, but also several soft tissue components. The mass is displacing the right kidney anteriorly, as well as the liver and bowel anteromedially.