What are the CT and MRI features of a retroperitoneal sarcoma?
Retroperitoneal sarcoma typically presents as a large retroperitoneal mass that may contain fat, soft tissue, myxoid tissue, cystic/necrotic change, hemorrhage, and/or calcification. Fatty components have attenuation and signal intensity properties similar to macroscopic fat located elsewhere in the body and when present indicate presence of a liposarcoma. Soft tissue components have soft tissue attenuation and in general low-intermediate T1-weighted and intermediate-high T2-weighted signal intensity relative to skeletal muscle with variable amounts of enhancement. Myxoid tissue and cystic/necrotic change both have fluid attenuation and very high T2-weighted signal intensity, although the former enhances, whereas the latter does not. Hemorrhagic areas typically show soft tissue attenuation (30 to 70 HU) and high T1-weighted signal intensity but do not enhance. Calcifications appear as very high attenuation foci on CT and are sometimes seen as very low signal intensity foci although they are much more difficult to visualize on MRI.