Imaging description

When a well-differentiated liposarcoma is located in the extremities it can reveal fatty densities on a radiographic examination. This is not the case with a retroperitoneal well-differentiated liposarcoma. Occasionally tumor calcifications or ossifications can be detected radiographically. CT or MRI is essential for making a definitive diagnosis. Both modalities show that the well-differentiated liposarcoma consists primarily of fatty tissue. What differentiates a well-differentiated liposarcoma from a lipoma is the presence of thick septa greater than 2 mm in thickness or nodular non-fatty tissue within the lesion (Figure 77.1). The septa and nodular structures show enhancement on gadolinium-enhanced MR images. It is important to remember that lipomas can be septated, however the septa are thin (< 2 mm). In planning a needle biopsy under CT guidance the radiologist should target areas that contain a high density of thick septa or nodularity to ensure better sampling of the tumor.

Imaging of myxoid liposarcoma is often more difficult than imaging of a well-differentiated liposarcoma. Radiography in myxoid liposarcoma is often negative or shows a non-specific soft tissue mass. CT and MRI may reveal what looks like a large lobulated cystic lesion because of its high content of myxoid tissue. The high water content of the myxoid tissue is represented on MRI with homogeneous low signal intensity on T1-weighted images and intensely high signals on T2-weighted images (Figure 77.2). In this respect a myxoid liposarcoma may be confused with a soft tissue cyst, however gadolinium enhancement will differentiate between a myxoid liposarcoma which shows enhancement following gadolinium injection compared with a cyst which does not enhance. A myxoid liposarcoma with a predominantly round cell component can reveal totally non-specific imaging features on cross-sectional imaging and therefore becomes very difficult to differentiate from other soft tissue sarcomas.