A 73-year-old woman presents with abdominal discomfort and flank pain.

Fig. 118.1 Coronal reformatted contrast-enhanced CT image shows a heterogeneous, ill-defined mass in the left perinephric region surrounding the left kidney. The lesion shows areas of fat density and foci of calcifications adjacent to the left kidney.

Dedifferentiated retroperitoneal liposarcoma

• Malignant fibrous histiocytoma
  
• Retroperitoneal lymphoma
  
• Metastases
  
• Retroperitoneal dermoid
  
• Infection (rare)

Liposarcoma is the second most common type of soft tissue sarcoma in adults and is most commonly seen in the 5th decade of life.