Objective  To investigate the computed tomography (CT) and magnetic resonance imaging (MRI) features of retroperitoneal dedifferentiated liposarcoma (DDL), and improve the understanding of DDL and the accuracy of preoperative diagnosis.

  Methods  Clinical and imaging features of 25 patients with retroperitoneal DDL from Tianjin Medical University Cancer Institute & Hospital, confirmed by pathology from January 2012 to June 2022, were retrospectively analyzed.

  Results  Among 25 cases of retroperitoneal DDL, 19 and 6 had single and multiple tumors, respectively and 10 and 15 were oval and irregular shaped tumors, respectively. Most lesions had unclear boundaries, with 15 cases invading the surrounding tissues and organs. Small vessel shadows were visible in 15 cases, while calcifications or ossifications were observed in 7 cases, and cystic necrosis was observed in only 3 cases. Enhanced scanning exhibits a centripetal and progressive continuous augmentation characteristic defined as “slow in and slow out.” According to its manifestations in CT and MRI, it can be divided into two types: type I (soft tissue mass type), where the tumor has a soft tissue component with no fat content (14 cases); and type Ⅱ (fat containing), where the tumors exhibit both soft tissue and adipose components, most of which are clearly defined and rarely present in a mosaic shape. In abnormal fat areas, cord-like fibrous septa can be seen. Among them, the intratumoral fat composition <50% was Ⅱa type (10 cases). Intratumor fat composition ≥50% was type Ⅱb (1 case).

  Conclusions  Combined with imaging classification, a comprehensive analysis of the CT and MRI imaging characteristics of retroperitoneal DDL is of great value for its preoperative qualitative diagnosis.