Introduction Dedifferentiated liposarcoma (DDLP) was initially defined as a tumor containing differentiated liposarcoma and distinct regions of nonlipogenic spindle cell or pleomorphic sarcoma. Retroperitoneal liposarcomas feature a characteristic appearance with a predominantly fatty component, and cystic liposarcomas are rare. We describe a case of retroperitoneal DDLP predominantly consisting of multilocular cysts. Case Presentation A 77-year-old man previously visited a doctor because an echo scan unexpectedly revealed an abdominal tumor. Contrast computed tomography (CT) disclosed a large multilocular cystic tumor spanning from the left upper abdomen to the retroperitoneum, and poorly marginated soft tissue structures were present around the abdominal aorta, inferior vena cava, pancreas, mesentery, and left kidney. CT also revealed a right lung mass. The soft tissue structures in the retroperitoneal cystic tumor and right lung mass were strongly enhanced on 2-deoxy-2-[fluorine-18] fluoro-d-glucose positron emission tomography, suggesting a malignant retroperitoneal tumor and lung metastasis. CT-guided percutaneous biopsy targeting the left perirenal soft tissue structure was performed, and the tumor was diagnosed as DDLP. Lung metastasis was present, and the retroperitoneal tumor surrounded multiple organs. Therefore, the tumor was not suitable for surgical resection but it was indicated for chemotherapy based on multidisciplinary discussion. Conclusion We experienced a case of retroperitoneal cystic DDLP diagnosed by percutaneous image-guided biopsy and treated appropriately based on the pathological diagnosis.

中文翻译：

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经皮图像引导活检诊断囊性腹膜后去分化脂肪肉瘤一例。

引言 去分化脂肪肉瘤（DDLP）最初被定义为含有分化脂肪肉瘤和不同区域的非脂肪生成梭形细胞或多形性肉瘤的肿瘤。腹膜后脂肪肉瘤具有以脂肪成分为主的特征性外观，囊性脂肪肉瘤很少见。我们描述了一例主要由多房性囊肿组成的腹膜后 DDLP 病例。病例介绍 一名 77 岁的男子此前曾因回声扫描意外发现腹部肿瘤而去看医生。对比计算机断层扫描 (CT) 显示从左上腹部跨越至腹膜后的大型多房性囊性肿瘤，腹主动脉、下腔静脉、胰腺、肠系膜和左肾周围存在边缘较差的软组织结构。CT 还显示右肺肿块。2-脱氧-2-[氟-18]氟-d-葡萄糖正电子发射断层扫描显示腹膜后囊性肿瘤和右肺肿块的软组织结构强烈增强，提示恶性腹膜后肿瘤和肺转移。CT引导下针对左侧肾周软组织结构进行经皮活检，肿瘤诊断为DDLP。存在肺转移，腹膜后肿瘤包围多个器官。因此，该肿瘤不适合手术切除，但经多学科讨论，建议进行化疗。结论 我们经历了一例经皮影像引导活检确诊的腹膜后囊性DDLP，并根据病理诊断进行了适当的治疗。