Liposarcomas are rare malignant tumors arising from adipose tissue, with dedifferentiated liposarcoma being an aggressive subtype. Retroperitoneal liposarcomas pose diagnostic and therapeutic challenges due to their deep location and potential for extensive invasion. This report presents a 76-year-old female with a dedifferentiated liposarcoma involving the right kidney, emphasizing diagnostic and management complexities.

Case Presentation A 76-year-old female presented with sudden-onset right upper abdominal pain. She had a history of anemia, prediabetes, hypertension, and hyperlipidemia. Abdominal CT identified an 8.5×5.5 cm hypodense lesion in the right perirenal region. CT-guided drainage revealed dark-red fluid, prompting further evaluation. Recurrent cyst formation led to multiple percutaneous nephrostomy (PCN) insertions. Due to rapid cyst progression and persistent symptoms, laparoscopic renal cyst unroofing was performed on December 4, 2024. Pathology suggested malignancy, raising concerns of a more aggressive underlying disease. Subsequent imaging revealed a large 13.7×20.8×23.6 cm cystic tumor originating from the right kidney, potentially invading the liver. The patient underwent a right radical nephrectomy on February 13, 2025. Intraoperative findings included extensive adhesion and suspected liver invasion. Pathological examination confirmed dedifferentiated liposarcoma with retroperitoneal involvement. Postoperatively, the patient experienced persistent bloody drainage (700–800cc/day), requiring prolonged infection control with cefuroxime. Hypercalcemia raised concerns for bone metastasis, leading to the initiation of calcitonin therapy. Additionally, a large cystic mass in the renal fossa necessitated CT-guided drainage, revealing malignant peritoneal fluid. Given disease progression, the patient received her first course of palliative chemotherapy with doxorubicin liposome on March 17, 2025, alongside nutritional and hydration support.

Dedifferentiated liposarcoma is aggressive, with high recurrence and poor prognosis. It often mimics renal cell carcinoma, complicating diagnosis. Complete surgical resection remains the best treatment but is challenging due to tumor invasion. Postoperative management, including drainage, infection control, and palliative care, plays a key role in patient outcomes.