Lipoma or Liposarcoma? Robotic Resection of a Retroperitoneal Mass

This video demonstrates a robotic excision of a large retroperitoneal lipomatous mass in a 48-year-old female with a known fibroid uterus. Computed tomography was performed for nephrolithiasis, and an incidental 7-cm fatty prominence in the right hemipelvis was found. Retroperitoneal tumours like benign lipomas and low-grade liposarcoma are difficult to differentiate. The latter has a high rate of local recurrence if incompletely resected; therefore, complete resection should be the goal of surgery. The patient underwent robotic-assisted laparoscopy that revealed a large lipomatous mass in the right retroperitoneal space consistent with radiographic imaging. The lipomatous tumour was carefully dissected and resected from the pararectal space without complication. Pathology revealed partially encapsulated, mature adipose tissue consistent with lipoma with negative fluorescent in situ hybridization (FISH) analysis using a dual-colour MDM2/CEN12 probe set, confirming the likely benign behaviour of the mass. Retroperitoneal lipomatous tumours are rare. Distinguishing between lipomas and liposarcomas is a diagnostic challenge both radiographically and intraoperatively. Confirmatory histopathology and, often, molecular pathology is necessary for the final diagnosis. Knowledge of the differing pathology and disease processes of retroperitoneal lipomatous masses, related surgical anatomy, careful surgical technique, and goals for complete excision are imperative for optimal management. © 2021 The Society of Obstetricians and Gynaecologists of Canada/La Société des obstétriciens et gynécologues du Canada