A rare case of a giant retroperitoneal lipoma with multiple limb and trunk lipomata without familial multiple lipomatosis

Retroperitoneal lipoma is exceedingly rare, and due to the difficulty in distinguishing between retroperitoneal lipoma and well-differentiated liposarcoma (WDLS), recommendation is en-bloc resection. A 58-year-old male was investigated for scrotal swelling, ultrasound and computed tomography showed a well-defined lipomatous mass occupying much of the left side of the lower abdomen. At laparotomy, a large left-sided retroperitoneal mass was found. Histology reported a 160 mm × 150 mm × 90 mm fatty tumour weighing 1540 g. MDM2 gene amplification was not present on fluorescence in situ hybridization. No significant somatic signatures were identified on whole exome sequencing. Retroperitoneal fatty tumours represent a diagnostic dilemma. Sampling via core biopsy has been recorded at 85% accuracy for WDLS. Positive amplification of the MDM2 gene supports a diagnosis of WDLS; however, a negative biopsy does not exclude the diagnosis due to varied amplification among different cells in the same tumour.