Renal Angiomyolipoma Mimicking a Well-Differentiated Retroperitoneal Liposarcoma

Diagnosing liposarcoma on (peri)-renal mass biopsy: A clinicopathological study of 30 cases

AIMS

Classification of renal neoplasms on small tissue biopsies is in increasing demand, and maintaining broad differential diagnostic considerations in this setting is necessary. When evaluating a renal or perirenal tumour biopsy with sarcomatoid morphology, together with sarcomatoid renal cell carcinoma and sarcomatoid urothelial carcinoma as top diagnostic considerations, it is vital to additionally consider the possibility of well-differentiated and de-differentiated liposarcoma.

METHODS AND RESULTS

This study reports a series of 30 biopsy samples from sites in or around the kidney collected from four institutions in which the correct diagnosis was either well-differentiated or de-differentiated liposarcoma. The majority (26 of 30, 87%) of lesions were accurately diagnosed on biopsy sampling, all of which incorporated testing for MDM2 by immunohistochemistry (IHC), fluorescence in-situ hybridisation (FISH) or a combination of the two as part of the diagnostic work-up. Tumour expression of MDM2 by IHC without confirmatory FISH analysis was sometimes (30%) sufficient to reach a diagnosis, but demonstration of MDM2 amplification by FISH was ascertained in the majority (57%) of biopsy samples. A diagnosis of de-differentiated liposarcoma was not definitively established until resection in four (13%) patients, as no MDM2 testing was performed on the corresponding pre-operative biopsies.

CONCLUSIONS

When a retroperitoneal tumour is not clinically suspected, histological consideration of a liposarcoma diagnosis may be overlooked. Implementation of ancillary immunohistochemical and cytogenetic testing can ultimately lead to a definitive diagnosis in this potentially misleading anatomical location.

A Large Retroperitoneal Liposarcoma Mimicking an Angiomyolipoma on Pre-operative Imaging: A Case Report

Retroperitoneal masses present a diagnostic challenge due to their elusive origin and varied clinical manifestations. Among these masses, retroperitoneal liposarcomas, rare tumors of mesenchymal origin, often grow asymptomatically until compressing surrounding structures, necessitating accurate and early diagnosis. Renal angiomyolipomas (AMLs) have also been reported to mimic retroperitoneal liposarcomas on radiographic imaging, further complicating diagnostic processes. The presented case report describes a rare instance of a large well-differentiated liposarcoma that mimicked a renal angiomyolipoma on imaging in a 58-year-old male patient. The patient initially presented with worsening abdominal distension, early satiety, and left-sided flank pain for the past year. Radiographic imaging revealed a large mixed echogenic lesion measuring 22 x 13 cm in the left kidney with diffuse fat contribution, suspected to be a giant renal angiomyolipoma. The patient underwent selective arterial embolization by interventional radiology. Follow-up imaging eight months later showed an increase in the size of the mass, raising suspicion of a liposarcoma. Surgical resection of the mass and a radical left nephrectomy were performed, with final pathology confirming the diagnosis of a well-differentiated liposarcoma. This case highlights the importance of accurate diagnosis and the potential for liposarcomas to mimic other masses on imaging, despite their rarity.