# A case report and literature review on a large MDM2 negative retroperitoneal/psoas muscle well-differentiated liposarcoma mimicking intramuscular myxoma

## TL;DR

A rare case of a large retroperitoneal liposarcoma mimicking a myxoma is reported, emphasizing the need for comprehensive diagnosis.

## Contribution

Highlights diagnostic challenges of MDM2-negative WDLPS mimicking myxoma through a case report and literature review.

## Key findings

- Presented a 22 cm MDM2-negative WDLPS in the psoas muscle mimicking intramuscular myxoma.
- Emphasized the importance of integrating clinical, radiologic, and pathologic data for accurate diagnosis.
- Demonstrated that WDLPS can lack macroscopic fat and MDM2 amplification, complicating diagnosis.

## Abstract

Well-differentiated liposarcoma (WDLPS) typically presents as a large soft tissue mass in the retroperitoneal region. Amplification of the MDM2 gene is considered the gold standard for pathologic diagnosis. We present a case of 22 cm large intramuscular mass, located in the psoas muscle of the retroperitoneum. No macroscopic fat was identified on imaging, and the lesion featured extensive myxoid stroma, closely mimicking an intramuscular myxoma on both radiological and histopathological evaluation from biopsy sample. Final diagnosis was however revised to MDM2-negative WDLPS.

This case highlights the diagnostic challenge posed by WDLPS with extensive myxoid stroma lacking MDM2 amplification and macroscopic fat on imaging. Accurate diagnosis relies on the integration of clinical, radiologic, and pathologic data, as well as thorough sampling of the tumor.