# Retroperitoneal Myolipoma with Hip Invasion: A Case Report

## TL;DR

A rare case of a retroperitoneal myolipoma in a young boy that invaded the hip was successfully treated with surgery.

## Contribution

Reports a previously unrecorded case of myolipoma in a male child with hip infiltration.

## Key findings

- Myolipoma was diagnosed in an 11-year-old male with hip involvement using MRI and confirmed via histology.
- Surgical excision was effective without complications, and the histology showed mature adipose tissue and lymphocyte infiltration.
- This case highlights the importance of considering myolipoma in the differential diagnosis of retroperitoneal masses in children.

## Abstract

Background and Clinical Significance: Myolipoma is a rare benign tumor, typically found in the retroperitoneum and characterized by a combination of mature adipocytes and well-differentiated smooth muscle cells. Myoplipomas usually present a delay in diagnosis due to the painless and slow-growing clinical behavior; therefore, the lesion can reach a large dimension with challenging treatment. Case Presentation: We present the case of a retroperitoneal myolipoma infiltrating the left hip of an 11-year-old male. It was suspected based on magnetic resonance imaging. The patient has been successfully treated with surgical excision without complications. Histological examination revealed mature adipose tissue infiltrating smooth muscle cells. The muscle fibers appeared normal, while the dense connective tissue was infiltrated by clusters of mature lymphocytes. Conclusions: Although myolipoma is extremely rare in male children and has never been reported to infiltrate the hip, it should be considered in the differential diagnosis of fat-containing retroperitoneal masses.