# Retroperitoneal Ewing Sarcoma Masquerading as an Intraabdominal Abscess in a Teenager: A Rare Diagnostic Challenge

## TL;DR

A rare case of retroperitoneal Ewing sarcoma in a teenager was initially mistaken for an abscess, highlighting the difficulty in diagnosing this aggressive cancer.

## Contribution

This case report adds to the limited literature on retroperitoneal Ewing sarcoma and underscores the need for improved diagnostic approaches.

## Key findings

- The patient was diagnosed with retroperitoneal Ewing sarcoma after imaging and biopsy confirmed the tumor.
- FISH analysis showed 98% of cells had an EWSR1 gene rearrangement, a key diagnostic marker.
- The case highlights the challenges in early detection due to nonspecific symptoms and delayed diagnosis.

## Abstract

Retroperitoneal Ewing sarcoma is a rare and aggressive extraskeletal variant of Ewing sarcoma, often presenting with nonspecific symptoms that can delay diagnosis. We discuss the case of a 19-year-old male who presented to the emergency room with progressive left abdominal and flank pain. Imaging revealed a retroperitoneal, necrotic mass and biopsy with immunohistochemistry confirmed retroperitoneal Ewing sarcoma with NKX2.2 and CD99 positivity. Fluorescence in situ hybridization (FISH) analysis showed that 98% of cells had an EWSR1 gene rearrangement. For treatment, the patient underwent a CT-guided biopsy and chemotherapy was initiated.

The sometimes-insidious progression of retroperitoneal Ewing sarcoma, coupled with the retroperitoneal space’s ability to accommodate tumors without significant symptoms, often leads to late-stage diagnosis and poor prognosis. This report emphasizes the importance of early recognition and highlights the need for further research into optimal diagnostic protocols and treatment strategies.