# A Rare Case of Retroperitoneal Tumefactive Fibroinflammatory Lesion Related to IgG4-Sclerosing Disease

## TL;DR

A rare case of a retroperitoneal mass caused by IgG4-related disease was identified through imaging and confirmed with histology.

## Contribution

This case highlights a rare manifestation of IgG4-related disease as a mass-like lesion rather than typical diffuse fibrosis.

## Key findings

- A 49-year-old man had a retroperitoneal mass confirmed by MRI with concentric circle patterns.
- Histological analysis confirmed the lesion was IgG4-related fibroinflammatory disease.
- This case expands the known clinical spectrum of IgG4-related disease.

## Abstract

We present a unique case of a retroperitoneal tumefactive fibroinflammatory lesion related to IgG4-sclerosing disease; it is a rare manifestation of the IgG4-related disease, which usually causes diffuse fibrosis when located in the retroperitoneum, rather than mass-like lesions. A 49-year-old man presented to the emergency department complaining of abdominal pain and vomiting. Subsequent testing with abdominal ultrasound, CT, and MRI revealed a large retroperitoneal mass of unknown origin, heterogenous, with a concentric circles pattern best visualized in MRI. The lesion was resected, and the histological and immunohistochemical studies revealed an IgG4-related tumefactive fibroinflammatory lesion of the retroperitoneum.