Peritoneal Desmoplastic Small Round Cell Tumor on FDG PET/CT.

A 21-year-old man presented with 1-month intermittent abdominal pain and distension. Contrast-enhanced CT and 18F-FDG PET/CT demonstrated diffuse peritoneal thickening and multiple hypermetabolic masses, initially raising suspicion for malignant disease. Biopsy showed nests of small round blue cells within a desmoplastic stroma. Fluorescence in situ hybridization (FISH) confirmed EWSR1‑WT1 gene fusion, establishing the diagnosis of desmoplastic small round cell tumor (DSRCT). This case highlights that DSRCT should be considered in young men with extensive peritoneal involvement, and that molecular confirmation is essential to avoid diagnostic delay.