Variant Pseudocystic Desmoplastic Small Round Cell Tumor With Heterologous Mullerian Cysts

A desmoplastic small round cell tumor (DSRCT) presented in a 13-year-old female with an acute abdomen due to torsion of a fallopian tube cyst. She was found to have an incidental 2 cm pedunculated, solid, and multicystic mass attached to the pelvic floor on laparoscopy. The neoplasm had a variably myxoid and spindle cell pattern with nests and cords of small cells, forming pseudocysts, and true cysts lined by ciliated epithelium which were PAX-8+ and ER+/PR+. The tumor had the EWSR1::WT1 fusion. Numerous peritoneal nodules less than 1 cm were noted on repeat laparoscopy 3 months later. These had similar features including the ciliated epithelial cysts. Our case illustrates yet another potential variant pattern of DSRCT with Mullerian-like ciliated epithelial cysts.