Metanephric stromal tumor: a challenging diagnostic entity in children.

A case with a renal mass diagnosed as metanephric stromal tumor is presented. A 6-year-old boy presented with frequently recurring urinary tract infections. He had been followed up at different medical centers for the last 2 years with a 2 × 2 cm simple cyst localized in the inferior pole of the left kidney. At our center, ultrasonography revealed a heterogeneous mass in the left kidney with a central cystic component. The patient underwent operation for left renal mass, and heminephrectomy was performed. The 5 × 4 × 2.5 cm left heminephrectomy specimen showed a partially cystic mass composed of bland spindle cells distributed haphazardly, entrapping tubules and glomeruli and producing fine collarettes around some tubules. The cysts were lined with a 1-layered flat or cuboidal epithelium. Histopathologically, the tumor was diagnosed as metanephric stromal tumor. Metanephric stromal tumor is a rare renal neoplasm of childhood that can present as a cystic mass, and the solid component can go radiologically undetected because of the blurring infiltrative margins. By presenting this rare entity, the authors suggest that this should be included in the differential diagnosis, thereby helping to avoid complications and unnecessary treatment.