A Multiloculated Mirage: Imaging Diagnosis of a Pediatric Cystic Nephroma.

Cystic nephroma (CN) is an uncommon benign pediatric renal neoplasm composed of multiloculated cysts separated by fibrous septa, lacking solid or blastemal elements. It occurs primarily in toddlers, often presenting as an asymptomatic abdominal mass. CN lies at the benign end of the spectrum that includes cystic partially differentiated nephroblastoma (CPDN) and Wilms tumor. We report a case of pediatric CN with detailed imaging and clinical correlation to highlight its distinguishing features. In this report, we present a case of a one-year-old boy who presented with a three-month history of a left-sided abdominal mass. Ultrasound showed a well-circumscribed multicystic lesion at the left kidney's lower pole, composed of anechoic loculi with thin septa (no solid component or vascularity). Contrast-enhanced CT confirmed a large (≈11 × 9 × 8 cm) encapsulated multiloculated cystic mass arising from the left kidney's lower pole, with enhancing thin septa and herniation of cysts into the pelvicalyceal system; no enhancing nodules or calcifications were seen. The patient underwent left nephroureterectomy; grossly, the specimen showed numerous clear-fluid cysts separated by fibrous septa. Microscopically, cysts were lined by flattened-cuboidal epithelium with focal hobnail change, and fibrous septa contained only mature stroma and inflammation, with no blastema or immature elements - consistent with CN (resection margins and sampled lymph nodes were free of tumor).