Fused right S-shaped kidney incidentally detected on multidetector CT during staging of periampullary adenocarcinoma: A case report

Supernumerary kidney is an uncommon congenital renal anomaly with complex vascular and collecting-system anatomy, making accurate preoperative imaging essential for diagnosis and surgical planning. We report the case of a 58-year-old man who underwent contrast-enhanced CT for staging of periampullary adenocarcinoma, which incidentally revealed an ipsilateral fused supernumerary kidney with an S-shaped configuration. Imaging demonstrated two fused right renal moieties with separate arterial supplies, distinct pelvicalyceal systems, distal ureteric fusion, and a common right renal vein. An associated undescended right testis was also identified. Multiplanar and three-dimensional CT reconstructions enabled detailed delineation of the renal vascular and collecting-system anatomy. This case highlights the pivotal role of multidetector CT in diagnosing and characterizing complex renal fusion anomalies and in defining variant vascular and ureteric anatomy, thereby facilitating accurate preoperative assessment and safe surgical planning.