RESUMEN

Crossed fused renal ectopia (CFRE) is a rare congenital anomaly in which a kidney is located on the opposite side from where its ureter connects to the bladder, merging into the other kidney. It has been linked to other rare congenital malformations, including the VACTERL association (vertebral anomalies, anal atresia, cardiac anomalies, tracheoesophageal fistula, esophageal atresia, renal anomalies, and limb abnormalities), the MURCS association (müllerian ducts, renal, and cervicothoracic spine anomalies), increased incidence of infections, obstruction, cystic dysplasia, and urolithiasis. Although the literature has documented only a small number of cases wherein CFRE coincides with neoplasia, we present the case of a 59-year-old patient with a right ectopic kidney fused to the left one and simultaneous primary renal cell carcinoma. We aim to report and discuss this case and the treatment approach, comparing it with existing literature to enhance our understanding and management of similar occurrences, as partial nephrectomy is uncommon due to the challenging anatomy of these cases.