Renal Cell Carcinoma in Crossed Fused Renal Ectopia: A Case Report of a Rare Congenital Renal Fusion.

Crossed fused renal ectopia (CFRE) is a rare congenital renal fusion anomaly in which both kidneys are located on the same side of the body and are usually fused. Simultaneous occurrence of primary renal cell carcinoma (RCC) in CFRE represents a rare entity. Although CFRE may remain asymptomatic, it can be associated with complications such as urinary tract infections, obstruction, calculi, rarely malignancy, and tumors within the fused kidneys, which are exceptionally rare. Although the literature reports only a very small number of cases of CFRE coexisting with RCC, we present a case of a 46-year-old man with CFRE and simultaneous RCC detected on contrast-enhanced computed tomography. Radiological imaging demonstrated that the right kidney was ectopically located in the left iliac region, inferior to the left kidney, with a fused upper pole. Further, a CFRE with a large necrotic renal tumor involving both kidneys was also observed, which suggests RCC within a fused ectopic kidney. Upon these radiological features, total nephrectomy of fused kidneys, hemodialysis afterward, and then renal transplant was decided.