Sonographically detected malignant transformation of a simple renal cyst

The clinical course is reported of a simple renal cyst which developed into a septated renal cyst, and finally to a cystic renal cell carcinoma. A 49- year-old man, who had been diagnosed as having a renal cyst, was found by r epeated ultrasonography over 6 years to have solid components developing wi thin the cyst. Radical nephrectomy was performed and pathological examinati on confirmed cystic renal cell carcinoma (RCC). This case clearly shows a n atural history of malignant transformation from a simple renal cyst, and em phasizes that careful follow-up of renal cysts, especially of complicated r enal cysts, is mandatory for successful treatment of RCC.