Multiple renal masses in patients with renal cell carcinoma: diagnostic pitfalls and surgical implications.

Additional renal masses were found in the same or contralateral kidney in 41 of 131 patients with renal cell carcinoma. In 35 of the patients the additional renal masses were simple renal cysts situated in the kidney contralateral to the renal cell carcinoma in 16 patients, in the same kidney in 11 and bilaterally in 8 patients. Four patients had bilateral renal cell carcinomas. One patient had polycystic kidney disease as well as renal cell carcinoma and another patient had a benign tumour in the contralateral kidney. In 3 of the 30 patients with additional renal masses in the kidney contralateral to the renal cell carcinoma the radiologic examinations were insufficient to exclude malignancy. Only explorative surgery could establish a true diagnosis of these masses.