[Coexistence of cyst and tumor in the same kidney: a case report]

A case of renal cyst associated with renal tumor is presented herein. A 40-year-old male patient visited our outpatient clinic for left renal cyst which had been found by ultrasonography on routine clinical examination. CT scan demonstrated an irregular area in the cyst wall measuring about 2 cm in thickness which showed enhancement of density with contrast medium. Magnetic resonance imaging (MRI) also demonstrated a round mass with abnormal signal on the cyst wall, protruding into the cyst cavity. Transabdominal radical nephrectomy was performed on 13 July 1987, and to the resected kidney was attached a cyst measuring 7 cm in diameter in the lower pole. Grossly, the cyst contained amorphous red-brown material which turned out to be old blood clots and the wall harbored a tumor (3.0 x 2.5 cm). Histologically, the tumor was renal cell carcinoma, the surface of which was covered with necrotic tissue. The coexistence of renal cyst and tumor is rare and 62 cases were collected from the Japanese literature including our case, and discussion was made in relation to the etiological factors.