Cystic renal oncocytoma mimicking renal cell carcinoma

Cystic renal lesions are one of the commonly encountered urological conditions. They can be either benign or malignant. The Bosniak classification is employed to differentiate benign cysts from the malignant ones and to recommend treatment options. Bosniak type 4 cysts are mostly malignant. Rarely, benign tumors can be encountered in Bosniak type 4 cysts. We present a 59-year-old female who presented with a hilar Bosniak type 4 cyst in the right kidney. She underwent open exploration of the right renal tumor. The tumor was infiltrating into the renal vessels and could not be separated from the renal vein. In view of preoperative and intraoperative suspicion of malignancy, radical nephrectomy was done. Postoperative histopathological examination revealed the tumor to be an oncocytoma. The benign nature of the cyst could not be conclusively determined by preoperative investigations and intraoperative findings. Postoperative histological examination uncovered the rare cystic presentation of this benign tumor.