An unusual case of multilocular cystic nephroma with prominent renal pelvis involvement.

Multilocular cystic nephroma (MCN) is a relatively rare, benign tumor of uncertain etiology. It typically arises from the renal parenchyma and is often treated with nephrectomy. We report a case of MCN with unusual prominent renal pelvis extension. A left nephrectomy was performed. A multilocular cystic lesion was found in the removed specimen, which had a direct tumor extension into the renal pelvis. There were no signs of malignancy. The tumor extension into the renal pelvis has been found in very few reports. This growth pattern might be one of the characteristics of this benign renal tumor.