Cystic renal cell carcinoma arising from multilocular cystic nephroma of the same kidney.

Multilocular cystic nephroma is an uncommon benign entity grouped among the cystic non-genetic diseases. It is characterized by variable-sized, non-communicating cysts separated by irregular thin walled septa. Though multilocular cystic nephroma is usually considered a benign lesion, malignant changes in the cysts should not be overlooked.