Extensively cystic renal neoplasms in adults (Bosniak classification II or III)--possible "common" histological diagnoses: multilocular cystic renal cell carcinoma, cystic nephroma, and mixed epithelial and stromal tumor of the kidney.

OBJECTIVE(S): To give an algorithm for resolution of extensively cystic renal neoplasms, preoperatively classified in the Bosniak classification as a category II and III.
METHODS: From 1991 to 6/2004, 701 patients with 727 renal tumours were surgically treated at our hospital. Extensively cystic tumours were found in 10 cases. Extensively cystic tumours were defined as multicystic tumours without any solid nodules visible neither on CT, nor grossly in the specimen at operation (the Bosniak classification type II or III).
RESULTS: Seven multilocular cystic renal cell carcinomas, three mixed epithelial and stromal tumour of the kidney and one cystic nephroma were diagnosed on histology. CONCLUSION(S): Extensively cystic renal tumours classified as the Bosniak type II or III correspond histologically to the entities mentioned above (multilocular cystic renal cell carcinoma, cystic nephroma, mixed epithelial and stromal tumour of the kidney). These entities cannot be distinguished one from another on preoperative imaging studies. A preoperative biopsy and intra-operative frozen-section analysis do not lead to a correct diagnosis in many cases. Fortunately, the operative strategy is the same for all these tumours. In such cases, the nephron sparing surgery is indicated, whenever technically feasible, as almost all extensively cystic renal tumours have a good prognosis.