[An atypical multilocular cystic nephroma presenting recurrent lumbago]

A 54-year-old female suffered from repeated flank pain. A large, irregular cystic mass that compressed and distorted the left pelviocalyceal system was found. She underwent left nephrectomy. The cyst arose from the inner zone of the kidney. Although monolocular grossly, it was compatible with the multilocular cystic nephroma on the microscopic examination.