Multilocular renal cyst: electron microscopic evidence of pathogenesis.

Two cases of multilocular renal cyst (MRC) are presented with electron microscopic findings. The epithelial cells of the cysts resembled renal collecting tubule cells and not convoluted tubule or Henle's loop cells. Intercystic areas contained only connective tissue elements. Simple MRC appears to be a congenital malformation that results from segmental maldevelopment of the ureteric bud. In some cases of MRC, the intercystic septa contain immature renal elements. The lesion is then called cystic poorly differentiated nephroblastoma (CPDN). However, in both MRC and CPDN, local recurrence or metastases have not been described. Treatment of these lesions should consist of nephrectomy, careful histologic evaluation to rule out obvious foci of Wilms' tumor, and conservative follow-up.