Multilocular renal cyst. Case report, ultrastructure and review of the literature.

Multilocular renal cyst is an uncommon focal, unilateral, cystic, epithelial lesion of uncertain pathogenesis. Because nephroblastomatous foci have been found on microscopic examination of several of the reported cases, some authors have proposed that multilocular cysts are differentiated and cystic forms of Wilms' tumour. This proposition is analysed and it is concluded that three possibly interrelated lesions may be defined: (1) Wilms' tumours showing cystic differentiation. (2) Lesions macroscopically indistinguishable from multilocular cyst containing variably differentiated nephroblastomatous foci. All such cases have been described in infants. (3) Typical multilocular renal cysts, which have described in children and adults. Review of the literature shows that several cases have been included in the second category solely because of the presence of small intraseptal tubules. Consequent anomalies of interpretation are highlighted and a further case of multilocular cyst in an adult female is reported in which ultrastructural examination, recorded for the first time, confirms the epithelial nature of the cyst lining cells which resemble simplified renal tubular epithelium.