Human cystic kidney diseases: epithelial hyperplasia in the pathogenesis of cysts and tumors.

Several examples of human renal cystic disease are associated with tubular epithelial hyperplasia. Micropapillary hyperplasia occurs in autosomal dominant polycystic kidney disease, in localized cystic disease, and in acquired cystic disease; neoplastic or severely dysplastic epithelial hyperplasia occurs in von Hippel-Lindau disease; a histopathologically distinctive epithelial hyperplasia occurs in tuberous sclerosis. In all of these conditions the epithelial hyperplasia appears to be responsible for cyst formation by causing tubular or ductal luminal obstruction, and in all of these conditions, save localized cystic disease (a rare condition with very few reported cases), epithelial hyperplasia imposes an increased risk of malignancy. The risk seems to be highest in patients under treatment with long-term hemodialysis for end-stage kidney disease. Some of these diseases may share common features, but it appears likely that the histopathological differences reflect different features converging on a common result.