The Classification of Renal Cystic Diseases and Other Congenital Malformations of the Kidney and Urinary Tract

Abstract

Renal cystic diseases and congenital abnormalities of the kidney and urinary tract comprise a heterogeneous group of lesions whose pathogenesis has eluded physicians for centuries. Recent advances in molecular and genetic understanding of these diseases may provide the solution to this riddle. The formulation of an effective classification system for these disorders has been elusive but is needed to introduce order while providing a conceptual framework for diagnosis. This review discusses the evolution, beginning in the 19th century, of postulates regarding the pathogenesis of cystic and developmental renal diseases. Selected classification systems proffered during this period are discussed in pursuit of an ideal classification schema that would account for morphologic features and their clinical importance, with logical links to pathogenesis and treatment. Although this remains an elusive target, its general outline is becoming clearer. A classification approach favored by the author is presented, which incorporates many of the strengths contained in several previous classifications. Genetic-and molecular-based postulates regarding the pathogenesis of the renal cystic and developmental diseases have implicated mutated master genes and the modification of genes that are crucial in renal development and genes that are central to the sensory effects of the renal tubular primary cilium on cell physiology. These scientific advances provide pathogenetic links between morphologically and genetically distinct entities and certain cystic and neoplastic entities, associations that seemed implausible not long ago. These advances may eventually provide the basis for future classification systems while suggesting targets for therapeutic approaches in the prevention and treatment of these diseases.