Evolving Concepts of Cystic Renal Lesions The Controversy Over Cystic Nephroma and Mixed Epithelial and Stromal Tumor of the Kidney

摘要

A subset of cystic renal lesions with a complex architecture and varying amounts of stroma includes cystic nephroma and mixed epithelial and stromal tumor of the kidney. Both these lesions are rare, and their histogenesis is unclear. Until recently, cystic nephroma was diagnosed in adults and in children,. However, recognition of differences in the clinical phenotype between pediatric and adult cystic nephromas and appreciation of the morphologic spectrum of Wilms tumor has led to the inclusion of pediatric cystic nephroma-like lesions into the spectrum of nephroblastoma. Hence, pediatric cystic nephroma-like lesions are considered to represents the most differentiated end of the spectrum of Wilms tumor. The concept of cystic lesions in adults is still evolving.Currently, cystic nephroma is recognized as an exclusively adult lesion that is composed of thin septa and cysts lined by flattened, cuboidal, or hobnail epithelium. In contrast, mixed epithelial and stromal tumor of the kidney has grossly recognizable spindle cell stroma in which tubules and cysts are embedded. However, most recently, this distinction has been challenged and the similarities between these 2 lesions have been emphasized, suggesting that both lesions may represent opposite ends of the spectrum of the same pathologic entity. In this paper, we present 2 adult cystic lesions: each represents a "classic" example of cystic nephroma and mixed epithelial and stromal tumor of the kidney. The clinical phenotype, morphology, and immunohistochemistry of both lesions are compared. The current literature is reviewed, and the potential relationship between these 2 cystic lesions is discussed.