So-called embryonal hyperplasia of Bowman's capsular epithelium: an immunohistochemical and ultrastructural study.

The so-called embryonal hyperplasia of Bowman's capsular epithelium (EHBCE) is a rather specific lesion occurring in kidneys of patients maintained on chronic dialysis. It consists of poorly differentiated cells proliferating around sclerosed or obsolescent glomeruli. In this study, immunohistochemical and ultrastructural characterization of EHBCE was performed. The poorly differentiated cells in the lesion exhibited a positive reaction for vimentin and a negative one for cytokeratin (PKK 1) and epithelial membrane antigen. On ultrastructural examination, specialized junctions between adjoining cells, microvilli-like structures on their surfaces, and immature basal folds were observed. These observations suggest that the cells of EHBCE may be associated with the anlage of glomerular epithelium. The background in which neoplasms like renal cell carcinoma or atypical epithelium of cyst wall develop in end-stage kidneys of adult patients on long-term dialysis may cause such a proliferation of poorly differentiated cells in young or paediatric age group patients.