The fine structure of Brunn's nests in human bladder urothelium

The aetiology, morphology and clinical significance of Brunn's nests in human bladder urothelium are poorly understood. In the present study, 9% of a population of 100 consenting patients undergoing diagnostic or review cystoscopies were histologically found to have Brunn's nests, although their presence was not detected endoscopically. Of the nine cases, four were diagnosed with cystitis cystica, two with bladder papillomata, one with transitional cell carcinoma and cystitis cystica, and two were considered to be macroscopically normal. Mucosal biopsies were removed from areas unaffected by macroscopic abnormalities. Brunn's nests consisted of rounded collections of cells, whose nuclei contained prominent nucleoli and occasional nuclear bodies. The cytoplasm frequently contained clusters of mitochondria, together with Golgi membranes and cisternae of granular endoplasmic reticulum while small membrane bound vesicles containing electron dense material were present in some cells. Presumptive lysosomes were rarely observed. Thus Brunn's nest cells generally resembled normal urothelial cells in both their nuclear and cytoplasmic fine structure. Brunn's nests were surrounded by a basal lamina and loose connective tissue containing fenestrated capillaries.