Surface ultrastructure of the epithelia lining the normal human lower urinary tract

The finding of cells with pleomorphic microvilli in urinary sediments has been proposed as an indicator for urothelial neoplasia. Recently, in addition to such cells, others with less bizarre, non-pleomorphic microvilli have also been found in urothelial cancers, and these cells are similar in appearance to others detected in the urinary sediments of healthy people. When using scanning electron microscopy as a diagnostic tool, these cells are a possible source of confusion. The entire lower urinary tracts from people free of urothelial neoplasia have therefore been examined to delineate the normal surface appearance of all cell types which could appear in the urine. There are 4 predominant cell types: the large, flat squamous cells of the urethral meatus which have abundant microridges; cells with mucus-coated, short, stubby microvilli lining the urethra and renal papilla; immature urothelial cells with chains and ridges of bleb-like processes in the ureters and bladder; and, also in the ureters and bladder, mature urothelial cells with microridges or ruffles. The lining epithelia of the normal urethra and renal papilla may thus contribute cells with non-pleomorphic stubby microvilli to urine sediments, which cannot be differentiated by scanning electron microscopy alone from similar cells derived from urothelial neoplasms. However, the normal complement of cells lining the adult lower urinary tract does not include any with prolific, long, pleomorphic microvilli such as characterize transitional-cell carcinomas of the urothelium.