Comparative ureteral microanatomy

Several animals have been used as models for experimental upper urinary tract surgery. Although minipigs have recently gained favor because their upper urinary tract is grossly similar to that of humans, the ureteral microanatomic features of the two species have not been compared. We evaluated the histologic features of human and animal ureters in order to provide addition information regarding experimental models for upper urinary tract surgery. Cross-sections of upper, middle, and lower ureteral segments from human autopsy specimens and animals (farm pig, minipig, dog, sheep, rabbit, and rat) were evaluated after preparation with Masson's trichrome stain. Morphology, computer-assisted morphometry, linear micrometry, and point-count estimation of smooth muscle/connective tissue ratios were assessed. The epithelium was remarkably consistent across all species, both morphologically and in terms of absolute size. The lamina propria was highly vascularized in all species, but the compactness varied with the overall ureteral dimensions. In the muscularis, the relative size and the percentage composed of smooth muscle differed widely among species, as did the ratio of muscularis to lamina propria cross-sectional surface area. Among the species evaluated, the sheep, farm pig, and minipig ureters were the best histologic approximations of the human ureter. Given the difficulties with manipulation of the small sheep ureter, the minipig and farm pig models appear to be optimal for experimental research on upper urinary tract surgery by an endourologic approach.