Histopathology of the nonrefluxing megaloureter: a clue to its pathogenesis.

We examined 23 nonrefluxing megaloureters histopathologically. In 18 ureters (group 1) the major anomalies were seen only in the ureterovesical junction, where the condition was characterized by more than well developed muscularity of the ureteral sheaths beside hitherto documented structural anomalies in the intravesical narrowed segment of the ureter. However, the ultrastructure of individual muscle cells was normal in the ureterovesical junction and the dilated portion. In the other 5 ureters (group 2) maldeveloped muscle cells scattered in large amounts of connective tissue were seen in the dilated portion, while in the nondilated narrow segment muscle structure was almost normal by light and electron microscopy. It was conjectured that the pathogenesis of megaloureter in group 2 resides not so much in the ureterovesical junction but more in the dilated ureteral wall, where the lack of actin filaments was documented. In group 1 ureteral sheaths were incriminated to have an additional role in the genesis of ureteral obstruction at the ureterovesical junction.