The development of the common nephric duct and its significance in upper urinary tract abnormalities

Abstract

Failure in the process of differentiation of the mesonephric duct is thought to be the cause of upper urinary tract abnormalities. The common nephric duct, the caudal portion of the mesonephric duct between the ureteral bud and its opening into the urogenital sinus, seems to play a central role in the development of this region. However, detailed morphologic studies of the common nephric duct cannot be found in the literature. Therefore, most theories about the embryogenesis of upper urinary tract abnormalities are highly hypothetical. We studied the development of the common nephric duct in rat embryos between the 11th and 17th days of gestation by scanning electron microscopy: in contrast to previous views, the common nephric duct can be discerned as an isolated structure for a long period. During this time the ureter is rotating around the axis of the common nephric duct, thus reaching its normal craniolateral position relative to the mesonephric duct. Incorporation into the urogenital sinus does not take place until this rotation is complete. These investigations provide exact data on the normal development of the common nephric duct in this critical period of development.