Major controversies still exist regarding the terminology, the etiology and the pathogenesis of congenital obstructive diseases of the ureter. To try to provide some additional information to this controversial subject, a comparative study of ureteral development in rat and human embryos, using light and electron microscopy, has been performed. During fetal development we observed and demonstrated the existence of obstructive phenomena, both at the level of the ureterovesical junction (Chwalla's membrane) and along the ureter. At the end of the embryonic period, the ureter undergoes a physiologic recanalization process.

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