Posterior urethral valves: theoretical considerations on embryological development.

Among congenital urethral malformations, posterior urethral valves represent one of the main causes of severe infravesical obstruction in children, the etiology and embryological development of which remains unclear. Posterior urethral valves of types I and III are supposed to be related to either the persistence of connective tissue along the pathway of migration of the Wolffian duct (type I) or a residual part of the endodermal urogenital membrane (type III). A possible reason for supramontane urethral valves (type II) is seen in the persistence of crest-shaped tissue along the ureter's pathway in embryological development to its final site, although there is some doubt as to the existence of type II valves and they were not seen in the 65 cases of posterior urethral valves in our own material.