Obstruction and normal recanalization of the ureter in the human embryo. Its relation to congenital ureteric obstruction.

In this work, after the study of 45 normal human embryos of 5-55 mm from vertex to coccyx, it is shown that the ureteric ducts, which in the first phases of development are permeable (embryos of 5-13 mm), constantly undergo a process of obstruction and posterior recanalization of their lumen, which takes place when they are from 14 to 22 mm. These processes begin in the middle zone of the ureters and progress proximally and distally until they cover its entire length, for which these ducts, which in embryos of approximately 17 mm in length form solid cords, but in the embryos of 23 mm are totally permeable. This obstructive process is found in relation to atrophy and loss of activity of the mesonephros, while that of recanalization follows the intense longitudinal growth of the ureters in this phase of development. These modifications, which the ureteric lumen normally undergoes during its embryonic development, are of great importance for correct interpretation of the pathogenic mechanism of congenital ureteric strictures and valves.