Embryology and pathophysiology of epispadias and bladder exstrophy

The mesenchyme from the primitive groove, migrating, grows between these two layers, strengthening the poductal region during the regression of the cloacal membrane. Before the rupture of the cloacal membrane, the urelectal fold joins it, dividing the cloaca into urogenital and anal components. As a result of rupture of the membrane, a urogenital (urogenital) hole appears in the base of the genital tubercle.

It is theorized that epispadia occurs when the genital tubercle blends caudally into the place where the urogenital fold separates the cloaca. A later rupture of the cloacal membrane may result in the dorsal part of the urethra being uncovered. Continuing caudal displacement of the tubercle prevents migration of the mesoderm to the midline and leads to bladder exstrophy. It can be assumed that if this pathology develops as a result of caudal displacement of the genital tubercle, then the anomalies associated with minimal dislocation (epispadia) should occur more often than the defects caused by later further displacement (classical bladder exstrophy), but this is not so.

If the displacement of the genital tubercle is the cause of the appearance of the blemish, it should be expected that a sharp shift of the penis away from the lumbar tubercle should occur at least occasionally, but this never occurs with bladder exstrophy. In view of the foregoing, it was theorized that the normal migration of the mesenchyme between the leaves of the cloacal membrane during bladder exstrophy is impaired because of the increased thickness of the membrane. A belated rupture of the membrane without its strengthening by the mesodermal layer can lead to the formation of bladder exstrophy.

An interesting theory of the etiology of the complex "exstrophy epispadia" and hypospadias was suggested by FD Stephens and JM Hutson (2005), who state that the tail of the embryo plays a key role in the development of this defect.

During the 13th stage of development (28 days), it is seen that the tail of the embryo is directed into the umbilical cord region, as a result of which embryonic hernias and other umbilical ring defects develop. By analogy, it has been suggested that the tail of the embryo can act by compressing the region of the developing genital organs and disrupting the connection of the cloacal tubercles and the cloacal membrane. Different duration and pressure force lead to anomalies of different degrees. Strong tail pressure on the area of cloacal tubercles and the cloacal membrane throughout the gestation period can lead to the formation of cloacal exstrophy. Less severe impact throughout the duration of pregnancy contributes to the emergence of classical exstrophy.

Strong tail pressure on the genital area in the first half of pregnancy and the elimination of this effect in the second half leads to closed forms of exstrophy or total epispadias with a divergence of the bones. The surface pressure of the tail of the embryo on the region of the penis in the second half of pregnancy creates conditions for the appearance of the trunk epispadia without disturbing the fusion of the pubic symphysis. This theory allows us to reasonably explain why the simpler forms of the defect, such as epispadia, are less common than the severe ones (classical exstrophy). Similar violations of embryogenesis lead to the development of another vice of the penis - hypospadias. According to the author of the hypothesis, the surface pressure of the tail on the genital area in later terms of fetal development prevents the closure of the urethral tube and the formation of the scrotum. This theory is also suitable for explaining the mechanism of cloacal exstrophy.

[1], [2], [3], [4], [5], [6], [7], [8], [9]