J.Jpn. Surg. Soc.. 100(6): 388-393, 1999

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Feature topic

EMBRYOLOGY OF ANORECTAL MALFORMATIONS : STUDIES ON A PIG MODEL

We have established a pig model for naturally occurring anorectal malformations and developed a method for mass producing these anomalies. Following one-stage operations in the neonatal period, the piglets were raised and used in experimental matings.
Anomalous fetuses were obtained at the gestational ages of 22 to 60 days and were used for embryological studies. One hundred and eight fetuses were sectioned sagittally and studied with 3-D analysis in a device of our own design.
The cause of the anomalies is considered to be failure of cloacal division into the urogenital sinus and anorectum, due to a defect of the cloacal plate at the most dorsal part.
The internal sphincter was shown to descend, thicken, and cover the area of the dorsal cloaca, that is, the anal canal, in the normal and fistulas in the anomalous pigs.
The comparative anatomy of the cloaca is discussed. This organ persists in all adult vertebrates, except for the higher mammals. Defects of the once obtained, cloaca-dividing genes cause anorectal malformations. We are now attempting to determine the disease-related genes in this pig model.

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