[Epithelium and anal glands in rectal pouches and fistula. Histologic studies of swine with congenital anal atresia].

The epithelial coating of the rectal pouch and fistula was studied morphologically in 33 newborn piglets with high and low forms of anal atresia and was found to be similar to the epithelial coating of the anal canal in normal piglets: the typical epithelium of the rectum changed its character into transitional epithelium at the region of the internal sphincter which surrounded the fistulae in all animals. In the caudal part of the fistula the transitional epithelium was followed by squamous epithelium. Only in male piglets with deformities and recto-urethral fistulae no squamous epithelium was found. In these cases transitional epithelium covered all parts of the fistula and the region of the internal sphincter. Anal glands were found in all animals, with or without anorectal malformations. They always invaded the internal sphincter. According to our morphological studies the fistula in anorectal malformations represents an ectopic anal canal.