3-DIMENSIONAL ANALYSIS OF ANORECTAL EMBRYOLOGY - A NEW TECHNIQUE FOR MICROSCOPIC STUDY USING COMPUTER-GRAPHICS

To clarify the embryological etiology of various malformations, we recently developed a computerized three-dimensional (3D) reconstruction system for analytical observation of real structures in a small fetus and applied this technique for the analysis of anorectal embryology. Fifty-one pig fetuses were obtained from two porcine families with anorectal malformations established in our facilities. They were sectioned sagittally and 3D structures of the anorectum were reconstructed from serial sections and analyzed. In the young pig embryo (24-30 days), the cloaca exists as a cloacal plate, a very thin, flat structure vertical to the body surface. It is filled with basophilic cells and contains no cavity. Therefore, the body surface covering the urogenital and rectal area may not be recognized as a single membranous structure. In the reconstructed image of the cloacal plate, the proximal part, which lies between the hindgut and tail groove, was defective in the specimens with anorectal anomalies whereas the cloacal plate existed from the entire anterior part to the posterior end of the tail groove in the normal specimens. This result supports the theory of van der Putte that anorectal malformations are caused by a defect of the cloacal plate between the hindgut and tail groove.