[Rotation of the intestine--an illusion or reality?]

Disorders of intestinal rotation present with a wide spectrum of abnormalities. This variety is attributed to the puzzling embryology of the midgut. Clinicians, as well as embryologists, believe that normally a process of rotation of the midgut takes place which can be hampered at any stage resulting in the different types of "malrotations". However, a "malrotated" gut has never been observed in normal embryos. Therefore all theories on the normal and abnormal development of the gut are still highly hypothetical. In an attempt to elucidate more clearly which events occur during the development of the gut, we studied its embryology in 58 normal rat embryos between the 13th and 20th day of gestation using scanning electron microscopy. In 13 day old rat embryos, the midgut already forms a loop. It can be subdivided into three parts: the central part (with its connections to rectum and stomach), the straight part (with the colorectum on the left and the "small bowel" on the right) and the tip of the loop (inside the umbilical cord). Obviously, these three parts show no signs of developmental synchronization. Each part develops according to its own developmental blue print: the duodenal and umbilical parts of the midgut show much developmental activity, while gross changes of the straight part of the midgut are missing. This finding is surprising because a process of rotation, if occurring, should result in notable morphological changes especially in this region. Further more, the coecum never achieved a position in the upper left abdomen, as it is often outlined by schematic drawings.(ABSTRACT TRUNCATED AT 250 WORDS)