Rotation of the gut: fact or fantasy?

Clinicians, as well as embryologists, believe that normally a process of rotation of the midgut takes place that 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, the authors 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 has already formed a loop. It can be subdivided into three parts: the central part with its connections to the stomach and leading to 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. These three parts show no signs of developmental synchronization. Each part develops according to its own developmental blueprint: the duodenal and umbilical parts of the midgut show much developmental activity, whereas gross changes of the straight part of the midgut are not seen. This finding is surprising because a process of rotation, if occurring, should result in notable morphological changes especially in this region. Furthermore, the coecum never achieved a position in the upper left abdomen, as is often outlined in schematic drawings. After the return of the bowel into the abdominal cavity, the coecum lies exclusively on the right side of the midline close to the ventral abdominal wall.(ABSTRACT TRUNCATED AT 250 WORDS)