ROTATION OF THE GUT - FACT OR FANTASY

Disorders of intestinal rotation present with a wide spectrum of abnor malities. 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 a t any stage resulting in the different types of ''malrotations''. Howe ver, a ''malrotated'' gut has never been observed in normal embryos. T herefore all theories on the normal and abnormal development of the gu t are still highly hypothetical. In an attempt to elucidate more clear ly which events occur during the development of the gut, we studied it s embryology in 58 normal rat embryos between the 13th and 20th day of gestation using scanning electron microscopy. In 13 day old rat embry os, the midgut already forms a loop. It can be subdivided into three p arts: the central part (with its connections to rectum and stomach), t he straight part (with the colorectum on the left and the ''small bowe l'' on the right) and the tip of the loop (inside the umbilical cord). Obviously, these three parts show no signs of developmental synchroni zation. Each part develops according to its own developmental blue pri nt: the duodenal and umbilical parts of the midgut show much developme ntal 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 especial ly in this region. Further more, the coecum never achieved a position in the upper left ab-domen, as it is often outlined by schematic drawi ngs. After the return of the bowels into the abdominal cavity the coec um lies exclusively on the right side of the midline close to the vent ral abdominal wall. According to these findings, malrotations of the i ntestines can no longer be described as a physiological developmental stage. At least in rat embryos, we could not find conditions similar t o the clinical picture of malrotations. In our opinion, these malforma tions are exclusively the result of localized growth failures of the d uodenal loop.