Topographical anatomy of the intestines during in utero physiological herniation.

Because most malrotations of the small intestine are thought to occur during repackaging, the location of the intestine should vary less during physiological herniation than afterward. Examination of serial sagittal sections of 27 embryos and fetuses (gestational age 6-9 weeks; crown-rump length 15-45 mm) during herniation showed that the jejunum and ascending colon passed through a small opening of the hernia sac at the levels of the stomach and pancreas in 16 specimens. Below the pancreas, a definite mesentery extended between the ascending and descending colon in the abdominal cavity. In the other 11 specimens, the descending colon passed through an opening of normal size and ran posteriorly along the urinary bladder, so the entire ilium, ascending colon, and transverse colon entered the sac. In these specimens, the duodenojejunal junction was usually situated in a window of the mesentery of the colon (internal herniation). The descending colon was observed at an outside location more frequently in earlier specimens. In contrast to our working hypothesis, the locations of the intestine were abnormal in 40.7% (11/27) of samples. In addition, no abnormal colon was observed in any of the seven specimens after repackaging. An outside location of the descending colon was not directly associated with malrotation because recovery was likely. However, the delayed development of the inferior mesenteric arterial branches could cause failure, including death in utero, during or after the repackaging associated with physiological herniation. Clin. Anat. 31:583-592, 2018.