Fetal intraluminal portion of the sphincter of Oddi: A histological study using human fetuses

The sphincter of Oddi surrounds a common duct after joining of the bile and pancreatic ducts in the adult ampulla of Vater, but the fetal development of the submucosal portion of the sphincter is still obscure possibly because previous studies used horizontal or frontal sections. We examined serial sagittal histological sections of 12 human fetuses with 36-65 mm crown rump length or CRL (approximately 9-11 weeks) and semi-serial sections of the other 3 fetuses with 210-250 mm (25-30 weeks). Except for 1 fetus (36 mm CRL), fourteen fetuses carried the "intraluminal portion" protruding and floating in the duodenal lumen. Twelve of them had the sphincter extending to the anal side in the duodenal lumen, whereas two extended to the stomach side. The distal end of the sphincter seemed to detach from the duodenal mucosa at and around 9 weeks, and subsequently the common duct seemed to elongate freely without mucosal attachment in mid-term fetuses and, finally, become embedded again in the duodenal mucosa in the postnatal life. A possible discrepancy in growth rate between the sphincter muscle and duodenal mucosa was likely to allow the specific intermediate morphology, i.e., the intraluminal common duct. The fetal accessory papilla did not show such morphology. A minority of cases whose common duct extended to the stomach side might connect with abnormal union of the bile and pancreatic ducts.