Development of pancreas in utero is a complex process resulting in a variety of anomalies, many of which are asymptomatic but some of which can produce symptoms. The anomalies that occur are best appreciated from an understanding of the anatomy at different stages:
At week 4, the dorsal and ventral buds of the forgut grow and it is from these that the pancreas develops. The ventral bud develops to the right of the duodenum, while the dorsal bud develops to the left.
In order for the pancreas to arrive at its final position, the ventral bud must rotate and this occurs at week 6. The dorsal duct drains the body tail and superior portion of the head via the minor papilla. The ventral duct drains the uncinate process and inferior portion of the head into the major papilla.
Around week 7, the dorsal duct fuses with the ventral duct and the pancreas is drained through the ventral duct into the major papilla. The distal segment of the dorsal duct regresses, forming an accessory duct of Santorini.
The pancreas drains through the ventral duct (of Wirsung) and the major papilla.
The dorsal duct may be partially or completely obliterated and the minor papilla is often not patent. If obliteration of the dorsal duct is incomplete, it will persist as an accessory pancreatic duct (of Santorini). However, there are many variations upon this normal arrangement.
The most commonly occurring anomalies are:
- Annular/semi annular pancreas: This results from incomplete rotation of the ventral portion resulting in either a complete or partial ring of tissue around the duodenum. This may be asymptomatic or produce a degree of obstruction resulting in pain and vomiting
- Pancreas divisum: This results from failure of fusion of the embryological dorsal and ventral buds. The ducts then remain separate with the dorsal duct draining the body, tail and superior portion of the head into the minor papilla and the ventral duct draining the uncinate process and inferior portion of the head into the major papilla
- Ectopic pancreas tissue
- Short pancreas: This most likely results from agenesis of the dorsal pancreas and may be isolated or in association with polysplenia
- Agenesis/hypoplasia and hyperplasia
- Ductal anomalies: Commonly seen ductal abnormalities are:
- Complete regression of the dorsal duct with the ventral and common bile ducts joining at the ampulla
- Junction of the ventral and common bile ducts at the ampulla with persistence of the dorsal duct
- Persistence of the dorsal duct and ventral duct without communication (pancreas divisum)
- Common channel with duct entering the common duct from 5-15 mm from the ampulla
- Separate entrance of the ventral duct into the duodenum with variable persistence of the dorsal duct