common bile duct
On ultrasound imaging, it is not always possible to confidently see where the cystic duct enters the common hepatic duct to form the common bile duct. Therefore it is common practice to use the term common duct (CD) as a term conflating the common hepatic and common bile ducts.
The CBD is approximately 8 cm long and usually <6 mm wide in internal diameter but this can be dependent on a number of factors including age and prior cholecystectomy. It joins the pancreatic duct at the ampulla of Vater, which drains into the second part of the duodenum through the major duodenal papilla.
The common bile duct is supplied by a network of arteries from several sources:
- from above: right hepatic artery and cystic artery
- from below: posterior superior pancreaticoduodenal artery, retroduodenal artery, and retroportal artery
There are four main relationships of the CBD with the pancreatic head :
- partially covered posteriorly (most common: ~50%)
- completely covered
- completely uncovered
- CBD may pass laterally to the pancreatic head (least common)