A choledochocele is formed when what occurs?

A choledochocele is a cystic dilation of the common bile duct that occurs when a segment of the common bile duct (CBD) enters the duodenum and enlarges, often creating a pouch-like structure. This condition can lead to obstruction of bile flow and associated complications due to its anatomical position. The enlargement typically happens at the point where the CBD joins the duodenum, which is often referred to as the ampulla of Vater. This abnormality can cause symptoms related to biliary obstruction, such as jaundice or pancreatitis, depending on the extent of the dilation and obstruction.

In the context of the other options, while CBD can be blocked by gallstones or gallbladder inflammation, these situations do not directly cause the formation of a choledochocele. Additionally, perforation of bile ducts would lead to different clinical issues and is not a mechanism that creates a choledochocele. Thus, the formation of a choledochocele is specifically linked to the dilatation of the CBD as it enters the duodenum.