What structure in the cystic duct can impede the passage of the choledochoscope?

Heister's valves are the correct structure in the cystic duct that can impede the passage of the choledochoscope. These are small, spiral folds found within the cystic duct. Their presence can create a mechanical barrier as they may obstruct the pathway, making it challenging for instruments like a choledochoscope to navigate through the duct into the gallbladder or beyond.

The anatomy of the cystic duct is such that it is relatively narrow, and the spiral configuration of Heister's valves can amplify this difficulty. When performing endoscopic procedures, particularly those involving the biliary system, awareness of these valves is important, as they may complicate access to the common bile duct.

In contrast, other structures mentioned in the options serve different roles in the biliary system. The Sphincter of Oddi regulates the flow of bile and pancreatic juice into the duodenum but is located at the ampulla of Vater and not within the cystic duct itself. The cholecystic sphincter pertains to the regulation of bile flow into the cystic duct from the gallbladder and does not directly impede a choledochoscope. The common bile duct is the more distal structure in the biliary tree and is not