Why is a stent used in ERCP?

ERCP (endoscopic retrograde cholangiopancreatography) is a procedure where a scope is used to access the bile and pancreatic ducts. A stent may be placed during ERCP for several reasons:

- To open a bile or pancreatic duct blockage - A stent can prop open ducts narrowed or obstructed by gallstones, tumors, scarring, sphincter issues, etc. This helps restore drainage.

- To seal bile or pancreatic duct leaks - A stent can bridge a leak and divert flow, allowing healing. Leaks may occur after surgery or trauma.

- To prevent post-ERCP pancreatitis - Placing a temporary pancreatic stent lowers pressure and can help prevent this complication.

- Prior to surgery - Stents can improve drainage before procedures like gallbladder removal or bile duct surgery.

- After surgery - Stents secure drainage while healing occurs after surgical procedures on the biliary tract. 

- Chronic conditions - For ongoing conditions like strictures or pancreatitis, stents provide long-term improvement of drainage.

- Tissue sampling - Stents allow brushings or biopsy samples to be collected from inside the duct during ERCP.

- Stone extraction - Stones can be removed through stents placed in the bile or pancreatic duct. 

So in summary, stents placed during ERCP hold structures open, close leaks, prevent complications, assist with procedures, and improve drainage in both the short and long term. Stents provide targeted treatment not possible with surgery alone.