The Ampulla of Vater is a nipple-like opening in the small intestines through which drains bile (from the bile ducts and gallbladder) and digestive juices from the pancreas. ERCP (endoscopic retrograde cholangiopancreatography) is a procedure in which the Ampulla of Vater is cannulated and x-ray contrast is injected. If gallstones are present in the bile ducts they may be removed endoscopically by first passing a wire through this tiny opening, splaying it open with a coagulating current, and then passing baskets or balloons to retrieve stones. Tumors and scarring may make this opening tiny. Stents may be passed through the endoscope in order to maintain the patency of ducts collapsed by tumor or scarring.