Gallstones are pebble-like substances that form in the gallbladder, ranging in size from a grain of sand to a golf ball. A gallbladder can develop one stone, or hundreds of tiny stones.
Gallstones can block the flow of a digestive fluid called bile through the hepatic ducts, the cystic duct, or the common bile duct. Trapped bile can cause inflammation or infection in the gallbladder, liver, or pancreas.
Some people with gallstones have no symptoms. Symptoms of blocked bile might include pain in the right abdomen, pain in the back between the shoulder blades, or pain under the right shoulder. These are often called a gallbladder attack.