Gallstones (biliary calculi) are small stones made from cholesterol, bile pigment and calcium salts, usually as a mixture that forms in the gall bladder.

The gall bladder is a small sac that holds bile, a digestive juice produced by the liver that is used in the breakdown of dietary fats. The gall bladder extracts water from its store of bile until the liquid becomes highly concentrated. The presence of fatty foods triggers the gall bladder to squeeze its bile concentrate into the small intestine.

Gallstones are a common disorder of the digestive system, and affect around 15 per cent of people aged 50 years and over. Some things which may lead to the formation of gallstones include the crystallisation of excess cholesterol in bile and the failure of the gall bladder to fully empty.

In most cases, gallstones don’t cause any problems. However prompt treatment may be necessary if stones block ducts and cause complications such as infections or inflammation of the pancreas (pancreatitis).