Types of gall stone and aetiology

Normal bile consists of 70% bile salts (mainly cholic and chenodeoxycholic acids), 22% phospholipids (lecithin), 4% cholesterol, 3% proteins, and 0.3% bilirubin. Cholesterol or cholesterol predominant (mixed) stones account for 80% of all gall stones in the United Kingdom and form when there is supersaturation of bile with cholesterol. Formation of stones is further aided by decreased gallbladder motility. Black pigment stones consist of 70% calcium bilirubinate and are more common in patients with haemolytic diseases (sickle cell anaemia, hereditary spherocytosis, thalassaemia) and cirrhosis.

Brown pigment stones are uncommon in Britain (accounting for <5% of stones) and are formed within the intraheptic and extrahepatic bile ducts as well as the gall bladder. They form as a result of stasis and infection within the biliary system, usually in the presence of Escherichia coli and Klebsiella spp, which produceβ glucuronidase that converts soluble conjugated bilirubin back to the insoluble unconjugated state leading to the formation of soft, earthy, brown stones. Ascaris lumbricoides and Opisthorchis senensis have both been implicated in the formation of these stones, which are common in South East Asia.

Clinical presentations