On the basis of their composition, gallstones can be divided into the following types: cholesterol stones, pigment stones, and mixed stones. An ideal classification system is yet to be defined. Cholesterol stones
Cholesterol stones vary from light yellow to dark green or brown or chalk white and are oval, usually solitary, between 2 and 3 cm long, each often having a tiny, dark, central spot. To be classified as such, they must be at least 80% cholesterol by weight (or 70%, according to the Japanese classification system). Between 35% and 90% of stones are cholesterol stones. Pigment stones
Bilirubin ("pigment", "black pigment") stones are small, dark (often appearing black), and usually numerous. They are composed primarily of bilirubin (insoluble bilirubin pigment polymer) and calcium (calcium phosphate) salts that are found in bile. They contain less than 20% of cholesterol (or 30%, according to the Japanese classification system). Between 2% and 30% of stones are bilirubin stones. Mixed stones
Mixed (brown pigment stones) typically contain 20–80% cholesterol (or 30–70%, according to the Japanese classification system). Other common constituents are calcium carbonate, palmitate phosphate, bilirubin and other bile pigments (calcium bilirubinate, calcium palmitate and calcium stearate). Because of their calcium content, they are often radiographically visible. They typically arise secondary to infection of the biliary tract which results in the release of β-glucuronidase (by injured hepatocytes and bacteria) which hydrolyzes bilirubin glucuronides and increases the amount of unconjugated bilirubin in bile.
A dysostosis is a disorder of the development of bone, in particular affecting ossification. Examples include craniofacial dysostosis, Klippel–Feil syndrome, and Rubinstein–Taybi syndrome. It is one of the two categories of constitutional disorders of bone (the other being osteochondrodysplasia). When the disorder involves the joint between two bones, the term synostosis is often used. References


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