Gallstone disease - Classification

Gallstones are classified:

• By localization: in the gallbladder; in the common bile duct; in the hepatic ducts.
• By the number of stones: single; multiple.
• By composition:
  • cholesterol - contain mainly cholesterol, have a round or oval shape, layered structure, diameter from 4-5 to 12-15 mm; typical localization is the gallbladder;
  • pigment (bilirubin) are characterized by small sizes, usually multiple; hard, fragile, completely homogeneous, located both in the gallbladder and in the bile ducts;

Pigment stones are stones that contain less than 30% cholesterol. There are black and brown pigment stones.

• Black pigment stones consist mainly of black pigment polymer, calcium phosphate and carbonate without cholesterol impurities. The mechanism of their formation is not fully understood, although the role of bile supersaturation with unconjugated bilirubin, changes in pH and calcium levels in bile, and excess production of organic matrix (glycoprotein) are known. Black pigment stones account for 20-30% of the total number of gallstones and are more common in elderly patients. They can migrate to the bile ducts. The formation of black pigment stones is characteristic of chronic hemolysis, such as hereditary spherocytic or sickle cell anemia, artificial heart valves and vascular prostheses, all forms of liver cirrhosis, especially alcoholic. Medicinal dissolution of black pigment stones is at the experimental stage.
• Brown pigment stones contain calcium bilirubinate, which is polymerized to a lesser extent than in black pigment stones, as well as calcium palmitate and stearate and cholesterol. Brown pigment stones form in the bile ducts against the background of bile stasis and infection; they are rare in the gallbladder and are usually radiolucent. Their formation is associated with the decomposition of bilirubin diglucuronide by bacterial beta-glucuronidase, resulting in the precipitation of insoluble unconjugated bilirubinate. Brown pigment stones form above strictures (in sclerosing cholangitis) or in dilated areas of the bile ducts (in Caroli disease). The formation of brown pigment stones in the absence of biliary tract diseases is associated with juxtapapillary diverticula of the duodenum. Bacterial inclusions are found in more than 90% of cases. In eastern countries, brown pigment stones complicate the invasion of the bile ducts by Clonorchis sinensis and Ascaris lumbricoides and are often located intrahepatically. From the common bile duct, they are removed by endoscopic papillosphincterotomy, and from the intrahepatic ducts - by lithotripsy, percutaneous drainage or surgery.
• Mixed (found most frequently) - often multiple, of the most varied form; they contain cholesterol, bilirubin, bile acids, proteins, glycoproteins, various salts, and microelements.

In Western countries, cholesterol stones are more common. Although the main component of cholesterol stones is cholesterol (51-99%), they, like other types of stones, contain various proportions of components such as carbonate, phosphate, bilirubinate and calcium palmitate, phospholipids, glycoproteins and mucopolysaccharides. According to crystallography, cholesterol in gallstones is present in the form of monohydrate and anhydrous. The nature of the stone core has not been established. The role of pigments, glycoprotein or amorphous material has been suggested.

It remains unclear how water-insoluble cholesterol is retained in the bile in a dissolved state and what mechanisms lead to its precipitation and the formation of gallstones.

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