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Author: Laurence Scott Bailen, M.D.
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1. Objectives: Gallstones

  1. To understand the epidemiology of gallstones with a focus on who is at risk for gallstones

  2. To understand the mechanism of cholesterol and pigment gallstone formation

  3. To be able to describe symptoms and complications of gallstones

  4. To understand how to treat gallstones

2. Research on Gallstones

  1. Before 1960: little basic research on stones, but cholesterol metabolism was defined

  2. Studies of biliary lipid interaction and solubility under conditions expected in vivo

  3. Valuable studies in Native American populations

  4. Lipid composition of bile determined in vivo

  5. Determinants of cholesterol solubility and then establishing principles of cholesterol gallstone dissolution

  6. NIH sponsored trials to dissolve stones; surgeons worry

  7. Gallstone dissolution shown feasible, but probably impractical; surgeons breathe sign of relief

  8. Newer methods for gallbladder removal: laparoscopic cholecystectomy

3. Epidemiology: Who gets gallstones?

  1. General risk:

    1. In US: 20% of women, 10% of men. Increases with age.

    2. Native American women: Pima, Chippewa – stones in nearly 100%

  2. Documented additional risks for cholesterol stones:

    1. Gender: women > men

    2. Weight: women overweight by 20lbs or more. Very obese women (body mass index > 30) is 6x that of normal weight.

    3. Age: prevalence increases with age. In a Danish study, every 5 years 3% more people get stones (in a population of individuals at least 40).

    4. Family history of gallstones in first degree relative

    5. Rapid weight loss (aggressive diets; gastric bypass surgery)

    6. Surgical absence of the ileum (less bile acids recirculate to liver)

    7. Certain drugs such as octreotide (somatostatin analogue that reduces gallbladder contractility)

  3. Possible additional risks for cholesterol stones:

    1. Progesterone therapy

    2. Oral contraceptives

    3. Estrogen therapy

    4. Cholestyramine use (a bile acid binding resin)

  4. Known NOT to be a risk for cholesterol stones:

    1. Serum cholesterol level

    2. Diabetes mellitus

    3. Alcohol intake

    4. Ingestion of coffee (may actually reduce risk of cholesterol stones possibly by stimulating more gallbladder contraction)

4. What is the composition of gallstones?

  1. Cholesterol

    1. 80% of stones in the US are cholesterol stones

  2. Pigment stones: brown or black

    1. 20% of stones in the US are pigment stones

  3. Overall, 15% of stones are heavily calcified – most (66%) are pigment stones

5. Cholesterol Gallstones

  1. Bile becomes supersaturated with cholesterol and is termed lithogenic bile.

  2. Major lipids in bile are bile acids, phospholipids (lecithin), and cholesterol.

    1. Cholesterol is a sterol that is insoluble in aqueous solution but is held in solution in bile.

    2. Phospholipid (lecithin) in water adopts a crystal form with the polar fatty acid and phosphorylcholine groups aligning to form hydrophilic and hydrophobic regions.

    3. Bile acids are amphipathic steroids and form micelles in water. They are products of cholesterol metabolism.

  3. Mechanisms of gallstone formation:

    1. Hypersecretion of cholesterol into bile

    2. Hyposecretion of bile acids into bile

    3. Nucleation factors

    4. Gallbladder mucin

    5. Role of the gallbladder (contractility)

  4. Cholesterol metabolism

    1. Sources of cholesterol:

      1. Diet → chylomicrons

      2. de novo synthesis primarily within the liver

    2. Cholesterol is either:

      1. Solubilized and secreted unchanged in bile

      2. Converted into bile acids

        1. Primary bile acids: cholate and chenodeoxycholate make up 35% of bile acid pool

        2. Secondary bile acids: deoxycholate (24% of bile acid pool) and lithocholate (1-3% of bile acid pool)

        3. Tertiary bile acid: ursodeoxycholic acid (4% of bile acid pool)

      3. Stored in the liver as cholesterol esters or

      4. Shunted to peripheral adipose and skeletal tissues

6. How is cholesterol held in solution in bile?

  1. Free cholesterol is insoluble in bile. It requires bile acids and phopholidpids.

  2. Cholesterol is held in solution in two ways:

    1. Mixed micelles

      1. Contents:

        1. Cholesterol

        2. Bile acids

        3. Phospholipids

      2. This form of cholesterol solubility dominates when bile flow is high, primarily after meals.

    2. Unilamellar vesicles

      1. Larger than mixed micelles

      2. Consist of phospholipids bilayer and cholesterol. They contain no bile acids.

      3. They are formed in hepatocytes and are the major way that hepatocytes handle cholesterol. They are exocytosed into bile across the canalicular membrane. Patients with gallstones secrete vesicles which are more concentrated with cholesterol.

      4. Unilamellar vesicles are primarily formed during periods of fasting.

      5. Multi-lamellar vesicles can be generated from unilamellar vesicles and form at higher cholesterol saturations.

7. How do gallstones form?

Gallstones form by the interaction of three factors: cholesterol supersaturation (lithogenic bile), accelerated nucleation, and gallbladder hypomobility.

  1. Cholesterol supersaturation: lithogenic bile

    1. Cholesterol HYPER-secretion (into bile)

      1. Obesity

        1. Increased hepatic synthesis

        2. Increased dietary cholesterol

      2. Hormones

        1. Estrogens; oral contraceptive pills

        2. Decreased conversion to cholesterol esters

        3. Increased hepatic uptake of cholesterol

      3. Genetic

        1. Increased transport and uptake

        2. Decreased 7-alpha hydroxylase activity (lower bile acid production)

      4. Rapid weight loss

        1. Mobilization of cholesterol stores

      5. Advancing age

    2. Bile acid HYPO-secretion

      1. Ileal disease

        1. Loss of enterohepatic circulation of bile acids.

      2. Congenital

      3. Cholestatic liver disorders

    3. May have problems with cholesterol hypersecretion, bile acid hyposecretion or both to produce lithogenic bile (bile supersaturated with cholesterol).

    4. Cholesterol saturation index (CSI): ratio of molar percentage of cholesterol, bile acid, and phospholipids needed to keep cholesterol in solution. When CSI is 1:0 bile is saturated and can precipitate out of solution, crystallize, and form gallstones. This is an idealized situation since 80% of patients with bile that is supersaturated with cholesterol do not have gallstones but have so-called “metastable” bile. Therefore, other factors are required to produce gallstones (see below).

      1. How ideal solutions of cholesterol, bile acids, and phospholipids behave in vitro.

      2. Composition of the bile acid pool is important in determining lithogenicity of bile

        1. More hydrophobic the bile acid the more likely it will induce cholesterol secretion and reduce bile acid synthesis.

        2. Patients with gallstones have smaller concentrations of cholic acid and larger amounts of deoxycholic acid. Deoxycholic acid is more hydrophobic and raises the cholesterol saturation index.

        3. Ursodeoxycholic acid is hydrophilic and can help dissolve gallstones. Ursodeoxycholic acid can lower the cholesterol saturation index and prolong nucleation time (see below).

  2. Cholesterol nucleation (the buildup of cholesterol crystal then stone formation)

    1. Nucleation is an early step in gallstone formation

    2. Nucleation promotes vesicular fusion and solid cholesterol crystal formation (crystallization). Crystals then agglomerate to form gallstones.

    3. Nucleation rates in patients with gallstones are shorter than patients without gallstones.

    4. Pronucleating factors:

      1. Mucin glycoprotein – most important

        1. Binds cholesterol, phospholipids, and bilirubin which aids in accelerating nucleation.

        2. Mucin enhances vesicle fusion

        3. Mucin glycoprotein is secreted by the gallbladder continuously and is excessive in lithogenic bile.

      2. Biliary calcium

        1. Calcium salts are in most cholesterol gallstones

        2. Calcium salts (calcium carbonate, calcium bilirubinate, calcium phosphate) can be a nidus for cholesterol crystallization.

  3. Gallbladder hypomotility

    1. Gallbladder absorbs water very efficiently which increases the concentration of bile and makes it easier to become saturated and form vesicles.

    2. Patients with gallstones have a diminished response to cholecystokinin (a potent hormonal stimulus of gallbladder contraction). Gallbladder stasis will make it easier for stones to form.

    3. Other hormones such as somatostatin (and its synthetic analog octreotide) may also play a role in gallbladder hypomotility.

    4. SLUDGE. Biliary sludge (also known as microlithiasis) may form in gallbladders that do not contract well. Sludge is an amorphous, thick gallbladder mucoprotein with small entrapped cholesterol crystals. It forms in a similar fashion as gallstones. Sludge is found in pregnancy, starvation, rapid weight loss, with use of ceftriaxone (antibiotic), TPN (total parenteral nutrition) use, and prolonged treatment with octreotide → all conditions associated with diminished gallbladder contractility.

      1. Sludge should not be ignored as it can be a cause of pancreatitis and cholecystitis

8. Pigment Stones

  1. Brown or Black

  2. They contain predominantly bilirubin pigments and calcium salts rather than cholesterol.

  3. Black pigment stones

    1. Excess production of unconjugated bilirubin

    2. Unconjugated bilirubin precipitates as calcium bilirubinate in the setting of excess mucin glycoproteins

    3. Seen in conditions associated with excess unconjugated bilirubin production:

      1. Chronic hemolysis (sickle cell, hereditary spherocytosis, β-thalassemia)

      2. Cirrhosis

  4. Brown pigment stones

    1. Form in gallbladder or biliary tree

    2. Seen when bile is colonized with bacteria or parasites

    3. More common in Asian populations

    4. Infections in the bile plus bile stasis leads to mucus and bacterial products within the gallbladder and bile ducts which can precipitate with calcium to form insoluble calcium salts and then stones.

9. Diagnosis of Gallstones

  1. History

    1. “Biliary colic”: attacks of right upper quadrant or epigastric pain which radiate to right back and right shoulder. Attacks typically begin 1-3 hours after a fatty meal and last 3-6 hours.

    2. Associated with nausea and vomiting

    3. Fever may be present

  2. Physical Examination

    1. Possible fever

    2. Tenderness to palpation in the right upper quadrant or epigastric area.

    3. Murphy’s sign: tenderness to palpation in right upper quadrant with inspiration

  3. Imaging

    1. Ultrasound (transabdominal) is most useful and most commonly used.

    2. CT scan less sensitive

    3. HIDA scan (nuclear medicine study using radiolabeled iminodiacetic acid). Radiolabeled compound is administered intravenously and taken up by hepatocytes, secreted into bile. Imaging performed to see if gallbladder “lights up."

      1. Used to determine patency of cystic duct and bile duct. If gallbladder does not “light up” this suggests cystic duct occlusion and likely cholecystitis.

10. Gallstone Complications (see Figure 2)

  1. Cholangitis: a severe and urgent infectious illness of the biliary tree, and secondarily the bloodstream. Comes about by bacterial entry and proliferation into the hepatic biliary tree, nearly always because of obstruction of the biliary tree at the ampulla of Vater, or perhaps higher in unusual circumstances. Now treated with biliary drainage as initial therapy with ERCP (endoscopic retrograde cholangiopancreatography).

  2. Cholecystitis: inflammation of the gallbladder itself, a painful (right upper quadrant) and febrile infection that needs treatment with antibiotics, followed by removal of the gallbladder surgically. Often associated with gallstones, but not necessarily (acalculous cholecystitis).

  3. Pancreatitis: 30% of all pancreatitis cases in the US are gallstone-related, thought to be caused by passage of gallstones (or sludge), but the mechanism for the pancreatitis has never been clearly explained.

11. Gallstone Treatment

  1. Stone dissolution methods

    1. The National Cooperative Gallstone Study undertook to dissolve existing cholesterol gallstones, with the principal that expanding the bile acid pool in the bile would dissolve stones. The rationale is clearly seen by examining the ternary diagram shown elsewhere in the syllabus. But the principal was wrong! A major surprise was that only oral supplemental chenodeoxycholic acid, not cholic acid, led to stone solution, even though both expanded the bile acid pool dramatically. This immediately suggested that chenodeoxycholic acid dissolved cholesterol stones in a way other than by simply expanding the pool.

      1. 1000 patients with functioning gallbladder (assessed by oral cholecystography)

      2. Chenodeoxycholic acid was given by mouth

      3. 13.5% had full dissolution of stones, 27% had partial dissolution after two years of treatment. When the drug was stopped the stones recurred.

      4. All patients had biliary chenodeoxycholic acid levels exceeding 70%.

      5. Chenodeoxycholic acid led to stone dissolution by reducing cholesterol output into bile and not necessarily by expanding the bile acid pool.

      6. Complications in this trial:

        1. Increased serum cholesterol (10% increase in LDL)

        2. Mild elevation in liver transaminases.

        3. Mild diarrhea

    2. Ursodeoxycholic acid

      1. Hydrophilic

      2. It lowers cholesterol saturation index and prolongs nucleation time

      3. In clinical trials it leads to a 30% stone dissolution rate after two years of treatment

      4. It reduces hepatic synthesis and secretion of cholesterol

      5. It does not increase serum cholesterol

    3. Because of the poor results with oral dissolution methods, these techniques are not used routinely to treat gallstones.

  2. Other non-surgical treatments

    1. Lithotripsy: Sonic treatment to fragment stones. Drawbacks are: expensive machinery, migration of stone fragments once formed, and need for cholesterol dissolving drugs after treatment. Side effects: skin petechiae, hematuria (3%), post-procedure biliary colic (30%), pancreatitis (not common), stone recurrence, and high cost. Only 15% of patients are suitable for this therapy. These limit value of lithotripsy in treating stones in otherwise healthy persons, and it has found modest use.

    2. Dissolving stones with MTBE (methyl tert-butyl ether). This is liquid at body temperature and dissolves stones rapidly. MTBE is instilled into the gallbladder or bile duct as it must have direct contact with stones. It is highly flammable. Some absorption systemically can lead to hemolysis. Can cause duodenal inflammation. This technique and a similar technique with mono-octanoin are not used in clinical practice.

  3. Surgery: Open and Laparoscopic Cholecystectomy

    1. Laparoscopic cholecystectomy was pioneered in France in 1989. It is now the standard method of gallbladder removal. Low complication rates.

  4. Who should have a cholecystectomy for removal of gallstones?

    1. Biliary symptoms

    2. Cholecystitis

    3. Cholangitis

    4. Pancreatitis

    5. Asymptomatic gallstones??? Most physicians will not remove gallstones detected incidentally during imaging studies performed for other reasons. This decision is based on data showing that the overall annual incidence of symptoms from gallstones that currently are asymptomatic is 2-5%. In a careful, novel study of 123 healthy University of Michigan Faculty members found to have asymptomatic gallstones, 18% had clinical symptoms needing treatment in the ensuing 15 years. In a recent Italian study the figure was 10% of people with asymptomatic stones in 10 years. In both studies the complications from gallstones (cholecystitis, cholangitis, pancreatitis) was very low, 3% or less and all complications were preceded by biliary type pain.