CHAPTER 43
Gallstones

Piero Portincasa¹ and David Q.‐H. Wang²

¹ University of Bari Medical School, Policlinico Hospital, Bari, Italy

² Albert Einstein College of Medicine, Bronx, NY, USA

Classification

Gallstones are composed of cholesterol monohydrate crystals, mucin gel, calcium bilirubinate, and proteins in the biliary system. Based on chemical composition, gallstones are often classified into three types: cholesterol, pigment, and rare stones (Figure 43.1). The majority (∼75%) of gallstones in the United States and Europe are cholesterol stones, which are usually subclassified as either pure cholesterol or mixed stones, with the latter containing at least 50% cholesterol by weight. Pigment gallstones contain mostly calcium bilirubinate and are subclassified into two groups: black (∼20%) and brown pigment stones (∼4.5%). Rare stones (∼0.5%) are composed of calcium carbonate stones and fatty acid–calcium stones. Gallstones are also classified by their location as intrahepatic, gallbladder, or common bile duct (choledocholithiasis) stones. The prevalence of gallstones varies from 5% to 50% in different populations and is 10–20% in industrialized countries (Figure 43.2).

Chemical composition

Bile is an aqueous solution containing organic solutes, inorganic electrolytes, and trace amounts of proteins (Figure 43.3). The major biliary lipids are unesterified cholesterol, phospholipids (>95% lecithins), bile acids, and bilirubin. Bile acids are composed of primary (cholic and chenodeoxycholic acids) and secondary bile acids (deoxycholic, lithocholic, ursodeoxycholic, sulfolithocholic, and 7α‐oxo‐lithocholic acids). Secondary bile acids are derived from 7‐dehydroxylation of primary bile acids in the liver and in the ileum and colon by intestinal bacteria.

Cholesterol gallstones

Two carriers are necessary for cholesterol dissolved in bile: micelles and vesicles (Figure 43.4). Major risk factors for cholesterol gallstones include increasing age, female gender, pregnancy, metabolic syndrome, insulin resistance, rapid weight loss, physical inactivity, high‐cholesterol diet, gallbladder stasis, estrogen and oral contraceptives, diabetes mellitus, and obesity. Pathogenic mechanisms leading to the formation of cholesterol gallstones involve five defects (Figure 43.5), in which supersaturation of cholesterol in bile is a predominant defect (Figures 43.6 and 43.7).

The liver and small intestine provide the major sources of excess cholesterol, leading to lithogenic bile. Hepatic hypersecretion of biliary cholesterol could result from increases in intestinal absorption, hepatic biosynthesis, and hepatic uptake of high‐density lipoproteins (HDL) from plasma, as well as decreases in the conversion of cholesterol into bile acids and the esterification of cholesterol. Cholesterol crystallization ultimately leads to the formation of solid plate‐like cholesterol monohydrate crystals (Figure 43.8).

Some factors in bile could act as “pronucleating” agents, including excess mucin gel, as found in biliary sludge that is a precursor of gallstones. Mucin gel also acts as a matrix for stone growth. Gallbladder stasis facilitates the precipitation and aggregation of solid cholesterol crystals (Figure 43.9). Sluggish gallbladder contractility due to impaired signal transduction might be induced by excess cholesterol molecules incorporated in the gallbladder muscle cells, acting as myotoxic agents. Excess cholesterol acts as a stimulant of proliferative and inflammatory changes in the mucosa and lamina propria of the gallbladder. Among intestinal factors, sluggish small intestinal transit may be associated with increased intestinal cholesterol absorption and biliary cholesterol hypersecretion, and impaired colonic motility is associated with increased biliary deoxycholate levels, promoting cholesterol crystallization and mucin hypersecretion.

Altogether, the above‐mentioned defects lead to cholesterol‐supersaturated bile, with the propensity for the precipitation and aggregation of solid cholesterol crystals and eventually growth into stones (Figure 43.10).

Photo depicts appearance of human gallstones. — **Figure 43.1** Appearance of human gallstones. **(a)** The cut surface of pure cholesterol stones with a small (left), absent (middle), and large (right) pigment center. **(b)** Mixed cholesterol stone with a concentric appearance, composed of a mixture of cholesterol monohydrate crystals, calcium bilirubinate, and nucin gel. **(c)** Black pigment stones. **(d)** Brown pigment stones, partially fragmented.

Source: Courtesy of P. Portincasa, MD.

Pigment gallstones

Black and brown pigment gallstones form due to abnormalities in bilirubin metabolism in the gut–liver axis (see Figure 43.1). Hemolytic anemia, liver cirrhosis, cystic fibrosis, Crohn’s disease, extended ileal resection, biliary infection, vitamin B₁₂/folic acid‐deficient diets, and aging are the most common risk factors. Genetic factors could play a critical role in the pathogenesis of pigment gallstones, for example, mutations in the UGT1A1 gene.

Black pigment stones consist of either pure calcium bilirubinate or polymer‐like complexes containing unconjugated bilirubin, calcium bilirubinate, calcium, and copper. A regular crystalline structure is not present. The formation of black pigment gallstones is mainly induced by hepatic hypersecretion of bilirubin conjugates (especially monoglucuronides) into bile. Unconjugated monohydrogenated bilirubin is formed by the action of endogenous β‐glucuronidase, which coprecipitates with calcium because of supersaturation in bile. An increased hydrolysis rate often leads to a high concentration of unconjugated bilirubin, which markedly exceeds the solubility of bilirubin in bile.

Brown pigment gallstones are composed primarily of calcium salts of unconjugated bilirubin, with varying amounts of cholesterol, pigment fraction, fatty acids, and mucin gel, as well as small amounts of bile acids, phospholipids, and bacterial residues (see Figure 43.1). These stones are formed not only in the gallbladder but also in other portions of the biliary tree, especially the intrahepatic bile duct. The formation of brown pigment gallstones usually requires the presence of bile stasis associated with biliary infection, especially with Escherichia coli, Clonorchis sinensis, roundworms, and their ova. Dead bacteria and/or parasites could act as nuclei that promote the precipitation of calcium bilirubinate. The presence of excess bacterial β‐glucuronidase dramatically reduces the inhibitory effect of β‐glucaro‐1,4‐lactone, thereby leading to significant hydrolysis of bilirubin glucuronide into unconjugated bilirubin and glucuronic acid. Mucin gel in the gallbladder can bind these complex precipitates and facilitate their growth into macroscopic stones. All these pathogenic factors contribute to the formation of brown pigment stones.

Diagnosis

Gallstones are discovered incidentally during different diagnostic tests in asymptomatic patients or when the typical biliary colicky pain (Figure 43.11) or complications emerge (Box 43.1). Besides the clinical presentation, imaging exams include abdominal ultrasonography (Figures 43.12 and 43.13), computed tomography (CT) (Figures 43.14 and 43.15), magnetic resonance cholangiopancreatography (MRCP) (Figures 43.16 and 43.17), and cholescintigraphy. Oral cholecystography is no longer used, while the plain x‐ray film of the right hypochondrium might detect calcified gallstones (Figure 43.18). Endoscopic retrograde cholangiopancreatography (ERCP) is usually performed when biliary drainage is required due to choledocholithiasis (Figure 43.19).

Photo depicts (a–g) the prevalence of gallstones in different populations is shown according to age range and gender. — **Figure 43.2** **(a–g)** The prevalence of gallstones in different populations is shown according to age range and gender. All studies were performed by abdominal ultrasonography, with the exception of the one in Pima Indians **(g)**, in which cholecystography was used. Overall, the prevalence is higher in females (F) than males (M) at each age group. A high prevalence is apparent in Mexican‐American females **(f)**. Of note, Pima Indians display an extremely high prevalence **(g)**.

Source: Data from: (a) Nomura H, Kashiwagi S, Hayashi J, et al. Am J Epidemiol 1992;136:787; (b) Everhart JE, Khare M, Hill M, Maurer KR. Gastroenterology 1999;117:632; (c) Heaton IW, Braddon FEM, Mountford RA, et al. Gut 1991;32:316; (d) Attili AF, Carulli N, Roda E, et al. Am J Epidemiol 1995;141:158; (e,f) Maurer KR, Everhart JE, Ezzati TM, et al. Gastroenterology 1989;96:487; (g) Sampliner RE, Bennett PH, Comess LJ, et al. N Engl J Med 1970;283:1358.

Schematic illustration of chemical composition of human gallbladder bile. — **Figure 43.3** Chemical composition of human gallbladder bile. Various components are expressed as a percentage of the total. Bile acids, phospholipids, and cholesterol are the three major lipids in bile. Primary bile acids are cholic acid (CA) and chenodeoxycholic acid (CDCA). After 7α‐dehydroxylation in the liver and in the ileum and colon by intestinal bacteria, they are converted to secondary bile acids, deoxycholic acid (DCA), ursodeoxycholic acid (UDCA), and lithocholic acid (LCA).

Schematic illustration of bile is composed mainly of water (90%). — **Figure 43.4** Bile is composed mainly of water (>90%). Following hepatic secretion across the canalicular membrane of hepatocytes, bile acids are found as monomers because of a low critical micellar concentration (CMC <3 mM). When CMC is higher than this cut‐off value, bile acids can self‐aggregate as simple micelles (∼3 nm in diameter). This step increases the solubility of cholesterol. Also, simple micelles are capable of solubilizing and incorporating phospholipids to form mixed micelles (4–8 nm in diameter). Compared to simple micelles, mixed micelles can solubilize at least three times the amount of cholesterol in bile. With typical gallbladder lipid concentrations and composition, simple and mixed bile acid micelles coexist in a ratio of 1:5. Phospholipids in an aqueous environment can self‐aggregate to form stable bilayer vesicles, containing also a trace amount of bile acids, if any. A large amount of the cholesterol molecules is inserted into these bilayers of vesicles between the hydrophobic acyl chains of phospholipids. Unilamellar vesicles (40–100 nm) are larger spherical carriers in which even more cholesterol is solubilized. The ratio of unilamellar vesicles to micelles depends on the bile acid and phospholipid concentrations of bile. Furthermore, at low bile acid concentrations and high phospholipid concentrations, these biliary phospholipids often form large multilamellar vesicles (~500 nm). High concentrations of bile acids can dissolve these vesicles to form mixed micelles. When the balance of cholesterol solubilization in bile fails, excess cholesterol starts precipitating as insoluble anhydrous or monohydrate crystals, the first step in cholesterol gallstone formation.

Source: Adapted from Di Ciaula A, Wang DQ, Bonfrate L, Portincasa P. Current views on genetics and epigenetics of cholesterol gallstone disease. Cholesterol 2013;2013:298421.

Schematic illustration of five defects lead to cholesterol gallstone formation. — **Figure 43.5** Five defects lead to cholesterol gallstone formation. *LITH* genes and genetic factors play a key role in the formation of cholesterol gallstones. Hepatic hypersecretion of biliary cholesterol leads to unphysiological supersaturation of gallbladder bile with cholesterol. At the enterocyte level, intestinal absorption of cholesterol is enhanced. As a consequence, accelerated phase transition in bile occurs, which is facilitated by prolonged gallbladder stasis due to impaired gallbladder motility, and immune‐mediated gallbladder inflammation, as well as hypersecretion of mucin and accumulation of mucin gel in the gallbladder lumen. In bile, the growth of solid plate‐like cholesterol monohydrate crystals to form gallstones is a consequence of persistent hepatic hypersecretion of biliary cholesterol together with enhanced gallbladder mucin secretion and incomplete evacuation due to sluggish gallbladder contractility.

*Source:* Wang HH, Portincasa P, Afdhal NH, Wang DQ. *Lith* genes and genetic analysis of cholesterol gallstone formation. Gastroenterol. Clin North Am 2010;39:185‐207.

Schematic illustration of equilibrium phase diagram of a mixed bile salt-cholesterol-phospholipid system shows five different pathways of cholesterol crystallization in bile. — **Figure 43.6** Equilibrium phase diagram of a mixed bile salt‐cholesterol‐phospholipid system shows five different pathways of cholesterol crystallization in bile. Each zone contains different cholesterol carriers. The one‐phase zone under the saturation curve contains only micelles, and represents the bile being unsaturated with cholesterol. Above, three other zones exist with cholesterol supersaturation: a left two‐phase zone containing saturated micelles and solid cholesterol crystals; a central three‐phase zone containing saturated micelles, vesicles, and solid cholesterol crystals; and a right two‐phase zone containing saturated micelles and vesicles. Cholesterol precipitation is rapid in bile with high concentrations of bile acids. However, at increasing amounts of phospholipids, cholesterol may reside in vesicles with phospholipids, and cholesterol crystallization is slower or absent.

Source: Adapted from Wang DQ, Carey MC. Complete mapping of crystallization pathways during cholesterol precipitation from model bile: influence of physical‐chemical variables of pathophysiologic relevance and identification of a stable liquid crystalline state in cold, dilute and hydrophilic bile salt‐containing systems. J Lip Res 1996;37:606.

Photo depicts photomicrographs of fused liquid crystals with Maltese cross birefringence and focal conic textures observed in gallbladder bile of mice by phase contrast and polarizing light microscopy. — **Figure 43.7** Photomicrographs of fused liquid crystals with Maltese cross birefringence and focal conic textures observed in gallbladder bile of mice by phase contrast and polarizing light microscopy. Similar structures can be found in human gallbladder bile.

Source: Wang DQ, Paigen B, Carey MC. Phenotypic characterization of Lith genes that determine susceptibility to cholesterol cholelithiasis in inbred mice: physical‐chemistry of gallbladder bile. J Lip Res 1997;38:1395. Reproduced with permission of Elsevier.

Management

Different guidelines have been developed for the treatment of gallstones (Figure 43.20). Gallstones remain asymptomatic in the vast majority of subjects, and under these circumstances, expectant management is the best choice. Prophylactic cholecystectomy is only warranted in specific conditions (Table 43.1). In symptomatic patients, first‐line therapy of the uncomplicated biliary colic requires medical attention and analgesia. Elective (laparoscopic, small‐incision, or open) cholecystectomy is the gold standard treatment of “symptomatic and uncomplicated” gallstone disease. The procedure is safe with reduced costs and is definitive in nature (Figure 43.21). Oral litholysis with (tauro‐) ursodeoxycholic acid is reserved for patients who cannot undergo surgery because of the overall operative risk, or refuse surgery, or have mild/moderate symptoms and stones amenable to dissolution. However, when complications develop, specific approaches are required (Figures 43.22–43.30).