Gallstone formation is directly related to the relative concentrations and solubility of bile contents, most notably cholesterol. Biliary “sludge” is a term used to describe a combination of cholesterol crystals, calcium bilirubinate, and mucin that congeals and acts as a precursor to stone formation. This sludge along with gallbladder dysmotility promotes the development of gallstones. Gallstones are classified as either cholesterol or pigment stones, and the particular classification depends on the relative cholesterol content. Cholesterol stones are composed mainly of cholesterol crystals as the name suggests and are due to an increased saturation of biliary cholesterol, a decrease in bile salts, and/or biliary stasis. Pigment stones can be further categorized as black or brown stones. Black pigment stones occur in those with conditions that result in high concentrations of unconjugated bilirubin. The primary composition of black pigment stones is calcium bilirubinate. Common etiologies include hemolytic disorders (e.g., sickle cell anemia) or changes in the enterohepatic circulation (e.g., Crohn disease, ileal resection, and cystic fibrosis). The third type of gallstone is the brown pigment stone, which results from hydrolysis of conjugated bilirubin or phospholipid by bacteria. This type of stone occurs in patients with infections of the biliary tract or strictures. Brown pigment stones have also been found as primary common bile duct stones.

Cholesterol stones comprise the vast majority of gallstones (75 %), especially in industrialized countries, with black pigment stones less frequently seen (20 %), and brown pigment stones being least common (5 %) [7]. Black pigment stones occur more prevalently in communities with higher frequencies of hemolytic disorders, and while rare in Western culture, brown pigment stones arise more commonly in Asian populations.

Several pharmacologic agents that are associated with the formation of gallstones have been identified. In children, intravenous ceftriaxone has been well documented, although the majority of patients remain asymptomatic [8–10]. In symptomatic patients, clinical improvement is generally seen with discontinuation of the medication [11–14]. Another drug known to contribute to gallstones is octreotide. Among its most common side effects is biliary tract pathology, including sludge or gallstone formation and ductal dilatation [15, 16]. Dysmotility of the gallbladder and decreased secretion of bile have been documented, even after administration of a single dose, and the risk of such side effects is proportional to the duration of therapy [17]. Lastly, gemfibrozil and other fibrate antihyperlipidemic agents have been associated with gallstones as the mechanisms of action of these agents increase cholesterol excretion through bile, promoting increased biliary cholesterol concentration [18].

Cholelithiasis can be classified as asymptomatic or symptomatic. Asymptomatic patients are defined as those with known gallstones—usually discovered incidentally—but without associated symptoms, termed asymptomatic cholelithiasis. Patients are deemed symptomatic if they experience the typical pain related to gallbladder disease, often referred to as “biliary colic.” The pain is described as constant, epigastric and/or right upper quadrant abdominal pain that usually resolves after several hours, occurs characteristically post-prandially, and is associated with nausea and vomiting [19].

As opposed to asymptomatic cholelithiasis, patients with symptomatic cholelithiasis are at an increased risk for developing complicated gallstone disease, including acute cholecystitis, choledocholithiasis and/or cholangitis, and gallstone pancreatitis. A randomized, prospective study showed that in patients with symptomatic cholelithiasis, 38 % per year experienced recurrent pain attacks and 2 % per year required cholecystectomy for significant biliary symptoms [20].

On the other hand, most patients with gallstones (up to 70 %) remain asymptomatic [21]. Of those with incidental (asymptomatic) gallstones, only 20 % will experience symptoms over a 15-year time point, and even then, their initial symptoms are normally biliary colic-type pain, rather than severe complications of gallstone disease [22]. Rarely does a patient with no symptoms experience complicated gallstone disease on first presentation. Risks for symptoms or complications from initially asymptomatic cholelithiasis are reported in the literature to be 1–4 % per year [23, 24]. Interestingly, one retrospective cohort analysis with propensity score matching found patients with coronary artery disease (CAD) to be significantly more likely to develop gallstone-related symptoms or complications than patients without CAD. The finding suggests that patients with CAD be monitored more closely than other patients with gallstone disease [25].

Individuals with silent gallstones do not undergo routine diagnostic imaging for this condition since, by definition, they are asymptomatic and therefore are unaware of the presence of stones. As such, gallstones in those without symptoms are usually detected as an incidental finding on abdominal imaging done for unrelated reasons. Below is a summary of different modalities used to assess the gallbladder and biliary tract.