INTRODUCTION — Choledocholithiasis (common bile duct stones) develops in up to 20 percent of patients with gallbladder stones [1]. It is generally accepted that stones in the common bile duct should be removed, even if patients are asymptomatic, because they could eventually cause abdominal pain, pancreatitis, and/or cholangitis.

Diagnosis of common duct stones is not always straightforward. Clinical evaluation and biochemical tests are insufficiently accurate to reliably establish a firm diagnosis without confirmatory testing. As a result, imaging tests are routinely used to clarify the diagnosis.

The gold standard test in the past was endoscopic retrograde cholangiopancreatography (ERCP), which (compared with other tests such as ultrasonography) has the advantage of permitting intervention if a common bile duct stone is present. However, ERCP is invasive, may miss small stones, and may cause complications such as pancreatitis. Thus, it is frequently desirable to confirm the presence of choledocholithiasis before embarking upon an ERCP. The optimal type, timing, and choice among specific tests have not been clearly established and continue to be reevaluated as new technologies emerge.

The most commonly used initial test is a transabdominal ultrasound examination of the hepatobiliary system. The sensitivity of ultrasound for the detection of dilated bile ducts from biliary obstruction ranges in various studies from 55 to 91 percent [1-6]. The sensitivity increases with the serum bilirubin concentration and the duration of jaundice [7]. A dilated extrahepatic bile duct on ultrasound suggests the possibility of an obstructing lesion. Ultrasound has similar sensitivity to computed tomography (CT) for detecting choledocholithiasis (75 percent in the presence of dilated ducts, 50 percent for nondilated ducts). Gas in the duodenum can obscure visualization of the distal common bile duct thereby decreasing sensitivity [8].

Four other approaches have also been used:

●CT (which, as described above, has similar sensitivity to ultrasound).

●Predictive models (statistical models that predict the likelihood of choledocholithiasis based upon clinical, biochemical, and radiographic data [9,10]).

●Magnetic resonance cholangiopancreatography.

●Endoscopic ultrasonography (EUS).

This topic review will provide recommendations for possible roles of EUS in the evaluation of patients with suspected common bile duct stones. A general approach to patients with suspected choledocholithiasis is presented elsewhere. (See "Choledocholithiasis: Clinical manifestations, diagnosis, and management".)

ACCURACY — A major advantage of endoscopic ultrasonography (EUS) compared with transabdominal ultrasonography is that it permits positioning of the ultrasound transducer in the second part of the duodenum, thereby allowing visualization of the entire extrahepatic biliary tree without interference from digestive gas or abdominal fat (image 1 and image 2 and image 3).

A number of studies have compared the accuracy of EUS to transabdominal ultrasonography, endoscopic retrograde cholangiopancreatography (ERCP), computed tomography (CT), and magnetic resonance cholangiopancreatography (MRCP) for detecting common bile duct (CBD) stones [11-13]. At least two meta-analyses have been performed, which reached similar estimates of test characteristics:

●A meta-analysis of 31 studies (with a total of 3075 patients) estimated an overall sensitivity of 89 percent (95% CI 87-91 percent) and specificity of 94 percent (95% CI 91-96 percent) compared with ERCP or intraoperative cholangiography as the reference standard [11].

●A meta-analysis of 27 studies (with a total of 2673 patients) estimated an overall sensitivity of 94 percent (95% CI 93-96 percent) and specificity of 95 percent (95% CI 94-96 percent) compared with ERCP, intraoperative cholangiography, or surgical exploration as the reference standard [12].

Despite its overall high accuracy, the role of EUS in the diagnosis of CBD stones has not been firmly established since EUS is relatively invasive compared with other imaging modalities and does not permit therapeutic intervention. A systematic review comparing EUS to MRCP found similar overall diagnostic performance [14] while a systematic review that included eight randomized trials demonstrated slightly higher overall accuracy for EUS as compared with MRCP (93 versus 90 percent) for detecting choledocholithiasis [15]. In practical terms, the major advantage of MRCP remains its non-invasive nature, making it a safer option for frail patients unfit for endoscopy; conversely, the advantage of EUS is its superior ability to detect small stones, especially those in the distal common bile duct, and its availability as an option to patients in whom magnetic resonance imaging (MRI) is contraindicated (eg, patients with pacemaker). Overall, because of the very marginal differences between these two modalities, the choice should be based on local availability and operator expertise.

WHEN TO CONSIDER USING EUS — As a general rule, patients with a high probability of choledocholithiasis (as determined by clinical presentation and noninvasive imaging) are best served by proceeding directly to endoscopic retrograde cholangiopancreatography (ERCP). Possible exceptions are those in whom prior attempts at ERCP were unsuccessful or in whom the risk of pancreatitis and/or radiation exposure would make confirmatory testing desirable. Examples of the latter include patients with gallstone pancreatitis, pregnant women, and those with other risk factors for complications from ERCP [16,17]. (See "Overview of endoscopic retrograde cholangiopancreatography (ERCP) in adults".)

We agree with society guidelines that advocate using EUS or MRCP to assess for common bile duct (CBD) stones in patients suspected of having CBD stones but who lack confirmatory findings on abdominal ultrasound [18,19]. In addition, a dilated CBD detected by abdominal ultrasound (in the absence of CBD stones) typically results in further diagnostic testing for many patients. (See "Choledocholithiasis: Clinical manifestations, diagnosis, and management", section on 'Initial diagnostic evaluation'.)

However, CBD caliber increases with advancing age and after cholecystectomy, and may not be a predictor of CBD stones for such patients [20,21]. For example, in a study including 82 postcholecystectomy patients with dilated CBD (≥7 mm), CBD stones (or sludge) were identified by EUS in three patients (4 percent) [21].

Predictive models — Several studies have proposed predictive models to define the pretest probability of choledocholithiasis to facilitate triage for either initial endoscopic ultrasonography (EUS) or for direct ERCP. One such study demonstrated that 70 percent of patients with a "high" probability of choledocholithiasis based on clinical criteria had common bile duct (CBD) stones [22]. Patients were considered to have a high probability of choledocholithiasis if they had a CBD stone on ultrasound (US) or computed tomography (CT) or if they had at least three of the following: dilated CBD on US (>7 mm), fever, bilirubin >2 mg/dL, elevated alkaline phosphatase, or serum alanine aminotransferase (ALT) >twice normal.

Based on the 70 percent prevalence of stones in the high risk group, the authors recommended that these patients proceed directly to ERCP. For patients who were not in the high risk category, EUS was the preferred initial modality because it avoided the risks of unnecessary ERCP and had a lower cost. However, other studies have failed to demonstrate a significant benefit to using predictive models [15,23].

EUS-guided ERCP — The use of EUS to determine if ERCP is indicated may avoid a significant number of ERCPs and result in fewer complications [24]. A systematic review of randomized controlled trials compared EUS-guided ERCP with ERCP alone for the detection of common bile duct stones [25]. Patients randomized to undergo EUS were able to avoid ERCP in 67 percent of cases and had lower rates of complications and pancreatitis compared with those in the ERCP alone group (OR 0.35 and 0.21, respectively). In that series, EUS failed to detect common bile duct stones in only 2 of 213 patients (0.9 percent).

Gallstone pancreatitis — EUS may have a role when there is uncertainty as to whether there is a stone in the common bile duct in a patient with gallstone pancreatitis who does not have a clear indication for urgent ERCP.

The accuracy of EUS in patients with pancreatitis was illustrated in a study of 100 consecutive patients with acute pancreatitis who underwent transabdominal ultrasound, EUS, and ERCP [26]. EUS was more sensitive than transabdominal ultrasound for detecting gallbladder stones (100 versus 84 percent). The sensitivities of ERCP and EUS for choledocholithiasis were both 97 percent, with overall accuracies of 96 and 98 percent, respectively. EUS correctly identified the absence of choledocholithiasis in 65 of 66 patients (specificity 98 percent).

Studies evaluating the role of ERCP in gallstone pancreatitis suggest that early ERCP does not appear to be beneficial in patients with acute biliary pancreatitis in the absence of obstructive jaundice or biliary sepsis. In other patients, the morbidity of ERCP with sphincterotomy may outweigh its benefits since many such patients have already passed the gallstone that led to pancreatitis. (See "Management of acute pancreatitis".)

However, the distinction between those who passed a stone and those with a possible retained common bile duct stone is not always clear. Up to 50 percent of patients with suspected gallstone pancreatitis without jaundice will have choledocholithiasis when investigated [27-29]. Many of these patients will require a postoperative ERCP if a CBD stone is detected during cholecystectomy. In addition, some of these patients will experience clinical deterioration ultimately requiring an urgent ERCP and sphincterotomy before a cholecystectomy can be performed. (See 'Role in patients undergoing laparoscopic cholecystectomy' below.)

EUS may have a role in reducing uncertainty about whether there is a retained CBD stone in patients with gallstone pancreatitis [8,22,30,31]. In addition, it may help clarify the diagnosis in those with apparent idiopathic pancreatitis or abdominal pain in whom a biliary source cannot be firmly excluded [32-34]. More studies are needed to better define the role of EUS in these settings, particularly when considering issues related to cost-effectiveness and comparison with other imaging modalities such as MRCP.

Role in patients undergoing laparoscopic cholecystectomy — As mentioned above, unsuspected common bile duct stones may be detected in as many as 50 percent of patients with gallstone pancreatitis undergoing cholecystectomy. Such patients usually require postoperative ERCP with sphincterotomy, and less commonly undergo common bile duct exploration at the time of cholecystectomy. As a result, there has been much debate as to the optimal strategy for evaluating patients with gallstone pancreatitis who are scheduled to undergo cholecystectomy [35,36].

The possible role of EUS in this setting was evaluated in a decision analysis that found that the least costly strategy for patients undergoing laparoscopic cholecystectomy depended primarily upon the risk of stones, although procedural costs and operator expertise were also critical [36]. Only patients who were at intermediate risk of bile duct stones (10 to 50 percent) were thought to benefit from EUS (or an intraoperative cholangiogram, if its cost was less than that of EUS). Unfortunately estimation of the risk of common bile ducts stones can be difficult. (See 'Predictive models' above.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Biliary infection and obstruction".)

SUMMARY AND RECOMMENDATIONS

●A major advantage of endoscopic ultrasonography (EUS) compared with transabdominal ultrasonography for the identification of choledocholithiasis is that it permits positioning of the ultrasound transducer in the second part of the duodenum, thereby allowing visualization of the entire extrahepatic biliary tree without interference from digestive gas or abdominal fat. (See 'Accuracy' above.)

●The role of EUS in the management of patients with suspected choledocholithiasis and biliary pancreatitis has not been well established, especially when considering costs and the availability of other imaging modalities such as magnetic resonance cholangiopancreatography. As a general rule, patients with a high probability of choledocholithiasis (as determined by clinical presentation and noninvasive imaging) are best served by proceeding directly to endoscopic retrograde cholangiopancreatography (ERCP). (See "Choledocholithiasis: Clinical manifestations, diagnosis, and management", section on 'Whom to suspect'.)

EUS can be considered for patients:

•Who have an intermediate risk (10 to 50 percent) of having a retained common bile duct stone in whom ERCP was unsuccessful or undesirable (eg, in pregnant women and those at increased risk from ERCP). (See 'When to consider using EUS' above.)

•With idiopathic pancreatitis in whom a biliary source (either a retained common bile duct stone or microlithiasis) cannot be excluded. (See 'Gallstone pancreatitis' above.)