GI Consult: Common Bile Duct Stones

The authors provide an update on the diagnosis and management of choledocholithiasis, focusing on the latest treatment options and the role of new imaging techniques.

By Michael F. Byrne, MD, Robert M. Mitchell, MB, and John Baillie, MB

What is the pathogenesis of common bile duct stones (CBDS)?

Three critical factors are involved in the pathogenesis of cholesterol gallstones: cholesterol supersaturation of bile; accelerated crystallization of cholesterol in bile involving nucleating agents (mucin and non-mucin glycoproteins); and reduced gallbladder contractility with resultant prolonged bile stasis. All these factors may lead to the formation of biliary sludge—an amorphous precipitant of mucin glycoproteins, bile pigments, protein, and lipids—and subsequent stone formation.

Pigment stones are composed mostly of calcium bilirubinate and other calcium salts. Less is known about the process of pigment stone formation than about cholesterol gallstones, but biliary stasis appears to play a dominant role, along with chronic hemolysis in conditions such as sickle cell disease and hereditary spherocytosis.

Common bile duct stones can be classified into two types: primary (originating within the CBD) and secondary (originating outside the CBD). It is believed that primary CBDS develop as a result of stasis and infection in the CBD, whereas secondary CBDS migrate from the gallbladder to the CBD through the cystic duct or, rarely, a cholecystobiliary fistula.
 

What signs and symptoms are produced by CBDS?

Common bile duct stones are present in 10% to 15% of patients with symptomatic gallbladder stones. Patients who present with acute pancreatitis or cholecystitis have a higher prevalence of CBDS. In addition, a recent history of jaundice or cholangitis or elevations in bilirubin or other liver enzyme levels may be present. Before newer imaging techniques emerged, imaging criteria that led to surgical exploration of the CBD included a dilated CBD (more than 7 mm in diameter) and an abnormal intraoperative cholangiogram (IOC).

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Which diagnostic tests should be used to detect CBDS? And in what order should they be performed?

All patients in whom choledocholithiasis is suspected should have a thorough history, physical examination, and serum chemistry evaluation. The most appropriate initial procedure is transabdominal ultrasound. Although this procedure may miss up to 40% of CBDS, it is nonetheless a useful screening test because it is noninvasive, inexpensive, and widely available. Even if stones are not detected by ultrasound, a dilated CBD may be found, which is suggestive of choledocholithiasis in the appropriate clinical context. In addition, ultrasound may reveal other biliary, liver, or pancreatic pathology.

Endoscopic retrograde cholangiopancreatography (ERCP) is a very sensitive and specific procedure for diagnosing CBDS, with the significant advantage of offering simultaneous therapy through stone clearance. However, ERCP has a morbidity of 5% to 10% and a mortality of 0.1% to 0.5% and therefore must be used selectively. For patients at low risk for CBDS, laparoscopic cholecystectomy and IOC should be done first, with ERCP reserved for those patients with abnormal findings on the cholangiogram. Laparoscopic ultrasound is also done with cholecystectomy. Both this test and IOC offer good accuracy rates for the detection of CBDS, although there is some concern about missing small intrapancreatic stones with laparoscopic ultrasound. Most surgeons feel that IOC does not need to be performed routinely and that its use should be selective.

Only in the following cases should ERCP be performed before laparoscopic cholecystectomy and an IOC:

• patients with acute cholangitis with or without a progressive rise in liver function test levels (including bilirubin) and selected patients with gallstone pancreatitis;
• patients with CBDS clearly identified on ultrasound or other cross-sectional imaging technique;
• patients with prior surgical rearrangement of the upper gastrointestinal tract (such as the Billroth II or Roux-en-Y diversions), where there is uncertainty about the endoscopist's ability to do postsurgical ERCP; and
• possibly in situations where expertise in cannulations is an issue and there is doubt about the likelihood of a successful ERCP after laparoscopic cholecystectomy and an IOC.

(In some elderly patients with comorbidities, we do sphincterotomy as an alternative to cholecystectomy, so that current and future stones can pass.)

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What is the role of magnetic resonance cholangiopancreatography (MRCP) in the diagnosis of CBDS?

Imaging of the biliary tree by MRCP is constantly improving. Indeed, MRCP provides images with a sensitivity and specificity approaching those obtained by ERCP. Results are suboptimal in the detection of small ductal stones, stones impacted near the ampulla, and in nondilated ducts. However, technical refinements in magnetic resonance technology are likely to address these concerns in the near future. Because MRCP is a safe, noninvasive test, it is likely to replace ERCP as the diagnostic procedure of choice for CBDS. Currently, its use is restricted by its high cost and limited availability. Compared to ultrasound, MRCP is more cumbersome to use as a screening tool for diffuse or unspecified abdominal problems. Nonetheless, it is already starting to replace ultrasound, ERCP, and IOC in some centers.
 

How successful is ERCP in patients with previous gastrointestinal surgery and CBDS?

It is often very difficult to reach the papilla in patients who have had a Billroth II resection. It may be easier to locate the papilla with a pediatric colonoscope, but the absence of an elevator (a special modification at the lower end of the instrument channel that moves up and down) makes subsequent cannulation and therapy difficult. If the papilla is reached, papillotomes are available to compensate for the reverse orientation after surgery. However, even in centers of excellence, the cannulation rate in patients with previous Billroth II surgery is no better than 60% to 70%; it is often much lower in routine clinical practice.

In patients who have undergone a Roux-en-Y procedure, the success of ERCP is very low. Most of these patients require surgical exploration of the CBD for stone removal.
 

How is endoscopic ultrasound (EUS) used in the detection of CBDS?

Transabdominal ultrasound is not particularly sensitive for detection of CBDS because of interference from bowel gas in the duodenum. This is not a problem with EUS, however, because the transducer is placed directly in the duodenal bulb. Several studies confirm that EUS and ERCP are equally sensitive in detecting CBDS—in the range of 90% and higher. Based on these findings, and the fact that EUS is less costly than ERCP and carries minimal risk of pancreatitis, EUS may be preferable as a screening test for patients with a low to intermediate risk for choledocholithiasis, while ERCP remains the preferred procedure for patients at high risk.

In addition, EUS has been compared directly with MRCP in the detection of CBDS. One study reported a sensitivity for both tests of 100%, but a specificity of 95% for EUS and only 73% for MRCP. However, the advantage of MRCP is that it is noninvasive. Intraductal ultrasound is also under investigation as a diagnostic tool. Interestingly, in a study of patients who had had an endoscopic papillary dilation and stone extraction, intraductal ultrasound detected small residual stones in 27 of the total 81 patients with "normal" cholangiograms. There is as yet no consensus regarding which imaging modality should be used in patients with suspected choledocholithiasis.

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What are the treatment options for CBDS?

In general, there are three treatment options for CBDS: stone removal during ERCP, laparoscopic bile duct exploration, and open CBD exploration. Several management algorithms have been proposed. A suggested one-step strategy for CBDS removal incorporates laparoscopic cholecystectomy and laparoscopic bile duct exploration. A two-step approach involves laparoscopic cholecystectomy and pre- or postoperative ERCP.

The strategy adopted at a particular center will depend to a large degree on staff expertise and available technology. The advantages of the one-step approach include a shorter hospital stay and potentially decreased morbidity. However, this approach is technically demanding and involves a longer operation. The two-step approach involves a shorter operation and the need for less expertise and equipment, but it is more costly, with longer hospital stays. Also, because there are two procedures, the risk of morbidity is increased. Open CBD exploration carries a higher mortality than endoscopic methods, and while it is a sound technique for removing stones, it is an option being used less frequently as endoscopic and laparoscopic advances continue to be made. In addition, surgeons in training may have little or no experience with this technique.
 

What are the recent advances in the endoscopic treatment of CBDS?

Although endoscopic papillotomy remains the procedure of choice, endoscopic papillary balloon dilation has been used with success, mainly in patients with small stones. It has been suggested that papillary balloon dilation preserves sphincter function, but its overall role in the management of CBDS remains to be determined. One concern about papillary balloon dilation relates to the risk of pancreatitis, which was three times higher than the risk after sphincterotomy in a recent multicenter trial.

Most stones can be removed during ERCP using a balloon catheter or dormia basket. Occasionally, however, stones are too large to be pulled through the sphincterotomy site. In these cases, one of several lithotripsy techniques can be used, including mechanical lithotripsy ("crushing basket"), electrohydraulic lithotripsy, laser shock-wave lithotripsy, and extracorporeal shock-wave lithotripsy. When these techniques fail to extract all the stones, a biliary endoprosthesis or nasobiliary drain must be inserted to maintain biliary drainage. The patient can then be sent home for several days or weeks before returning for a follow-up procedure.
 

Do all patients with CBDS need a cholecystectomy?

As a general rule, patients with CBDS should have a cholecystectomy after endoscopic clearance of their stones. However, in patients who are a poor operative risk, a wait-and-see approach may be justified.

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Do patients with acute pancreatitis and known or suspected choledocholithiasis require emergency ERCP?

This is an important question to address. Gastroenterologists are commonly asked to perform an urgent ERCP for stone extraction in patients with acute pancreatitis of presumed or known biliary origin. Some authors have proposed that early intervention for removal of CBDS with persistent impaction improves patient survival and prevents recurrent attacks. A biliary cause of pancreatitis should be considered in patients with known stone disease, elevated liver enzymes (especially if the alanine aminotransferase level is more than three times normal), jaundice, and a dilated CBD.

However, the studies to date in patients with gallstone pancreatitis suggest that early ERCP is beneficial only in those patients who have evidence of biliary obstruction (jaundice with or without cholangitis) or whose condition is clearly not improving. In fact, it appears that urgent ERCP in patients with no evidence of biliary obstruction may produce complications that worsen the disease. Folsch and colleagues found more respiratory failure and a higher mortality rate in patients who had urgent ERCP with no biliary obstruction compared to those who had conservative management.

In the majority of patients with gallstone pancreatitis, preoperative ERCP is not indicated. Most of these patients will pass their stones spontaneously and will thus be suitable candidates for surgery, during which they will ideally have an intraoperative cholangiogram.

Recent studies in patients with acute biliary pancreatitis suggest that EUS may play a role in determining which of these patients have choledocholithiasis and would thus benefit from early ERCP and stone extraction. Whether all patients with acute pancreatitis of presumed biliary origin should undergo EUS to determine which ones should have ERCP is an unanswered question. As noted earlier, MRCP is noninvasive and yields results comparable to EUS in this setting and thus may be the most appropriate procedure.

When considering all of these possible scenarios, it should be remembered that gallstones causing acute pancreatitis are usually small and tend to pass spontaneously. Also significant is the fact that ERCP will detect CBDS in less than 20% of patients with gallstone pancreatitis 48 to 72 hours after the onset of an attack.
 

Is medical management a viable option for patients with CBDS?

In the subgroup of patients for whom endoscopic or surgical treatment is considered risky or has failed, there may be a role for medical management of CBDS through dissolution therapy. However, because the efficacy of chemical dissolution of stones is at best limited, medical management should not be considered a first-line option.

The two types of dissolution therapy are oral therapy, mainly using ursodeoxycholic acid (UCDA), and contact dissolution using solvents such as methyl tertiary butyl ether or propyl acetate delivered by catheter directly to the site of stones. Dissolution of CBDS with oral agents has been disappointing, especially if the patient had a cholecystectomy, which prevents bile acids from concentrating in the CBD. However, one study in the early 1990s showed that UCDA treatment facilitated gallstone fragmentation and subsequent removal when it was used along with biliary stents. Solvents, infused either via a T-tube or a nasobiliary catheter, have no role in the treatment of CBDS; they are reported to yield only modest results with cholesterol stones and are even less successful with pigment stones. In addition, because solvents drain into the small bowel and are rapidly absorbed, side effects are relatively common. In practice, contact dissolution is not indicated but oral therapy may help in some patients who are clearly not operative candidates.
 

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