| Abstract|| |
When the clinical features strongly suggest the presence of bile duct stones, management is fairly straightforward; diagnostic and therapeutic endoscopic retrograde cholangiography (ERC) may in some cases constitute the entire strategy. Unfortunately, the clinical picture is often equivocal or uncertain. Although stones are unlikely to be present in the bile duct when the clinical index of suspicion is low, their presence can never be completely ruled out based on clinical and biochemical parameters. Thus, an accurate, noninvasive, reliable, and safe method for bile duct imaging would be highly advantageous. Low-risk tests, such as endoscopic ultrasound (EUS), are emerging as reliable substitutes for diagnostic ERC. This review highlights the technical aspects of examining the extra-hepatic biliary duct system and the performance and results of EUS in diagnosing patients who present with possible common bile duct stones.
Keywords: Endoscopic ultrasound, common bile duct stones, biliary
|How to cite this article:|
Aljebreen AM. Role of endoscopic ultrasound in common bile duct stones. Saudi J Gastroenterol 2007;13:11-6
Common bile duct (CBD) stones are common condition that can be associated with severe complications, such as pancreatitis and cholangitis., They occur in 10-15% of patients with symptomatic gallstones undergoing cholecystectomy., Until recently, endoscopic retrograde cholangiography (ERC) has been the standard of reference for both diagnosis and treatment of choledocholithiasis,, but the procedure can be associated with an overall complication rates of 5-10% and mortality rates of 0.02-0.5%.,,,
When the clinical features strongly suggest the presence of bile duct stones, management is fairly straightforward; diagnostic and therapeutic ERC may in some cases constitute the entire strategy. Unfortunately, the clinical picture is often equivocal or uncertain. Although stones are unlikely to be present in the bile duct when the clinical index of suspicion is low, their presence can never be completely ruled out based on clinical and biochemical parameters. Thus, an accurate, non-invasive, reliable, and safe method for bile duct imaging would be highly advantageous. Low-risk tests, such as endoscopic ultrasound (EUS) and magnetic resonance cholangiography (MRC), are emerging as reliable substitutes for diagnostic ERC. Both of these tests have been extensively evaluated independently and in comparison with ERC with uniformly encouraging results.,,,,
This review highlights the technical aspects of examining the extra-hepatic biliary duct system and the performance and results of EUS in diagnosis patients who presents with possible CBD stones.
EUS is a minimally invasive procedure with a procedural risk identical to that of gastroscopy (OGD) with low morbidity (the rate of perforation is less than 1 in 2000). The close proximity of the echoendoscope to the extra hepatic bile ductal system, lack of radiation and safety makes EUS an excellent method for examining the common bile duct and gallbladder such that small stones, biliary sludge, and even micro-lithiasis can be demonstrated. Choledocholithiasis is easily identified as curvilinear hyper echoic foci with strong acoustic shadowing. Low amplitude echoes without acoustic shadowing are considered sludge. Diagnostic accuracy of the radial or the linear echo endoscopes are equivalent., The extra hepatic ductal system can be visualized completely by EUS in 96% of patients.
| Examination technique|| |
The examination is performed with the patient in the left lateral decubitus position under mild intravenous sedation with midazolam and/or propofol. There are basically two positions that must be achieved to evaluate the extrahepatic portion of the bile duct. The first position is called the 'apical' position, which starts with advancing the echoendoscope along the greater curvature of the stomach to visualize the pylorus and once within the duodenal bulb, air is instilled along with slight downward tip deflection in order to visualize the apex of the duodenal bulb. The tip of the scope is then positioned in the area of the apex, the balloon is inflated until it occludes the lumen and slight clockwise torque is then applied to the instrument shaft. Ultrasound imaging then begins. There are four landmarks that one should look for. The most important is that we called the 'duodenal fall-off,' which represents the muscularis propria of the duodenum, the second is the CBD, third is the pancreatic duct and the forth is portal vein [Figure - 1],[Figure - 2]. Withdrawal and counterclockwise torque of the echoendoscope will allow visualization of the bile duct toward the hilum and clockwise torque and insertion of the endoscope shaft will allow visualization of the distal bile duct as it enters the papilla.
The second position is where the transducer is positioned directly perpendicular to the papilla. This is important in some cases in which a stone is impacted in the distal bile duct. The technique for imaging the bile duct with linear echoendoscope is the same as that described for the radial instrument. By using this method, the hepatic duct and CBD can be visualized in 95-100% of patients as reported in several studies.,,
By using high frequencies (7.5 and 12 MHz), the resolution of biliary EUS is less than 1 mm, ensuring EUS as the leading imaging technique of those currently available.
The limitations of biliary EUS have been clearly established and include (1) poor performance in the diagnosis of bile duct obstruction in the hilum or right hepatic duct; (2) inadequate visualization of the distal portion of the CBD when the pancreas is highly calcified and very poor visualization of the upper part of the CBD in severe necrotic acute pancreatitis; (3) difficulty in performing a biliary examination after gastrectomy with gastroenterostomy, although this difficulty is being reduced due to the advent of finer and more manageable videoechoendoscopes; and (4) difficulty in correctly examining the hepatic duct in the presence of air within the bile duct, particularly after endoscopic sphincterotomy or choledochoduodenostomy.
| Performance of EUS in detection of CBD stones|| |
In 1989, the first prospective and comparative blind study was published reporting the results of EUS in the diagnosis of CDB obstruction. In this study, in which the emphasis was not uniquely on stones, the diagnostic accuracy of EUS in diagnosing CBD stones was 100%. Moreover, this blind study showed that EUS was superior to US and CT in diagnosing choledocholithiasis. [Table - 1] summarizes the main recent studies published on the subject. EUS is extremely accurate in diagnosing CBD stones with a sensitivity of 95% (95% CI of 94-96), specificity of 98% (95% CI of 97-99) and an accuracy of 96% (95% CI of 95-97) in these patients [Figure - 3], who were with the exception of one series, presented an intermediate risk of CBD stones (20-50%).
These results are far superior to US (sensitivity 63%) and CT (sensitivity 71%) and were approximately equivalent to that of endoscopic retrograde cholangiopancreatography (ERCP). EUS is especially more sensitive than US or CT in detecting small stones and those stones that are situated within a small caliber CBD. The performance of EUS in recognizing CBD stones is not related to stone size [Figure - 4] or the diameter of the CBD, and high degrees of accuracy were also achieved with linear EUS. In addition, the learning curve require to obtain satisfactory results in diagnosing CBD stones is relatively short as physicians with less than 1 year experience achieve a high degree of skill in this indication.
Several studies have compared EUS and ERCP in a blinded fashion [Figure - 5], ERC performed subsequent to EUS and by two different operators).,, The sensitivity of ERC was found to be 79-90% compared to 88-100% for EUS with more false negative results were observed with ERC. The false negative results with ERC were due to small stones located within dilated bile ducts, whereas false negatives for EUS because of stones that were located in the proximal portion of the common hepatic duct or the intra-hepatic ducts during the examination., In addition to the excellent performance of EUS in the diagnosis of choledocholithiasis, EUS has several additional advantages. It allows diagnosis of unrecognized gallbladder micro-lithiasis in which its sensitivity is almost 100%. It is also interesting to underline that in 10-20% of cases a cause for biliary obstruction other than choledocholithiasis is found at EUS. Thus, EUS can provide additional information and in particular eliminate other obstructive pathologies such as small ampullary tumors, cholangiocarcinoma, and congenital bile duct or periampullary abnormalities.
A limitation of these studies is that cholangiography, either endoscopic retrograde (ERC) or intra-operative (IOC) was used predominately as the reference standard for the presence or absence of stones. This is potentially problematic because it is well recognized that stones, especially if small, may be missed by cholangiography. To overcome this problem, Napoleon et al . followed, for at least 1 year, 238 patients who had initial normal EUS and found the negative predictive value of EUS for diagnosing CBD stones was 95%, which is comparable to ERC/ IOC studies, so they concluded that negative initial EUS should obviate the need for an ERCP or IOC in patients with suspicion of CBD stones. A further limitation of most of available studies is that, by design, the patient enrolled had a moderate to high probability of having CBD stone. This is an obvious potential source of bias. Although the endosonographers were usually blinded to the results of other imaging studies, they were aware of the inclusion criteria and it is difficult to disguise jaundice, a major manifestation of bile duct obstruction.
The accuracy of intraductal ultrasound (IDUS) of CBD stones is also very high, reaching 100%.,,, The size of the probe (2 mm) allows an insertion inside the bile duct during an ERC. The high frequency (20 MHz) provides higher resolution than conventional EUS. Moon et al . compared the sensitivity of IDUS and MRC to the results of ERC with endoscopic sphincterotomy and stones removal. For the detection of CBD stones, the sensitivity of IDUS and ERC was 95 and 80%, respectively. The main drawback of IDUS remains the morbidity of ERC, which must be performed at the same time.
| Do benefits outweigh the costs?|| |
Cost-effectiveness of EUS in patients with CBD stones depends primarily on the risk of stones, stone-related symptoms and operator expertise. Expert intra-operative cholangiogram was the least costly for intermediate risk patients when risk of stones is between 17 and 34%, however, if expert EUS is available, 0-10% 'low' risk of stones merits expectant management, 11-55% 'intermediate risk' merits EUS; and greater than 55% "high risk" merits ERC. Buscarini et al . conducted a prospective study on 485 patients suspected to have CBD stones to evaluate the effectiveness, based on patient outcome and the potential clinical and economic benefits of EUS. EUS was highly reliable for diagnosis of CBD stones and its use offers considerable clinical and economic advantages by preventing inappropriate and more invasive evaluation of the CBD.
| EUS role in the management of acute pancreatitis|| |
EUS was compared with other imaging techniques in patients with acute pancreatitis thought to be gallstone induced in multiple prospective studies.,,,, EUS was found to be safe and superior to transabdominal US or abdominal CT scan or MRC and at least as accurate as ERC with an overall diagnostic accuracy of 90-97% for the detection of bile duct stones. Prat et al . suggested that rate of morbidity and mortality could be reduced by using systemically EUS in case of acute pancreatitis followed by ERC with sphincterotomy when EUS has demonstrated CBD stones. Recently Romagnuolo et al. assessed the relative costs and outcomes of EUS and MRC compared to ERC in patients with acute biliary pancreatitis (ABP). EUS was found to be significantly less costly in patients with severe ABP than both ERC and MRC with fewer complications than ERC.
| EUS or MRC for CBD stones?|| |
A systematic review of the five randomized, prospective trials,,,,, comparing EUS and MRCP [Figure - 6] showed no significant differences between these modalities in terms of sensitivity, specificity, positive and negative predictive values or likelihood ratios [Table - 2]. The differences between EUS and MRC were largely explained by stones size as the sensitivity of MRC in detecting stones above and below 5 mm was 100 and 67%, respectively., When deciding between EUS and MRCP, clinicians should consider other factors, such as resource availability, experience, and costs.
| Conclusions|| |
In summary, available data are sufficient to establish a role for EUS in the diagnosis and exclusion of bile duct stones. The examination combines the best performance and almost zero morbidity and unlike other indications, the results in relation to CBD stones depend little on the experience of the operator. Therefore, EUS may be considered in lieu of ERCP as a diagnostic test for patients felt to have a low to intermediate risk of CBD stones. The main advantage of EUS over MRC its sensitivity and specificity stones less than 5mm in size. Finally when EUS chosen as the imaging modality to identify CBD stones, it safe and seems logical to do ERC during the same session.
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Abdulrahman M Aljebreen
Gastroenterology Division, King Khalid University Hospital, Riyadh, 11321, PO Box 231494
Source of Support: None, Conflict of Interest: None
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6]
[Table - 1], [Table - 2]