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Keywords
Choledocholithiasis, EUS
Introduction
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Endoscopic ultrasonography (EUS) is an invaluable tool for the diagnosis of choledocholithiasis. The close proximity of the echoendoscope to the extra hepatic bile ductal system, lack of radiation and safety makes it an excellent method for examining the common bile duct and gallbladder such that small stones, biliary sludge and even microlithiasis can be demonstrated. Choledocholithiasis is easily identified as curvilinear hyper echoic foci with strong acoustic shadowing using either standard or catheter based EUS (1). Low amplitude echoes without acoustic shadowing are considered sludge. Diagnostic accuracy of the radial or the linear echo endoscopes are equivalent (2, 3). The extra hepatic ductal system can be visualized completely by EUS in 96% (4). Additionally, EUS can provide an alternative diagnosis in 14-21% of cases (2, 5). EUS is a minimally invasive procedure with a procedural risk identical to that of oesophagogastroduodenoscopy (OGD). In our series of 3,006 patients, complication from diagnostic EUS occurred in only 3 (0.1%) (6). Choledocholithiasis can occur as migrant from the gallbladder or forms de novo in the common bile duct (CBD). It is a disease that can cause morbidity (pain, fever, pancreatitis, etc.) or mortality especially if left untreated. The diagnosis, hence treatment rests on the accuracy of imaging modalities (transabdominal ultrasonography, CT scan, ERCP, MRCP, EUS, IDUS and IOC) to correctly confirm its presence or absence. Because of this, imaging modality with higher sensitivity, specificity, positive predictive value and negative predictive value is of immense value in patients with low to moderate probability of finding common bile duct stones prior to laparoscopic cholecystectomy to avoid any unnecessary procedures like ERCP or surgery with CBD exploration (open or laparoscopic) that may increase the risks, morbidity and cost to the patient.
EUS vs. TUS
Transabdominal ultrasonography (TUS) is usually used as the initial imaging diagnostic test when one suspects choledocholithiasis because it is non-invasive, widely available, safe, lacks radiation and inexpensive. However, extra hepatic bile duct is seen wholly in only 60-80% (4,7). The clinical reliability of TUS suffers due to its poor sensitivity of 25-82% and limited specificity of 56-100% for the detection of CBD stone (4,8-11). It has a reported positive predictive value of 69% and negative predictive value of 78% (12). The wide range of values for TUS can be partially explained by its operator dependency. Although EUS is also operator dependent to some extent, its close proximity to the extra hepatic biliary system makes identification and evaluation of CBD stones consistently possible. EUS gives a sensitivity of 88-97% and specificity of 93-100% for the detection of CBD stone (2-4,8,9,13-15). Because of the poor sensitivity of TUS, it cannot accurately rule in or out with confidence the presence or absence CBD stone.
EUS vs. CT SCAN
Computed tomography scanning (CT scan) can be employed to detect common bile duct stones. It is a readily accessible, relatively affordable procedure. However, patients are subjected to some amount of radiation and are given either intravenous or oral contrast agent that is contraindicated in patients who have allergy to iodine or patients with renal insufficiency. More importantly, the ability of CT scan to examine the extra hepatic bile duct entirely is only 80% as against 96% for EUS and furthermore, it is poorly diagnostic for small stone in a non-dilated duct (4). This would mean inadequate examination in at least 20% of patients undergoing CT scan for suspected CBD stones that can significantly influence the sensitivity of CT scan for detecting CBD stones. Studies have showed CT scan to have a sensitivity of 71-75% and specificity of 78-97% (4,9). Using unenhanced helical CT, the sensitivity is 65-88% and specificity is 84-100% (16-18). When contrast IV cholangiography was used in helical CT, the sensitivity is 85% and specificity is 88% (19). Comparison between CT scan and EUS for detecting CBD stones shows that EUS to be more superior for the detection of CBD stones.
EUS vs. ERC
Endoscopic retrograde cholangiography (ERC) is currently one of the gold standards for the diagnosis and treatment of CBD stones. It is an invasive procedure utilizing fluoroscopy and has a success rate of around 90-95% under experienced hands. Complications such as pancreatitis, sepsis, hemorrhage, perforation and death occur 3-6%, (20) particularly after endoscopic sphincterotomy, this figure increases to 5.3-6.5% (21,22). For patients with low to moderate probability of having common bile duct stones, this complication rate is unacceptable. Advantages of ERCP is its capability for therapy in the form of sphincterotomy and basket or balloon extraction of CBD stone, it can also examine proximal or intra-hepatic bile ducts (IHBR) and in patients with choledochoenteric communication, previous endoscopic sphincterotomy or surgery where aerobilia can be present may provide some difficultly for EUS examination. ERCP on the other hand, can miss small stone especially in patients with a very large CBD. Numerous studies, both prospective and retrospective comparing EUS with ERCP have been published. EUS has a sensitivity of 88-97%, specificity of 93-100% when compared with ERCP that has a sensitivity of 79-93%, specificity of 92-100% (2-4,8,9,13-15). The positive predictive value and negative predictive value of EUS are 98% and 87-88% respectively (3,15). In our series, 62 patients were referred for suspected CBD stone, we were able to examine the entire CBD, from the common hepatic duct down to the papilla in all patients. Comparing our EUS result with ERCP, surgery and clinical follow-up, we achieved a sensitivity of 100%, specificity of 99%, positive predictive value of 100% and negative predictive value of 100% for the detection of common bile duct stones. Even in patients with abnormal pancreaticobiliary junction (long common channel), EUS can detect CBD stone/sludge.
EUS vs. MRC
Magnetic resonance cholangiography (MRC) is a non-invasive imaging modality that is capable of imaging the biliary system without the need for radiation. This technology requires expensive state of the art equipment and like TUS and EUS is operator dependent to a certain extent. It cannot however be used in patients who have cardiac pacemakers and is relatively contraindicated in claustrophobic or uncooperative patients. MRC has been reported to have a sensitivity of 87.5-100%, specificity of 72.7-100%, positive predictive value of 62.5-100% and negative predictive value of 81.1-100% for the detection of common bile duct stones (23-29). Studies comparing MRC with EUS showed that both are as accurate for the detection of common bile duct stones (23,24). In patients with thin bile ducts and small stones, the sensitivity of MRC drops to 40-64% (29,30).
EUS vs. IDUS
Intraductal ultrasonography (IDUS) is a relatively novel procedure for the diagnosis of common bile duct stones. It is an invasive procedure that entails the use of duodenoscope and cannulation of the ampulla. Furthermore, the ultrasonic probes have limited durability and are expensive. In contrast to ERCP however, no contrast agent is use such that the risk for pancreatitis is probably lower. It was shown by Kubota et al. that patients with negative ERCP could harbor small stones seen on IDUS in 20% of cases (31). In a recent article, IDUS gave a sensitivity of 100%, specificity of 67% and overall accuracy of 97% for the detection of CBD stone (32). A current article comparing EUS and IDUS in negative ERC found out that EUS showed stone in 100% and IDUS in 87% of their patients (33). IDUS can be utilized as an adjunct in cases where ERC is doubtful as to whether a stone is present. More studies are needed on this subject to better define the role of IDUS on choledocholithiasis.
Conclusion
Endoscopic ultrasound is clearly superior to TUS and CT scan for the detection of choledocolethiasis. Magnetic resonance cholangiogram is comparable to EUS in accuracy, but is less reliable in patients with small bile ducts, where specificity of MRC is lower than EUS. The utility of IDUS in evaluating biliary stone pathology is exciting, but requires unique equipment, specialized skill of the endosocpist and further comparative studies to determine its role in the evaluation of these patients. The author would suggest that when probability of choledocolethiasis is high that conventional therapeutic ERCP would be the preferred test. The risk of therapeutic ERCP is outweighed by the benefit of combined diagnosis and institution of definitive treatment. However, when the preoperative probability of choledocolethiasis is only low to moderate, and the technical expertise to perform EUS is available, EUS should be the preferred test prior to cholecystectomy.
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Video Clip 1: EUS showing intrasphincteric CBD and MPD in the ampulla of vater.
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Video Clip 2: EUS showing small stone (3.8 mm) in the prepapillary portion of the CBD.
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Video Clip 3: EUS showing small stone in a dilated CBD with post acoustic shadowing. |
Video Clip 4: EUS showing minimal amount of sludge
in the lower CBD. |
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Note
Dr. Rathod and Dr. Dy work at Bhatia & Jaslok Hospitals in Mumbai, India. Please feel free to contact Dr. Vipul Rathod via e-mail at vr4ercp2eus@yahoo.co.in.
References
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