Endoscopy 2003; 35(5): 426-428
DOI: 10.1055/s-2003-38783
Editorial

© Georg Thieme Verlag Stuttgart · New York

Which Test to Replace Diagnostic ERCP - MRCP or EUS?

C.  L.  Kay
  • 1Dept. of Radiology, Bradford Royal Infirmary, Bradford, UK
Further Information

Publication History

Publication Date:
17 April 2003 (online)

Choledocholithiasis coexists with cholelithiasis in a significant number of patients (15 - 20 %) [1], and is present in 1 - 5 % of patients who have undergone cholecystectomy [2]. As clinical and biochemical abnormalities associated with this condition are neither sufficiently accurate nor specific, transcutaneous ultrasound (TUS) remains the initial imaging test in the evaluation of patients with suspected bile duct calculi. TUS, although it is noninvasive, quick, cheap, and readily available, has a widely variable sensitivity for the detection of choledocholithiasis of 20 - 80 % [2], not least because of its highly operator-dependent nature. Endoscopic retrograde cholangiopancreatography (ERCP) has been widely used for the detection of common bile duct (CBD) calculi, and serves not only as an accurate diagnostic modality, but also as a therapeutic manoeuvre. ERCP is, however, invasive, operator-dependent, and is associated with significant morbidity and mortality rates of 1 - 6 % and 0.1 - 0.6 %, respectively [3] [4] [5], as a result of pancreatitis, sepsis, perforation, and haemorrhage. While such complication rates may be acceptable in therapeutic ERCP, as an alternative to the higher risks of surgical management, these levels of morbidity and mortality are not acceptable when only diagnostic ERCP is necessary. Consequently, the need for safe, noninvasive imaging of the pancreaticobiliary tree has resulted in the development of magnetic resonance cholangiopancreatography (MRCP).

Since the introduction of MRCP in 1991 [6], a variety of techniques and sequences have been used to generate images of the pancreaticobiliary tree [7] [8] [9] [10] [11] [12] [13]. The basic principle of MRCP is that by using heavily T2-weighted sequences, stationary fluid such as that in the biliary tree and pancreatic duct appears as a high-intensity (bright) area, while the background tissues appear as low-intensity (dark). The resulting image can then be portrayed in a similar fashion to ERCP, with bile duct calculi represented as signal voids (low-intensity areas) (Figures [1] [2]). Many advances in the technique have taken place, with particular attention focused on successfully minimizing motion and respiratory artifacts. Its accuracy has been further enhanced by increasing experience with the technique and through improvements in image quality as a result of technical modification in sequences and the use of phased-array imaging coils. MRCP is performed noninvasively without the use of ionizing radiation, iodinated contrast, or routine sedation.

Figure 1 Magnetic resonance cholangiogram, showing a 2-mm calculus in the distal bile duct.

Figure 2 a Magnetic resonance cholangiogram, showing multiple calculi in the distal bile duct. Cholelithiasis is also seen. b Endoscopic retrograde cholangiogram confirming multiple bile duct calculi.

Most studies have shown that MRCP is 95 % accurate in differentiating between normal and dilated bile ducts [14] and that it is comparable to ERCP in the detection of obstruction, with sensitivity, specificity, and accuracy rates of 91 %, 100 %, and 94 %, respectively [15]. MRCP is comparable to ERCP in the detection of choledocholithiasis, with recent studies demonstrating sensitivities of 81 - 100 % and specificities of 85 - 100 % [16] [17]. In the largest published series of patients with choledocholithiasis [18], in only one of the 46 cases was the diagnosis of bile duct calculi missed by MRCP (a sensitivity of 97 - 98 %). In the same study, MRCP correctly identified the 12 patients with biliary strictures [18]. Farrell et al. [19] showed that the use of MRCP could have avoided 44 % of ERCP procedures and could have reduced the endoscopy workload by 13 %. MRCP, routinely a 15 - 20 min examination, may be further complemented by a range of further sequences providing multiplanar imaging in the evaluation of a wide spectrum of disease [20].

There are, however, several limitations to MRCP, not least because of its absolute contraindications in patients with a permanent pacemaker or cerebral aneurysm clips. Approximately 4 % of patients are too claustrophobic to undergo the examination. Specifically in relation to choledocholithiasis, the nature of the signal voids is nonspecific, and apart from calculi they may also be due to air, mucus, or blood. Perhaps the main limiting factors, however, are the issues of accessibility and cost-effectiveness - although as the number and quality of MRI scanners increases, these issues should become less problematic.

In recent years, endoscopic ultrasound (EUS) has been suggested as an excellent means of evaluating the biliary tree in patients with suspected choledocholithiasis, with sensitivities of 93 - 97 % and specificities of 97 - 100 % [21] [22]. In this issue of Endoscopy, Napoléon et al. [23] report a 1-year prospective follow-up of 238 patients, initially referred with a suspicion of choledocholithiasis, but in whom the initial biliary EUS was normal. They report a high negative predictive value of EUS for choledocholithiasis of 95.4 %. The role of MRCP was not assessed in this study.

There have been only a handful of studies that have attempted to evaluate the relative roles of EUS and MRCP in the detection of bile duct calculi. De Lédighen et al. [24] reported a higher accuracy for EUS (96.9 %) compared to MRCP (82.2 %) - but significantly, the sensitivity and negative predictive values of MRCP and ERCP all equalled 100 %. Furthermore, there were only 10 cases of choledocholithiasis in this study of 32 patients. Scheiman et al. [25] reported that EUS was superior to MRCP for choledocholithiasis. However, in this study of 30 patients, only five had bile duct calculi. Whilst it appears likely that EUS is superior to MRCP in the detection of microlithiasis, this technique is more expensive and the risk of complications greater than with magnetic resonance cholangiography (MRC) [26]. Burtin [26] estimated the cost of EUS as $ 438 per procedure versus $ 361 for MRCP. The same study noted more morbidity and mortality with EUS than with MRC (0.05 % vs. 0 % and 0.01 % vs. 0 %, respectively). Furthermore, there is considerable controversy in the literature regarding the natural history of asymptomatic small stones [27]. Finally, despite EUS being more than 20 years old, it remains highly inaccessible and very operator-dependent, almost certainly more so than is the case with MRCP.

So where does all this leave us in the debate of whether it is MRCP or EUS which should replace diagnostic ERCP? Whilst acknowledging the many potential benefits of the so-called “one-stop” investigation, it is my view that an overriding principle of care should be that patients undergo the least invasive, least harmful, and most widely available investigations initially, reserving the more invasive, potentially harmful and less widely available investigations for later should they be required. In parallel to such a principle, better decision-making algorithms are required to guide investigation and therapy. Specifically, in relation to choledocholithiasis, and based on the currently available literature, only patients with a high probability of requiring intervention - e. g., those with cholangitis or obstructive jaundice - would be offered therapeutic ERCP directly [28]. By the same token, low-risk patients (with minimally dilated bile ducts or minimally disordered liver function studies) would be screened by MRCP. Where clinical concern for choledocholithiasis persists in “MRCP-negative” patients, it would seem entirely appropriate to proceed to EUS.

Above all else, we should move away from the idea that investigations merely exist to compete with one another, but instead accept that investigations often provide complementary information which ultimately results in optimum patient care.

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C. L. Kay, F.R.C.P., F.R.C.R.

Dept. of Radiology · Bradford Royal Infirmary

Bradford · England · United Kingdom

Fax: + 44-1274-364661

Email: kaycl44@hotmail.com

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