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Original Report |
1 Department of Diagnostic Radiology and Research Institute of Radiological
Science, Yonsei University College of Medicine, 134 Shinchon-dong,
Seodaemun-gu, Seoul 120-752, South Korea.
2 Department of Internal Medicine, Yonsei Institute of Gastroenterology, Yonsei
University College of Medicine, Seoul, South Korea.
3 Department of Surgery, Yonsei University College of Medicine, Seoul, South
Korea.
Received June 6, 2004;
accepted after revision September 9, 2004.
Address correspondence to M. J. Kim
(kimnex{at}yumc.yonsei.ac.kr).
Abstract
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CONCLUSION. Use of MR cholangiography preferentially before laparoscopic cholecystectomy, on patients who have a moderate or high risk of common bile duct stones, can significantly reduce purely diagnostic endoscopic retrograde cholangiography.
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Many authors have compared the accuracy of MR cholangiography (MRC) with that of endoscopic retrograde cholangiography (ERC) [6-15]. However, no consensus has been reached on the criteria for deciding which technique should be used for evaluation of calculous cholecystitis before cholecystectomy and for diagnosis of coexistent choledocholithiasis. In many cases, selection of a diagnostic technique is based on the surgeon's preference, the endoscopist's skill, or the facilities available at an institution.
The aim of this study was to suggest criteria for selection of preoperative diagnostic techniques by analyzing the clinical course and biochemical and sonographic results of patients undergoing MRC or ERC before laparoscopic cholecystectomy (LC).
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The preoperative evaluation for all patients consisted of abdominal
sonography and serum biochemical tests (total bilirubin, transaminase
[aspartate aminotransferase and alanine aminotransferase], 
-glutamyl
transferase, alkaline phosphatase, amylase, and lipase). MRC or ERC was
performed because of suspected choledocholithiasis. Physicians or surgeons
chose between MRC and ERC according to the clinical and laboratory findings
and personal preference. However, no strict indication dictated that MRC or
ERC would be performed; similarly, no selection criteria were used to choose
between MRC and ERC.
Retrospectively, patients were categorized into two groups. The MRC/ERC group (n = 57) preferentially underwent first MRC and then ERC if clinically indicated, and the ERC-only group (n = 91) preferentially underwent ERC without MRC.
The patients also were retrospectively divided into four risk groups (group 1, very high; group 2, high; group 3, moderate; and group 4, low) based on the level of suspicion of CBD stones. Group 1 included patients with cholelithiasis, biliary colic, a CBD diameter of 6 mm or more on sonography, two or more significant serum chemistry abnormalities, and no evidence of biliary pancreatitis. Group 2 included patients with cholelithiasis, a CBD diameter of 6 mm or more, two or more significant serum chemistry abnormalities, and biliary pancreatitis or resolving choledocholithiasis. Group 3 included patients with cholelithiasis, a CBD diameter of less than 6 mm, one or more significant serum chemistry abnormalities, and acute pancreatitis or resolving choledocholithiasis. Group 4 included patients with cholelithiasis, a CBD diameter of less than 6 mm, normal or minor serum chemical abnormalities, and no evidence of pancreatitis. Resolving choledocholithiasis was defined as a case that initially presented with significant serum biochemistry abnormalities that subsequently resolved or decreased before LC, probably because of passage of stones. Biliary pancreatitis was defined as the presence of cholelithiasis, persistent abdominal pain, a serum amylase or lipase level three times normal, and no other causes of pancreatitis. The criteria for the risk groups and the definition of significant serum chemistry abnormalities are listed in Table 1. We used the criteria previously suggested by Liu et al. [9], with modification.
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The findings of each MRC examination were consensually interpreted by a proficient radiologist who had at least 3 years of experience with such interpretations and two or three residents or fellows. The examiners were unaware of laboratory and other imaging findings at the initial interpretation, knowing only that the purpose of the MRC was to rule out choledocholithiasis in a gallstone patient. The results of the MRC interpretations were used for the analysis in the current study. A CBD stone was defined as a nodular area of low signal intensity within a high-signal-intensity lumen. ERC was performed and interpreted by an expert gastroenterologist.
The presence or absence of CBD stones was confirmed by ERC or intraoperative cholangiography (IOC). In the patients who had undergone only MRC, the presence of CBD stones was excluded if laboratory findings were normal and stone-related symptoms absent during follow-up. The patients were followed up in an outpatient clinic 1 week after the LC routinely and 6 months or 1 year after the LC if they had no biliary symptoms. The patients were considered well if they did not visit a hospital during the follow-up period.
Age and laboratory values were compared using an independent-sample t test, and sex ratio was compared using the chi-square test. The chi-square test was also used to determine whether the incidence of choledocholithiasis, the number of purely diagnostic ERC examinations, and the rate of symptomatic retained CBD stones during the follow-up period (10-26 months) were different between the two technique groups in each risk group. One-way analysis of variance was performed with a multiple-comparison post hoc test using Tamhane's T2 to determine differences in age, laboratory values, and incidence of stones among the four risk groups. Statistical analyses were performed with SPSS software (release 10.0, SPSS Inc.) for Windows (Microsoft).
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-glutamyl transferase. CBD stones were diagnosed in
45 (30.4%) of the 148 patients, 33 (36.3%) of the 91 ERC-only patients, and 12
(21.1%) of the 57 MRC/ERC patients, with no statistically significant
difference between the two technique groups (chi-square test). Comparisons
between the ERC-only and MRC/ERC groups are summarized in
Figure 1 and
Table 2.
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In the ERC-only group, CBD stones were present in 33 patients (36.3%) and endoscopically removed, whereas ERC showed no CBD stones in 49 patients (53.8%), of whom 14 underwent endoscopic sphincterotomy. ERC had technically failed to cannulate the bile duct in nine patients (9.9%). Therefore, the ERC was purely diagnostic in 35 patients (38.5%).
In the MRC/ERC group, CBD stones were present in 12 patients (21.1%). MRC depicted CBD stones in 13 patients, 12 of whom preoperatively underwent ERC and the remainder, IOC. Three of the 13 patients showed no CBD stones by ERC or IOC (false-positive MRC findings, 5.3%). These three patients were regarded clinically as having passed a CBD stone because the serum total bilirubin and alkaline phosphatase levels, which had been elevated before MRC, were decreased at the time of ERC. MRC showed no CBD stones in 44 patients, of whom 32 subsequently underwent LC without undergoing ERC or IOC. Twelve patients underwent ERC despite negative MRC findings, and CBD stones were detected in two patients (false-negative MRC findings, 3.5%). One of the two patients had normal results on biochemical testing at the time of MRC but abnormal results at the time of ERC. A tiny stone was shown by endoscopic sphincterotomy in the remaining patient. Five of the 12 patients underwent endoscopic sphincterotomy in the absence of CBD stones. The ERC was purely diagnostic in the remaining five patients (8.8%).
The sensitivity, specificity, and accuracy of MRC in identifying CBD stones with reference to direct cholangiography (ERC or IOC) were 83%, 93%, and 91%, respectively.
Risk Groups
The proportion of each risk group in each technique group is presented in
Figure 2. The serum chemistry
data and statistical differences among the risk groups are summarized in
Figure 3 and
Table 3. Group 2 versus group 3
showed no statistical difference in serum biochemistry results except for
amylase level.
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The incidence of CBD stones was 32 (86.5%) of 37 patients in group 1, eight (22.9%) of 35 in group 2, five (13.5%) of 37 in group 3, and zero (0%) of 39 in group 4. The rates of occurrence of CBD stones in the MRC/ERC and ERC-only groups, according to risk group, are listed in Figure 4. In each risk group, the incidence of CBD stones was not significantly different between the MRC/ERC and ERC-only groups.
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Retained CBD Stones After LC
The follow-up period after LC was 10-26 months. Biliary obstructive
symptoms due to retained CBD stones were identified in two patients. CBD
stones were detected 6 months and 1 year after LC in the two patients, and
their preoperative risk groups were 1 and 3, respectively. These patients were
included in the ERC-only group, and retained CBD stones were not detected in
the MRC/ERC group.
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Currently, most physicians and radiologists agree on the need to reduce the diagnostic use of ERC, but no consensus has been reached on the indications for the use of MRC. Some authors recommend the use of MRC for moderate-risk groups only [7, 9, 15], and others recommend MRC for both high- and moderate-risk groups [8, 13].
We previously reported the accuracy of MRC according to clinical risk groups in symptomatic gallstone patients [8]. In that study, patients were categorized into three groups—with a high, moderate, and low risk for CBD stones. We suggested the use of MRC not only for the moderate-risk group but also for the high-risk group because CBD stones were not identified in 30% of patients in the high-risk group and the frequency of diagnostic ERC could not be ignored.
In the present study, we modified the criteria for risk groups suggested by Liu et al. [9], who classified patients into four risk groups—namely, extremely high, high, moderate, and low. The criteria of Liu et al. are similar to those generally used but different in that patients with acute biliary pancreatitis or resolving choledocholithiasis are classified into either a moderate-risk group or a high-risk group rather than a very-high-risk group. The criteria of Liu et al. are reasonable because, in patients with acute biliary pancreatitis, the incidence of choledocholithiasis has been reported to be low, presumably because of the early passage of gallstones [18, 19]. The difference between our current criteria and the criteria of Liu et al. is that we defined an upper limit of 6 mm for the diameter of a normal CBD. Conversely, they used 5 mm as the upper limit because the patients in their study were relatively young (mean age, 36.8 years). However, the mean age of the patients in our study was 54.7 years, so we used the generally accepted standard [20-24]. If we had used 5 mm as the upper limit, the difference in the incidence of CBD stones between group 2 and group 3 might have been smaller.
In the present study, the incidence of CBD stones was 86.5% in the very-high-risk group (group 1) and 0% in the low-risk group (group 4). Because the rate of purely diagnostic ERC was acceptably low (5.4%) in the very-high-risk group (group 1), it would have been optimal to perform ERC without intervening MRC in this group. Meanwhile, the incidence of purely diagnostic ERC was relatively higher in the ERC-only group, with high and moderate risks as compared with the MRC/ERC group with similar risks. Therefore, we suggest that MRC be recommended first for these high- and moderate-risk groups. Our data suggest that neither MRC nor ERC is indicated for low-risk groups. The patient management algorithm that we recommend is depicted in Figure 5.
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In the current study, CBD stones were not detected in group 4, and no morbidity due to retained stones occurred during the follow-up period. Hence, preoperative bile duct imaging could be omitted in the low-risk group, and MRC is recommended only if the patient presents with newly developed symptoms or laboratory abnormalities.
This study was limited because its retrospective design did not allow randomization of the choice of ERC or MRC. Because the selection of diagnostic technique was based on the clinician's preference or subjective confidence in the presence of a CBD stone, ERC was used more frequently for the groups at higher risk and MRC, for the groups at lower risk. We expect that the rate of purely diagnostic ERC would have been higher if this study had been randomized.
In conclusion, our modification of the criteria for selecting risk groups could effectively predict CBD stones in gallstone patients. Use of MRC preferentially before LC in patients who have a moderate or high risk of CBD stones can significantly reduce the purely diagnostic use of ERC.
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