Our study showed no statistical difference in patient outcomes between CT only group and MRCP group in benign gallbladder disease (Table 2). However, the MRCP group may have been more susceptible to complications and bile duct injury due to factors such as older age, higher frequency of diabetes, higher levels of the inflammatory markers, AST and ALT, higher rate of conversion, and higher rate of vague Calot triangle in the operative field compared to the CT only group (Table 1). It is well known that various factors such as patient demographics, inherent disease, and surgeon experience contribute to development or possibility of complications after cholecystectomy [16,17,18,19]. Based on subanalysis (Supplementary Table 1), other factors of male sex, older age, hypertension, comorbidities, inflammatory markers, and vague Calot triangle in the operation field significantly affected the development of complications, as in prior studies [16,17,18,19]. Hence, there is a limit of statistical evaluation to determine if there is difference in clinical outcomes between 2 groups.

With regard to hospitalization, in our study, mean length of hospital stay was longer (13 days) than reported in prior study (1.3–6.3 days) [20,21]. The reason for this disparate result could be different characteristics of the study population. Our study included patients with acute cholecystitis that needs to be treated with biliary intervention which may increase the length of stay, whereas previous study included only patients underwent cholecystectomy.

Diagnostic accuracy of MRCP for detecting CBD stones has been clearly demonstrated and is comparable to that of ERCP and intraoperative cholangiography; in addition, the sensitivity and specificity are greater than 90% [22,23,24]. Detection and elimination of CBD stones before operation is important because residual CBD stones can induce postoperative complication such as early biliary leakage, jaundice, cholangitis, and pancreatitis [25]. According to the new guidelines on CBD stone management based on a systematic literature review by the European Society of Gastrointestinal Endoscopy, stone extraction is recommended in all patients with CBD stones, regardless of size or symptoms [25]. It means that additional detection of CBD stones subsequently changes patient management. In our study, silent CBD stones were detected in 6.5% of cases with added MRCP and 88% of our patients with detected CBD stones underwent biliary procedures for stone removal. Detection rate of silent CBD stones in our study (6.5%) was slightly lower than that of previous studies (8%–18%) [20,21]. This discrepancy could be attributable to different study cohort. We included benign gallbladder diseases including polyps, adenomyomatosis, and acalculous cholecystitis as well as gallstones, whereas previous studies included patients that underwent cholecystectomy due to symptomatic gallstones.

Since the introduction of laparoscopic cholecystectomy, the change of surgical treatment from open to laparoscopic cholecystectomy has resulted in an increased incidence of iatrogenic bile duct injury, reported at more than 2–6 times the previous rate, and an increase from 0.1%–0.5% up to 3% compared to open cholecystectomy [26]. Any major bile duct injury may result in significant morbidity, increased mortality, and financial burden on the patient [27]. Therefore, prevention of bile duct injury is critical, and it is very important for surgeons to preoperatively understand bile duct anatomy. At the beginning of this study, in our institute, MRCP was performed only when the results of ultrasonography or CT were equivocal for diagnosing choledocholithiasis, or cholangitis was suspected based on the laboratory finding. However, since last 2 years, preoperative MRCP has been performed in most patients undergoing cholecystectomy to prevent bile duct injury as well as to detect silent stones. MRCP can play a major role in identifying potentially risky variants of bile duct anatomy, which were reported at 3.2% in our study.

Routine performance of MRCP prior to laparoscopic cholecystectomy has been controversial due to the associated financial considerations. Prior research has demonstrated that routine use of preoperative MRCP was not cost-effective for diagnosing and managing gallstone disease with asymptomatic choledocholithiasis [28]. However, we believe that MRCP is necessary under specific conditions and can play a significant role in the diagnosis and subsequent treatment of patients, which can have positive effects on patient outcomes. Based on our results, elevated γ-GT was the only independent factor for additional detection of CBD stones (adjusted OR, 2.89; P = 0.029) and subsequently undergoing biliary procedures (adjusted OR, 3.34; P = 0.018) when additional MRCP was performed. In our study, total bilirubin and ALP were significant factors in univariate analysis, but they were eliminated in multivariate analysis.

According to the American Society for Gastrointestinal Endoscopy criteria, derangements of liver function tests other than bilirubin are one of the moderate predictors for assessing the likelihood of choledocholithiasis [29]. However, to the best of our knowledge, none of the studies have been conducted to find clinical predictors for silent CBD stones not identified by CT. Therefore, further comprehensive studies would be needed to identify factors to select candidates who undergo preoperative MRCP in order to detect silent CBD stones.

The strength of our study is the largest comparative study to investigate the impact of preoperative MRCP on the outcomes and management of patients scheduled for laparoscopic cholecystectomy. Nevertheless, there are several limitations of this study. We performed a single-institution, retrospective review, which always presents challenges for data interpretation and can be subject to selection bias. Moreover, different environments for availability or qualification of equipment and presence of a skilled practitioner complicate generalization of our results to other institutions. The enrolled patients in our study had varied entities associated with benign gallbladder disease; therefore, there could also be differences in the rate of complications, readmission, and hospitalization between the group with stones and the group without stones. However, the majority of our enrolled patients (80%) had symptomatic gallstones. Moreover, preoperative MRCP in the non-stone group who are at a higher risk for operation or biliary obstruction such as older age, diabetes, past history of jaundice or choledocholithiasis, or abnormal laboratory markers was not uncommon at our institute, which is the reason we included various disease entities that underwent cholecystectomy. In this study, the detection rate for choledocholithiasis when MRCP was added could be over- or underestimated. A standard reference was difficult to determine because not all cases that additionally detected CBD stones underwent stone extraction. Identification of choledocholithiasis by ERCP can be limited, especially in regard to size and location of stones. In addition, there was a time interval between MRCP and ERCP, which could also have allowed some stone passage. Finally, to assess the significant variation of bile duct anatomy by MRCP, we could not identify all cases of aberrant bile ducts or cystic ducts in the operative fields or using intraoperative cholangiography as the standard of reference.

MRCP is valuable for identification of bile duct variation and CBD stones. Preoperative MRCP can be considered, particularly in patients with elevated γ-GT, for proper preoperative management and avoidance of complications.