Occult bile duct stones refer to small stones in the common bile duct in combination with gallbladder stones, which do not cause dilatation of the bile ducts inside and outside the liver, do not cause jaundice and obstruction symptoms, and are not easily detected by ultrasound in the common bile duct. If there are common bile duct stones or suspicious stones found by MRCP, ERCP will be performed first to confirm the presence of common bile duct stones before performing duodenal papillotomy for stone extraction, thus avoiding the missed diagnosis and treatment of hidden stones in the common bile duct. From January 2005 to February 2010, 20 cases of common bile duct occult stones were found among 1490 patients with gallbladder stones. 1. Clinical data and methods (1) General data Among the 20 patients, 9 were male and 11 were female, aged 32-74 years, with an average age of 43.5±2.1 years. All of them were diagnosed as gallbladder stones by ultrasound examination before the operation, and the invisible stones in the common bile duct were found accidentally by MRCP examination in our hospital before the minimally invasive biliary surgery. 12 cases had single stones and 8 cases had multiple stones, and the diameter of the stones was less than 0.8 cm. (2) Surgical method All the patients who were clearly diagnosed with invisible stones in the common bile duct by MRCP examination underwent ERCP examination again, and those who had stone shadow clearly by imaging underwent duodenal papillotomy for stone extraction. 16 cases did not have ENBD drainage tube, 2 cases had ENBD drainage tube, and then underwent minimally invasive gallbladder retrieval after a week of recovery from the common bile duct stone extraction. In one case, papillotomy could not be performed because the papilla was located in the diverticulum, and the success rate of papillotomy was 95%. In one case, the papillotomy could not be performed because the papilla was located in the diverticulum, and the success rate of papillotomy was 95%. Those who were unsuccessful in imaging and incision were treated by transabdominal surgery, and biliary stone extraction was performed. (3) Postoperative complications and follow-up results 15 cases showed transient elevation of blood amylase, 1 case showed acute simple pancreatitis which was improved by conservative treatment, and there were no serious complications. There were 2 cases of wound infection after biliary lithotripsy, which were cured after drug change. All 20 patients were cured. 18 patients underwent ERCP+EPT first and then minimally invasive biliary stone extraction after 1 week of stabilization. 2 patients had unsuccessful ERCP+EPT and underwent direct transabdominal surgery with minimally invasive biliary stone extraction and common bile duct exploration. 12 T-tube was placed for drainage after exploration because the common bile duct was not dilated. 2 weeks later, the T-tube could be removed if there was no abnormality in the imaging. About 10% of patients with gallbladder stones have coexisting common bile duct stones, and it is not uncommon to have surgery for gallbladder stones but miss the diagnosis of preoperative asymptomatic common bile duct stones, resulting in postoperative recurrence of biliary colic and acute cholangitis, which increases the psychological burden of patients and causes stress to medical staff. Cryptogenic choledochal stones are a new concept and can originate from primary or secondary common bile duct stones, which are small, less than 0.8 cm, multiple or single, and these small stones do not lead to dilatation of the intra- and extra-hepatic bile ducts, do not cause jaundice and obstructive symptoms, and are combined with gallbladder stones. Occult stones in the common bile duct are not easily detected by ultrasound due to the influence of gas in the digestive tract and the special anatomical location, but MRCP has an accuracy of up to 100% in the localization of common bile duct stones. In patients with gallbladder stones, if MRCP is not performed preoperatively, only ultrasound examination may lead to missed diagnosis of occult stones in the common bile duct. Although intraoperative cholangiography through the cystic duct is possible, the imaging conditions are not good and the resolution is not high, so the accuracy of diagnosis of small stones is not high and the diagnosis is easily missed. Even if the intraoperative diagnosis of small stones in the common bile duct is clear, but the common bile duct is not dilated, performing choledochal exploration has the risk of causing bile duct stricture and other risks. If the preoperative diagnosis of common bile duct stone is clear, ERCP examination can be performed first, and intraoperative imaging is feasible to remove the stone by duodenal papillotomy, because the stone is small, most of them can be removed completely. 18 out of 20 patients in our hospital completed the stone extraction treatment, and the success rate reached 90%. 2 patients were unsuccessful because of diverticulum and inability to cooperate. The preoperative removal of common bile duct stones reduces the risk of reoccurrence of acute cholangitis after surgery. The preferred treatment for occult bile duct stones is ERCP + EPT, which is less invasive, faster recovery, less damage to the common bile duct, and fewer postoperative complications. 15 of the 18 patients had transient elevated blood amylase, and one had acute simple pancreatitis that improved with conservative treatment, with no recurrent biliary tract infections and no recurrent fever or other abnormalities during the 5-year follow-up period. The papilla of the duodenum opens within the diverticulum or next to the diverticulum, and there is a risk of intestinal perforation if the papilla is cut, then papillotomy cannot be performed, which is a contraindication. Balloon dilatation of the papilla is not advisable and may lead to inability to remove stones or stone impaction. If acute cholangitis is prevented after papillotomy or if the stone is suspected to be incomplete, an ENBD drain can be placed to drain the bile, and two cases of ENBD drain were placed in our hospital. Surgical exploration of occult stones in the common bile duct is a last resort. The common bile duct is not dilated and has a thin diameter, so a suitable T-tube must be placed after incision and stone extraction to prevent bile duct stricture. Extubation can only be considered 2 weeks after surgery, which prolongs the hospital stay. Surgical exploration can be done either open or laparoscopically. The treatment of gallbladder stones is based on the principle of minimally invasive cholecystectomy to preserve the gallbladder if it is functional, or cholecystectomy if it is not functional. Minimally invasive cholecystectomy requires that the cystic duct and common bile duct be kept open to prevent the occurrence of biliary fistula. Preoperatively, patients with gallstones are routinely examined with MRCP to exclude occult stones in the common bile duct, and we found 20 patients with occult stones in the common bile duct among 1490 patients with gallstones, accounting for more than 10% of the patients and reaching more than 13%. MRCP was used as a reference for common bile duct occult stones before ERCP, and the compliance rate of both was 100%. We believe that MRCP examination is decisive for the diagnosis of common bile duct occult stones and recommend all patients with gallbladder stones to undergo MRCP examination before surgery.