In this study, the balloon-occlusion cholangiography failed to detect residual bile duct stones in 4.8%. This tool cannot accurately confirm complete bile duct clearance following EST/EPBD for stone extraction. A previous report had showed that residual stones were significantly correlated with diverticulum, stone size, and use of ML and electrohydraulic lithotripsy (EHL). Compression or bending of the lower bile duct by the parapapillary diverticulum would generally promote lesser spontaneous residual stone passage. Moreover, large biliary stones (i.e., those requiring ML or EHL for extraction) promote significantly increased rates of residual stones. Hence, ML has been considered to induce increased rates of fragmented residual stones . However, in this study, the presence of diverticulum, maximum stone diameter, and frequency of lithotripsy between sessions with or without residual stones have no marked difference.
To confirm complete bile duct clearance, some endoscopists perform IDUS . After performing IDUS following stone extraction, Tsuchiya et al. found no residual CBD stones in 23.7% (14/59) of the patients via balloon-occlusion cholangiography . However, accurate IDUS evaluation to confirm the presence residual stones may be difficult given that the procedures for papilla, such as EST, may cause pneumobilia, which makes obtaining echo imaging in the bile duct challenging. Therefore, we rarely perform IDUS to confirm the presence of residual stones.
POCS has been described in the evaluation of residual stones that are not detected by cholangiography. POCS is particularly appropriate when pneumobilia exists. After performing POCS, Itoi et al. reported that 24% of the patients still had residual stones after stone extraction by ERCP . Moreover, a multicenter study utilizing POCS revealed that POCS alone identified bile duct stones in 11% of patients (7/66) . However, considering the cost and complexity, POCS is difficult to perform when confirming complete extraction of bile duct stones in all cases.
Univariate analyses conducted herein identified a large number of stones (P = 0.01), long procedure time (P = 0.005), and use of P-GW (P = 0.01) as factors contributing to residual stones, while multivariate logistic regression analysis identified the used of P-GW as an independent factor for residual stones (AOR, 3.44; 95% CI, 1.19–9.88; P = 0.02). The aforementioned results therefore suggest that complicated procedures may lead to residual stones.
Previous studies on P-GW efficacy have reported varying results, with biliary cannulation success rates ranging from 43.8% to 92.6%. Furthermore, P-GW techniques are useful for patients with difficult biliary cannulation [17-21].
Another advantage of P-GW includes the ease of pancreatic stent placement following the procedure, granting that P-GW can be completed using the guidewire placed in the pancreatic duct. Difficult biliary cannulation has thus been considered a procedure-related risk factor for PEP . As such, a pancreatic duct stent should be provided to patients with difficult biliary cannulation who underwent successful biliary cannulation through P-GW to prevent PEP even when EST had been performed . Therefore, we generally place a pancreatic duct stent over the guidewire used during P-GW at the end of the examination. Therefore, we removed bile duct stone with the pancreatic duct guidewire in place. However, the complexity of this procedure may contribute to the incomplete removal of stones. Keeping the wire in place may have negative effects, such as prolonged procedure times, insufficient EST, and restricted applications of devices. Early pancreatic stent placement after guidewire insertion can be associated with reduced incidences of PEP and residual stones . However, spontaneously dislocated pancreatic duct stents may fall off during the procedure, while indwelling pancreatic duct stents may lead to a risk for pancreatitis when removed immediately after the procedure, thereby requiring some time and effort to remove it. Another option might be removing P-GW after bile duct cannulation. This method requires repeating pancreatic duct cannulation and inserting a pancreatic duct stent after the procedure. However, re-cannulation of the pancreatic duct after EST or stone removal may be difficult and may increase the risk of pancreatitis if it fails.
Although data had been retrospectively collected, none of the patients underwent intentional or inadvertent guidewire removal and pancreatic guidewire replacement. When we perform P-GW for bile duct stone extraction, we should pay attention to the values of hepatobiliary enzymes in blood tests after the procedure because residual stones may exist. If the increase in hepatobiliary enzymes persists after the procedure, early image evaluations, such as CT and MRCP, should be performed. As mentioned above, IDUS is not useful when pneumobilia exists, and POCS is not available in every institution.
To the best of our knowledge, this has been the largest study to investigate risk factors of residual bile duct stones after extraction via ERCP. Several limitations must be considered when interpreting the results. The possibility of a stone falling from the gallbladder to the CBD could not be ruled out; therefore, we excluded cases of bile duct stone recurrence of more than 2 months after the first ERCP session for analysis. However, even for residual stone cases in this study, completely ruling out of falling stones from the gallbladder to the CBD is impossible. Therefore, patients with gallstones need to undergo cholecystectomy after ERCP as soon as possible given that stones may enter into the CBD. Moreover, considering that all data had been retrospectively collected from a single center, a prospective study including a larger cohort will be necessary.