This study showed that there was no significant difference in surgery outcome or postoperative complications between small and large CBD groups, which confirmed that LCBDE is feasible and safe for choledocholithiasis with small CBD.

Choledocholithiasis is one of the most common diseases in general surgery. With the improvement of living standards and the adjustment of diet structure, the incidence of choledocholithiasis increases year by year[17,18]. Currently, the preferred less invasive treatment is preoperative EST or LCBDE, which is recommended by the British Society of Gastroenterology[19]. However, EST is associated with a series of postoperative complications such as bleeding, pancreatitis, perforation, and even death. The overall postoperative complication rate of EST reached 5%-14%, and the mortality rate was 0.3%-2.3%[20-22]. Some studies[23,24] have shown that compared with two-stage perioperative EST and subsequent LC, single-stage LC + LCBDE can reduce the overall hospital stay and cost. Ding et al[8] indicated that the single-stage LC + LCBDE and two-stage preoperative EST followed by LC are equally effective in achieving initial CBDS clearance, but recurrent CBDS is more likely to occur in patients who had undergone two-stage treatment (9.47% vs 2.06%). This result may be due to the fact that EST disrupts the integrity of the Oddi sphincter, which will make it easier for the duodenal contents to reflux into the biliary system, leading to bacterial colonization and the subsequent CBDS formation. Although no high-level evidence indicated that EST will cause atypia or malignancy, EST has been demonstrated to cause reactive and proliferative changes in the CBD biliary epithelium[25].

T-tube drainage has been widely used in laparoscopic choledochotomy in order to decompress the biliary tree, reduce the complications such as bile leak and CBD stenosis, and provide an access for postoperative trans-T–tube tract choledochoscopy to detect any residual stones and removal them. However, T-tube drainage is associated with a postoperative complication rate of around 10.5%-20%, including fluid and electrolyte imbalance, accidental T-tube displacements, bile leak and wound cellulites around the T-tube, and bile peritonitis after T-tube removal[26,27]. An updated meta-analysis has shown that compared with primary CBD closure, planned T-tube insertion prolongs overall hospital stay and operating time without any evidence of benefit[28]. Thus, among patients undergoing laparoscopic choledochotomy for CBDS, T-tube drainage may not be necessary.

LCBDE can be carried out via the transductal approach or the transcystic approach, the latter is known as laparoscopic transcystic common bile duct exploration (LTCBDE). This approach protects the integrity of the CBD and avoids suture repair after choledochotomy, which is thought to be associated with lower morbidity compared to the transductal approach. A study from Tokumura et al[29] found only one bile leak in 91 patients (1%) with successful stone clearance using the transcystic approach. Another study from Waage et al[30] found one bile leak in 110 patients (0.9%) using the transcystic approach. However, it should be pointed out that their study did not indicate the diameter of the CBD. In fact, it is very difficult to perform LTCBDE in choledocholithiasis with small CBD. For those patients, cystic duct is always smaller than 3 mm, making it difficult for the 5 mm cholangioscope to pass through the cystic duct. Fang et al[31] successfully performed LTCBDE in 205 cases, but none of them was with small CBD. Thus, we believe that LTCBDE is safe and efficacious for the management of choledocholithiasis with large CBD but that it might not be appropriate for those with small CBD.

Although more and more studies have confirmed that LCBDE is a safe and cost effective option for choledocholithiasis, these studies mainly focused on cases whose CBD was larger than 1.0 cm[11-13]. Whether it is feasible or safe to undergo LCBDE for those with small CBD still remains controversial. The controversy mainly focuses on the difficulty of CBD suture and its complications. It was believed that LCBDE for small CBD is more likely to lead to postoperative bile leak and CBD stenosis.

Hua et al[32] showed that choledocholithiasis with a non-dilated CBD (CBD diameter < 8 mm) was more likely to suffer postoperative bile leak than those with dilated CBD (CBD diameter ≥ 8 mm) (22.2% vs 3.0%). However, it should be noted that in their studies, the sample size of small CBD choledocholithiasis was small (only nine cases). It was speculated that the reason for this result may be the lack of experience in LCBDE for choledocholithiasis with small CBD. Khaled et al[33] reported that there was a learning curve with the procedure of LCBDE, and the risk of bile leak was reduced with growing experience of the surgeon as the rate of bile leak was decreased from 3.5% (2/57) in the first 5 years to 1.5% (1/68) in the subsequent 5 years (the average CBD diameter was 9.4 mm). In our opinion, appropriate patient selection is essential to avoid postoperative bile leak for choledocholithiasis with small CBD. In patients with small CBD, inflammatory edema of the CBD wall is more likely to cause difficulty in suture if complicated with acute cholangitis, and it will cause relaxation of the suture when the inflammatory edema subsides after surgery. All of these causes would increase the risk of postoperative bile leak. In this study, all surgeries were performed by highly experienced general surgeons with a wealth of laparoscopic suture techniques, and those patients with acute cholangitis were excluded to reduce the effect of CBD wall edema. The overall postoperative bile leak rate was 5.8% in this study, which was comparable to that of 3.8%-11.3% reported by others[34-37]. Besides, the bile leak rate was found to be 5.4% in patients with small CBD, which was not significantly different from those with large CBD (6.2%), and this is comparable to the bile leak rates of 5.8%-8.1% in patients with CBD ≥ 10 mm as reported previously[35,38]. Thus, it was believed that it is safe and feasible for small CBD patients to perform LCBDE and that it will not increase the risk of postoperative bile leak as long as appropriate cases are selected.

Hua et al[32] found that CBDS clearance is a significant risk factor for bile leak. With residual stones, intraluminal pressure in the bile duct will increase, and bile fluid will leak from the suturing site. Lauter et al[39] reported that 11 of 71 patients (15.5%) had residual stones after LCBDE. However, in our series, the rate of residual stones was 2.3%, which is lower than that in previously published series. This may be due to the development of choledochoscopy technology with optical magnification, direct visualization, and clearer vision. Besides, repeated confirmation before closing the CBD also increased the clearance rate of CBDS.

As for postoperative choledochal stenosis, no evidence has shown that LCBDE with primary closure would increase the risk of choledochal stenosis, even in small CBD patients. Cai et al[40] showed that no postoperative choledochal stenosis was found in 223 patients with a median follow-up of 26 mo, including 137 patients of primary closure and 102 patients of T-tube drainage. Khaled et al[33] reported postoperative choledochal stenosis was found in one of 120 patients (0.8%), with primary closure following LCBDE with a median follow-up of 39.2 mo (mean CBD diameter was 9.4 mm). In this study, no postoperative choledochal stenosis was found in either the small CBD group or the large CBD group with a mean follow-up period of 39 mo. Postoperative choledochal stenosis after LCBDE seems to occur rarely regardless of the CBD diameter. These results revealed that the primary closure after LCBDE can be performed without increasing the risk of postoperative choledochal stenosis in patients with small CBD.

This study also has its limitations. Although the effects of confounding factors were adjusted by performing propensity score matching, due to its retrospective nature, there may be selection bias between the two groups. Additional randomized controlled trials are needed to validate further these findings.