At our institution, the adoption of LATEST in LBDE was associated with an increased stone clearance rate and a higher proportion of patients who received transcystic exploration, resulting in significantly improved post-operative outcomes. Choledocholithiasis is a common condition and this paradigm shift in practice has led to reduced post-operative morbidity (including bile leak and post-procedural pancreatitis) and shorter post-operative hospital stay.

During the evolution of LBDE at our institution over that last 23 years, we have changed practice and adapted the technique in order to increase the transcystic exploration rate. We recently proposed the concepts of Biliary Surgery 2.0 and Leveraging Access to Technology and Enhanced Surgical Technique (LATEST) in LBDE [16, 17, 28]. Leveraging access to technology includes using thinner and more flexible choledochoscopes combined with fragmentation techniques such as laser or electrohydraulic lithotripsy. Prior to lithotripsy techniques, transcystic LBDE was limited to smaller CBD stones that were amenable to flushing into the duodenum or extraction via the cystic duct. In 2017, we published our initial results using holmium laser lithotripsy (HLL) during what we coined as the Lithotripsy-Assisted Bile duct Exploration by Laparoendoscopy (LABEL) technique [25]. Since then, we have demonstrated that using lithotripsy alone increased the transcystic exploration rate from 67 to 83% [26]. Without lithotripsy, we estimate that the ceiling of transcystic LBDE is somewhere around 60–70% [29–31]. More recently, we published a scoring tool (the ABCdE score) for PREdicting Lithotripsy Assistance during transcystic Bile duct Exploration by Laparoendoscopy (PRE-LABEL) [21, 32]. Over the last seven years, we have been routinely using single-use ultra-thin (~ 3 mm) choledochoscopes at our institution to facilitate transcystic LBDE [12]. Similarly, other authors have reported the use of ultra-thin choledochoscopes (with laser lithotripsy) to enable higher rates of transcystic exploration [33, 34]. Enhanced surgical technique refers to full mobilisation of the gallbladder followed by complete dissection of the cystic duct to the cysticocholedochal junction. The cystic duct is then retracted through the abdominal wall to create an optimal 90° cystic duct-common bile duct angle prior to attempting cannulation [12]. Enhanced surgical technique also refers to the trans-infundibular approach, which we have previously described, and is indicated when Calot’s triangle cannot be safely dissected due to a ‘frozen’ hepatic hilum secondary to severe inflammation and/or fibrosis [18].

The benefits of transcystic, over transductal, LBDE have been well described at our institution and in the literature [12–15]. The post-operative morbidity associated with transcystic exploration is not too dissimilar to that of laparoscopic cholecystectomy. A recently published Society of American Gastrointestinal and Endoscopic Surgeons (SAGES) clinical spotlight review quoted a successful stone clearance rate via a transcystic approach of up to 71% [29, 30]. The findings from this study suggest that adhering to four principles, focused around technology and surgical technique, can increase the transcystic exploration rate to > 90% in an unselected group of patients. In the last 100 unselected patients, when all four LATEST principles were fully observed, the transcystic LBDE rate was 94%. The trend of transcystic LBDE at our institution over 20 years since starting the technique is represented in Fig. 4. A steep increase in transcystic exploration rates is evident after 2014, when the LATEST principles were implemented. Of the preceding 50 patients who underwent LBDE prior to LATEST, 28% were by the transcystic route, which is similar to the pooled data from randomised trials comparing LBDE to two-staged laparoendoscopic management of CBD stones (~ 32% transcystic) [5, 11]. Exploration of the bile duct transcystically not only leads to improved outcomes, but also lowers the threshold for choledochoscopy. An equivocal intra-operative cholangiogram often poses a difficult question to the surgeon: end the procedure accepting a small risk of a retained stone or explore the bile duct which more than likely will be normal. The transcystic approach swings the balance towards exploration and should be considered as a viable option if there is any diagnostic doubt. In the LATEST group, the negative exploration (negative choledochoscopy) rate was almost double compared to the pre-LATEST era, with these patients having a very low incidence of post-operative morbidity. The lower threshold to perform transcystic choledochoscopy in such equivocal cases should be weighed up against the extra cost of the disposable ultra-thin choledochoscope (range: £800-£1,800).

Our technique to correct the cysticocholedochal angle, as described, involves the following sequence: (1) dissection of Calot’s triangle to achieve the critical view of safety followed by ligation of the cystic artery (2) mobilisation of the gallbladder from the liver (3) complete skeletonization of the cystic duct to the cysticocholedochal junction (4) retraction of the infundibular-cystic duct junction through the abdominal wall (Fig. 3A-C). To our knowledge, this technique has not previously been described by other authors. However, in 1994, DePaula et al., described their technique of transcystic stone extraction (mainly using baskets under fluoroscopic control) with dissection of the cystic duct to the junction of the common bile duct without using cautery [35]. The authors specified that management through the cystic duct was considered the first option and choledochotomy was used for patients in which the cystic approach was not possible or unsuccessful, and achieved a transcystic stone clearance rate of 84%. Full dissection of the cystic duct, including the junction between the cystic duct and CBD has also been described by other authors [34]. Complete dissection of the cystic duct is key to the success of transcystic LBDE, particularly when it is not dilated. Correction of the cysticocholedochal angle will also facilitate proximal (intra-hepatic) choledochoscopy using the wiper blade manoeuvre.

Since the first choledochoscopy in the UK by Longland in 1975, the quality and availability of devices have substantially improved [36]. The inability to pass a choledochoscope through the cystic duct has been a cause of failure for transcystic LBDE in previous studies, largely due to the non-availability of thinner endoscopes [37, 38]. The use of an ultra-thin (~ 3 mm) choledochoscope will allow access to the CBD through a non-dilated cystic duct with minimal requirement for dilatation (Fig. 2A). We routinely use a 9.5–12F ureteral access sheath (Flexor Ureteral Access Sheath, Cook Medical, Bloomington, IN, USA) to intubate and gently dilate the cystic duct over a PTFE guidewire (0.035-inch diameter, 145-cm length, 3-cm flexible tip, Cook Medical, Bloomington, IN, USA), which then affords access for a 3-mm choledochoscope (Fig. 2B). Ido et al., published an early report of transcystic choledochoscopy in 1996 [39]. The authors were able to gain access to the CBD via the cystic duct in 65 out of 70 (93%) patients, mainly due to gentle dilatation of the cystic duct lumen with Maryland forceps and the use of an ultra-thin (3.1 mm) choledochoscope. Furthermore, when performing LBDE in the 1990s, Thompson and Tranter discovered that the proportion of patients undergoing transcystic exploration rose from 21 to 37% after the acquisition of a 3-mm choledochoscope in addition to a 5-mm endoscope [40]. More recently, Xia and colleagues have successfully demonstrated that use of an ultra-thin (< 3 mm) choledochoscope was instrumental in achieving high rates of transcystic LBDE [34]. An ultra-thin choledochoscope was used in 63.5% of patients and contributed to an overall transcystic LBDE success rate of 93.7%. In their study, holmium laser lithotripsy was also used in 32.2% of patients, demonstrating the synergistic action of ultra-thin choledochoscopy and lithotripsy to increase transcystic stone clearance, a finding confirmed by the results of the current study.

In 2019, we demonstrated that the use of lithotripsy techniques alone had increased our rate of successful transcystic LBDE to over 80% [26]. Fang et al., successfully performed 205 transcystic explorations using a 5-mm choledochoscope [41]. Their operative technique to gain access via the cystic duct was different to that described here. When the cystic duct was non-dilated (< 5 mm), a T-shaped incision of the cystic duct was made, with the stem of the ‘T’ extending towards the cysticocholedochal junction. Furthermore, the duct was routinely dilated using a balloon catheter. The reported bile leak rate within this group was 3.3%, which is higher than expected following transcystic LBDE (~ 1%). We would not advocate this manoeuvre as the T-shaped incision can easily extend to the bile duct (effectively performing a choledochotomy) either during the incision itself or when performing balloon dilatation. It is possible that this modified cystic duct incision could be avoided altogether if an ultra-thin choledochoscope was used. Nevertheless, FREDDY (frequency-doubled double-pulse neodymium/YAG) laser lithotripsy was required in 36.1% of patients, which otherwise would have necessitated choledochotomy and transductal extraction, resulting in failure of transcystic LBDE. The increased financial burden associated with laser lithotripsy is related to the one-off cost of the device (approximately £50,000) and the single-use of a laser fibre (£300-£500) [22].

The retrospective, non-random nature of this study is the primary limitation to generalising the results. In particular, the four principles of LATEST were not all implemented at exactly the same time. The earliest use of our preferred method to correct the cysticocholedochal angle was in May 2012, but was routinely used after 2014. The inaugural use of an ultra-thin choledochoscope at our institution was in October 2014. At that time, a reusable fibre-optic choledochoscope was used. The first attempted laser lithotripsy (LABEL procedure) was performed using the trans-infundibular approach (TIA) to the bile duct in February 2014. This date was chosen to define the LATEST era. Another major limitation of a ‘before and after’ study of a single series is that any learning curve associated with the procedure is likely to have an effect on outcomes. Even without any significant change to practice, the second half of a series will likely yield better outcomes when compared to the first half, which may contain part or all of the learning curve. This sample selection could have introduced bias, however, the cohort of patients from this study represents an ‘all-comers’ series who unselectively underwent LBDE at our institution. Despite a learning curve in transductal and transcystic LBDE, the former requiring advanced skills in laparoscopic suturing and the latter advanced skills in laparoendoscopy, this study demonstrates that four principles have been largely responsible for increasing the rate of transcystic LBDE, which is independent to its learning curve. Further research is required to determine the optimal treatment strategy for managing choledocholithiasis with concomitant gallstones. Most of the available randomised trial data is dated, with the LBDE arms mainly performing transductal clearance (from pooled analysis, less than one-third of patients underwent transcystic LBDE). Prospective randomised studies comparing contemporary (mainly transcystic) LBDE to alternative laparoendoscopic strategies (namely pre-operative ERCP followed by laparoscopic cholecystectomy and laparoscopic cholecystectomy with intra-operative ERCP) should be the focus of future research.