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Monsieur Le Professeur

Laurent Poincloux

PROFESSEURS DES UNIVERSITES-PRATICIENS HOSPITALIERS

Monsieur le Professeur Armando ABERGEL, Président du Jury, Je vous remercie d'avoir accepté de présider ce jury de thèse. Merci pour vos conseils avisés, prodigués tout au long de mon internat. Je vous prie d'accepter l'expression de toute ma considération et mon profond respect.

For such patients, biliary drainage is the key point of the best supportive care strategy enhancing survival and life quality, notably by improving jaundice, poor appetite and general weakness.

Non-surgical approaches are now preferred for management of unresectable malignant biliary obstruction and endoscopic drainage is deemed less invasive and more physiological in comparison to surgical and percutaneous approaches [START_REF] Webb | Endoscopic Management of Malignant Bile Duct Strictures[END_REF].

Nevertheless, it should be considered that many factors impact the success of malignant hilar biliary obstruction (MHBO) drainage.

LIVER VOLUME

Assessment of liver volume requires pre-operative imaging data and is a major information to consider before scheduling a biliary drainage for MHBO. Both computed tomography scan (CT scan) and magnetic resonance imaging (MRI) are available for hepatic volumetry, with a strong positive correlation. CT remains the preferred imaging technique due to its availability, cost and images quality (3) (Figure 1).

Before 2010, drainage of only one hepatic duct was recommended, usually the right hepatic duct, if pre or per-endoscopic retrograde cholangiopancreatography (ERCP) data showed that it drains more than 25% of total liver volume (4).

In (Figure 2).

PERCUTANEOUS OR ENDOSCOPIC DRAINAGE

The position of percutaneous and endoscopic drainage remains unclear for unresectable MHBO management. Percutaneous transhepatic biliary drainage (PTBD) offers greater technical feasibility and higher success rate in comparison with endoscopic drainage, and stent patency is superior if internal PTBD with metallic stent is performed (8,9) (Figure 3). mortality. However, this meta-analysis also reported a higher rate of bleeding issue in PTBD arm and a decrease in life quality of patients undergoing external PTBD [START_REF] Dumonceau | Endoscopic biliary stenting: indications, choice of stents, and results: European Society of Gastrointestinal Endoscopy (ESGE) Clinical Guideline -Updated October 2017[END_REF][START_REF] Moole | Endoscopic versus Percutaneous Biliary Drainage in Palliation of Advanced Malignant Hilar Obstruction: A Meta-Analysis and Systematic Review[END_REF]. Internal PTBD with metallic stent implantation sometimes requires a two-steps procedure, increasing infectious and bleeding issues [START_REF] Rerknimitr | Asia-Pacific consensus recommendations for endoscopic and interventional management of hilar cholangiocarcinoma[END_REF]. On the other hand, one step procedure has been described since at least 2006, with a higher risk of biliary leakage than the two steps procedure, furthermore, the catheter has to be left in place at the insertion site for correct hemostasis, and can only be removed 2 or 3 days after procedure [START_REF] Yoshida | One-step palliative treatment method for obstructive jaundice caused by unresectable malignancies by percutaneous transhepatic insertion of an expandable metallic stent[END_REF].

In addition, a systematic review published in 2019 aimed to compare the incidence of seeding metastasis (SM) after pre-operative endoscopic or percutaneous treatment of MBO, and showed a significant higher rate of SM after percutaneous drainage (22% vs 10.5% (p<0.00001)) ( 13).

More recently, several studies reassert the position of endoscopic biliary drainage (EBD) as a safe and efficacy way to manage Bismuth III & IV strictures.

The emergence of endoscopic ultrasound biliary drainage (EUS-BD) is a true revolution in the management of biliary strictures after ERCP failure, partial ERCP drainage (unilateral) or when ERCP is impossible (surgically altered anatomy). In 2021, Kongkam et al, showed that a combination of ERCP + EUS-BD is an interesting alternative to PTBD alone or to PTBD + ERCP, with a significant lower recurrent biliary obstruction (RBO) rate in ERCP + EUS-BD arm, similar complication rate and no mortality difference (14) (Figure 4).

Latest ESGE 2022 Guidelines now recommends EUS-BD as a second line therapy after ERCP failure, over ERCP + PTBD, regarding its similar technical success with lower post-procedural adverse event and longer median time to RBO [START_REF] Van Der Merwe | Therapeutic endoscopic ultrasound: European Society of Gastrointestinal Endoscopy (ESGE) Guideline[END_REF][START_REF] Vanella | EUS-guided intrahepatic biliary drainage: a large retrospective series and subgroup comparison between percutaneous drainage in hilar stenoses or postsurgical anatomy[END_REF]. Improvement of life quality is also important to notice in such palliative situations.

A 2020 literature review on biliary stenting for MHBO seems to favor endoscopic approach if experienced endoscopist is available, reminding us the local specificities of each hospital and the importance of multi-disciplinary concertation in those challenging situations [START_REF] Lee | Biliary stenting for hilar malignant biliary obstruction[END_REF].

UNILATERAL OR BILATERAL DRAINAGE

Several studies tried to compare unilateral and bilateral biliary drainage in MHBO (Figure 5a & 5b).

A single stenting is clearly recommended in Bismuth I stricture, as that kind of stricture stenting is technically similar to distal biliary obstructions [START_REF] Dumonceau | Endoscopic biliary stenting: indications, choice of stents, and results: European Society of Gastrointestinal Endoscopy (ESGE) Clinical Guideline -Updated October 2017[END_REF][START_REF] Rerknimitr | Asia-Pacific consensus recommendations for endoscopic and interventional management of hilar cholangiocarcinoma[END_REF].

In Bilateral metallic stenting is a technical challenge because of the great difficulty to achieve insertion and deployment of a contralateral second stent, so, the emergence of new endoscopic devices improved the technical and clinical success of bilateral endoscopic drainage.

In a 2009 retrospective study, Naitoh et al. showed similar technical and clinical success, with similar early and late complications in both unilateral and bilateral drainage, but bilateral metallic stenting provided a significantly better stent patency, reducing reintervention for recurrent biliary obstruction [START_REF] Naitoh | Unilateral versus bilateral endoscopic metal stenting for malignant hilar biliary obstruction[END_REF]. Those results were confirmed in a randomized clinical trial in 2017, where 133 patients were enrolled with the intention of comparing unilateral and bilateral metallic biliary stenting for unresectable MHBO and showed similar technical success with lower reintervention rate and prolonged stent patency in the bilateral stenting arm [START_REF] Lee | Bilateral versus unilateral placement of metal stents for inoperable high-grade malignant hilar biliary strictures: a multicenter, prospective, randomized study (with video)[END_REF].

Two recent meta-analysis confirmed that both bilateral and unilateral stenting for unresectable MHBO are similar in terms of clinical success and safety profile. Technical success was significantly higher in unilateral group (97% vs 89%, p=0.003)( 21) and significantly longer stent patency was observed in the bilateral stenting arm (HR 1.28, p=0.01) [START_REF] Yang | Endoscopic metal stenting for malignant hilar biliary obstruction: an update meta-analysis of unilateral versus bilateral stenting[END_REF].

STENT TYPE

While optimal strategy of biliary drainage in unresectable MHBO is still being debated, the choice of self-expandable metallic stent (SEMS) is no longer contested, since it showed its superiority in several randomized clinical trials and multicentric study (Figure 6 & 7).

It has been proved that SEMS is superior to plastic stent in this indication, providing a significantly higher clinical success, better stent patency and reducing the number of reintervention for stent dysfunction [START_REF] Xia | Comparison of endoscopic bilateral metal stent drainage with plastic stents in the palliation of unresectable hilar biliary malignant strictures: Large multicenter study[END_REF][START_REF] Sangchan | Efficacy of metal and plastic stents in unresectable complex hilar cholangiocarcinoma: a randomized controlled trial[END_REF][START_REF] Mukai | Metallic stents are more efficacious than plastic stents in unresectable malignant hilar biliary strictures: a randomized controlled trial[END_REF].

Furthermore, the American Society of Gastrointestinal Endoscopy (ASGE) reversed its stance concerning the use of plastic stents in patients with short life expectancy (<3 months) and now recommends since 2021 the use of SEMS for all patients with MHBO in palliative situation [START_REF] Qumseya | ASGE guideline on the role of endoscopy in the management of malignant hilar obstruction[END_REF][START_REF] Pfau | Pancreatic and biliary stents[END_REF].

STENT IN STENT OR SIDE BY SIDE (SEQUENTIAL AND SIMULTANEOUS PROCEDURES)

Recent studies reported that endoscopic bilateral drainage is now a first-line option for management of unresectable MHBO regarding lower cholangitis rate and physiological concerns [START_REF] Sherman | Endoscopic drainage of malignant hilar obstruction: Is one biliary stent enough or should we work to place two?[END_REF]. Two main techniques have been developed those past years: "side-by-side" and "stent-in-stent" methods.

The procedure begins with the initial stenting of one intrahepatic duct, followed by placement of a second stent in another intrahepatic duct: parallel to the first stent (i.e "side-by-side" technique), or by crossing through the mesh of the initial stent (i.e "stent-in-stent" technique)(28) (Figure 8).

Overall technical success rates of those two methods range from 73.3% to 100% [START_REF] Lee | Bilateral versus unilateral placement of metal stents for inoperable high-grade malignant hilar biliary strictures: a multicenter, prospective, randomized study (with video)[END_REF], and no difference have been shown regarding clinical success, adverse event and stent patency duration [START_REF] Lee | Biliary stenting for hilar malignant biliary obstruction[END_REF].

One of the limiting factors for a successful stent-in-stent (SIS) placement is the difficulty for inserting the second metallic stent trough the mesh of the first stent. 9b).

Before 2010, side-by-side (SBS) technique required a "sequential" procedure: first stent placement, followed by second stent placement. Second stent placement is frequently very difficult to achieve because of the resistance of the second delivery system against the first deployed stent [START_REF] Lee | Technical Tips and Issues of Biliary Stenting, Focusing on Malignant Hilar Obstruction[END_REF] and the radial forces exerted on the bile duct wall, resulting in the impaction of the delivery system of the second stent [START_REF] Hookey | Use of a temporary plastic stent to facilitate the placement of multiple self-expanding metal stents in malignant biliary hilar strictures[END_REF].

Development of a new type of uncovered biliary metallic stent, carried by an ultra-thin (6Fr)

delivery system (Zilver ® ; Cook Medical, Ireland), permitted the rise of a new type of bilateral biliary drainage procedure: "simultaneous side-by-side technique" (Figure 10).

The thin design of the new delivery system allows to insert two stents, simultaneously, in the same 4,2mm working channel of a duodenoscope. The two stents are sequentially introduced over left and right guidewires; stents are then carefully released across the strictures simultaneously [START_REF] Chennat | Initial performance profile of a new 6F self-expanding metal stent for palliation of malignant hilar biliary obstruction[END_REF]. In 2013, Law & Baron confirmed safety, feasibility and effectiveness of simultaneous bilateral stenting using this new delivery system [START_REF] Law | Bilateral Metal Stents for Hilar Biliary Obstruction Using a 6Fr Delivery System: Outcomes Following Bilateral and Side-by-Side Stent Deployment[END_REF].

Some concerns exist regarding both new type of stent. Because of it specific wide-open mesh design, such stent may favor tumor ingrowth, which might lower stent patency and the need for biliary reintervention [START_REF] Chen | Side-by-side versus stent-in-stent bilateral stenting for malignant hilar biliary obstruction: a meta-analysis[END_REF][START_REF] Heo | Clinical Outcomes of Bilateral Stent-in-Stent Placement Using Self-Expandable Metallic Stent for High-Grade Malignant Hilar Biliary Obstruction[END_REF]. It is important to note that biliary reintervention may be harder with stent-in-stent technique. It is indeed difficult to catheterize the stent mesh in the hilar region again [START_REF] Inoue | Multi-center study of endoscopic revision after side-by-side metal stent placement for malignant hilar biliary obstruction[END_REF] and achieve bilateral biliary desobstruction: contrary to side by side drainage, where both distal tips of stents are visible in the duodenal lumen, desobstruction of the crossing stent must be achieved by its catheterization through the main stent (which is the only stent visible the duodenal lumen).

Side-by-side stenting may increase post-procedure complication, particularly cholangitis, due to the risk of portal vein occlusion caused by the overexpansion of the common bile duct [START_REF] Moon | Topic controversies in the endoscopic management of malignant hilar strictures using metal stent: side-by-side versus stent-in-stent techniques[END_REF].

In order to reduce such complication and to improve clinical success, the use of a SEMS carried by a 6Fr delivery system may be now preferred, with no shorten in stent patency [START_REF] Kawakubo | Singlestep simultaneous side-by-side placement of a self-expandable metallic stent with a 6-Fr delivery system for unresectable malignant hilar biliary obstruction: a feasibility study[END_REF] and a higher success rate when reintervention after recurrent biliary obstruction is needed.

However, in a prospective randomized multicentric study, Lee et al. [START_REF] Lee | Prospective comparison of endoscopic bilateral stent-in-stent versus stent-by-stent deployment for inoperable advanced malignant hilar biliary stricture[END_REF] drainage as a first-line option, using preferentially uncovered metallic stents over plastic stents [START_REF] Dumonceau | Endoscopic biliary stenting: indications, choice of stents, and results: European Society of Gastrointestinal Endoscopy (ESGE) Clinical Guideline -Updated October 2017[END_REF][START_REF] Rerknimitr | Asia-Pacific consensus recommendations for endoscopic and interventional management of hilar cholangiocarcinoma[END_REF][START_REF] Xia | Comparison of endoscopic bilateral metal stent drainage with plastic stents in the palliation of unresectable hilar biliary malignant strictures: Large multicenter study[END_REF][START_REF] Sangchan | Efficacy of metal and plastic stents in unresectable complex hilar cholangiocarcinoma: a randomized controlled trial[END_REF][START_REF] Mukai | Metallic stents are more efficacious than plastic stents in unresectable malignant hilar biliary strictures: a randomized controlled trial[END_REF]. Bilateral drainage must be preferred to unilateral drainage in high-grade malignant hilar stricture because it provides a longer stent patency, with a lower reintervention rate for recurrent biliary obstruction (RBO), with similar clinical outcomes and adverse event [START_REF] Naitoh | Unilateral versus bilateral endoscopic metal stenting for malignant hilar biliary obstruction[END_REF][START_REF] Lee | Bilateral versus unilateral placement of metal stents for inoperable high-grade malignant hilar biliary strictures: a multicenter, prospective, randomized study (with video)[END_REF][START_REF] Meybodi | Unilateral versus bilateral endoscopic stenting in patients with unresectable malignant hilar obstruction: a systematic review and meta-analysis[END_REF][START_REF] Yang | Endoscopic metal stenting for malignant hilar biliary obstruction: an update meta-analysis of unilateral versus bilateral stenting[END_REF]. If unilateral drainage is performed, drainage of at least 50% of total liver volume must be obtained [START_REF] Vienne | Prediction of drainage effectiveness during endoscopic stenting of malignant hilar strictures: the role of liver volume assessment[END_REF]. Bilateral drainage can be performed using either side by side or stent in stent techniques, with no difference regarding technical and clinical success, stent patency and survival [START_REF] Lee | Prospective comparison of endoscopic bilateral stent-in-stent versus stent-by-stent deployment for inoperable advanced malignant hilar biliary stricture[END_REF][START_REF] Naitoh | Optimal endoscopic drainage strategy for unresectable malignant hilar biliary obstruction[END_REF]. Nevertheless, bilateral biliary drainage using metallic still is a technical challenge, including many failed procedures even for a trained operator.

Emergence of a new ultra-thin (6Fr or smaller) delivery system enables, since a few years now, simultaneous side by side metallic stent deployment. To date, there are few data reported in the literature regarding the simultaneous bilateral biliary stenting with this new device, only a small series of Inoue et al. reported a higher technical success and a shorter procedure time for simultaneous drainage compared with sequential side by side procedure [START_REF] Law | Bilateral Metal Stents for Hilar Biliary Obstruction Using a 6Fr Delivery System: Outcomes Following Bilateral and Side-by-Side Stent Deployment[END_REF][START_REF] Kawakubo | Singlestep simultaneous side-by-side placement of a self-expandable metallic stent with a 6-Fr delivery system for unresectable malignant hilar biliary obstruction: a feasibility study[END_REF][START_REF] Inoue | Simultaneous Versus Sequential Side-by-Side Bilateral Metal Stent Placement for Malignant Hilar Biliary Obstructions[END_REF].

In this study, we aimed to compare simultaneous side-by-side versus sequential ("side by side" and "stent in stent") bilateral biliary drainage in a large monocentric series.

METHODS

Patients

We investigated all patients who underwent bilateral biliary metallic stenting during ERCP for MHBO in Clermont-Ferrand University Hospital Centre between January 1 st 2010 and January Unresectable status was assessed according to general medical condition, locoregional or metastatic extent, after medico-surgical multi-disciplinary approach.

The study was approved by local Ethics Committee (IRB00013412, "CHU de Clermont Ferrand IRB #1", IRB number 2023-CF003) with compliance to the French policy of individual data protection and was performed in accordance with the principles of the Declaration of Helsinki.

transpapillary catheterism was unsuccessful. In some cases, sphincterotomies had been previously performed.

Sequential "side by side" technique

Once deep biliary catheterism was achieved, multiple guidewires (0.035 inch straight or angle tip hydrophilic guidewire (JagWire ® or DreamWire ® , Boston Scientific Co, USA)) were inserted whenever possible in both left and right hepatic ducts. Contrast agent was injected selectively only after a guidewire was passed through the hilar stricture. Following the insertion of the guidewires into the main left and right intrahepatic bile ducts, both strictures were dilated using 6 or 8mm diameter dilation balloons (Hurricane ® , Boston Scientific Co, USA), followed by bilateral SEMS placement (sequential "side by side" or "stent in stent" technique and simultaneous technique).

After dilation of both strictures, a first SEMS (10mm diameter, 8, 10 or 12cm length, 8Fr delivery shaft catheter, uncovered Wallflex Biliary RX Stent ® , Boston Scientific Co, USA) (Figure 11b) was placed, usually in the left biliary duct because of a more challenging stent placement due to the sharp angulation between the left and main bile ducts, compared with right bile duct. The second SEMS was next inserted and placed alongside the first SEMS over the other guidewire and then deployed parallel to the first SEMS.

Sequential "stent in stent" technique

We used a Y-shaped stent with a wide wire mesh design (either M-Hilar Bonastent ® , Mi-Tech, South Korea or Y-Type Niti-S Stent ® , Taewoong Medical, South Korea) (Figure 9) to perform the "stent in stent" technique (or "through the mesh"). These stents have a thin delivery catheter of 7Fr allowing to cross the wide wire mesh and an 8mm diameter once they are deployed. For this technique, a firstly bilateral guidewire catheterism is not mandatory. After deployment of the first stent across the hilar stricture, the guidewire left across the primary stent was carefully withdrawn, without pulling it back completely, and was then inserted into the undrained contralateral hepatic duct through the central wide mesh of the primary stent. Another uncovered SEMS was then introduced over the guidewire and deployed in the contralateral hepatic duct.

Simultaneous "side by side" technique

For this technique, we used SEMS with an ultra-thin delivery system that allows simultaneous SBS bilateral hilar stenting achievement with a 4.2mm working channel duodenoscope. First, a laser-cut SEMS aixstent ® (Leufen Medical GmbH, Berlin, Germany) carried by a 5Fr delivery system from 2017 to 2020, then the Niti-S [M-Type] ® (TaeWoong Medical, Seoul, Korea) carried by a 6Fr delivery system from 2020 to 2023 (easier to use in our own experience) (Figure 11a). Due to the ultra-thin delivery system, we had to use only 0.025 inch guidewire (either straight VisiGlide ® (Olympus, Japan) or angle tip JagWire ® Revolution (Boston Scientific Co, USA) when selective insertion of the guidewire into intrahepatic duct was difficult) to achieve bilateral main left and right bile duct catheterism. Biliary strictures were dilated using a 4,6 or 8mm balloon dilation (Hurricane ® RX, Boston Scientific, USA), followed by simultaneous insertion of two SEMS delivery system devices and pushed over each guidewire. Then, the two SEMS were simultaneously deployed across the hilar stenosis in a SBS configuration.

This procedure required the assistance of two endoscopy nurses. All SEMS had an 8mm diameter, with a varying length from 10 to 12cm, according to the length of the stricture and the need for all SEMS to be positioned above the duodenal papilla. Furthermore, alignment of the distal stent ends was attempted. Nevertheless, if needed, a third distal stent could be inserted in the distal tip of one of the initial SEMS to achieve duodenal lumen expansion.

Outcomes and definitions

The primary outcome for this study was to determine technical success rate for each procedure (sequential or simultaneous bilateral stenting).

Secondary outcomes included clinical success, procedure duration (in min), early adverse event rate and stent-related adverse event rate, recurrent biliary obstruction (RBO) rate and time to RBO (or stent patency, in days).

Technical success was defined by the accurate positioning of two metallic stent across left and right hilar strictures ("side by side" (SBS) in simultaneous group, "side by side" or "stent in stent" (SIS) in sequential group).

Clinical success was defined by decrease of at least 50% of total bilirubin (in µmol/L) at D7 compared to D0.

Adverse events were classified as early adverse event when they occurred in intra procedural time or within one week after procedure and were graded according the new AGREE (Adverse Event GastRointEstinal Endoscopy) Classification (44) (Figure 12).

Stent dysfunction was defined as recurrent biliary obstruction.

Statistical analysis

Study data were collected and managed using REDCap electronic data capture tools hosted at CHU de Clermont-Ferrand, France. Statistical analysis was performed, using STATA 15 (Stata Corp LLC, Texas, USA). Categorical variables are expressed as effectives and percentages.

Continuous variables are expressed as mean or median (+/-IQR). Group differences were evaluated, using Fisher's or Chi²'s tests for categorical variables. For continuous variables, group differences were evaluated, using Wilcoxon's, Mann-Whitney's or Kruskal Wallis' tests.

Survival time was determined using Kaplan-Meier method. Univariate and multivariate analyses were evaluated using logistic regression model.

Significance was defined as p < 0.05.

RESULTS

Patient characteristics

We identified 146 patients who benefited bilateral drainage for MHBO between 2010 and 2023. 1 and we observed no significant differences between the two groups.

Technical success

Technical success was achieved in 94% of patients in simultaneous group and in 77% of patients in sequential group (p=0.008). In sequential group, technical success was significantly more often achieved for SIS technique (95%) than with SBS technique (57%) (p=0.001). A total of 58 patients underwent technical success in simultaneous group: 21 using aixstent BDH ® device (Leufen Medical GmbH (Berlin, Germany)), 37 using Niti-S [M-Type] ® device (TaeWoong Medical (Seoul, Rep. of Korea)).

Technical failure was associated with a higher risk of death (HR 1. 35, p=0.22).

Baseline bilirubin rate did not appear to impact technical success. In univariate and multivariate analysis, technical success was less often observed for Bismuth & Corlette IV type and metastatic hilar obstruction (Table 2).

Patient outcomes are presented in Table 3.

Clinical success

Clinical success was observed in 75% of patients in simultaneous group and in 72% of patients in sequential group. There was no significant difference observed concerning clinical success between SBS and SIS techniques in the sequential group (76% and 69% of success respectively) (p=0.823).

Procedure duration

Median procedure time was 80 minutes in sequential group and 72 minutes in simultaneous group (p=0.92). Median procedure time was not different between sequential SBS and SIS techniques, 75 and 80 minutes respectively (p=0.75).

Early adverse events related to the procedure

Overall early adverse event was observed in 31% of patients in sequential group and 21% in simultaneous group, with no significant difference (p=0.205). Complication rates were similar between SBS and SIS techniques in sequential group, 34% and 29% respectively (p=0.39).

Early adverse event included 13 pancreatitis (none patient required ICU admission or endoscopic/surgical intervention), 16 cholangitis (2 patients admitted in ICU, 4 died), 6 hemorrhagic complications (due to sphincterotomy or iatrogenic duodenal ulcer related to distal tip of metal stents, all medically managed) and 1 duodenal perforation occurred (in SBS sequential group, surgically managed). Cholangitis was more often observed in sequential group (16% vs 6%, p=0.07), with no differences between SBS or SIS techniques (17% and 16% respectively, p=0.19). Early adverse event rates are represented in Figure 14.

Among adverse events, most were graded AGREE II (64% of overall AE). We observed 3 fatal complications (AGREE V) in sequential group and 1 fatal complication in simultaneous group; both were infectious complications due to cholangitis.

Technical and clinical failures were associated with a higher rate of AGREE V complications We did not report procedure-related death, excepted for patients who suffered cholangitis with multivisceral failure due to septic shock (4 patients (3% of overall patients)).

Repartition of adverse event severity is represented in Figure 15.

Recurrent biliary obstruction (RBO)

RBO was observed in 13 patients in simultaneous group and 9 patients in sequential group (22% and 18% respectively, p=0.049). In sequential group, RBO occurred in 1 patient (5%) in SBS group and in 8 patients (20%) in SIS group.

Mean time to RBO was 144 and 112 days in simultaneous and sequential groups respectively.

Only one patient experienced RBO in sequential group, after 182 days. Mean time to RBO in sequential SIS group was 103 days.

After RBO, all patients underwent endoscopic reintervention, excepted 2 patients in simultaneous group (15%, p=0.49) whom general condition was not compatible with general anesthesia.

Technical and clinical success were obtained in 82%, 75% and 100% of cases in simultaneous, "stent in stent" and "side by side" groups respectively.

Reintervention seems to be more efficient when "side by side" bilateral drainage (either simultaneous or sequential) was performed, compared to "stent in stent" technique (83% versus 75% (p = 0.53)).

DISCUSSION

Complete biliary drainage in case of MHBO frequently requires bilateral drainage, a technically challenging endoscopic procedure.

Zilver 635® (Cook Medical, Ireland) device carried by a 6Fr delivery system, was thought initially to allow parallel insertion of the two stents in a duodenoscope working channel to achieve a simultaneous bilateral biliary stenting, but in our own experience with this device, a simultaneous bilateral stent placement in MHBO was unsuccessful due to severe frictions of the two parallel devices, with the consequence of a weak pushability of the delivery systems.

Law & Baron [START_REF] Law | Bilateral Metal Stents for Hilar Biliary Obstruction Using a 6Fr Delivery System: Outcomes Following Bilateral and Side-by-Side Stent Deployment[END_REF] reported the use of this device in MHBO to perform a bilateral stent deployment thanks to a SIS or SBS approach and reported 71% of technical success, a success that seems far from the reality we observed in our center, whether with SBS or SIS techniques.

Moreover, this high technical success might be explained by the proportion of type II of

Bismuth & Corlette patients treated in that study (close to 50%).

The emergence of the new aixstent® BDH (Leufen Medical GmbH, Berlin, Germany) carried by a 5Fr delivery system & Niti-S [M-Type]® (TaeWoong Medical, Seoul, Korea) carried by a 6Fr delivery system has been a true revolution in our practice, highly increasing technical success without impacting clinical outcomes or RBO rate, compared with sequential stenting.

Our study shows that simultaneous bilateral biliary drainage, using a 6 or 5Fr delivery system, is superior to sequential drainage, when a side by side approach is chosen. Technical success was achieved in 94% of cases, a success rate that is similar with previous studies which evaluated feasibility of simultaneous side by side drainage, with a technical success ranged from 71 to 100% [START_REF] Chennat | Initial performance profile of a new 6F self-expanding metal stent for palliation of malignant hilar biliary obstruction[END_REF][START_REF] Law | Bilateral Metal Stents for Hilar Biliary Obstruction Using a 6Fr Delivery System: Outcomes Following Bilateral and Side-by-Side Stent Deployment[END_REF][START_REF] Kawakubo | Singlestep simultaneous side-by-side placement of a self-expandable metallic stent with a 6-Fr delivery system for unresectable malignant hilar biliary obstruction: a feasibility study[END_REF][START_REF] Inoue | Simultaneous Versus Sequential Side-by-Side Bilateral Metal Stent Placement for Malignant Hilar Biliary Obstructions[END_REF]. Our results concerning technical success of sequential SBS drainage are comparable with Inoue et al. results (71% of technical success, p=0.045).

We also observed a high technical success rate of 95% for stent in stent procedure, also comparable with previously existing literature (≈ 100%).

Interestingly, we observed a higher rate of technical failure for patients who suffered hilar metastatic obstruction and for type IV of Bismuth & Corlette strictures. Baseline bilirubin rate did not appear to interfere with technical success or failure.

A high technical success is even more important because it is closely related to the risk of postprocedure adverse event, particularly cholangitis, even though contrast agent injection in the non-catheterized liver segments was carefully avoided, whatever technique we used.

We reported a lower rate of early adverse event in simultaneous group compared with sequential group (21% vs 31%, p=0.205). Cholangitis was more observed in sequential group, regardless of side-by-side or stent-in stent technique (Figure 16). The higher rate of cholangitis in sequential SBS group might be explained by the higher rate of technical failure, however, we found no explanation for the higher rate in the sequential SIS group. Recent meta-analysis evaluating SIS and SBS bilateral drainage found no differences in terms of AE between the two techniques (Risk Difference -0.09, p=0.07) [START_REF] De Souza | Endoscopic retrograde cholangiopancreatography drainage for palliation of malignant hilar biliary obstructionstent-in-stent or side-by-side? A systematic review and meta-analysis[END_REF], despite the fact that some authors suggest a higher rate of cholangitis with "side by side" techniques due to higher incidence of portal vein occlusion or obstruction of one of the two stents [START_REF] Naitoh | Side-by-Side Versus Stent-in-Stent Deployment in Bilateral Endoscopic Metal Stenting for Malignant Hilar Biliary Obstruction[END_REF]. [START_REF] Chen | Side-by-side versus stent-in-stent bilateral stenting for malignant hilar biliary obstruction: a meta-analysis[END_REF].

That observation might also explain the lower RBO rate we observed in our study (18% and 22%, p=0.049), knowing that usual RBO rate ranges from 18.2% to 52.9% in the studies who compared SIS & SBS, with a median stent patency of 118 days to 262 days [START_REF] Chen | Side-by-side versus stent-in-stent bilateral stenting for malignant hilar biliary obstruction: a meta-analysis[END_REF]. Mean time to RBO was 144 days in simultaneous group and 103 days in "stent in stent" group, a difference that might be explained by the large cell mesh design of the stents used in SIS technique, favorizing tumor ingrowth [START_REF] Chen | Side-by-side versus stent-in-stent bilateral stenting for malignant hilar biliary obstruction: a meta-analysis[END_REF][START_REF] Heo | Clinical Outcomes of Bilateral Stent-in-Stent Placement Using Self-Expandable Metallic Stent for High-Grade Malignant Hilar Biliary Obstruction[END_REF].

Reintervention after RBO seems to be more successful with SBS stenting (sequential and simultaneous combined) than with SIS stenting (83% vs 75%, p=0.53), a non-significant difference, that might be explained by the easier access to both stent with SBS drainage rather than with SIS techniques (two end-tip stents in the duodenal lumen with SBS technique, versus one with SIS technique).

To date, this study is the largest concerning comparison of simultaneous and sequential bilateral biliary drainage. Patients were recruited over a large period of 13 years, and procedures were realized all along by only 2 trained operators. Most reinterventions for RBO were proceed in our tertiary center. Those results are even more valuable that both groups were appaired, reducing the risk of selection bias.

The limits of this study are the single center retrospective design and a potential lack of power, with missing data concerning especially clinical success and procedure duration. It is important to note that the only study which compared simultaneous and sequential bilateral biliary drainage was also a retrospective monocentric study, with a smaller effective of 34 patients [START_REF] Inoue | Simultaneous Versus Sequential Side-by-Side Bilateral Metal Stent Placement for Malignant Hilar Biliary Obstructions[END_REF]. Furthermore, due to a large recruitment period, technical success of sequential technique might have been negatively impacted (procedures performed from 2010 to 2017, in comparison with simultaneous technique which was performed from 2017 and 2023).

CONCLUSION

In conclusion, simultaneous side by side endoscopic bilateral metallic stent placement using a new SEMS device with an ultra-thin (5 or 6Fr) delivery system is technically easier and as efficient as sequential bilateral stenting in unresectable MHBO to achieve bilateral drainage and can be useful to avoid the risk of a failed second stent placement. However, we reported a similar technical and clinical success in simultaneous SBS and sequential SIS groups with a higher rate of infectious complications in sequential group, even after successful SIS placement.

Technical failure was significantly associated with fatal infectious complications. RBO rate was similar in simultaneous and sequential SIS groups, but with a shorter time to RBO in SIS group.

We failed to show a difference in terms of procedure duration between the two techniques.

Both simultaneous SBS and sequential SIS are valuable options for palliative endoscopic drainage in MHBO. Further prospective multicentric trials are needed to investigate the place of simultaneous SBS technique as a first-line treatment in unresectable MHBO compared to SIS technique. Je donnerai mes soins gratuits à l'indigent et je n'exigerai jamais un salaire au-dessus de mon travail. Admis dans l'intérieur des maisons, mes yeux ne verront pas ce qui s'y passe, ma langue taira les secrets qui me seront confiés et mon état ne servira pas à corrompre les moeurs ni à favoriser le crime.

Pierre CLAVELOU Doyen -Directeur

Respectueux et reconnaissant envers mes MAÎTRES, je rendrai à leurs enfants l'instruction que j'ai reçue de leurs pères.

Que les HOMMES m'accordent leur estime si je suis fidèle à mes promesses. Que je sois couvert d'OPPROBRE et méprisé de mes confrères si j'y manque.

DIRECT COMPARISON OF SIMULTANEOUS AND SEQUENTIAL ENDOSCOPIC METALLIC BILATERAL STENTING IN MALIGNANT HILAR BILIARY OBSTRUCTION: A SINGLE CENTER SUPERIORITY STUDY

Background

Endoscopic bilateral biliary drainage is a first line palliative treatment for unresectable MHBO but remains technically challenging. The emergence of news SEMS carried by an ultra-thin (6Fr or smaller) delivery system now permits simultaneous bilateral stent placement. To date, only few data comparing this new method to conventional sequential bilateral stenting are reported. We conducted a monocentric retrospective study to evaluate a possible superiority of simultaneous "side by side" (SBS) biliary drainage.

Methods

We identified 135 patients who benefited from bilateral drainage using uncovered SEMS between 2010 and 2023. Among them, 62 benefited from simultaneous SBS bilateral drainage between 2017 and 2023, and 73 benefited from sequential bilateral drainage (38 using "stent in stent" (SIS) technique and 35 using SBS technique, between 2010 and 2017).

Results

Technical success was significantly more observed in simultaneous drainage compared to sequential drainage (94% vs 75%, p=0.008). However, simultaneous SBS drainage and sequential SIS drainage had a similar technical success (94% vs 95%). We observed no differences regarding clinical success, procedure duration and RBO rate. Stent patency was shorter in SIS group compared with simultaneous group (103 vs 144 days). Early adverse events (AE) were more frequent in sequential group (31% vs 21%, p = 0.205), with no differences regarding SIS or SBS technique. Technical failure was associated with a higher rate of infectious fatal AE (9.5% vs 1.7%, p=0.02). Reintervention after RBO seems to be more successful after using SBS rather than SIS techniques (83% vs 75%, p=0.53).

Conclusion

Simultaneous side by side endoscopic bilateral metallic stent placement using an ultra-thin delivery system is technically easier and as efficient as sequential bilateral stenting in unresectable MHBO to achieve bilateral drainage. Stent in stent procedure remains a good option in unresectable MHBO. Further prospective multicentric trials are needed to investigate the place of simultaneous SBS technique as a first-line treatment compared to SIS technique.

Keywords : MHBO -ERCP -SEMS -SIMULTANEOUS DRAINAGE -SIDE-BY-SIDE -STENT-IN-STENT

  UFR DE MÉDECINE ET DES PROFESSIONS PARAMÉDICALES THÈSE D'EXERCICE pour le DIPLÔME D'ÉTAT DE DOCTEUR EN MÉDECINE par GUILMOTEAU Thomas Présentée et soutenue publiquement le 27 avril 2023 DIRECT COMPARISON OF SIMULTANEOUS AND SEQUENTIAL ENDOSCOPIC METALLIC BILATERAL STENTING IN MALIGNANT HILAR BILIARY OBSTRUCTION : A SINGLE CENTER SUPERIORITY STUDY Directeur de thèse : Monsieur le Professeur POINCLOUX Laurent, CHU de Clermont-Ferrand (hépato-gastro-entérologie), UFR de Médecine et des Professions Paramédicales Président du jury : Monsieur le Professeur ABERGEL Armando, CHU de Clermont-Ferrand (hépato-gastro-entérologie), UFR de Médecine et des Professions Paramédicales Membres du jury : Monsieur le Professeur GAGNIERE Johan, CHU de Clermont-Ferrand (chirurgie viscérale), UFR de Médecine et des Professions Paramédicales Madame le Docteur JARY Marine, CHU de Clermont-Ferrand (oncologie médicale) Monsieur le Docteur MAGNIN Benoît, CHU de Clermont-Ferrand (radiologie et imagerie médicale)

Figure : Usual liver volume distributionFigure : Figure : Figure : Figure : Figure : Figure : Figure : FlowchartFigure : Figure : Figure : Figure :

 ::::::::::: Figure : Usual liver volume distribution

1 st 2023 .

 2023 Conventional sequential SBS placement was performed at our institution between 2010 and 2017. Since 2017, simultaneous SBS placement has been performed on patients with unresectable MHBOs, requiring bilateral drainage. Patient's cohort was divided into those who underwent sequential SBS or SIS placement between 2010 and 2017 (sequential group) and those who underwent simultaneous SBS placement between 2017 and 2023 (simultaneous group). The two groups were compared retrospectively.Exclusion criteria were patients with no jaundice, resectable obstruction, minors, pregnant woman or patients concerned with limited judicial protection.Malignancy of hilar biliary obstruction was proved after histological or cytological analysis (EUS-FNA or FNB, ERCP bile duct brushing, single-operator cholangioscopy system biopsy (SpyGlass ® , Boston Scientific Corporation, USA) or percutaneous biopsy) when possible and recommended. Due to the poor diagnosis rentability of cytological brushing and the difficulties to obtain direct endoscopic biopsies in cholangiocarcinoma, histological/cytological proof was not systematically achieved, thus, diagnosis was sometimes confirmed regarding medical history, biological and imaging findings.

( 9 ,

 9 5% and 7,4% respectively, p=0.02). Patients who benefited technical success less suffered from infectious complications (OR = 0.25 [0.08-0.78], p = 0.016), and technical failure was more exposing patients to fatal sepsis (AGREE V) (OR 5.89 [0.78-44.4], p=0.085).

FIGURESFigure 1 :Figure 2 :

 12 FIGURES

Figure 3 :

 3 Figure 3 : Schematic representation of internal-external percutaneous transhepatic biliary drainage in 4 steps, for the management of distal biliary obstacle. First step, insertion of a catheter inside the intrahepatic bile duct, followed by the placement of a guidewire through the obstacle. The catheter is removed, guidewire left in place and a plastic tube is passed over the guidewire. The guidewire is removed and the external tip of the tube is stitched to the skin. From UW Health website, 2019.

Figure 4 :

 4 Figure 4 : 4a : Malignant hilar biliary obstruction with dilated intrahepatic bile ducts. 4b : After failure of bilateral stent placement during ERCP, left intrahepatic bile duct remains undrained. Hepaticogastrostomy was performed using EUS-BD. 4c : After failure of bilateral stent placement during ERCP, right intrahepatic bile duct remains undrained. Hepaticoduodenostomy was performed using EUS-BD. 4d : After failure of stent placement during ERCP, both right and left intrahepatic bile ducts remain undrained. Hepaticoduodenostomy associated with hepaticogastrostomy were performed using EUS-BD. From Kongkam et al (14).

Figure 5a :

 5a Figure 5a : Post-operative x-ray showing "stent in stent" (left) and "side by side" (right) bilateral endoscopic drainage.

Figure 7 :

 7 Figure 7 : An uncovered self-expandable-metallic-stent (SEMS) (Niti-S Biliary Uncovered Stent ® , TaeWoong Medical, Seoul, Rep. of Korea). Delivery system 7Fr. Diameter 10mm.

Figure 8 :

 8 Figure 8 : Schematic representation of SBS (left) and SIS (right) biliary stenting. From De Souza GMV et al. (45).

Figure 9a :

 9a Figure 9a : Niti-S Biliary Uncovered Metallic Stent (Y-Type) ® (TaeWoong Medical, Seoul, Rep. of Korea) with central wide-open mesh. Delivery system 8Fr. Diameter 10mm.

Figure 9b :

 9b Figure 9b : BONASTENT M-HILAR ® (Standard Sci-Tech Inc., Seoul, Rep. of Korea). Delivery system : 7 Fr. Diameter 10mm.

Figure 10 :

 10 Figure 10 : Zilver 635 ® Biliary Self-Expanding Stent (Cook Medical, Ireland). Delivery system 6Fr. Diameter 8mm.

Figure 11a :Figure 11b :Figure 14 :

 11a11b14 Figure 11a : Stents used in our study (simultaneous group) Above : Niti-S [M-Type]® (TaeWoong Medical, Seoul, Korea). Delivery system : 6Fr Below : laser cut aixstent® BDH (Leufen Medical GmbH, Berlin, Germany). Delivery system : 5Fr

Figure 15 :

 15 Figure 15 : Repartition of severity according the AGREE classification, among patients who suffered from adverse event.

Figure 16 :

 16 Figure 16 : Repartition of severity according the AGREE classification, among patients with cholangitis.

Figure 17 :

 17 Figure 17: Survival time curves by Kaplan-Meier analysis. We observed no significant differences in overall survival between groups (p=0.24).

DE CONFERENCES DES UNIVERSITES -PRATICIENS HOSPITALIERS HORS CLASSE

  CONTENTS BACKGROUND ................................................................................................ INTRODUCTION .............................................................................................................. LIVER VOLUME .............................................................................................................. PERCUTANEOUS OR ENDOSCOPIC STENTING .................................................... UNILATERAL OR BILATERAL DRAINAGE ............................................................. STENT TYPE .....................................................................................................................

	 UNIVERSITE CLERMONT AUVERGNE PROFESSEURS DES UNIVERSITES DE MEDECINE GENERALE 1ère CLASSE
	M. MORVAN Daniel Mme GOUMY Carole	1ère CLASSE Biophysique et Traitement de l'Image ___________________ Cytologie et Histologie, Cytogénétique
	M. VORILHON Philippe Mme VERONESE Lauren Mme LAPORTE Catherine Mme MIRAND Audrey M. OUCHCHANE Lemlih		Cytologie et Histologie, Cytogénétique Médecine Générale Bactériologie Virologie Médecine Générale Biostatistiques, Informatique Médicale
			et Technologies de Communication
	PRESIDENTS HONORAIRES M. LIBERT Frédéric PROFESSEURS DES UNIVERSITES : JOYON Louis UFR DE MEDECINE Pharmacologie Médicale Mme COSTE Karen Pédiatrie
	UNIVERSITE D'AUVERGNE Mme AUMERAN Claire ET DES PROFESSIONS PARAMEDICALES Hygiène Hospitalière : DOLY Michel Mme NOURRISSON Céline Parasitologie -Mycologie
	Mme PONS Hanaë M. COLL Guillaume M GODET Thomas		Biologie et Médecine du Développement : TURPIN Dominique et de la Reproduction 2ème CLASSE Neurochirurgie : VEYRE Annie Anesthésiologie-Réanimation et Médecine
			Péri-Opératoire	: DULBECCO Philippe
	DOYENS HONORAIRES		: DETEIX Patrice
	Mme MALPUECH-BRUGERE Corinne	: ESCHALIER Alain : CHAZAL Jean Nutrition Humaine 2ème CLASSE
	PRESIDENTS HONORAIRES UNIVERSITE BLAISE PASCAL DOYEN PROFESSEURS ASSOCIES DES UNIVERSITES : CABANES Pierre M. MOUSTAFA Farès Médecine d'Urgence : CLAVELOU Pierre RESPONSABLE ADMINISTRATIVE M. CHENAF Chouki Pharmacologie Clinique : ROBERT Gaëlle M. ANIORT Julien Néphrologie : FONTAINE Jacques Mme DUPUY Claire Médecine Intensive -Réanimation
	Mme BOTTET-MAULOUBIER Anne Mme JULIAN Valérie M. CAMBON Benoît M. LAHAY Clément	Médecine Générale Physiologie : BOUTIN Christian Médecine Générale Gériatrie et Biologie du Vieillissement
	M. BERNARD Pierre M. TANGUY Gilles M. CLERFOND Guillaume		Médecine Générale : MONTEIL Jean-Marc Médecine Générale Cardiologie
			1ère CLASSE	: ODOUARD Albert
	: LAVIGNOTTE Nadine : BERNARD Mathias : FOGLI Anne Biochimie Biologie Moléculaire VICE PRESIDENTE CHARGEE DE LA FORMATION PRESIDENT DE L'UNIVERSITE PREMIERE VICE-PRESIDENTE CHARGEE DU PILOTAGE ET DES MOYENS Mme FOGLI Anne : PEYRARD Françoise Nutrition Mme VAILLANT-ROUSSEL Hélène Médecine Générale MAITRES DE CONFERENCES DES UNIVERSITES MAITRES Mme BOUTELOUP Corinne HORS CLASSE
	VICE-PRESIDENTE CHARGEE DE LA RECHERCHE Mme GOUAS Laetitia Cytologie et Histologie, Cytogénétique : PREVOT Vanessa M. DELMAS Julien Bactériologie M. BLANCHON Loïc Biochimie Biologie Moléculaire
	DIRECTEUR GENERAL DES SERVICES M. ROBIN Frédéric M. MARCHAND Fabien M. MARCEAU Geoffroy Mme VAURS-BARRIERE Catherine	Bactériologie Pharmacologie Médicale : PAQUIS François Biochimie Biologie Moléculaire Biochimie Biologie Moléculaire
	Mme MINET-QUINARD Régine	Biochimie Biologie Moléculaire

STENT IN STENT OR SIDE BY SIDE (SEQUENTIAL AND SIMULTANEOUS PROCEDURES)

.

................................................................................................................ ARTICLE ........................................................................................................... INTRODUCTION .............................................................................................................. METHODS ......................................................................................................................... Patients ......................................................................................................................................... Data collection .............................................................................................................................. Procedures .................................................................................................................................... Outcomes and definitions............................................................................................................ Statistical analysis ........................................................................................................................ RESULTS ............................................................................................................................ Patient characteristics ................................................................................................................. Technical success ......................................................................................................................... Clinical success ............................................................................................................................ Procedure duration ..................................................................................................................... Early adverse events related to the procedure .......................................................................... Recurrent biliary obstruction (RBO) ........................................................................................ DISCUSSION ..................................................................................................................... CONCLUSION ................................................................................................................... REFERENCES .................................................................................................. TABLES ............................................................................................................. FIGURES ...........................................................................................................

TABLE AND FIGURE CONTENTS

 AND

Table 1 :

 1 Patient characteristics

Table 2 :

 2 Univariate and multivariate analyses for technical success

Table 3 :

 3 Patient outcomes

Magnetic Resonance Imagery PTBD : Percutaneous Transhepatic Biliary Drainage

	INTRODUCTION
	Complete biliary drainage of malignant hepatic hilar strictures, which frequently requires a
	bilateral drainage still is a technical challenge. Malignant causes of hepatic hilar obstruction
	commonly include peri-hilar cholangiocarcinoma (Klatskin's tumor), gallbladder
	adenocarcinoma with hilar extension, central liver metastasis (mostly from colonic or breast
	cancer), hepatocellular carcinoma with endoluminal biliary invasion and hilar
	lymphadenopathy (1).
	The only curative treatment for biliary malignant disease remains surgery, however, regardless
	of tumor's histology, less than 30% of patients are suitable for curative resection because of
	locoregional/metastatic disease, poor ECOG-PS or comorbidities.
	RCT : Randomized Clinical Trial
	RBO : Recurrent Biliary Obstruction
	SBS : Side-by-side
	SEMS : Self Expandable Metallic Stent
	SFAR : Société Française d'Anesthésie et de Réanimation
	SIS : Stent-in-stent
	SM : Seeding Metastasis

ABREVIATIONS AE : Adverse Event AGREE : Adverse Event GastRointEstinal Endoscopy CT : Computed Tomography EBD : Endoscopic Biliary Drainage ECOG-PS : Eastern Cooperative Oncology Group -Performance Status ERCP : Endoscopic Retrograde Cholangiopancreatography ESGE : European Society of Gastrointestinal Endoscopy EUS : Endoscopic Ultrasound EUS-BD : Endoscopic Ultrasound -Biliary Drainage FNA : Fine Needle Aspiration FNB : Fine Needle Biopsy Fr : French (=0.33mm) MHBO : Malignant Hilar Biliary Obstruction MRI :

  showed no difference in terms of efficacy for both techniques, regarding technical and clinical success, adverse event rate, stent patency and survival.In 2017, Inoue et al compared technical success of sequential (side by side or stent in stent) and simultaneous bilateral biliary drainage. He showed a significantly higher technical success and shorter intervention time to the benefit of simultaneous drainage, using a 5.7Fr delivery system, compared with sequential technique (regardless the use of side by side or stent in stent technique)[START_REF] Inoue | Simultaneous Versus Sequential Side-by-Side Bilateral Metal Stent Placement for Malignant Hilar Biliary Obstructions[END_REF].

	ARTICLE
	DIRECT COMPARISON OF SIMULTANEOUS AND SEQUENTIAL ENDOSCOPIC
	METALLIC BILATERAL STENTING IN MALIGNANT HILAR BILIARY
	OBSTRUCTION: A SINGLE CENTER SUPERIORITY STUDY
	INTRODUCTION
	Management of malignant hilar biliary obstruction (MHBO) remains today a challenging
	situation. Most obstructions are unresectable, due to patient's general condition or
	local/metastatic tumor extension (41). Latest guidelines recommends endoscopic biliary

  Technical failure was associated with a significant higher rate of fatal cholangitis, (OR 5.89 [0.78-44.4], p = 0.085), reminding us the absolute necessity of adequate drainage of all opacified biliary areas, using if necessary, in case of ERCP failure, alternative techniques such as PTBD or EUS-BD. Furthermore, Vienne et al. proved that drainage of an atrophic biliary area is useless and improved cholangitis, supporting the necessity for hepatic volumetry assessment prior to ERCP, in order to reduce post-procedural cholangitis[START_REF] Vienne | Prediction of drainage effectiveness during endoscopic stenting of malignant hilar strictures: the role of liver volume assessment[END_REF]. et al. compared the association of ERCP + EUS-BD over PTBD for unresectable MHBO, and showed a high technical success rate with similar clinical success rate and a significant lower RBO rate at 3 and 6 months (14). Vanella et al. confirmed superiority of EUS-BD over PTBD after failed ERCP, and purposed EUS-BD as a first option after failure of retrograde stenting[START_REF] Vanella | EUS-guided intrahepatic biliary drainage: a large retrospective series and subgroup comparison between percutaneous drainage in hilar stenoses or postsurgical anatomy[END_REF]. Those results are supported by latest 2022 ESGE recommendations, who now suggest hepaticogastrostomy using EUS-BD after ERCP or PTBD failure[START_REF] Van Der Merwe | Therapeutic endoscopic ultrasound: European Society of Gastrointestinal Endoscopy (ESGE) Guideline[END_REF]. Paik et al. reported a clinical success rate of 69% to 97% after using metallic stent, those results are comparable to our findings[START_REF] Paik | Palliative treatment with self-expandable metallic stents in patients with advanced type III or IV hilar cholangiocarcinoma: a percutaneous versus endoscopic approach[END_REF]. Those results support the fact that despite the use of less wide stents in simultaneous group (8mm versus 10mm diameter), we did not observe a decrease of clinical success or stent patency.

	anesthetic induction and/or orotracheal extubation, that probably increased procedure time in
	our study.
	Clinical success was defined in our study as a decrease of at least 50% of bilirubin rate at day
	7. Recent ESGE recommendations suggest that clinical success should be defined as a decrease
	of 50-75% bilirubin rate after 2 to 4 weeks. We observed a similar clinical success rate (72 to
	75%, p=0.82) between sequential and simultaneous group, a result that might be better with a
	different definition of clinical success, such as recommended by ESGE (47). Though, due to retrospective collection of data in our study, missing data would have been too important with Kongkam We expected a shorter procedure time in simultaneous group, since Inoue et al. and Kawabuko such definition. We observed a shorter median survival time compared with other studies (61 days in sequential
	et al. proved that simultaneous drainage shortens procedure time compared to sequential group and 67 days in simultaneous group in our study), especially in sequential stent in stent
	procedure (22 and 25 minutes for bilateral stenting in their study, respectively) (38,40). In our group (43 days), that might be explained by the higher proportion of metastatic disease in this
	study, median procedure time was not different between simultaneous and sequential procedure population (Kaplan-Meier curves for survival time are represented in Figure 17). In comparison,
	(80 and 72 minutes, p=0.92), but close to simultaneous procedure time found by Chennat et al. median survival time ranges from 146 days to 381 days in Chen et al. meta-analysis (5 studies
	and Law & Baron (64 and 75 minutes respectively) (32,33). We suffered from a lack of data comparing SIS & SBS, 250 patients)
	concerning procedure duration, explained by the possibility for a same patient to benefit from
	both diagnosis EUS and therapeutic ERCP in the same procedure time. We excluded from
	procedure duration analysis, all patient who benefited the two procedures at the same time, in
	order not to interfere with data of ERCP alone. Procedure time could sometimes include

Table 3 :

 3 Patient outcomes.

Remerciements (Conseil national de l'ordre des médecins) SERMENT D'HIPPOCRATE

Au moment d'être admis(e) à exercer la médecine, je promets et je jure d'être fidèle aux lois de l'honneur et de la probité.

Mon premier souci sera de rétablir, de préserver ou de promouvoir la santé dans tous ses éléments, physiques et mentaux, individuels et sociaux.

Je respecterai toutes les personnes, leur autonomie et leur volonté, sans aucune discrimination selon leur état ou leurs convictions. J'interviendrai pour les protéger si elles sont affaiblies, vulnérables ou menacées dans leur intégrité ou leur dignité. Même sous la contrainte, je ne ferai pas usage de mes connaissances contre les lois de l'humanité.

J'informerai les patients des décisions envisagées, de leurs raisons et de leurs conséquences.

Je ne tromperai jamais leur confiance et n'exploiterai pas le pouvoir hérité des circonstances pour forcer les consciences.

Je donnerai mes soins à l'indigent et à quiconque me les demandera. Je ne me laisserai pas influencer par la soif du gain ou la recherche de la gloire.

Admis(e) dans l'intimité des personnes, je tairai les secrets qui me seront confiés. Reçu(e) à l'intérieur des maisons, je respecterai les secrets des foyers et ma conduite ne servira pas à corrompre les moeurs. Je ferai tout pour soulager les souffrances. Je ne prolongerai pas abusivement les agonies. Je ne provoquerai jamais la mort délibérément.

Je préserverai l'indépendance nécessaire à l'accomplissement de ma mission. Je n'entreprendrai rien qui dépasse mes compétences. Je les entretiendrai et les perfectionnerai pour assurer au mieux les services qui me seront demandés.

J'apporterai mon aide à mes confrères ainsi qu'à leurs familles dans l'adversité.

Que les hommes et mes confrères m'accordent leur estime si je suis fidèle à mes promesses ; que je sois déshonoré(e) et méprisé(e) si j'y manque.

Data collection

We retrospectively collected clinical data from patients charts including: demographic information, type of procedure (sequential or simultaneous), the type of stent and deliverysystem catheter used, date of procedure, tumor's type and biliary extent according to Bismuth & Corlette classification, procedure duration (in min), post-operative chemotherapy status, total bilirubin rate (µmol/L) at D0 and D7, early adverse event related to the procedure (D0-D7), late stent-related complications (RBO i.e stent patency and/or dysfunction), type and success of reintervention after RBO, time until death or latest news.

Procedures

All patients underwent sectional cross imaging (computed tomography or magnetic resonance imagery) to evaluate hepatic volumetry, biliary extension of the malignant hilar obstruction and to assess surgical resectability. All procedures were performed using carbon dioxide insufflation with a 4.2mm working channel duodenoscope (TJF-160 ® and TJF-190 ® , Olympus Medical Systems Corp., Tokyo, Japan).

All patients underwent complete biliary sphincterotomy when deep biliary catheterism (either transpapillary or using "double guidewire technique") was achieved, or large fistulotomy if


Santiago Cuesta-Lopez

Dimitar Angelov

Michel Peyrard

Adding a New Dimension

Keywords: 87.15.Hp -Dynamics and conformational changes 82.39.Pj -Nucleic acids, DNA and RNA bases 87.15.Cc -Folding: thermodynamics, statistical mechanics, models, and pathways

published or not. The documents may come

DNA melting, i.e. the separation of the two strands of the double helix, and its reverse process hybridisation are ubiquitous in biology, in vivo for instance for DNA transcription in the reading of the genetic code of a gene, as well as in vitro in biological laboratories for PCR (Polymerase Chain Reaction) or the use of DNA microarrays. This is why DNA melting has been extensively studied even in the early days of DNA structural studies [1]. An approximate understanding of the melting curves of long DNA segments, with thousands of base pairs, can be provided by simple statistical physics models, using empirical parameters because, at this large scale, the subtle effects of the base pair sequence are smoothed out. Understanding the fluctuations and melting of short DNA fragments of a few tens of base pairs with a high degree of heterogeneity is much more challenging. And it is also very important because this size is the scale at which the genetic code can be resolved. This would have some significant biological consequences to unravel the processes by which specific binding sites are recognised by proteins, drugs, mutagens and other molecules. This would also have a lot of practical importance in the design of the PCR primers which are used everyday in most of the biological laboratories [2].

The two kind of base pairs which exist in the DNA double helix have different thermal stability, the AT pair, bound by two hydrogen bonds, being weaker than the GC pair bound by three hydrogen bonds. This explains why the melting curve of a heterogeneous DNA sequence, which shows the fraction of open pairs as a function of temperature, can exhibit complex features. Those curves are easy to record experimentally because the UV absorbance of a DNA solution increases drastically when the bases are unstacked, which is (a) Mailing Address: Santiago.Cuesta.Lopez@ens-lyon.fr the case in the broken regions of the molecule. But such a curve only provides an integral information on the open fraction of base pairs. Getting more local information requires involved methods. Using a clever choice of sequences such that single strands can form hairpins, and a combination of heating and quenching, Montrichok et al. [3,4] managed to get some data on the melting process of short DNA sequences, detecting whether they open at one end or by starting with an open bubble in the centre. The kinetics of proton-deuterium exchange for the protons involved in the hydrogen bonds within pairs, coupled with NMR studies to detect the location of the exchanged protons, can also provide partial information on the spatial aspect of DNA fluctuations, at the expense of heavy experiments [5]. Another approach relies on special molecular constructs which attach a fluorophore and a quencher to DNA to detect its local opening at a particular site [6,7]. Only one position can be monitored, and one cannot exclude local perturbations of the fluctuations by the large residues attached to the DNA.

Due to their importance, the statistical and dynamical properties of DNA fluctuations and their relation to biological functions have been the subject of many theoretical studies [8][9][10]. These studies raised a debate on the role of statistical properties and dynamical phenomena in connection to biological function. But the validity of those theoretical approaches can only be tested if one can compare their predictions to measurements of the local fluctuations of the molecule. Moreover the study of dynamical and conformational phenomena in DNA requires a method not only able to give a precise local information, but also able to provide coupled information of events along the chain. In this letter we present an original method that can provide a mapping of the strength of the fluctuations of the double helix as function of their position along the sequence. This adds a new dimension, space, to the traditional melting curves. Our approach does not require special molecular constructs like those using dyes or fluorophores. Instead it uses DNA itself to report on its internal state and gives a snapshot of the opening of DNA at each guanine site at once. The method relies on the oxidative chemistry of the guanine bases G, and their propensity to be ionised by a two step resonance excitation [11] from a strong UV laser pulse. Two guanine modifications, oxazolone and 8-oxo-7,8-dihydro-2-oxoguanine (8-oxodG) have p-2 been identified as the major one-electron oxidative DNA lesions. Their formation depends on the local DNA conformation and on the charge-transfer efficiency, which is affected by local fluctuations [12][13][14]. While oxazolone is the unique product resulting from one-electron oxidation of the free 2 ′ -deoxyguanosine, 8-oxodG appears as soon as the nucleoside is incorporated in a helical structure. Hence the measurement of the relative yield of these photoproducts at each G site (labelled R F pg /R pip due to the method used for its detection [START_REF]fragments of length l are those which were cleaved at a guanine situated at distance l from the marked end. The ratio RF pg /Rpip of the number of radioactively labeled fragments of length l produced by Fpg cleavage or by piperidine cleavage indicates the probability of closing for this particular guanine, which is unambiguously identified by its distance from the marked end[END_REF]) tells us whether this G was in an helical structure (closed) or whether it was open when the molecule was hit by the laser pulse. As the experiment is not performed on a single molecule but in solution the results are obtained on a statistical ensemble and they give a signal representative of the probability that each G site is closed at the temperature of the study. Standard biological methods can be used to measure the relative yield of the production of oxazolone and 8-oxodG [START_REF]fragments of length l are those which were cleaved at a guanine situated at distance l from the marked end. The ratio RF pg /Rpip of the number of radioactively labeled fragments of length l produced by Fpg cleavage or by piperidine cleavage indicates the probability of closing for this particular guanine, which is unambiguously identified by its distance from the marked end[END_REF]. However, it is important to notice that the value of R F pg /R pip should not be considered as a quantitative measure of the local closing probability because it is also affected by the configuration of the DNA molecule near the probe, which depends slightly on the sequence and influence the charge transfer. Only the temperature dependence of this ratio for a given probe can be analysed quantitatively [16].

By splitting the sample into several aliquots, the measurement can be performed at different temperatures, which allows us to produce a set of melting curves for each guanine in the sequence. Figure 1 shows the results of a UV laser irradiation analysis for two guanines, labelled S1-G1 and S1-G2, belonging to a test sequence S1 (details of the sequence are provided in the figure caption and in Figure 3). It demonstrates how our method reports two complementary curves at once for the same single DNA sequence, adding a valuable information of the state of the system. The results that it provides changes the view in which DNA denaturation can be studied, adding the spatial correlations to the notion of local conformation (melted or packed helix).

In order to quantitatively analyse the measurements shown in Fig. 1 we have fitted the experimental curves by the function

f (T ) = A -B 1 tanh[C 1 (T -T 1 )] -B 2 tanh[C 2 (T -T 2 )],
selected according to the shape of the curves, particularly that of the probe S1-G1. Once the p-3 optimal parameters are determined, we plot df (T )/dT for each probe (right part of Fig. 1), to highlight the fine structure of each melting curve. Figure 1 clearly shows that, at the level of probe S1-G1, the melting occurs in two steps, with a precursor at T 2 = 45.7 • C while the full melting is achieved at 55.0 • C. Although a slight precursor effect can be detected for probe S1-G2 it is very weak and hardly visible on the figure. The fit of the data indicates that it occurs at T ′ 2 = 51.8 • C, very close to the full melting detected at T ′ 1 = 54.4 • C for this probe. Interestingly these results show that the conformational melting can follow different paths in various parts of the same short sequence.

For longer sequences such as sequence S2 (Fig. 3), the existence of several guanine probes, located in some interesting domains, allows us to obtain a collection of snapshots for the local state of the system that can be combined to build a three-dimensional melting profile like the one shown in Figure 2. This 3D plot shows the ratio R F pg /R pip for a particular DNA sequence containing four guanines (S2-G1 to S2-G4) that are monitored as probes.

The study as a function of temperature provides a melting profile for each probe, together with a view of the spatial correlations along the full sequence. In order to get a more precise insight on the origin of the two-step melting detected at the level of probe S1-G1, and to relate it to the effect of bubble nucleation in DNA, we have studied several artificial sequences specially designed and synthesised [START_REF]DNA Oligos have been HPLC-RP purified and artificially synthesized by Eurogentec[END_REF] to investigate possible non-local effects of the fluctuations. They are shown on Figure 3. Sequences S1 and S2 contain a 10 base-pair-long AT-rich fragment which is analogous to the "TATA-box', a motif that exists in the transcription-initiation regions of the genes of various species. As the AT base pairs bound by only two hydrogen bonds are weaker than the GC pairs, these segments are expected to exhibit large fluctuations even at biological temperature because they are closer to their melting temperature.

All sequences S1, S2 and S3 contain different guanines labeled Sn-Gx, where n refers to the sequence and x to the particular guanine. They are spread along the strand, and according to the basis of our method, act as probes informing us about the local structural state at each temperature. As mentioned above the level of the R F pg /R pip signal that we record depends on the structure in the vicinity of the guanine of interest. This is why, in order to allow a quantitative comparison between different sequences, we have selected guanines with the same environment. For instance guanines S1-G1, S2-G1, S3-G1 are all parts of the sequence CGA, and guanines S1-G2 and S2-G2 are part of the sequence AGT.

The major difference between sequences S1 and S2 lies in the length of the domain that separates probe G1 from the AT-rich region. This "buffer region", which is an heterogeneous domain with AT and GC pairs, has been extended from 7 base pairs in sequence S1 to 13 base pairs in sequence S2. In sequence S3 we have eliminated the large "TATA box" to keep only short AT-rich domains around probe S3-G1. In all cases these short DNA molecules are terminated by GC rich domains which act as clamps to prevent large fluctuations of the free ends of the molecules, and hold the two strands together even when we heat the sample up to 60 • C. [18].

The variation versus temperature of the ratios R F pg /R pip for all the guanine probes studied in sequences S1, S2, S3, are summarised in Fig. 4. The comparison of the various curves gives some clues to understand the differences between the two melting curves of probes S1-G1 and S1-G2 discussed above, and points out some interesting features of DNA fluctuations, which can be revealed by an experimental method able to record local melting profiles. When they are analysed in the context of the particular sequences that we studied, the curves suggest three important properties of DNA fluctuations: i) a large AT-rich domain undergoes very large fluctuations, even at room or biological temperature, and therefore tends to easily form an "open bubble".

ii) there is a minimum size of the AT-rich domain that allows the formation of such a bubble.

iii) the influence of such a bubble does not only affect its immediate vicinity, but extends to some distance.

Let us see how these statements are supported by our results.

As our method relies on the ionisation of the guanines, we do not directly measure the opening of the AT pairs but their fluctuations can be inferred from their influence on the adjacent guanines. Although we stressed that quantitative comparisons cannot be made between different probes because the signal that we record depends on the local structure of DNA, the very small value of R F pg /R pip for probe S1-G2 is nevertheless a strong indication that the closing probability of this guanine, which lies next to a series of 10 AT pairs is very low even at room temperature. This can be understood as an effect of the strong tendency of the large AT rich region to open into transient bubbles, called "premelting phenomena", starting at physiological temperatures [START_REF] Erfurth | [END_REF][20][21][22], which certainly affects the base pair which is right next to it. Probe S3-G1 is also surrounded by AT-rich regions, but its closing probability deduced from the corresponding value of R F pg /R pip , shown on the top panel of Fig. 4, appears to be much higher that for probe S1-G2. This indicates that the fluctuations of the five-base-long AT regions which are next to probe S3-G1 are not sufficient to form open bubbles that would promote the opening of this probe. This is in agreement with the existence of a minimum size needed to allow the formation of a bubble [3].

The striking point is that the large fluctuations of the TATA box do not only perturb the adjacent geometry but also induce conformational changes that distort the closed packed helicoidal structure in regions distant from the bubble nucleation segment, giving rise to premelting intermediate structural states that coexist in consonance with the nucleated bubbles. This shows up in the two-step denaturation that we observed for probe S1-G1, as discussed above. Although this probe is 7 base-pairs away from the TATA box, Fig. 1 shows that precursor effects appear well below the full denaturation of this probe. Those precursors are also visible in Fig. 4. Note again how the melting at the level of probe S1-G1 differs from a simple sigmoidal curve, particularly in the temperature range from 37 • C to 52 • C. It is tempting to assign them to the influence of the fluctuations of the TATA, which grow when the temperature is increased and might influence the opening structure and fluctuations of the double helix even rather far away. But, to confirm such an assignment control experiments are necessary. Their results are shown on the bottom panel of Fig. 4 which shows the thermal variation of the ratio R F pg /R pip for several guanine probes in sequence S2.

In this sequence the TATA box is present, as in sequence S1, but the length of the buffer p-5 region that separates it from probe S2-G1, which has the same local structure as probe S1-G1, has been increased. Moreover this buffer region is strengthened because it contains several GC pairs, including two adjacent ones at the site of probe S2-G3. In this sequence the existence of the large fluctuations of the TATA box are attested by the very low closing probability of probe S2-G2, similar to what is observed for probe S1-G2. But, contrary to what was observed for probe S1-G1, the denaturation of probe S2-G1 does not show any significant precursor effect. Similar one-step transitions are also observed for probes S2-G3 and S2-G4. In summary, these experiments clearly suggest that thermal fluctuations, which are stronger in AT-rich tracks, induce bubble nucleation phenomena and structural changes that affect not only the local geometry and dynamics of DNA in the breathing portion, but also to some distance along the helix. How this happens is highly dominated by the characteristics of the fragment sequence as well as the length of the sections involved. Sigmoidal non-linear fits (dotted lines) have been used to describe the evolution of probes S1-G1 and S3-G1. Both fits have been performed with the same identical functional form. While the response of S3-G1 agrees with a one step standard melting transition, the result for S1-G1 suggests a two steps transition, with a premelting region, clearly shown in Fig. 1. The bottom panel shows the ratio RF pg /Rpip for the guanine probes of sequence S2 versus temperature. For probe S2-G1, the premelting effect has been suppressed due to the existence of a longer more stable intermediate buffer region.

p-6

Those results are only accessible because we have introduced a method which is able to provide a spatial information that was not available until now for the study of local melting in short DNA fragments. Further studies are certainly necessary to confirm and precise the non-local effect of the fluctuations of large AT-rich regions that we have presented in this letter. They become possible with the "three-dimensional melting curves" that can now be measured.

Finally, we would like to emphasise the importance of taking into account the structural modifications induced by bubble dynamics in terms of DNA-protein binding interactions, Transcription Factor recognition or DNA-drug binding. Further studies of local fluctuations in DNA may be of significant importance in the analysis of these biological phenomena.

We would like to thank the program CIBLE of Région Rhône-Alpes which supported this work.

Fig. 1 :

 1 Fig.1: Local melting curves for different sections of a DNA sequence (S1). Symbols represent the thermal evolution of the rate RF pg /Rpip exhibited by two guanines G1 and G2, used as probes located along the molecule. This ratio reports on the closing probability of each guanine at a given temperature. The lines are the fitting curves described in the paper and the insets plot the derivative of the fitting curve for each probe. They highlight the fine structure of the melting curves and point out the existence of different local conformational transitions along the DNA sequence.

Fig. 2 :

 2 Fig. 2: Adding a new dimension to the study of a short DNA fragment melting profile: the figure displays a 3D view of the spatially resolved ratio RF pg /Rpip, showing the closing for different guanine probes placed along a longer DNA sequence S2.

Fig. 3 :

 3 Fig. 3: Sequences of the DNA fragments investigated in this study. S1 and S2, are artificial sequences containing a large TATA box and guanines on the 5'-3' strand, used as probes. S3 is a shorter control sequence that eliminates the TATA motif. All sequences are completed by GC-rich terminal domains (marked as dotted boxes) to stabilise them and ensure proper closing of these short DNA helices.

Fig. 4 :

 4 Fig. 4: The top panel shows the melting profiles for the probes studied in sequences S1 and S3.Sigmoidal non-linear fits (dotted lines) have been used to describe the evolution of probes S1-G1 and S3-G1. Both fits have been performed with the same identical functional form. While the response of S3-G1 agrees with a one step standard melting transition, the result for S1-G1 suggests a two steps transition, with a premelting region, clearly shown in Fig.1. The bottom panel shows the ratio RF pg /Rpip for the guanine probes of sequence S2 versus temperature. For probe S2-G1, the premelting effect has been suppressed due to the existence of a longer more stable intermediate buffer region.