Segment IV approach for difficult laparoscopic cholecystectomy

Abstract Although achieving the critical view of safety (CVS) is useful for avoiding vasculobiliary injury during laparoscopic cholecystectomy (LC), the CVS cannot always be achieved in cases of severe cholecystitis because of technical difficulties. Herein, we focused on segment IV of the liver and its diagonal line (D‐line) as a feasible landmark for carrying out difficult LC. The D‐line connects the right dorsal and left ventral corners of segment IV and is used as the vectoral landmark, which is where the gallbladder is first dissected to achieve CVS without misidentification. Conversion to subtotal cholecystectomy along the D‐line is also feasible when gallbladder wall scarring is severe. We named this procedure the segment IV approach for LC. Sixty‐two consecutive difficult LC (including 27 scheduled LC after percutaneous transhepatic gallbladder drainage [PTGBD] and 35 conservatively treated cases of Tokyo Guidelines [TG] grade II cholecystitis) were managed by the segment IV approach. Successful gallbladder extraction along the D‐line was achieved in 44 (71%) cases; all of these cases also achieved CVS following total cholecystectomy. The other 18 (29%) cases were converted to subtotal cholecystectomy because gallbladder extraction along the D‐line failed as a result of severe cholecystitis with inflammatory adhesion with surrounding structures. Median operative time and intraoperative blood loss were 135 (range, 54‐290) min and 10 (range, 0‐100) mL, respectively. No intra‐ or postoperative complications were observed. The segment IV approach is feasible for achieving CVS and for considering subtotal cholecystectomy in difficult LC cases where scarring of the gallbladder wall is present.

IV and is used as the vectoral landmark, which is where the gallbladder is first dissected to achieve CVS without misidentification. Conversion to subtotal cholecystectomy along the D-line is also feasible when gallbladder wall scarring is severe. We named this procedure the segment IV approach for LC. Sixty-two consecutive difficult LC (includ-

| INTRODUC TI ON
The critical view of safety (CVS) has been proposed as a means of avoiding major vasculobiliary injury (VBI) that occurs during laparoscopic cholecystectomy (LC) and is caused by misidentification of cystic structures. [1][2][3] The CVS is a technique for anatomical identification, which targets the cystic duct and the cystic artery. 4 It has been accepted as a result of a sudden increase in the occurrence of VBI after the introduction of LC. 1 Achievement of CVS requires dissection of the proximal one-third of the cystic plate and skeletonization of the cystic structure; however, these tasks are not easy in the scenario of difficult gallbladder because of severe scarring around the neck of the gallbladder. 5,6 Recently, the 2018 Tokyo Guidelines (TG-18) proposed imaging of a connecting line between the base of segment IV of the liver and the roof of Rouviére's sulcus as the appropriate first step for achieving CVS during LC. 7 However, when managing a difficult gallbladder, a more anatomically specific landmark should be designated to achieve LC, as the "base" of segment IV provides obscure and anatomically non-specific positional information. Rouviére's sulcus is also widely accepted as a landmark, at least in the posterior view, as it indicates the bifurcation point of hepatic inflow structures to the right hepatic lobe. However, Rouviére's sulcus is recognizable in only 75% of patients as its visibility can be obscured by omental fusion or by inflammatory changes in acute cholecystitis, precisely when it is most needed. 8 Rouviére's sulcus is not always recognizable because of gallstones impacting the neck of the gallbladder in difficult LC. In the present study, we advocate the diagonal line of segment IV of the liver as a feasible anatomical landmark for difficult LC and as a reference for specifying gallbladder dissection. cases. All LC were electively scheduled. Patient characteristics and outcomes of the difficult and non-difficult gallbladder procedures are summarized in Tables S1 and S2.

| Surgical technique
All LC were carried out using the conventional four-port method. The operator's 5-mm working port (for the operator's right hand) was inserted at the epigastric lesion. A 5-mm port for the operator's left hand was inserted at the right subcostal area along the right mid-clavicular line. A 5-or 10-mm flexible videoscope was inserted through the 12-mm port that was placed at the umbilicus. For gallbladder retraction, a 5-mm port was placed at the subcostal area along the anterior axillary line. Under pneumoperitoneum, visualization of the hepatic hilar region was provided by cranial retraction of the gallbladder fundus. After dissection of a cholecystitis-related adhesion around the gallbladder, superficial landmarks such as Rouviére's sulcus and segment IV of the liver, the infundibulum of the gallbladder, and the common bile duct were recognized. Rouviére's sulcus is fundamentally confirmed as an essential surface landmark to ensure the D-line lies above it ( Figure S1). Alternatively, we use these findings instead of Rouviére's sulcus when its border is obscured so that the liver surface at the posterior side of the gallbladder is continuously recognized from the gallbladder fundus to the D-line.  Figure S3 shows the microscopic view of the resected gallbladder from Video S3, which indicates that the gallbladder is initially dissected on the D-line within the subserosal layer of the gallbladder.

| Distance between Rouviére's sulcus and D-line
In the present study, we introduced the D-line as a vectoral reference line along which the gallbladder is dissected safely. However,

| Ethical considerations
This study was conducted in accordance with the Declaration of Helsinki with approval of the Ethics Committee of Jikei University School of Medicine (approval no. 30-150 (9171)). All patients provided written informed consent prior to undergoing surgery.

| D ISCUSS I ON
Although it was predicted that the VBI rate would decrease over time as the learning curve of LC flattened, the incidence of VBI remained steady at 0.5%. 13,14 Recent data suggest a declining trend in the occurrence of bile duct injury (0.32%-0.52%) without any significant changes in the morbidity and mortality after LC. 15 One explanation for the increasing risk of VBI may be misidentification; the common bile duct is commonly mistaken for the cystic duct; less commonly, an aberrant hepatic duct is misidentified as the cystic duct. 2,3 Thus, although the concept of CVS is useful for avoiding VBI due to misidentification, it is not always feasible for difficult LC for the following reasons. First, although severe-grade cholecystitis is often accompanied by shrinkage of the hepatocystic triangle, 16 the procedure used to achieve CVS also carries the risk of VBI. Second, separating the lower section of the gallbladder from the liver bed while achieving CVS is difficult, unless the cystic structure is divided. 17 With such a background, TG-18 recommends surgeons to consider a bailout procedure, such as subtotal cholecystectomy (rather than total cholecystectomy) without achieving CVS in difficult LC cases. 7 In the present study,