Laparoscopic procedures are considered a standardized approach for the treatment of benign gallbladder diseases [1]. With the development of surgical techniques and instruments and the accumulating experience in laparoscopic surgery, many surgeons have attempted to reduce the number of incisions. Single-incision laparoscopic cholecystectomy (SILC), which emerged as a result of these efforts, has been widely accepted since it was first introduced in 1997 [2]. Initially, SILC was performed only in highly selected patients; however, the indications were gradually expanded as the surgeons’ experience accumulated. Nevertheless, no definite indications for SILC have been established thus far. Although previous studies have reported the safety and feasibility of SILC in patients with acute cholecystitis (AC) [3–5], some controversies remain about the safety of SILC for AC. Several systematic reviews have cautioned that attention should be paid to the application of SILC in patients with AC, obesity (body mass index [BMI] of ≥30 kg/m²), and advanced age [6–8].

At our institution, SILC has been performed for benign gallbladder diseases since 2010. We have reported the evolution of our surgical method for SILC [9,10], as well as the risk factors for conversion to conventional multiport laparoscopic cholecystectomy (CMLC) [11] and prolonged operation time [12]. The current study aimed to identify the optimal indications for SILC by analyzing the difficulty of surgery and postoperative outcomes from our experience of >10 years.

Patients and indications for single-incision laparoscopic cholecystectomy

We evaluated patients with benign gallbladder diseases who underwent SILC performed by three hepatobiliary surgeons at Konyang University Hospital between April 2010 and June 2020. A total of 1,405 patients were included in this study. Initially, when we selected candidates for SILC, we excluded patients aged >70 years and those with systemic disease, variation of bile duct, or complications of AC. After 50 cases, SILC was applied to all patients with benign gallbladder diseases except when malignancy was suspected. After reporting the risk factors for conversion and prolonged operation time [11,12], we carefully performed SILC in patients with complicated AC.

Surgical technique of single-incision laparoscopic cholecystectomy

Our surgical methods have evolved over time and cautiously expanded indications. In the first period, SILC was performed with a handmade three-channel port using surgical gloves. We named this the Konyang Standard Method (KSM). In the second period, SILC was performed using a handmade four-channel port with a snake liver retractor to expose the Calot triangle. We referred to this method as the modified KSM. In the third period, SILC was performed using a commercial four-channel port (Glove port; Nelis, Bucheon, Korea), which is the final version of our standardized SILC method. We referred to this method as the commercially modified KSM. For the commercially modified KSM, a 20-mm transumbilical incision was made and a glove port was inserted. The flexible laparoscope was inserted into the left lower channel, the snake retractor into the right lower channel below the laparoscope, and the grasper into the left upper channel located on the right side of the laparoscope. Meanwhile, the dissector, scissors, and electrocautery suction–irrigation device were inserted into the right upper channel below the grasper. The detailed surgical technique has been described in our previous study [10].

Definitions of demographics and treatment outcomes

The diagnosis of AC was based on the 2018 Tokyo Guidelines (TG18) [13]. Imaging findings were confirmed using abdominal ultrasonography, computed tomography, or magnetic resonance cholangiopancreatography. The severity of AC was classified according to TG18 [13]. The general condition and physical fitness of each patient were evaluated using the American Society of Anesthesiologists physical status (ASA PS) classification [14]. Postoperative complications were graded according to the Clavien-Dindo classification [15]. The length of hospital stay after surgery was defined as the number of days of hospital stay after the SILC procedure. Operation time was calculated as the time from skin incision to skin closure. Blood loss estimates were obtained from surgical records. Bile duct injury was defined as damage to the biliary tract, excluding the cystic duct and gallbladder, and was classified according to the timing of recognition. Adjacent organ injury recognized during surgery was defined as damage to adjacent organs, such as the duodenum, colon, and hepatic artery, excluding the bile duct. Bile duct injury and adjacent organ injury recognized during surgery were not included as postoperative complications.

An incisional hernia was defined as a hernia at the umbilical incision site that was postoperatively confirmed with physical examination and imaging studies.

Definitions of difficult surgery and poor postoperative outcome

We evaluated the surgical difficulty and postoperative outcomes to confirm the safety and feasibility of SILC. We defined difficult surgery (DS) as the occurrence of the following intraoperative outcomes: conversion to multiport or open cholecystectomy, adjacent organ injury during surgery, operation time of ≥90 minutes, or estimated blood loss of ≥100 mL. We defined poor postoperative outcome (PPO) as postoperative hospital stay of ≥7 days or postoperative complications of Clavien-Dindo grade ≥II. Operation time of ≥90 minutes, estimated blood loss of ≥100 mL, and postoperative hospital stay of ≥7 days, which are the criteria for DS and PPOs, were all determined based on 95% of the study population.

Statistical analysis

Categorical variables are presented as counts and percentages and were compared using the chi-square test. Continuous variables are summarized as means and standard deviations and were compared using Student t test. Multivariate analyses of the significant factors identified in the univariate analyses were performed using a logistic regression model. All tests were two-sided, and statistical significance was set at p < 0.05. Analyses were performed using IBM SPSS version 24 (IBM Corp., Armonk, NY, USA).

Study population

The patient demographics, disease characteristics, and surgical outcomes are listed in Table 1. The mean age at surgery was 51.2 years, and 802 patients (57.1%) were female. Of the 1,405 patients, 338 (24.1%) underwent SILC for gallbladder stones, 121 (8.6%) for gallbladder polyps, 474 (33.7%) for chronic cholecystitis, and 427 (30.4%) for AC. According to the TG18 classification of AC severity, 358 patients (83.8%) had grade I AC and 69 patients (16.2%) had grade II/III AC. A total of 105 patients (7.5%) had a BMI of ≥30 kg/m², and 97 patients (6.9%) had an ASA PS classification of ≥III. In addition, 324 patients (23.1%) had a history of prior abdominal surgery. Preoperative percutaneous transhepatic gallbladder drainage (PTGBD) was performed in 137 patients (9.8%). Preoperative endoscopic sphincterotomy for common bile duct stones was performed in 132 patients (9.4%).

The mean operation time was 51.8 minutes, and the mean estimated blood loss was 14.8 mL. One additional port was inserted in six of the 1,405 patients (0.4%), two additional ports were inserted in 27 patients (1.9%), and open conversion was performed in only one patient (0.1%). Bile duct injury occurred in three patients, which was recognized during surgery in two patients and during the postoperative period in one patient. Four adjacent organ injuries (0.3%) were recognized during surgery, two in the duodenum and two in the hepatic arteries (one in the left hepatic artery and one in the right hepatic artery). No intraoperative transfusions were performed. Postoperative complications occurred in 49 patients (3.5%). The mean length of postoperative hospital stay was 2.5 days. Pathologic examination revealed that 1,128 (80.3%) patients had chronic cholecystitis, 188 (13.4%) had AC (emphysematous or gangrenous cholecystitis), and five (0.4%) had gallbladder cancer. Postoperative incisional hernia at the umbilical site was observed in five patients (0.4%). No postoperative 30-day mortality occurred.

Difficult surgery

According to the definition of DS, the study population was divided into two groups: non-DS (NDS) and DS. Table 2 shows a comparison of patient demographics between the two groups. No significant sex differences were observed between the two groups (p = 0.084). The DS group included more patients aged ≥70 years (10.0% vs. 20.2%, p = 0.002), patients with BMI of ≥30 kg/m² (7.1% vs. 14.6%, p = 0.009), and patients with an ASA PS classification of ≥III (6.2% vs. 16.9%, p < 0.001) than the NDS group. The proportion of patients with AC was also higher in the DS group than in the NDS group (28.4% vs. 59.6%, p < 0.001). Preoperative PTGBD was performed more frequently (8.5% vs. 28.1%, p < 0.001) in the DS group than in the NDS group. With respect to preoperative laboratory findings, leukocytosis or leukopenia (18.2% vs. 43.8%, p < 0.001), elevated aspartate transaminase level (26.2% vs. 38.2%, p = 0.014), and hyperbilirubinemia (16.7% vs. 29.2%, p = 0.003) were more common in the DS group than in the NDS group.

In the multivariate logistic regression model that included the significant factors identified in the univariate analysis, grade I AC (odds ratio [OR], 2.157), grade II/III AC (OR, 5.108), and BMI of ≥30 kg/m² (OR, 2.163) were significant predictors of DS (Table 3).

Poor postoperative outcome

According to the definition of PPO, the study population was divided into two groups: non-PPO and PPO. Table 2 shows a comparison of patient demographics between the two groups. No significant sex differences were found between the two groups (p = 0.631). The PPO group included more patients aged ≥70 years (9.6% vs. 36.5%, p < 0.001) and patients with an ASA PS classification of ≥III (6.4% vs. 19.2%, p < 0.001) than the non-PPO group. The proportion of patients with AC was also higher in the PPO group than in the non-PPO group (29.4% vs. 55.8%, p < 0.001). Preoperative PTGBD (8.9% vs. 30.8%, p < 0.001) and endoscopic sphincterotomy (8.9% vs. 21.2%, p = 0.003) were performed more frequently in the PPO group than in the non-PPO group. With respect to preoperative laboratory findings, leukocytosis or leukopenia (19.3% vs. 32.7%, p = 0.017) and hyperbilirubinemia (17.1% vs. 28%, p = 0.028) were more common in the PPO group than in the non-PPO group. Furthermore, DS was more common in the PPO group than in the non-PPO group (5.4% vs. 30.8%, p < 0.001).

In multivariate analysis, age of ≥70 years (OR, 3.496) and DS (OR, 5.681) were statistically significant predictors of PPO, and the severity of AC was not statistically related to PPO (Table 4).

Patients with acute cholecystitis

A subgroup analysis of patients with AC was conducted according to the TG18 classification of AC severity; grade I AC group vs. grade II/III AC group. Table 5 shows the comparison of patient demographics, disease characteristics, and surgical outcomes between the two groups. The patients in the grade II/III AC group were older than those in the grade I AC group (53.1 years vs. 63.5 years, p < 0.001). More patients with an ASA PS classification of ≥III were included in the grade II/III AC group than in the grade I AC group (8.9% vs. 31.9%, p < 0.001). Preoperative PTGBD was performed more frequently (23.2% vs. 78.3%, p < 0.001) in the grade II/III AC group than in the grade I AC group. DS (9.5% vs. 27.5%, p < 0.001) and PPO (5.0% vs. 15.9%, p = 0.001) were more common in the grade II/III AC group than in the grade I AC group. The grade II/III AC group showed poorer outcomes than the grade I AC group in terms of operation time (57.1 minutes vs. 67.4 minutes, p < 0.001), conversion to multiport or open cholecystectomy (3.9% vs. 15.9%, p < 0.001), postoperative complications (4.5% vs. 15.9%, p < 0.001), and postoperative hospital stay (2.7 vs. 3.7 days, p = 0.001).

Although minimally invasive surgery has been widely accepted in many surgical fields, it remains highly technically challenging in the field of hepatobiliary surgery. Nevertheless, laparoscopic cholecystectomy is performed in 1.2 million patients per year worldwide [16] and is considered the treatment of choice for benign gallbladder diseases. To improve the attendant benefits of minimally invasive surgery with CMLC using three to four ports, SILC was developed, which is recently increasing in popularity. As SILC cannot yet be considered a standard treatment, careful decision making is required when selecting patients suitable for SILC. However, few studies have investigated the optimal indications for SILC. The present study is meaningful because it analyzed a large number of patients who underwent SILC at a single institution and suggested the optimal indications for SILC.

To determine the optimal indications for SILC, both the difficulty of surgery and postoperative surgical outcomes need to be evaluated. Various factors including operation time, estimated blood loss, adjacent organ injury, postoperative complications, and length of hospital stay should also be considered. Evaluating each of the various factors in one study to determine the optimal indications for a procedure is challenging, and the factors need to be evaluated in an integrated manner. Therefore, we defined DS and PPO for a comprehensive evaluation of surgical difficulty and outcomes. In addition, since the decision of the surgical method whether to apply SILC or CMLC is made before surgery, this study evaluated the optimal indication for preoperative factors rather than intraoperative factors.

Although the safety of SILC in patients with AC remains controversial, its application in clinical practice is gradually expanding [17]. Patients with AC may have severe inflammation in the porta hepatis, which greatly distorts the anatomy. In addition, the gallbladder is often distended, friable, and difficult to grasp, and persistent oozing of blood often obscures the surgical field. All of these factors may impede the safety of SILC. Several previous case-controlled studies on SILC in patients with AC reported a 3.6% to 18.3% rate of postoperative complications, 2.7% to 60.0% rate of additional port insertion, 0.4% to 18.3% rate of open conversion, and 5.7 to 9.4 days of postoperative hospital stay [3,4,18,19]. Despite a large number of patients with AC compared with previous studies, the surgical outcomes in the present study were relatively acceptable. However, no studies have investigated the safety of SILC in patients with AC according to disease severity as done in the present study. Our results revealed that most surgical outcomes were worse in patients with grade II/III AC than in those with grade I AC in terms of conversion rate, operation time, postoperative hospital stay, and complication rate. Careful patient selection for safe surgery is more important than expanding the indications for SILC. Therefore, in patients with AC, the indications for SILC should be established according to disease severity.

SILC is an easy-to-perform and safe procedure for experienced laparoscopic and hepatobiliary surgeons. Previous studies have reported that the learning curve for the successful completion of SILC seems to be 8 to 25 cases [20–22]. However, in those studies, patients with AC were either excluded or only partly included. SILC should only be applied after overcoming the learning curve in patients with AC or other factors increasing surgical difficulties.

In the present study, age of ≥70 years (OR, 3.496) and DS (OR, 5.681) were statistically significant predictors of PPO. Old age is a predictor of PPO in most surgical procedures. Similar results were observed in the present study. SILC should be applied with caution in elderly patients to improve the postoperative outcomes. Importantly, DS was the most significant predictor of PPO, and the severity of AC was not statistically related to PPO. In SILC, reducing the difficulty of surgery is the most important way to achieve better surgical outcomes. Therefore, SILC should be carefully applied in patients with risk factors for DS, such as AC and high BMI, and should be avoided in patients with grade II/III AC, which is the most important cause of surgical difficulty.

This study had several limitations. First, this was a retrospective, single-center study, and some bias may exist in the results. As SILC is performed using various surgical methods across different institutions, the results may vary depending on the surgical method. In addition, although checking “critical view of safety” is considered the gold standard for securing the safety of cholecystectomy, this study was a retrospective study and could not confirm whether “critical view of safety” was checked during surgery. Second, this is the first study to recommend the optimal indications for SILC by defining DS and PPO for a comprehensive evaluation of surgical difficulty and postoperative outcomes. The disadvantages of this study are that the effectiveness of the integrated analysis has not been confirmed and a detailed analysis of each factor was not performed. Third, this study included only patients who underwent SILC. A comparison of perioperative outcomes according to AC severity is not sufficient to confirm the safety of SILC for AC. Therefore, we plan to compare the perioperative outcomes between SILC and CMLC in patients with AC using a propensity score-matched analysis.

In conclusion, owing to surgical difficulty and poor surgical outcomes, SILC is not recommended in patients with grade II/III AC and should be carefully performed by experienced and well-trained surgeons. Further studies comparing SILC with CMLC are needed to confirm the safety and effectiveness of SILC in patients with AC, high BMI, or advanced age.

Ethics statements

This study was approved by the Institutional Review Board of Konyang University Hospital, and the requirement for informed consent was waived owing to the retrospective study design (No. 2021-02-004).

Authors’ contributions

Conceptualization, Formal analysis, Methodology, Visualization: SJL, ISC, JIM

Data curation, Investigation: All authors

Writing-original draft: SJL

Writing-review & editing: SJL, ISC, JIM

All authors read and approved the final manuscript.

Conflict of interest

All authors have no conflicts of interest to declare.

Funding/support

None.