Severe obesity is a life-threatening disease, one that is known to cause premature death (1). Bariatric surgery is the most effective therapy available to the obese, and of the available procedures, laparoscopic sleeve gastrectomy (LSG) is among those most frequently performed worldwide (2, 3). LSG results in long-term reduction of weight and its co-morbidities comparable to the benefits of the roux-en-y gastric bypass (RYGB) (4). Yet these drastic weight-loss measures are not without risk. One of the most feared complications of bariatric surgery is staple-line leakage, which can end in sepsis, peritonitis, and even death (5). The underlying causes of such complications remain unclear. In addition to demographic and medical aspects, such as age, sex, and BMI (5), technical factors including thermal injury, reinforcement of the staple line, or bougie size were shown to predispose patients for staple-line leakage (6–11). Staple height and fundus-wall thickness have also been discussed as parameters that may increase the risk of developing a leak (6, 12–14). The fundus wall is demonstrably thinner than the wall of the corpus and antrum, and is therefore at greater risk of becoming a leakage site (12). In addition, staple height must correlate properly with the dissected fundus wall so as to correctly adapt the tissue to achieve hemostasis while avoiding ischemia of the tissue (8).

In an earlier study, we investigated the correlation between fundus-wall thickness and clinical and demographic data. A correlation was seen only for gender, with a thicker fundus wall in male patients. During the review process for that paper, the reviewers noted the small sample size (141 patients), and stated that it was insufficient to show any significant influence of staple-line leakage in a study population with a leak likelihood as small as 2%. Thus, no further correlation could be found within this group of patients, only three of whom suffered leakage (15). For this reason, we continued our measurements and investigated another 306 gastric specimens. The results found for this cohort of 447 patients are presented here. Surgical technique was changed during the study period: The staple line was reinforced by either Gore Seamguard® or oversuture, while bougie size was changed from 34 to 40 Charrier.

The aim of our recent work was to determine the impact of fundus-wall thickness and staple heights on leak risk after LSG. Factors such as gender, age, comorbidities, and reinforcement of the staple line and their influence on leak likelihood were also investigated.

The mean thickness of the proximal fundus wall was 2,904 μm, 3,172 μm in men and 2,784 μm in women. The mean values of the different layers (mucosa, tela submucosa, muscularis propria) are shown in Table 2. Mean BMI was higher in men.

In our sample, greater age was significantly associated with a higher incidence of staple-line leakage. This issue has become controversial in the literature; interestingly, Benedix et al. reported more leaks in younger patients in 2014 (5). In a later-reported larger cohort, there was no difference in mean age for patients with a leak vs. patients without a leak (22). The same results were reported by Sakran for a large Israeli cohort (23). Another study conducted by Benedix et al. in 2017 comparing the leak likelihood of adolescents to that of adults revealed no difference (1.9 vs. 1.4%) (24).

Our investigation of 447 LSG specimen indicated that fundus-wall thickness influenced the development of leaks. Staple-line leaks after LSG occur close to the angle of His in 90% of patients (25); for this reason, we analyzed the wall thickness of this area. There was a strong effect for the tunica muscularis propria on leakage. The same trend was seen for the tunica mucosa propria, the tela submucosa, and the whole fundus wall. In each category, the fundus wall was thinner in the leak group, meaning that a thinner fundus wall may have influenced the development of leaks. However, statistical significance could not be reached.

Another finding of this study was a strong effect of gender and BMI on leak occurrence, although significance could not be reached. Fundus walls were thinner for female vs. male subjects, and there was a higher incidence of leaks in females (6.6%) than in males (2.2%). This might indicate a higher risk of leakage due to thinner fundus walls for female patients in our study group. But with little influence and no significance, gender as a covariate variable showed only a small effect on the likelihood of developing a leak.

These results are in line with previously published data that showed thicker fundus walls in male patients, among the 141 fundus-wall-thickness measurements performed by our group (15). Because three patients of the leak group were female, and male gender was associated with thicker tissue, we concluded that female patients might be at higher risk for developing a leak due to a thinner fundus wall. In contrast to this finding, Benedix et al. reported significantly more leaks among male patients in a large German cohort (5).

Elariny et al. were the first to show a decreasing gastric wall thickness from the antrum to the fundus, with a thicker fundus wall for male patients. The same authors stated that a thicker gastric wall in males might be due to thicker muscle tissue (12). Rawlins and Rawlins found that the antrum is thicker in male patients with a BMI above 50 kg/m² (13). Lee et al. reported a thicker gastric wall in patients whose characteristics included advanced age, male sex, diabetes mellitus, and smoking (26), but the sample size was small (n = 30), and average BMI was below 40 kg/m². Correlation of staple-line leakage was not investigated in these studies.

The presence of a thinner wall might lead to the conclusion that smaller staple sizes are to be used at the angle of His. Abu-Ghanem showed the safety of smaller staple heights as hemostasis is provided (27). Previously, other authors had questioned the safety of using smaller staple heights (6). Huang and Gagner postulated that a measuring device is needed to gauge the tissue intraoperatively and define the appropriate staple height (14). In the present investigation, staple size did not show a significant effect, nor did staple-line reinforcement or oversuture. Regarding an inconsistent study situation reported in the literature, staple size should remain the surgeon's choice based on experience (5, 28, 29).

Lower risk of developing a leak for patients with thicker fundus wall—as shown by our investigation—supports the findings of other studies, which revealed a vulnerable area in the proximal staple line. Marie et al. were able to demonstrate the fragility of the fundus wall under high pressure in the sleeve by investigating the bursting pressure and the probability of leakage (30).

Basso et al. discussed an ischemic region of the proximal sleeve in certain patients, depending on the existence and route of a posterior gastric artery (10). Also, surgical and tissue-based issues play a role in the occurrence of leaks; the incidence is multifactorial and entails local ischemia, increased intraluminal pressure, and extensive lateral traction during resection as well as viscosity of the tissue (31, 32).

To the best of our knowledge, this is the first study to investigate the fundus-wall thickness of a large patient cohort (447 in all) following LSG. The strength of our study may rest in the size of the study population; by comparison, former studies investigating fundus-wall thickness included no more than 60 patients. One limitation of this study might be the technique used for measurement, as the formalin-fixated tissue does not represent the in vivo situation; formalin fixation is known to cause tissue shrinkage of up to 20% (33). Nevertheless, all specimens had been prepared identically, such that a comparison within our study group was possible and reproducible. While the study population was large, the cohort of 447 patients was still too small to show statistical significance in all but one parameter we investigated, but it was possible to indicate trends.

Cartridge color (i.e., size) was the personal choice of the surgeon, and was not randomized. Additionally, strengthening the staple line by oversuture or buttressing in 295 of the last 306 procedures was not randomized.

Furthermore, we should discuss the high leak rate of 4.9% compared to what is reported in the current literature (3, 6, 22, 23, 25, 29, 34–36). This factor might result from a high BMI in our cohort (52 kg/m²), and from high turnover on our surgical team. We are a teaching hospital, and eight leaks occurred in the course of training junior surgeons. As a lesson learned, we reduced the team of operating surgeons to three senior bariatric surgeons, and adapted a stricter teaching curriculum. The surgical technique was changed to continuous oversuture of the staple line, and the resection of the fundus near the angle of HIS will be performed with 1cm distance from the esophagus, avoiding intense transversal traction of the fundus to the patient's left side.

In conclusion, the development of leaks following LSG is a multifactorial and complex process. While a thinner fundus wall along with female gender might predispose patients to staple-line leaks, significance could not be reached. Our study revealed that older age alone showed a significant negative influence on leak risk following LSG; cartridge size should remain the surgeon's choice based on clinical experience. With these things in mind, further research is needed to obtain more information about the impact of influencing factors on leakage following LSG.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Hannover Medical School, Hanover, Germany. No. 2760-2015. The patients/participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

CB, JM, CR, IH, and HK contributed to conception and design of the study. CB and BS organized the database. BS and LW performed the histopathological measurements. VM performed the statistical analysis. CB and HK wrote the first draft of the manuscript. BS and VM wrote sections of the manuscript. CS reviewed the final article. All authors contributed to manuscript revision, read, and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.