Laennec's Approach for Laparoscopic anatomical Hemihepatectomy

Wei Hu Nanjing Medical University https://orcid.org/0000-0003-2304-0040 Gongming Zhang Nanjing Medical University Meng Chen Nanjing Medical University Chengcheng Zhong Nanjing Medical University Mingxu Li Nanjing Medical University Kai Li Nanjing Medical University Titai Sun Nanjing Drum Tower Hospital: Nanjing University Medical School A liated Nanjing Drum Tower Hospital Zhong Wang (  18961326366@189.cn ) Nanjing Medical University


Introduction
Laparoscopic liver surgery, a widely accepted standard surgical practice for the management of liver neoplasm, has evolved over the past two decades, and the procedure has expanded from initial local hepatectomy to anatomical hepatectomy. Laparoscopic hepatic resection has attained an equivalent status of safety and e cacy as conventional open surgeries, but the expansion of the procedure depends on the experienced surgical team in hepatobiliary surgery, laparoscopic skills, and specialized centres with advanced laparoscopic surgery. Nevertheless, laparoscopic anatomical hemihepatectomies (LAH) are very challenging and technically demanding procedures. Notably, for deep-seated or invisible lesions, the development of LAH is greatly limited because of their deep anatomical position, surgical complication during exposure of the resection plane, and complexity in identifying the boundary of hemihepatectomy, and di cult hemorrhage control [1,2]. In LAH, identi cation and anatomical separation of the Glissonean pedicle (GP) at the hepatic hilum and exposure of the landmark hepatic vein represents the critical steps in deciding the transection plane. However, there is a lack of consensus on the standardized approach to LAH [3].
Laennec's capsule, the liver's intrinsic membrane, represents an essential structure for the comprehensive understanding of the surgical anatomy of the liver and standardization of the surgical approach to LAH [4,5]. Some studies have suggested that there is a gap between the extrahepatic GP and Laennec's capsule that could be used as an anatomical gap to isolate GP and hepatic vein [6][7][8]. However, LAH based on Laennec's capsule is rarely reported. Here we described the relevant application of Laennec's approach for LAH based on Laennec's capsule, and highlighted the surgical anatomical description of the liver and related clinical experience. After that, we retrospectively analyzed the technical details and the surgical outcomes of our standardized approach performed on 15 patients who underwent LAH in our hospital between May 2017 and July 2020. We also investigated the safety and e cacy of this approach to expand our understanding of the membranous anatomy of the liver.

General Information
This study comprised 15 patients with benign or malignant neoplasms or hepatolithiasis who underwent LAH between May 2017 and July 2020. Of the 15 patients, 4 patients were diagnosed with hepatic hemangioma, 2 patients had hepatolithiasis, and 9 patients had primary liver cancer. The mean patient age was 62.1 ± 6.5 years old. The preoperative liver function of patients was Child-Pugh class A, and the indocyanin green retention rate at 15 min (ICGR15) was less than 10%. There was no apparent surgical contraindication before the surgery. None of the lesions affected the anatomy of the rst or the second porta hepatis. Laennec's approach for LAH was performed during the hemihepatectomy by isolating the GP and hepatic vein. The liver tissue specimens adjacent to the GP, hepatic veins, and inferior vena cava (IVC) were collected for hematoxylin and eosin (H&E) and Mallory's Phosphotungstic Acid Hematoxylineosin staining. The study protocol was approved by the Research Ethics Committee of the First A liated Hospital of Kangda college of Nanjing Medical University (Approval number: KY20170514001). This study was performed in accordance with the Declaration of Helsinki, and written informed consent was obtained from each patient before surgery.

Surgical methods
All procedures were performed under general anesthesia. Patients were placed in the supine position for resection. The 5-port technique was performed. The pneumoperitoneum pressure was maintained at 14-mmHg. The central venous pressure was maintained between 0 and 3 cm H 2 O during surgery in all cases.
The hepatoduodenal ligament was encircled with extraperitoneal blocking tape through Winslow's foramen by the Pringle maneuver. For right hemihepatectomy, the following procedures were performed: 1. Laennec's approach for dissection of GP: the hepatic hilar plate was lowered after cholecystectomy.
The peritoneum between segment 4 and the surface of GP was incised through the Laennec's capsule. After su cient dissection, the right GP was ligated using a Gold nger dissector for traction and transected with a laparoscopic vascular stapler (if the right GP was di cult to dissect, the liver parenchyma dissecting-rst method through the hepatic Cantle line was applied to reveal the root of the right GP [9]). After transection of the right GP, the demarcation line was determined and marked with an electrocoagulation hook ( Figure 1A-H). 2. Laennec's approach for isolation of hepatic vein: the branches of the middle hepatic vein were dissected under the laparoscopic magni ed caudal view, clamped by Hem-o-lok clips, and transected separately. The gap between the main trunk of right hepatic vein and the Laennec's capsule was exposed using an ultrasound scalpel to reveal the second porta hepatis. The ligament of IVC and the root of the right hepatic vein was excised individually ( Figure 1I-P). 3. Laennec's approach for the division of perihepatic tissues: through the anatomical space close to the Laennec's capsule, the right adrenal gland, IVC and short hepatic veins and diaphragm were dissected separately.
Hemostasis of the bleeding points on the hepatic resection surface or the trunks of hepatic veins was achieved using electrocoagulation or prolene sutures ( Figure 1Q-T).
The procedure followed for the left hemihepatectomy was similar to that of the right hemihepatectomy as described above: 1. Laennec's approach for separation of the left hepatic pedicle: the gap between the left hepatic pedicle and Laennec's capsule in front of the Arantius ligament were dissociated, the left hepatic pedicle was dissected after full dissociation, and the ischemic line was marked (Figure 2A-H Laennec's approach for separation of the hepatic vein: the hepatogastric ligament adjacent to the liver was excised, and the gap between the Arantius ligament and the Laennec membrane was dissected to reveal the gap between the left hepatic vein and the Laennec's capsule. Left hemihepatectomy was performed by exposing the space between middle hepatic vein and Laennec's capsule through a dorsal approach ( Figure 2I-L).

H&E and Mallory staining
Two semi-liver specimens were collected from the livers of two patients undergoing laparoscopic anatomical right and left hemihepatectomies. The specimens were routinely stained with the H&E method. The tissues were xed in neutral-buffered formalin, embedded in para n, and sectioned. The para n sections were oxidized with prepared PTAH oxidizer (Mallory staining) for 5 min, bleached with the oxalic acid solution for 1 min, rinsed with tap water for 2 min, washed with distilled water once, and stained with PTAH staining solution for 24-48 h. Then, the sections were sealed after the removal of excess staining with 95% alcohol.

Postoperative observation and treatment
For the patients' perioperative care, we applied enhanced recovery after surgery strategy with preventive anti-in ammatory, uid replacement, and symptomatic support treatment. The vital signs and thoracic and abdominal parameters were closely monitored after surgery, and the abdominal drainage uid was observed.

Statistics
Statistical analyses were performed using SPSS 23 statistical software (SPSS Inc., Chicago, IL, USA). Data were expressed as mean ± SD for continuous data, and as numbers with percentages for categorical data. Differences in continuous variables between groups were tested using the student t-test. The Chi-square or Fisher exact test was used to compare categorical variables. P <0.05 denotes the presence of statistically signi cant differences.

Results
Dissection of the liver with Laennec's approach for laparoscopic view Although the Glissonean approach is widely accepted for hepatectomy, there are yet no anatomical guidelines for the GPs or the hepatic veins isolation. According to the pathological examination, a natural gap exists between the whole parenchyma and adjacent tissues, such as the GPs, the naked area, the hepatic veins, the adrenal gland, and IVC. Based on the anatomical understanding of the Laennec's capsule, Laennec's approach for LAH was applied as described above. Brie y, the liver mobilization was performed from central location to peripheral isolation with Laennec's approach for LAH. There are two advantages of this method. The possibility of tumor dissemination caused by squeezing is avoided consistently with the no-touch isolation technique; in situ hemihepatectomy without dissecting the perihepatic ligament decreases liver mobilization di culty under laparoscopy.
Outcomes of the patients undergoing LAH with Laennec's approach All 15 patients were successfully treated by surgery, and none of the patients was converted to laparotomy. The operation time was 193 ± 49 min, and the mean blood loss was 247 ± 120 mL. The intraoperative blood transfusion was not needed in any patient. The gastrointestinal decompression tube was not placed during the surgery, and the liquid diet was provided on the rst day post-surgery, and the patient was assisted out of bed on the second to third day after surgery. None of the 15 patients had bile leakage and bleeding, and all patients had different degrees of pleural effusion and ascites after surgery. 1 patient underwent right thoracic puncture and drainage because of dyspnea, and there was no perioperative mortality. The length of hospital stay was 8.7 ± 2.0 days. No signi cant difference was observed in the hospital stay or pleural effusion between laparoscopic anatomical right and left hemihepatectomies. The postoperative pathological analysis con rmed that 4 patients had hepatic hemangioma, 2 patients had hepatolithiasis, and 9 patients had primary liver cancer.
Laennec's capsule does exist around the peripheral hepatic vein At present, it is still controversial whether there is Laennec's capsule around the branches of the peripheral hepatic vein in the hepatic parenchyma [5,[10][11][12]. According to the HE and Mallory staining, we not only found that the Laennec's capsule covers the trunk of the hepatic vein, but also con rmed that there is a gap between the Laennec's capsule and the peripheral vein branches of the segment -in the hepatic parenchyma ( Figure 3A-N). However, we then observed that near the terminal course of the peripheral vein branches, the Laennec's capsule gradually becomes less apparent or even disappears as the hepatic veins become thinner ( Figure 3O and 3P). Therefore, the hepatic vein could be dissected along this gap to achieve accurate anatomical segmental hepatectomy from a novel surgical anatomy.

Discussion
In 1802, French physician Laennec rst described the Laennec's capsule, a proper membrane of the liver, as the distinct structure from the serosa and covered the entire liver. However, Laennec's capsule was confused with the liver serosa or misunderstood as Glissonean sheath and ignored by liver surgeons for about 200 years. In 2008, Hayashi et al. revealed that the sheath of GPs and hepatic veins is continuous with the liver capsule [4]. Furthermore, in 2017, Sugioka et al. con rmed that Laennec's capsule not only covers the entire surface of the liver under the serosa but also has gaps surrounding the liver plate, GPs, hepatic veins, and IVC, and pronounced that Laennec's capsule could be applied as an anatomical structure to isolate and expose the GPs [5].
The Glissonean approach is an important technique in open and laparoscopic anatomical hepatectomy [13][14][15]. Compared to the conventional individual hilar dissection, it produces less intraoperative bleeding and requires less surgery time for transection of the GPs during parenchymal transection. However, while it stresses in ow system control, it has paid little attention to the approach of out ow control or the anatomy of the peri-Glissonean approach.
Laennec's approach combines the in ow occlusion (Glissonean sheath) and out ow control (hepatic veins) for anatomic hepatectomy. Laennec's approach serves to isolate GPs and Laennec's capsule and achieves parenchymal dissection from the trunk of hepatic veins, reaching the goal of anatomical hepatectomy. Laennec's approach can achieve a bloodless condition in the half liver to be removed while maintaining normal blood ow in the remaining liver tissues, thus reducing the time and frequency of complete blocking of the rst hepatic hilum. Therefore, Laennec's approach further ensures the safety of the procedure. The results of this study revealed that anatomic hepatectomy based on Laennec's capsule was successfully performed on 15 patients. The surgery time was 193 ± 49 h, and the mean loss of blood was 247 ± 120 mL. There are no evident complications or mortality occurred. Together, these ndings suggested that anatomic hepatectomy under laparoscopy based on Laennec's capsule is a safe, feasible, and effective approach.
The following insights can be drawn from the exploration and practice of anatomic hepatectomy based on Laennec's capsule under laparoscopy: (1) Before the procedure, an improved understanding of the anatomical position of GPs and the presence (or absence) of anatomical variation based on liver enhanced CT and MRCP examination helps to isolate the GPs during surgery. (2) During surgery, the correct operating plane must be identi ed. Laennec's capsule is close to the entire liver, so anatomical separation should be performed in Laennec's inter-membrane space when dissecting the rst, second, and third hepatic hilum, and perihepatic tissues. The operation may not enter the sneath or go deep into the liver parenchyma. (3) In case of the thickening and fattening of the middle lobe of liver, or the trapping of the rst hepatic hilum in the liver parenchyma due to liver atrophy, hepatic hilum translocation, or other reasons, it may be very di cult to separate Laennec's capsule from GPs under laparoscopy. In that case, no separation should be forced, as it may cause unnecessary medical injuries. We can rst transect the liver parenchyma along the anatomy Cantlie line, and then excise when the root of GPs to be removed is revealed. (4) In-place excision of semi-liver excision should be performed from central to peripheral isolation, thus avoiding the di culty of mobilizing the liver and removing the peripheral ligaments of the liver under laparoscopy. (5) The gap of the post-hepatic IVC can be revealed together with the trunk of hepatic veins, so as to accurately show the liver section. There are also limitations to the application of Laennec's capsule for laparoscopic anatomic hepatectomy. One of the contraindications of this procedure is that the tumor location is adjacent to, or infringes upon, GPs or the trunk of hepatic veins. Therefore, it is important to ensure that the tumor is separated by a safe distance from GPs or the hepatic venous trunk.
At present, some scholars believe that there exists no Laennec's capsule around peripheral branches of the hepatic veins [13][14][15]. However, we con rmed through H&E and Mallory staining that Laennec's capsule also covers the branches of the peripheral hepatic vein of the segment -VIII, and there is a gap between Laennec's capsule and the veins. In precision liver excision, dissecting Laennec's capsule gap along the liver venous trunk and its branches can effectively achieve segmental anatomic liver excision.
This study highlights that Laennec's approach provides a new perspective for laparoscopic anatomical hepatectomy. It is bene cial to the procedure and standardization of laparoscopic anatomical hepatectomy. Laennec's capsule can be used as an anatomical marker for anatomical hepatectomy, expecting to promote liver surgeons' understanding of liver membrane anatomy and the development of LAH.

Conclusions
Laennec's approach is safe and feasible for LAH. Precise isolation of Laennec's approach based on Laennec's capsule helps to standardize the surgical techniques for laparoscopic anatomical hepatectomy.

Declarations
Authors' contributions WH and XS conceived the new approach used in this study. WH and GZ performed the histological examination of the liver. WH, XS and KL performed the surgery. WH, CZ, MC and ML wrote the manuscript. All authors read and approved the nal manuscript.