Liver resection is the only curative treatment strategy for many malignant primary and secondary tumors. Liver is vital, highly vascularized organ with complex anatomy, therefore, a lot of expertise is required to perform liver resections. Lortat-Jacob et al[1] described the first right hepatectomy in 1952. In 1957, Claude[2] presented new concept of liver anatomy and defines 8 liver segments as main anatomic-functional liver units. This Couinaud’s liver segmentation remains still today a basis for understanding of segmental and major liver resections. In these early phases, liver resection was associated with high morbidity and mortality rates. Only after introduction of ultrasound into clinical practice in 1980s, more precise and safer resections could be achieved. As a results, Bismuth[3] published: “Surgical anatomy and anatomical surgery of the liver“ which gives profound description of liver anatomy from surgical aspect.
Simultaneously, computed tomography has become standard diagnostic method and liver transection techniques evolved. All this allowed segmental liver resections based on Couinaud’s concept and resulted in expansion of criteria for tumor resectability. This again led to increased risk of postoperative liver failure, but over the last three decades, methods for induction of future liver remnant hypertrophy were developed to address this issue. For a long time, the technique for managing vascular and biliary structures was to isolated them separately within liver hilus. However, in 1990, Takasaki et al[4] demonstrated that there is Glissonean sheath that envelope the hilar structures inside the liver. In addition, they described that the hilar structures can be approached together without dissecting Glisson's sheath. The technique was called Extra-Glissonean (EG) or Takasaki approach. The main advantage of the technique is easier, faster and more precise control of hepatic inflow. With ligation of whole Glissonean pedicle, the liver segment to be resected is completely disconnected from portal triad. In this way, parenchymal transection can be performed and segment can be removed after ligation of hepatic vein branches. In the beginning, not many surgeons adopted this technique as it required extensive knowledge of liver anatomy, especially anatomy of liver sheaths and hilar anatomy. There were also concerns related to intraoperative bleeding during pedicle isolation and development of biliary fistula. However, over the last 10 years, surgeons started to adopt this technique especially for multioperated patients and when selective clamping of the hemi liver is required[5,6]. At first, it was predominantly used for hemihepatectomies or sectionectomy, but recently, mono segmental resections are described as well[7]. Virtually every single liver segment can be selectively clamped using EG approach. As in other fields of surgery, the utility of laparoscopic or robotic techniques was investigated in EG approach as well and results are promising so far.
Laparoscopic extra glissonean approach to single segment resection
The first laparoscopic liver resection (LLR) was reported by Gagner et al[8] in 1992. Laparoscopic approach in this field developed much slower when compared to colorectal surgery, mostly due to complexity of liver anatomy and a steep learning curve. Therefore, laparoscopic technique was utilized only in high volume centers, and we had to wait for 2010s and later to reach a sufficient number of cases and fully adopt the technique. Studies demonstrated the clear benefits of LLR: Quicker recovery, decreased perioperative pain, decreased morbidity, fewer pulmonary complications, and simplification of subsequent surgery[9]. The only drawback was the fact that the technique is technically challenging, but the rise of robotics in hepatic surgery may overcome these obstacles[10]. The first laparoscopic major hepatectomy using the LLR-EG was reported by Cho et al[11] in 2012, and in later years the technique was progressively refined, but it was used only for major liver resections.
In 2018, Kim et al[12] described the use of LLR-EG for resection of segment 6, and Okuda et al[13] for resection of segment 7 one year later. Likewise, Monden et al[14] described segment 8 segmentectomy. By now, the utilization of LLR-EG for most liver segments was described, but generally only as case reports or case series[15,16]. The authors managed to standardize the procedure for every single section or lobe, but there is still room for improvement related to monosegmental resections, mostly from a technical and technological aspect.
In the article by Wang et al[17], all 8 types of liver segmentecomy via laparosopic EG approach are described. This is the first such report that collects all 8 cases and provides valuable insights into the safety and efficiency of the technique. The authors demonstrate that every single liver segment can be approached by an EG approach, and the most important thing is to identify correctly the Glissonean pedicle for the segment to be resected. Each segment has its own specific anatomy, but there are landmarks that help with successful pedicle identification and isolation. Authors present technical and clinical characteristics for each case and support it with high-quality intraoperative images and even videos in supplementary material. All this is sufficient for replication of the procedures and represents a great source of operative knowledge for Hepato-Pancreato-Biliary (HPB) surgeons. Both advantages and disadvantages of LLR-EG are discussed, and special emphasis is put on difficulties in the identification of different “gates” which are required for safe and reliable pedicle ligation. Although this is a case series and studies on a larger number of patients are required, it can be concluded that laparoscopic techniques along with the EG approach are reliable and safe methods that can and should be standardized. In addition, the use of ICG for detection of liver ischemia contributes to more precise liver resection.
Most relevant studies demonstrated clear clinical benefits of laparoscopic over open approach in both minor and major hepatectomy. The laparoscopic approach resulted in a shorter hospital stay, and the pooled analysis of eight randomized controlled trials showed a lower risk of complications in the laparoscopic group compared with the open surgery group (relative risk = 0.57, 95%CI: 0.4-0.76, P < 0.0001). At the same time, there was no statistical difference in operating time, intensive care unit admission, and blood loss[18].
Similarly, the EG laparoscopic approach is not less safe and may seem to offer advantages when compared with the standard laparoscopic approach. In a study from Machado et al[19] that compared EG and standard approach there was no difference in age, sex, tumor types, or comorbidities between the groups. There were fewer complications in the EG group compared with the standard group (P < 0.05). Operative time was greater, and more transfusions were given in the standard group; in addition, more patients had positive margins (P < 0.01). Overall hospital stay was less in the EG group[18].
However, surgeons should be aware of difficulties and potential drawbacks related to the LLR-EG approach. First, there is a steep learning curve, and a lot of experience with both open and laparoscopic procedures is required in order to fully master LLR-EG technique. Second, it requires sophisticated instruments such as cavitron ultrasonic surgical aspirator and laparoscopic ultrasound. Thirdly, the challenging exposure and limited visualization of deep liver tissue may complicate the radical removal of liver tumors. Cost and availability of laparoscopic or robotic systems, as well as organizational difficulties, are other problems related to LLR-EG approach.
Further innovations in liver surgery are awaited in the future, and most are expected from artificial intelligence, augmented reality, and intraoperative tools for precise liver resection, such as hologram projections. CT volumetry and AI-based prediction tools for prognosis, risk of postoperative liver failure, or prediction of liver remnant hypertrophy are other potential advancements in this field. The combination of advanced surgical techniques, modern instruments, and a minimally invasive approach to the above-mentioned tools will definitely contribute to more precise and safer liver resections. In conclusion, HPB surgery will be characterized by continuous innovations and developments from theoretical, technical, and technological aspects.
