Minimally invasive liver resection (MILR)

INTRODUCTION — Minimally invasive liver resection (MILR) includes both laparoscopic liver resection (LLR) and robotic liver resection (RLR). LLR was first reported in the early 1990s [1,2]. In 2008, the first international consensus meeting established the feasibility and safety of LLR and defined its indications [3]. Subsequent consensus conferences expanded the scope of LLR [4,5].

RLR was first reported in 2006 [6] and has seen faster adoption due to the already established principles of LLR. A 2018 international consensus published recommendations for the safety, feasibility, indications, techniques, and cost effectiveness of RLR [7].

Over the last two decades, the prevalence of MILR has increased exponentially [8-11]. A 2016 review documented close to 10,000 cases of LLR performed worldwide [10]. The technical expertise associated with MILR has also improved as more procedures have been performed [3,4,12,13].

In this topic, we review the indications, patient selection, learning curve, surgical techniques, and outcomes of MILR. Other aspects of liver surgery, such as preoperative imaging to determine future liver remnant and techniques for open liver resection (OLR), are discussed in other topics. (See "Overview of hepatic resection" and "Open hepatic resection techniques" and "Surgical resection of hepatocellular carcinoma".)

INDICATIONS — MILR is performed with the same objectives as open liver resection (OLR), namely to remove malignant and benign lesions of the liver. Worldwide, 35 percent of MILRs are performed for benign conditions, while the other 65 percent are performed for primary and secondary malignant liver tumors (table 1) [10,12]. The role of minimally invasive surgery is also expanding in the area of living donor hepatectomy for transplantation [14]. (See "Overview of hepatic resection", section on 'Indications for hepatic resection'.)

Malignant tumors — Hepatocellular carcinoma (HCC) is the most common indication for MILR worldwide [10]; approximately half of MILRs for malignancy are performed for HCC [15], and up to 30 percent of hepatectomies for HCC are minimally invasive [16]. Patients with cirrhosis and/or ascites may particularly benefit from MILR because of smaller incisions and a faster recovery [17]. (See "Surgical resection of hepatocellular carcinoma".)

Colorectal liver metastasis (CRLM) is the most common indication for MILR in the United States [18-20]; approximately a quarter of LLRs for malignancy are performed for CRLM [21], and up to 70 percent of patients with CRLM may be candidates for MILR at high-volume centers [22]. Minimally invasive major hepatectomy or even two-stage hepatectomy for CRLM has also been reported at such centers [23,24]. (See "Potentially resectable colorectal cancer liver metastases: Integration of surgery and chemotherapy".)

MILR for hilar cholangiocarcinoma or gallbladder carcinoma is less frequently performed because it typically requires extensive portal lymphadenectomy and/or biliary/vascular reconstruction [10,12,25,26]. For such patients, MILR has mostly been applied to early-stage disease with good oncologic results [27]. MILR for intrahepatic cholangiocarcinoma is feasible and safe at high-volume centers, though open hepatectomy remains more common for larger tumors [28]. (See "Surgical resection of localized cholangiocarcinoma" and "Surgical management of gallbladder cancer".)

MILR for other (noncolorectal) metastatic tumors to the liver, such as carcinoid (neuroendocrine), breast, and renal cell cancer, has also been reported [29].

Benign conditions — In large case series from institutions in the United States, the most commonly excised benign lesions by MILR are giant hepatic cyst, followed by focal nodular hyperplasia and hemangioma. Hepatic adenoma and benign biliary lesions are less commonly resected [26].

Over the past decade, the overall volume of liver surgery for benign indications has risen substantially, with a concomitant shift from OLR to MILR [30]. However, experts caution that the availability of MILR is not a reason to expand the resection criteria for benign conditions [3,31].

Common indications for resecting benign hepatic lesions include relevant clinical symptoms, size >5 cm in patients with hepatic adenoma, lesions with potential for malignant transformation (eg, mucinous cystadenoma), and imaging findings concerning for malignancy (eg, suspicious nodules in a cirrhotic liver or malignant-appearing mass with nonspecific tissue diagnosis). Patients not meeting these criteria are best managed with observation rather than surgery [32]. (See "Diagnosis and management of cystic lesions of the liver" and "Focal nodular hyperplasia" and "Hepatic hemangioma" and "Hepatocellular adenoma".)

PATIENT SELECTION — Generally, patients are selected for MILR following the same preoperative evaluation and preparation as for open liver resection (OLR) (see "Overview of hepatic resection", section on 'Preoperative evaluation and preparation'). Those with underlying liver diseases (eg, cirrhosis, chemotherapy) must have sufficient future liver remnant after resection as determined by preoperative imaging. Additionally, the following disease and patient factors determine whether or not a patient is a good candidate for MILR:

●Lesions most amenable for MILR are solitary masses of ≤5 cm located in one of the peripheral liver segments (II to VI) (figure 1) [3]. Minimally invasive resection of such lesions typically entails a minor hepatectomy, which is widely performed. (See 'Major versus minor hepatectomy' below.)

●Larger (>5 cm), posterosuperior segment (VII and VIII), multiple, or bilobar lesions are anatomically more difficult to resect with MILR techniques. However, laparoscopic parenchymal-sparing resection [33] or robotic liver resection (RLR) [34] may be feasible in some of these situations. Approaches using transthoracic port(s) are also reported for this scenario [35].

●Hilar lesions and centrally located tumors in close proximity to major hepatic vessels or the inferior vena cava remain relative contraindications for MILR [3,36], although some centers have performed MILR of such lesions with outcomes comparable to those of OLR [25,37].

●Patients with intolerance of pneumoperitoneum due to cardiopulmonary disease should not undergo MILR [38].

●Patients with upper abdominal adhesions that cannot be lysed using a minimally invasive approach should not undergo MILR [39].

●In the authors' experience, advanced liver cirrhosis, including portal hypertension, is not a contraindication to MILR, particularly for minor hepatectomy of small peripheral tumors. However, underlying cirrhosis is associated with worse outcomes after MILR [40].

●The rate of conversion from MILR to OLR in the literature ranged from 0 to 20 percent [15] and is similar between a laparoscopic and robotic approach [41]. In one report, risk factors for conversion included age >75 years, diabetes, body mass index (BMI) >28 kg/m², tumor >10 cm, and biliary reconstruction [42]. Patients with one of these risk factors should be warned about the possibility of a conversion.

MAJOR VERSUS MINOR HEPATECTOMY — A minor hepatectomy removes two or fewer Couinaud segments. Minor resections comprise the vast majority of MILR procedures [43]. In 2014, a second consensus conference concluded that laparoscopic liver resection (LLR) had become standard practice for minor hepatectomy [4]. Use of robotic liver resection (RLR) for minor hepatectomy is also safe and feasible [34]. Nevertheless, many experts recognize that various two-segment resections are not equal, with posterior/superior segments being far more difficult to resect than anterior/inferior segments [3]. Consequently, most MILR minor hepatectomies reported in the literature are left lateral sectionectomy or resection of mainly the anterior and inferior segments (eg, segment II, III, IVB, V, and VI (figure 1)).

A major hepatectomy removes three or more Couinaud segments. Minimally invasive major hepatectomy is still considered (by the second consensus conference) to be an "innovative procedure" with incompletely defined risks [4]. Although MILR for major hepatectomy is less common than for minor hepatectomy, a study using National Surgical Quality Improvement Project (NSQIP) data shows that outcomes of MILR for major hepatectomy may even be superior to those of conventional open surgery at some institutions [24].

LEARNING CURVE — MILR is a difficult procedure that requires expertise in both liver surgery and advanced minimally invasive techniques. A systematic review and meta-analysis of 40 studies reported that laparoscopic liver resection has a learning curve of 50 cases (range 25-58) and robotic liver resection has a learning curve of 25 cases (range 16-50) [44].

Studies evaluating the skill acquisition process for MILR suggest a learning curve of 45 to 60 cases for major hepatectomy and 20 to 25 cases for minor hepatectomy [45-50]. For resection of the posterosuperior segments, which is particularly challenging, the learning curve is estimated to be 40 procedures for minor hepatectomy and 65 procedures for anatomical resection [51]. Operating room time, blood loss, and length of stay tend to decrease as case numbers increase [52].

The learning curve for MILR is often not linear; an initial steep rise is followed by a plateau, only to be followed by a second steep rise brought on by attempting more complex cases [45-50]. A nonlinear learning curve calls for continued vigilance while performing MILR and a graduated approach to taking on more challenging and complex resections (eg, right hepatectomy) as the surgeon's experience grows.

For complex MILRs such as right hepatectomy, standardizing techniques and dividing the procedure into smaller components (steps) have been proposed to make the operation more reproducible and teachable. A standardized, stepwise approach also permits identification of variances in performance and suggesting areas for improvement [53]. There is also evidence to suggest that the surgical learning curve for MILR can be dramatically shortened when surgeons are trained by other experienced surgeons rather than being "self-taught" [54].

SURGICAL TECHNIQUES — MILR can be performed with purely laparoscopic or robotic, hand-assisted, and hybrid techniques. The choice depends primarily on the training and experience of the surgeon but can also be influenced by patient and tumor factors. As examples, large or posterior tumors are more amenable to a hand-assisted resection than a purely minimally invasive approach, and both the hand-assisted and hybrid techniques may be beneficial for donor hepatectomy or training surgeons in major resectional procedures [4].

●Pure MILR is the most common method used and is accomplished using only laparoscopic or robotic instruments. Besides trocar placement, only a small incision is required for specimen extraction. This approach is least invasive but more technically challenging. In case of unexpected bleeding, there are fewer options for rapid control than the other techniques.

●Hand-assisted MILR uses a 5 to 9 cm abdominal incision to admit the surgeon's or assistant's hand into the operative field via a gas-tight port (hand port). Having a hand in the operative field permits palpation of the liver with tactile feedback, facilitates manipulation of the liver during dissection, and enables manual compression in case of unexpected bleeding. Extraction of the specimen is also done through the hand port site. Compared with a purely laparoscopic or robotic approach, hand-assisted MILR has disadvantages of a greater risk of incisional hernia at the hand port site and partially obstructed laparoscopic visualization by the hand. Hand ports are not usually used during robotic liver resection (RLR).

●The hybrid technique mobilizes the liver with minimally invasive instruments and transects the liver parenchyma through a small laparotomy [3,47,50]. The hybrid technique was advocated early in the development of MILR primarily due to concerns of gas embolus associated with exposing the raw cut surface of the liver to carbon dioxide under pressure of the pneumoperitoneum. Subsequent studies have ameliorated this concern [3]. Thus, the hybrid technique is used less commonly than the other two techniques.

Anesthesia — Patients typically require secure intravenous access to allow large-volume fluid and blood product resuscitation, intra-arterial blood pressure monitoring, and low central venous pressure until the liver parenchyma is divided. In a trial of 146 patients undergoing laparoscopic hepatectomy, reducing central venous pressure by anesthetic intervention to a goal of <5 cm H₂O reduced total intraoperative blood loss (188±162 mL versus 346±336 mL) without affecting perioperative adverse events [55]. (See "Anesthesia for the patient with liver disease", section on 'Anesthesia for hepatic resection'.)

Patient positioning — The supine position is used for left or right hepatectomy and minor hepatectomies such as left lateral segmentectomy or nonanatomic resection of lesions in segments IV or V (figure 1). Patients with right posterior sector tumors (segments VI and VII) are placed in a left semilateral decubitus position with the right side up at approximately a 45° angle. Patient position may need to be modified for RLR based on surgeon experience and specific robotic platform.

Patients are secured in that position with a bean bag, the right arm is supported by an armrest, and pillows are placed between the legs that have a slight bend at the knees (figure 2). Following this, the patient's knees and upper chest are strapped or taped to the bed in anticipation of possible radical changes in the bed position, including steep Trendelenburg (head down) or reverse Trendelenburg (head up) positions. All bony prominences must be appropriately padded.

An orogastric tube and Foley catheter are routinely placed. A nasogastric tube is appropriate if bile duct resection with bile duct to bowel anastomosis is planned.

The abdomen is then prepped and draped from midchest to symphysis pubis and bilaterally to the midaxillary lines. We outline a bilateral subcostal incision with a marker in all patients in preparation for possible conversion to open surgery.

Peritoneal access — We prefer to establish pneumoperitoneum with a Veress needle placed 2 cm below the left costal margin at the midclavicular line. After confirmation of intra-abdominal position of the needle, the abdomen is insufflated with carbon dioxide to a pressure of 15 mmHg. A history of prior abdominal operations, hepatosplenomegaly, or left upper quadrant adhesions may require an alternative technique, such as the open Hasson technique or the optical trocar peritoneal entry technique. (See "Abdominal access techniques used in laparoscopic surgery", section on 'Initial port placement'.)

Trocars are then placed under direct vision based on the planned procedure. Although the general locations of trocars are standardized for each procedure (figure 3), the surgeon still needs to fine-tune trocar placement for each patient by taking into account the patient's body habitus, liver size, and tumor location/size. Robotic trocar placement is partially dependent on the platform utilized but generally follows a curvilinear or straight line targeted toward the region of interest.

Because MILR approaches the abdomen anteriorly, posterior (segment VII) or superior tumors (segment VIII) are particularly challenging to resect (figure 1). These tumors may lend themselves to additional modifications in technique by combining abdominal and transdiaphragmatic trocars for optimal access [56].

Laparoscopic and ultrasound exploration — After gaining peritoneal access, a 30° 5 mm laparoscope is inserted and the abdominal cavity is assessed for metastatic disease or other contraindications to resection. The liver surface is inspected for tumors and/or evidence of liver cirrhosis or fibrosis. Large or peripheral tumors can be readily identified laparoscopically.

Laparoscopic ultrasound is then performed to identify tumors deep in the parenchyma, characterize the intrahepatic vascular anatomy, and search for unexpected pathology in the future liver remnant. For RLR, the robot may be docked immediately after trocar placement or after initial laparoscopic assessment and ultrasound. Some robotic platforms allow use of robotic-assisted ultrasound including simultaneous view of the camera and ultrasound at the working console.

Mobilization of liver — Using electrocautery or a bipolar vessel-sealing device, the falciform and round ligaments are divided (figure 4).

In circumstances where the right lobe of the liver contains the target lesion, the right triangular ligament and right coronary ligament are divided to the level of the hepatocaval confluence (figure 4). Division of avascular attachments to the right liver should avoid injury to the right diaphragm, right adrenal gland, and inferior vena cava. During right hepatectomy, division of short venous branches to the vena cava is typically required and can be accomplished more expeditiously with a bipolar vessel-sealing device or hemoclips than with ties or suture ligatures. (See "Instruments and devices used in laparoscopic surgery", section on 'Devices for hemostasis'.)

For lesions located in the left lobe of the liver, the left triangular ligaments are divided to the level of the left hepatic vein (figure 4). This dissection should avoid injury to the left diaphragm and can occasionally be difficult because of diaphragmatic motion caused by the beating heart.

Cholecystectomy — Removal of the gallbladder is required for major hepatectomy but is infrequently necessary for nonanatomic resections, with the exception of tumors in segment IVB or V (figure 1). In major hepatectomy, the gallbladder is sometimes used as a handle for retraction and not removed until a later time of the operation. When performed, laparoscopic cholecystectomy should follow the standard technique established to ensure identification of the critical view of safety before division of the cystic artery and duct and removal of the gallbladder. (See "Laparoscopic cholecystectomy", section on 'Standard procedure'.)

Vascular control — In major hepatectomy (eg, right or left hepatectomy), control of vascular inflow and outflow minimizes blood loss during parenchymal transection. Inflow control during MILR has been associated with decreased blood loss and operative time [57] and has been advocated by experts along with other methods of bleeding control such as maintaining pneumoperitoneum at a pressure of at least 10 to 14 mmHg and low central venous pressure of <5 mmHg [58]. Minor hepatectomy does not typically require formal vascular control before parenchymal transection.

Inflow control — Vascular control can be accomplished in the extrahepatic space or within the liver parenchyma. Extrahepatic inflow control is accomplished by dissection and division of the right or left hepatic artery and portal vein in the porta hepatis. Dissection in the porta hepatis begins by dividing anterior connective tissue and small vessels with a vessel-sealing device. It is safe to dissect the hilar plate close to the liver capsule and "drop" the critical structures (ie, exposing more length of vessels beyond the respective bifurcations). In order to perform this maneuver, dissection occurs at the posterior border of the quadrate lobe, immediately superior to the hilar structures.

Assuming normal anatomy, the common hepatic artery is identified on the anteromedial (left) side of the portal triad (figure 5). Once the hepatic artery bifurcation is confirmed, the right or left hepatic artery is divided with a vascular stapler, hemoclips, or suture ligation. A vessel loop can be helpful with retraction of vascular structures prior to division. The bifurcation of the portal vein is easier to identify once the divided hepatic artery has retracted away, and division of the right or left portal vein is also accomplished using similar techniques to the artery. A curved-tip stapler may be helpful for division of the portal vein because the portal vein bifurcation is close to the liver capsule and the space to insert a stapler is often limited. At this juncture, the right or left bile duct may be divided using suture, clips, or a surgical stapler, if feasible. The biliary anatomy may be more easily visualized using indocyanine green fluorescence. (See "Instruments and devices used in laparoscopic surgery", section on 'In vivo fluorescence imaging'.)

A Glissonian approach permits division of the hepatic inflow from within the liver parenchyma. We most commonly use a Glissonian approach for right hepatectomy. The Glissonian approach to inflow control begins with making small incisions in the liver capsule in the gallbladder fossa and the caudate process. Through these small incisions, the right hepatic inflow is bluntly dissected and encircled with a silk suture. The suture then guides passage of a vascular stapler. It usually takes three or four serial "firings" of the stapler to completely divide the vascular pedicle with associated liver parenchyma. Other surgeons have described Glissonian approaches to dividing second-order vascular pedicles, which would permit sectorial or segmental resections [59,60]. Depending on the clinical situation, location of the lesion, and surgeon expertise, the Glissonian approach can be performed with either the purely minimally invasive or hand-assisted technique (picture 1).

Outflow control — Extrahepatic control of the right or left hepatic vein begins with elevation of the posterior liver off the vena cava and division of the short hepatic veins.

For the right hepatic vein, dissection between the right and middle vein is facilitated by a "notch" typically visible on the anterior surface of the liver along the medial edge of the right hepatic vein. Along the undersurface of the liver, a thick, often vascularized ligament of tissue along the lateral aspect of the vena cava ("caval ligament") is located just below the origin of the right hepatic vein (figure 6). This is divided with a stapler facilitating the encircling of the right hepatic vein with dissection from anterior and posterior surfaces. The right hepatic vein is then divided with a vascular stapler.

The left and middle hepatic vein typically have a common origin, and therefore both are divided if extrahepatic vascular outflow control is needed in the setting of left hepatectomy. Dissection on the anterior surface is facilitated by the same "notch" on the lateral side of the middle hepatic vein described above. On the undersurface of the liver, connective tissue over the caudate lobe (gastrohepatic ligament/pars flaccida) is divided. A vessel loop is then passed around the origins of both the middle and left hepatic veins to retract the veins and facilitate division with a vascular stapler.

Intrahepatic division of the hepatic vein is most often done with a vascular stapler during the final portion of liver parenchymal transection. Such divisions typically proceed in an anterior/caudal to posterior/cranial direction.

Parenchymal transection — We place umbilical tape around the portal triad through the foramen of Winslow for selective use of temporary complete vascular inflow occlusion (Pringle maneuver) whenever necessary during parenchymal transection. (See 'Vascular control' above.)

Once major hepatic inflow (hepatic artery and portal vein) has been interrupted to either the right or left lobe of the liver, a line of ischemic demarcation should become evident. Intraoperative ultrasound may again be used to confirm that the target lesion lies within the devascularized hepatic parenchyma and not the future liver remnant. When in doubt, it may be necessary to extend a portion of the parenchymal transection beyond the line of ischemic demarcation and prepare for greater blood loss.

Electrocautery is typically used to score the hepatic capsule and create the initial line of transection. Liver parenchyma is then transected with a combination of vessel-sealing (energy) bipolar devices for liver tissue and small vascular and biliary structures and a vascular stapler for larger intrahepatic vascular structures [61]. A layer-by-layer approach allows for clear visualization of vascular and biliary structures, which may require use of a vascular stapler or surgical clips. Monopolar sealers use a combination of radiofrequency energy and saline. The authors use these during MILR procedures requiring lengthy parenchymal division for sealing bleeding vessels that persist after the bipolar device is used.

Hemostasis — For hand-assisted MILR, we first apply direct manual pressure to the cut surface of the liver with a warm sponge for 5 to 10 minutes. Following that, we routinely use a bipolar vessel-sealing device (eg, Aquamantys) to treat the liver surface (see "Instruments and devices used in laparoscopic surgery", section on 'Devices for hemostasis'). Other commonly used methods of achieving hemostasis include the argon beam electrocautery device and hemostatic agents such as oxidized cellulose, bovine collagen, and fibrin-based sealants (see "Fibrin sealants" and "Overview of topical hemostatic agents and tissue adhesives", section on 'Hemostatic agents'). Since pneumoperitoneum may tamponade some bleeding, we release the pneumoperitoneum for several minutes before re-insufflating and examining the cut surface for bleeding for the final time.

Once the liver parenchyma is divided and hemostasis is achieved, it is important to communicate to the anesthesia team so that the patient can be fluid-resuscitated back to euvolemia [58,62]. (See "Anesthesia for the patient with liver disease", section on 'Anesthesia for hepatic resection'.)

Specimen extraction and closing — An impermeable bag is introduced through one of the larger trocars and used for specimen removal with slight extension of the incision. A Pfannenstiel incision is also commonly used for specimen extraction. For robotic procedures, the robot is undocked prior to specimen extraction. In hand-assisted MILR, the specimen is usually removed through the hand port incision while keeping the wound protector portion of the hand port device in place. Trocar sites >5 mm are closed at the fascial level. (See "Abdominal access techniques used in laparoscopic surgery".)

Prior to closing the abdomen, we place one closed suction drain along the cut surface of the liver after major hepatectomy if there are any intraoperative concerns for bile leak. Otherwise, no drain is placed. In several retrospective studies, perihepatic drain placement did not prevent bile leak or the need for subsequent interventions and might have actually increased the complication rate [63,64].

COMMONLY PERFORMED PROCEDURES — The basic steps of minimally invasive right hepatectomy, left hepatectomy, left lateral segmentectomy, and nonanatomical resection are described below (table 2):

Minimally invasive right hepatectomy

●Position the patient supine and insert trocars (figure 3). (See 'Patient positioning' above and 'Peritoneal access' above.)

●Rotate the bed to a reverse Trendelenburg and slightly right-side up position.

●Divide the falciform ligament and perform intraoperative ultrasound.

●Divide the right triangular ligament and retract the liver anteriorly and cephalad. This step may also be performed at the end of the procedure. (See 'Mobilization of liver' above.)

●Elevate the liver off the inferior vena cava by dividing the short hepatic veins and the caval ligament. (See 'Inflow control' above.)

●Drop the hilar and cystic plates. (See 'Inflow control' above.)

●Retract the gallbladder cephalad to divide the right hepatic artery if extrahepatic control is used. (See 'Inflow control' above.)

●Divide the right portal vein with vascular stapler if extrahepatic control is used (retraction facilitated by suture or vessel loops). (See 'Inflow control' above.)

●Perform cholecystectomy. (See 'Cholecystectomy' above.)

●Divide the right hepatic duct if extrahepatic control is preferred (the authors of this topic prefer intrahepatic division of the bile duct unless the operative indication is hilar cholangiocarcinoma).

●Divide any accessory or replaced right hepatic artery if present.

●Divide the right hepatic vein with a vascular stapler if extrahepatic control is used (retraction facilitated by suture or vessel loops). (See 'Outflow control' above.)

●Divide the liver parenchyma and achieve hemostasis. (See 'Parenchymal transection' above and 'Hemostasis' above.)

Minimally invasive left hepatectomy

●Position the patient supine and insert trocars (figure 3). (See 'Patient positioning' above and 'Peritoneal access' above.)

●Rotate the bed to a reverse Trendelenburg and slight left-side up position.

●Divide the falciform and left triangular ligaments. This step may also be performed at the end of the procedure. (See 'Mobilization of liver' above.)

●Perform intraoperative ultrasound.

●Perform cholecystectomy, then retract the liver anteriorly. (See 'Cholecystectomy' above.)

●Divide the pars flaccida and dissect the base of the umbilical fissure.

●Divide any accessory or replaced left hepatic artery if present.

●Divide the left hepatic artery and left portal vein with a vascular stapler if extrahepatic control is used (retraction facilitated by suture or vessel loops). (See 'Inflow control' above.)

●Divide the left hepatic duct if extrahepatic control is used (the authors of this topic prefer intrahepatic division of the left hepatic duct unless the operative indication is hilar cholangiocarcinoma).

●Divide the left and middle hepatic vein common trunk if extrahepatic control is planned (retraction facilitated by suture or vessel loops). (See 'Outflow control' above.)

●Divide the liver parenchyma and achieve hemostasis. (See 'Parenchymal transection' above and 'Hemostasis' above.)

Minimally invasive left lateral segmentectomy

●Position the patient supine and insert trocars (figure 3). (See 'Patient positioning' above and 'Peritoneal access' above.)

●Rotate the bed to a reverse Trendelenburg and slight left-side up position.

●Divide the left triangular ligament. (See 'Mobilization of liver' above.)

●Perform intraoperative ultrasound.

●Divide the pars flaccida and any accessory or replaced left hepatic artery if present. (See 'Inflow control' above.)

●Divide the liver parenchyma (the authors of this topic perform intrahepatic division of inflow to segments II and III, followed by division of the left hepatic vein). (See 'Vascular control' above.)

●Achieve hemostasis. (See 'Hemostasis' above.)

Minimally invasive nonanatomic resection

●Position the patient supine or in left lateral decubitus if the target lesion(s) are located in the posterior sectors, and insert trocars. (See 'Patient positioning' above and 'Peritoneal access' above.)

●Rotate the bed to reverse Trendelenburg and right/left side up depending on the location of the target lesion.

●Perform intraoperative ultrasound.

●Demarcate the boundaries of resection of the target lesion using electrocautery.

●A Pringle maneuver may be utilized to aid with control of bleeding during parenchymal transection.

●Divide the parenchyma circumferentially until the depth of desired resection is attained, then transect the inferiormost parenchyma to complete resection. (See 'Parenchymal transection' above.)

●Achieve hemostasis. (See 'Hemostasis' above.)

OUTCOMES — In general, MILR is superior to open liver resection (OLR) in several aspects (eg, postoperative complications, length of stay, blood loss) and not inferior to OLR in all other aspects [4]. The outcomes of laparoscopic liver resection (LLR) and robotic liver resection (RLR) are similar [7]. However, almost all available studies on MILR are observational studies, and only one randomized trial (OSLO-COMET) has been published to date [65]. A second trial (ORANGE II) was prematurely stopped due to slow accrual before reaching a conclusion on functional recovery after OLR or LLR [66].

Mortality and morbidity — MILR has been associated with mortality rates from 0 to 3.7 percent. Causes of death include liver failure, cerebral infarction due to hypotension, postoperative hepatorenal failure, pseudomembranous colitis, massive hemorrhage, acute respiratory distress syndrome, bleeding from esophageal varices, and multiorgan failure [11,15].

Morbidity rates of MILR range from 0 to 43 percent. Surgical morbidities include bile leak, liver abscess, and transient liver failure. Medical morbidities include pleural effusion, pneumonia, urinary tract infection, and cardiac arrhythmia [11,15].

In one study, factors that increased the risks of postoperative complications after MILR included simultaneous application of radiofrequency ablation at the time of a major hepatectomy, need for intraoperative blood transfusion, and bilobar hepatic resection [67].

Comparison with open liver resection

Technical performance — MILR offers several technical advantages over OLR, including improved (magnified) visualization of small hepatic vascular branches and reduced bleeding during parenchymal transection because of the tamponade effect of pneumoperitoneum.

Potential disadvantages of MILR include the loss of tactile feedback, inability to manually palpate the liver, and inability to quickly obtain vascular control in case of unexpected bleeding. These disadvantages can be mitigated by use of a hand port or the minimally invasive Pringle maneuver [58,61,62].

Perioperative outcomes — MILR has been associated with decreased length of stay, blood loss, postoperative pain, incidence of bile leak, and wound infection rate compared with OLR [68-70].

In a 2016 meta-analysis of 87 studies comparing MILR (2900 cases) with OLR (3749 cases), blood loss, transfusion requirement, length of stay, and rate of complications were all lower in the MILR group (table 3) [10]. Operative time was comparable between MILR and OLR. It should be pointed out that all studies included in the meta-analysis were retrospective, in which selection bias may influence outcomes.

The OSLO-COMET trial reported improved complication rates and shorter hospital stay in the LLR group compared with the OLR group. Rates of blood loss, operative time, positive margin status, and readmission were similar [65]. However, the trial was limited to minor hepatectomy, and as such, results are not necessarily applicable to MILR for major hepatectomy.

An analysis of National Surgical Quality Improvement Program (NSQIP) and Nationwide Inpatient Sample (NIS) data over a 12 year period also demonstrated that the use of MILR was increasing and that MILR was associated with a shorter length of stay and similar morbidity and mortality rates compared with OLR [12,71,72].

In a propensity score-matched international study of over 13,000 patients, the incidence of postoperative bile leak was significantly lower in patients after MILR compared with patients after OLR (2.6 versus 6.0 percent; p <0.001) [73]. Patients with bile leak after MILR also experienced less severe postoperative complications, a shorter hospital stay, and a lower 90 day/in-hospital mortality (0 versus 5.4 percent; p = 0.027) compared with those with bile leak after OLR.

Specific patient groups may derive additional benefits from MILR. In cirrhotic patients with hepatocellular carcinoma, for example, several case-control series have associated MILR with less blood loss, shorter length of stay, lower overall complication rate, higher R0 resection rate, and, in one study, decreased postoperative ascites compared with open resection [17,74-76].

In older adult patients, the potential benefits of LLR, including shorter hospital stay and decreased complications, may be particularly beneficial [77]. Purely laparoscopic liver resection was safely performed in older adult patients with hepatocellular cancer and appeared to confer similar advantages, such as decreased blood loss and length of stay [78]. In a study of patients >65 years of age with malignant hepatic lesions, MILR was as well tolerated as radiofrequency ablation [79].

Compared with OLR, MILR has been shown to be cost-neutral or even cost-saving [80-82]. The use of Enhanced Recovery after Surgery (ERAS) protocols is more common with minimally invasive surgery, including MILR. ERAS principles include preoperative education and prehabilitation, oral carbohydrate supplementation prior to operation, goal-directed fluid therapy, early mobilization and oral intake, postoperative nausea and vomiting prophylaxis, and multimodal pain control. Use of ERAS with MILR is associated with shorter hospital stay, reduced cost, fewer complications, and greater patient satisfaction [83,84].

Oncologic outcomes — When performed for malignant indications, there is no evidence to suggest that MILR is inferior to OLR in oncologic outcomes. Multiple large case-control series have demonstrated comparable disease-free survival, overall survival, and margin-free status between MILR and OLR [19,20,36,72,85-87].

The surgical margins were free of cancer in 87 to 100 percent of patients in the published series of LLR [15]. The margin-free rate of MILR was similar or superior to that of OLR [36,88]. Achieving a negative resection margin is more important to patients undergoing liver resection for malignant tumors than the technique employed or segments resected.

Patients undergoing MILR for hepatocellular carcinoma (HCC) had recurrence-free survivals at one, three, and five years that were comparable to those of OLR, according to propensity score matched studies controlling for factors such as hepatitis status; degree of liver damage; and number, size, and location of lesions [72,85,89]. A study demonstrated comparable 10 year overall survival (69 percent LLR versus 57 percent OLR) in cirrhotic patients who underwent surgery for hepatocellular carcinoma [86].

Patients undergoing LLR for colorectal liver metastases also have comparable short- and long-term overall and disease-free survival rates to those of OLR, according to propensity score matched series [20,22,87,90]. The OSLO-COMET trial reported comparable five-year overall survival (54 percent LLR; 55 percent OLR) and recurrence-free survival (30 percent LLR; 36 percent OLR) between the two techniques [91].

At the cellular level, one study showed that patients with colorectal liver metastasis expressed lower levels of multiple inflammatory markers and lower levels of oncogenic proteins after MILR than after OLR [92]. Reduced inflammatory response has been associated with greater immune competence postoperatively and may confer a survival advantage for patients with colorectal liver metastasis [93].

Cost — Increasing use of MILR may be associated with additional health care spending. Studies examining this question should include analysis of operative and postoperative cost since benefits like shorter length of stay may offset higher equipment expense. One systematic literature review found that the operative costs of LLR were higher than those of OLR for major hepatectomy and found lower hospitalization costs for LLR in both major and minor hepatectomy. RLR was possibly more expensive than LLR [94]. This issue requires further study as MILR expands and available technology evolves.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Liver resection and ablation" and "Society guideline links: Laparoscopic and robotic surgery".)

SUMMARY AND RECOMMENDATIONS

●Indications – Minimally invasive liver resection (MILR) is a safe option that is increasingly used to treat patients with benign and malignant liver tumors. (See 'Indications' above.)

●Patient selection – MILR is ideally suited for resecting small (<5 cm) peripheral tumors (segments II to VI) (figure 1). However, more complex operations involving posterosuperior segments and major hepatectomy (left or right hepatectomy) are feasible and safe in experienced hands. (See 'Patient selection' above and 'Major versus minor hepatectomy' above.)

●Learning curves – The learning curve is approximately 45 to 60 cases for laparoscopic major hepatectomy and 20 to 25 cases for laparoscopic minor hepatectomy. (See 'Learning curve' above.)

●Surgical techniques – MILR can be performed with purely laparoscopic or robotic, hand-assisted, and hybrid techniques. Hand-assisted and hybrid techniques are suitable for large or posterior tumors, donor hepatectomy, and training purposes. (See 'Surgical techniques' above.)

●Outcomes – MILR has been compared with open liver resection in operative and oncologic outcomes:

•Compared with open liver resection, MILR is associated with reduced length of stay, blood loss, transfusion requirement, postoperative pain, and wound infection rate. (See 'Comparison with open liver resection' above.)

•Oncologic outcomes of MILR, including short- and long-term survival and margin-free rate, are comparable to those of open laparoscopic resection. (See 'Comparison with open liver resection' above.)