Segment-oriented anatomic liver resections: Indications and outcomes

Overview

Segment-oriented hepatectomy is defined as the removal of one or more of the eight anatomic segments of the liver. The techniques of segment-oriented anatomic liver resection are based on the pioneering work of Claude Couinaud, who identified intrahepatic anatomy by creating vascular and biliary casts of the liver (see Introduction and Chapter 2 ) Couinaud established that the liver is subdivided into eight autonomous segments, each having its own biliary drainage and vascular inflow and outflow. Anatomic resection was originally described by Lortat-Jacob and Robert in 1952 and subsequently by Pack and Miller (1961) and McBride and Wallace (1972). Because each liver segment has individual function, each segment can be removed without affecting the others. ^, Segment-oriented liver resection is now a refined technique that allows safe removal of liver disease while preserving normal liver parenchyma (see Chapter 118B ).

Driven largely by the increased surgical management of colorectal cancer liver metastasis (CRCLM), there has been a significant increase in the use of nonanatomic, parenchymal-sparing liver resection in the past 2 decades. ^, However, segmental liver resection remains indicated in a variety of situations. The ability to resect one or more segments, rather than the entire lobe, allows parenchymal preservation in patients with diseased parenchyma or in repeat resection patients with limited residual volume. In addition, anatomic resection facilitates the removal of tumor-bearing biliary and portal tributaries, which may help eradicate any tumor that has spread along these structures and improve oncologic outcomes for select tumors. Finally, in specific situations, segmental resection may be technically more feasible and safer than nonanatomic parenchymal-sparing liver resection. This chapter will provide an overview of indications, important technical and anatomic considerations when performing segmental resections, and technical aspects of various segmental liver resections.

Segmental resections for hepatocellular carcinoma (see Chapters 89 and 101B )

Surgery remains the treatment of choice for hepatocellular carcinoma (HCC). However, high recurrence rates after curative-intent R0 hepatectomy have prompted ongoing research to determine the optimal extent of resection. HCC appears to spread via the portal pedicles, and therefore removal of tumor-bearing portal tributaries by a segmental approach may better eradicate intrahepatic metastases in the vicinity of the primary tumor.

It is hypothesized that oncologic outcomes may be improved with anatomic resections over nonanatomic resections for patients with HCC. ^, Multiple independent series have reported better overall and disease-free survival with an anatomic approach. However, there are conflicting data, with other studies identifying no outcome differences between anatomic and nonanatomic resection. ^, Although the literature lacks randomized data, a meta-analysis of 16 observational studies including 2917 patients with HCC (1577 anatomic and 1340 nonanatomic resections) found anatomic resection to be superior to nonanatomic resection in terms of overall and disease-free survival. An updated meta-analysis of 25 observational studies (10216 patients) also demonstrated a 5-year survival advantage for patients undergoing anatomic resection compared with nonanatomic resection, with no difference in morbidity between the two groups. Nevertheless, achieving a balance between parenchymal-sparing and radical oncologic clearance remains of utmost importance in HCC patients with cirrhosis. Segmental liver resection is a bridge between major hepatectomy and nonanatomic resection, and can preserve liver volume and functional reserve in order to minimize postoperative liver insufficiency. ^,

In situations in which anatomy is unsuitable or when the residual liver would be at high risk of complications after an anatomic resection, nonanatomic resection must be used. In recent years there has been an increasing effort to determine the ideal resection margin in HCC. Although some institutional series have found that narrow resection margin (<1 cm) was not associated with worse oncologic outcomes, a meta-analysis and multi-institutional series have demonstrated improved survival with wide margins. A prospective randomized trial examining wide (2 cm) versus narrow (1 cm) resection margins for solitary HCC demonstrated improved overall survival in the wide margin cohort, including in the subset of patients with tumors less than 2 cm. In addition, an international multi-institutional analysis of patients with T1 HCC undergoing negative-margin hepatectomy demonstrated that wide resection margins (>1 cm) were associated with decreased local recurrence. However, in this series, wide resection margin was not associated with lower recurrence rates in the subset of patients undergoing anatomic resection (80% of the overall cohort), suggesting that a narrower margin may be sufficient when performing an anatomic resection. Recently, an institutional series of 2508 consecutive patients who underwent liver resection for solitary hepatitis B virus–related HCC demonstrated improved oncologic outcomes with wide margins (>1 cm); however, a survival advantage was seen only in patients with microvascular invasion.

Segmental resections for colorectal liver metastases (see Chapters 90 and 101B )

Despite early reports of improved outcomes with anatomic resection for CRCLM, ^, subsequent studies failed to confirm this observation. Current data support parenchyma-sparing nonanatomic resection in the vast majority of patients. Resections are designed to encompass the tumor as well as an adequate margin of nontumor liver. Recent series have subsequently confirmed the safety, and even oncologic benefit, of parenchymal-sparing nonanatomic resection for most CRCLM when technically feasible. A parenchymal-sparing approach is also supported in patients with multifocal or bilobar lesions. Thus anatomic resections are largely reserved for patients with multiple or large tumors in contiguous segments. Even when anatomic resection is needed, parenchymal-sparing principles can be applied by using segmental/bisegmental resection instead of hemihepatectomy. This is particularly beneficial in patients who are heavily pretreated with chemotherapy, given the association among chemotherapy, steatohepatitis, and hepatic sinusoidal congestion. ^,

The molecular profile of colorectal cancer may influence resection planning. Mutations in KRAS are the most commonly studied in CRCLMs (occur in 15%–50% of patients) and are associated with aggressive clinical behavior and early recurrence. Margonis et al. found that that nonanatomic resection was associated with worse disease-free survival in patients with KRAS -mutated tumors compared with patients undergoing anatomic resection (10.5 vs. 33.8 months). Another study by Brudvik et al. reported that KRAS mutations were independently associated with higher rates of positive margins compared with patients with wild-type tumors. Similarly, BRAF mutations in tumors are seen in approximately 10% of patients with colorectal cancer and are associated with early recurrence after resection. ^, However, there are limited data on how BRAF mutations affect outcomes after resection, likely because of its rarity and association with poor prognosis.

Other indications for segmental resections

Beyond a biologic rationale, anatomic considerations are also important indications for segmental resection. For example, segmental resection is commonly used when there is tumor invasion of a major portal pedicle or hepatic vein. Segmental resection also may be indicated for biliary tumors or in the setting of stone disease or biliary strictures. In select situations, segmental resection may also be more technically feasible and safer than a nonanatomic approach. Deeply seated lesions, such as in segments IVa or VIII may benefit from the formal vascular control afforded by an anatomic approach to better manage bleeding, particularly when a large parenchymal transection surface is involved. An anatomic resection may also minimize the risk of bile leak resulting from an orphan bile duct, which occurs when a biliary radical is separated from its draining biliary system in a nonanatomic resection. However, data to support these potential benefits are limited because most series report an overall equivalent complication rate between colorectal cancer patients undergoing anatomic and nonanatomic resections. ^, An exception to this, however, is hepatic insufficiency, which is lower in patients undergoing parenchymal-sparing nonanatomic approaches compared with major hepatectomies. Living donor liver transplantation is also an indication to perform a segmental liver resection, which often involves a left lateral sectionectomy (see Chapter 121 ).

Liver anatomy (see introduction and Chapter 2 )

The current understanding of the segmental anatomy of the liver has come from the original 1952 descriptions of Couinaud. ^, ^, These segments have evolved to become the standard for hepatic nomenclature. The Brisbane terminology eliminated confusing terminology of “lobes” and “sectors” used in the American, European, and Japanese descriptions of liver anatomy. The terms hemiliver (first-order division), section (second-order division), and segment (third-order division) are not interchangeable, providing universal terminology for better communication among liver surgeons.

The first-order divisions are right liver (segments V through VIII) and left liver (segments II through IV), or hemiliver, the boundary of which lies along Cantlie’s line marked by the path of the middle hepatic vein (MHV) from the middle of the gallbladder fossa to its termination in the inferior vena cava (IVC) ( Fig. 102B.1 ). The second-order division into liver sections is based on hepatic arterial supply and biliary drainage. The sections are derived from the primary divisions of the major right and left portal triads. The right hemiliver is divided into sections known as the right anterior (segments V and VIII) and right posterior (segments VI and VII), separated by the right hepatic vein (RHV). The left hemiliver is divided into left lateral (segments II and III) and left medial (segments IVa and IVb) sections by the umbilical fissure and falciform ligament. Together, segments II and III are often erroneously referred to as the “left lateral segment.” The third-order division, segments I through VIII, is defined by hepatic arterial supply and biliary drainage. The axial plane is at the level of the intersection of the hepatic veins and the axial plane of the bifurcation of the portal vein ( Table 102B.1 and Fig. 102B.2 ).

FIGURE 102B.1, Diagram depicting the relationship of the eight liver segments with the major hepatic veins and portal veins of the idealized liver (see Chapter 2 ).

TABLE 102B.1

Anatomic Boundaries of Each Liver Segment

SEGMENT	VERTICAL BOUNDARY	HORIZONTAL BOUNDARY	OTHER
I	Middle of IVC		Posterior to PV
II	Left of left PV (falciform)	Cephalad to left HV
III	Left of left PV (falciform)	Caudate to left HV
IVa	Right of left PV (falciform)	Cephalad to bifurcation of PV
	Left of middle HV
IVb	Right of left PV (falciform)	Caudate to bifurcation of PV
	Left of middle HV
V	Right of middle HV	Caudate to bifurcation of PV
	Anterior to right HV
VI	Posterior to right HV	Caudate to bifurcation of PV
VII	Posterior to right HV	Cephalad to bifurcation of PV
VIII	Right of middle HV Anterior to right HV	Cephalad to bifurcation of PV

HV, Hepatic vein; IVC, inferior vena cava; PV, portal vein.

FIGURE 102B.2, A, Axial computed tomography (CT) image through the upper liver, demonstrating the anatomic boundaries of segments II, IVa, VIII, and VII. B, Axial CT image through the lower liver, demonstrating the anatomic boundaries of segments I, III, IVb, V, and VI. LHV, Left hepatic vein; MHV, middle hepatic vein; RHV, right hepatic vein; RPV, right portal vein (see Chapter 2 ).

Biliary and vascular variations are common and should be anticipated in segmental resections (see Chapter 2 ). Mapping of vital vascular and biliary structures before resection facilitates high-quality surgery. Biliary and arterial anomalies are most common, with up to 50% of patients having nonstandard biliary anatomy and approximately 30% of patients having a major arterial variant. Major anatomic variants (e.g., a right posterior sectoral biliary duct draining into the left hepatic duct) and common hepatic arterial abnormalities should be identified on preoperative imaging and considered before performing any resection. However, there are also less common minor variants that must be considered when performing resections of isolated segments (discussed further later). A more comprehensive list of anatomic variants that may have an impact on the safety and feasibility of segmental resections can be found in Chapter 2 .

Preoperative planning

Assessment of the suitability of segmental resection requires precise mapping of the vascular and biliary anatomy and associated variants. This is typically achieved using preoperative computed tomography (CT) and/or magnetic resonance imaging (MRI) (see Chapter 14, Chapter 15, Chapter 16 ). With the appropriate protocols for arterial and venous enhancement, third- and fourth-level vascular structures can be accurately defined, and most major anatomic variants can be identified preoperatively and planned for accordingly. Angiography and ultrasound are occasionally used when additional details of hepatic anatomy are required for surgical planning. In addition to high-quality preoperative imaging, many surgeons use intraoperative ultrasonography (discussed further later).

In recent years, numerous computer-assisted surgical planning software programs have become available. It has been proposed that these technologies can improve patient selection, operative planning, identification of variant anatomy, and better delineate resection margins. These programs typically involve three-dimensional reconstructions of the liver that can be manipulated preoperatively and even intraoperatively. Systems include MeVIS imaging system (MeVisLab, Bremen, Germany), Vital’s Vitrea Enterprise Imaging (Canon Group Company, Minnetonka, Minnesota), Myrian XP-Liver (Intrasense, Paris), and Synapse 3d (Fujifilm, Tokyo). Three-dimensional printed models of the liver have also been made to aid in preoperative planning, but to date they are primarily used for surgical education and training. Finally, augmented reality has been proposed to improve intraoperative navigation. Although these technologies continue to evolve, data remain limited on whether they improve outcomes over current best practice.

General operative principles

Preoperative assessment, preparation, and mobilization for liver resections are described in Chapters 4 , 26 , and 118 ). Volumetric analysis should be performed in patients with potentially marginal residual liver volume and function and is discussed in Chapters 4 , 102C , and 102D .

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