978-981-13-0668-6_1

2. Faria, L. L., Darce, G. F., Bordini, A. L., Herman, P., Jeismann, V. B., de Oliveira, I. S., Ortega, C. D., & Rocha, M. S. (2022). Liver Surgery: Important Considerations for Pre- and Postoperative Imaging. Radiographics : a review publication of the Radiological Society of North America, Inc, 42(3), 722–740. https://doi.org/10.1148/rg.210124

Executive Summary

This document synthesizes the critical principles of the liver's clinical and surgical anatomy. The core takeaway is the distinction between outdated morphological descriptions and modern functional anatomy, which is essential for safe and effective hepatic resection. The Couinaud system of liver segmentation, based on the intrahepatic distribution of the portal and hepatic veins, has become the clinical standard, superseding classifications based on unreliable external landmarks like the falciform ligament.

To address inconsistencies in terminology between different systems (e.g., Couinaud vs. Healey), the Brisbane 2000 Terminology was established to create a standardized nomenclature for liver anatomy and resections. A key concept for surgeons is the Glissonean sheath, a fibrous capsule that encases the portal triad (hepatic artery, portal vein, and bile duct). Dissection along this sheath is technically simpler and safer because it contains all anatomical variations of these structures.

Finally, the liver's vascular and biliary systems are characterized by a high degree of anatomical variation. Surgeons must be aware of common variants, such as replaced or accessory hepatic arteries (present in ~40% of cases), portal vein trifurcation (10.9–15%), and the frequent existence of a common trunk for the middle and left hepatic veins (60–95%). Misidentification of these variations, particularly the common venous trunk, can lead to catastrophic surgical complications.

I. Liver Anatomy: Morphological vs. Functional Perspectives

The understanding of liver anatomy has evolved from a reliance on external landmarks to a functionally-based system crucial for modern surgery.

Morphological Anatomy: This traditional description is based on external features. The liver is divided into a large right hemiliver and a smaller left hemiliver by the falciform ligament on the anterior surface and the round ligament/umbilical fissure on the inferior surface. This descriptive model, however, has "no strict relationship to functional anatomy."
Functional Anatomy: The modern, surgically relevant view of the liver is based on its internal vascular and biliary architecture. It is now widely accepted that the liver "does not have reliable external landmarks as guides for anatomical hepatic resection." Functional anatomy provides the true map for performing parenchymal-sparing resections.

II. Functional Segmentation Systems

To perform precise hepatic resections, surgeons rely on systems that divide the liver into independent functional units. Several systems have been proposed, leading to some terminological confusion that has since been addressed.

Couinaud's Classification

The Couinaud system is the most widely used classification in clinical practice as it is best adapted for surgery.

Basis: It is based on the identification of the three hepatic veins (right, middle, left) and the plane of the portal vein bifurcation.
Divisions:

The three hepatic veins divide the liver into four sectors (suprahepatic segmentation).
The middle hepatic vein runs in the main portal scissura (mid-plane), which separates the functional right and left hemilivers. This plane runs from the gallbladder fossa to the left of the inferior vena cava (IVC).
The right hepatic vein (in the right portal scissura) divides the right hemiliver into a right anterior sector and a right posterior sector.
The left hepatic vein (in the left portal scissura) divides the left hemiliver.

Segments: The sectors are further subdivided into a total of eight functional segments (Segment 1, the caudate lobe, is separate). Each segment has its own portal pedicle (branch of hepatic artery, portal vein, and bile duct).

Comparison with Healey's System

The terminology proposed by American surgeons, based on Healey's arteriobiliary segmentation, differs from Couinaud's, particularly regarding the left hemiliver.

Right Hemiliver: Healey's "sections" are identical to Couinaud's "sectors" (anterior and posterior).
Left Hemiliver: Healey's "sections" are not the same as Couinaud's "sectors."

Healey: Defines a left medial section (Segment 4 only) and a left lateral section (Segments 2 and 3).
Couinaud: Defines a left medial sector (Segments 3 and 4) and a left lateral sector (Segment 2 only).

The Brisbane 2000 Terminology

To resolve the confusion between competing systems, the International Hepato-Pancreato-Biliary Association (IHPBA) created a standardized nomenclature in 2000.

Purpose: To clarify and unify the terminology of liver anatomy and hepatic resections.
Key Changes:

Sectors become Sections: Couinaud's "sectors" were officially renamed "sections."
Redefinition of Left Hemiliver: The Brisbane terminology adopts a structure for the left hemiliver based on the line of the falciform ligament and umbilical fissure. The left hemiliver is defined as having a left lateral section (Segments 2 and 3) and a left medial section (Segment 4).

Divisions: The system establishes three orders of division for the main liver:

First-order: Hemilivers (Right and Left).
Second-order: Sections.
Third-order: Segments.

Standardized Hepatic Resection Terms

The Brisbane terminology provides standard names for anatomical resections corresponding to these divisions.

III. The Glissonean Sheath and Hilar Plate System

The Glissonean sheath is a critical anatomical structure that facilitates safer hepatic surgery.

Definition: Also known as the Walaeus sheath, it is a fibrous sheath that is an extension of Glisson's capsule (the connective tissue capsule wrapping the liver). It encases the portal triad—the bile duct, hepatic artery, and portal vein—as these structures enter and branch within the liver parenchyma.
Surgical Significance: The intrahepatic and extrahepatic portions of the hepatic pedicle can be viewed as a continuous "Glissonean pedicle tree." Its primary advantage for surgery is that "all anatomical variations in the branching of the sectional and segmental pedicles are within the Glissonean sheath." This makes dissection of an individual sheath to control a specific territory "technically simple and safe."
Hilar Plate System: This is formed by the union of Glisson's capsule with the connective tissue sheaths at the liver's inferior surface. It is composed of the hilar plate, cystic plate (gallbladder bed), umbilical plate, and Arantian plate (ligamentum venosum).

IV. Hepatic Vascular Anatomy and Variations

Significant anatomical variation is common in the liver's vasculature, and knowledge of these patterns is essential to prevent surgical injury.

Hepatic Artery

Aberrant arterial anatomy is present in approximately 40% of cases.

Standard Anatomy: The common hepatic artery typically originates from the celiac trunk (>80% of cases), becoming the proper hepatic artery, which gives rise to the right and left hepatic arteries.
Common Variations:

Replaced Artery: An aberrant branch that substitutes for the normal branch.
Accessory Artery: An aberrant branch that is present in addition to the normal branch.
Left Hepatic Artery (LHA): A replaced LHA, usually from the left gastric artery, occurs in 10–20% of individuals. It passes through the gastrohepatic ligament and can be injured if not identified.
Right Hepatic Artery (RHA): A replaced RHA, often from the superior mesenteric artery, passes laterally to the common bile duct. An accessory RHA from the superior mesenteric artery is seen in over 5% of cases.

Portal Vein

Variations in the main portal vein at the hepatic hilum occur in 20–35% of individuals.

Standard Anatomy: The main portal vein (MPV) bifurcates into the right portal vein (RPV) and left portal vein (LPV). This pattern is present in 65–80% of individuals.
Common Variations:

Trifurcation (10.9–15%): The MPV divides into the right anterior portal vein (RAPV), right posterior portal vein (RPPV), and LPV at a single point.
Early RPPV Origin (0.3–7.0%): The RPPV branches directly from the MPV, which then bifurcates into the RAPV and LPV. (Note: The source text contains a typo, stating "RAPP" instead of RAPV.)
RPPV from LPV (2.9–4.3%): The MPV divides into the RAPV and LPV, with the RPPV arising directly from the LPV. (Note: The source text contains typos, stating "RPPV" instead of RAPV and vice versa in this description.)

Hepatic Veins

The drainage pattern of the three main hepatic veins (right, middle, left) has critical surgical implications.

Left and Middle Hepatic Veins (LHV, MHV):

Common Trunk: In 60–95% of the population, the LHV and MHV form a common trunk before draining into the suprahepatic IVC. This trunk is often 5 mm or less in length.
Surgical Warning: Due to the prevalence of a common trunk or a shared wall, a strict surgical rule is that "there are only two major hepatic veins draining in the suprahepatic inferior vena cava—the right hepatic vein and the common trunk of the middle and left hepatic veins." Any attempt to separate them extrahepatically is described as "rude, unwise and even lethal as any injury... can cause massive bleeding."

Right Hepatic Vein (RHV): This is the largest hepatic vein. Variations include having a short main trunk or being small in the presence of a large right inferior hepatic vein (RIHV) or an accessory right hepatic vein.

V. Biliary Anatomy and Variations

The biliary drainage system generally follows the portal venous supply but has its own set of common and clinically significant variations.

Standard Anatomy: Right anterior and posterior sectional ducts join to form a short (~1 cm) right hepatic duct. Segmental branches (2, 3, 4) form a longer (~2–3 cm) left hepatic duct. These join to form the common hepatic duct.
Common Variations:

Triple Confluence (10–15%): The right anterior, right posterior, and left hepatic ducts join at a single point.
Aberrant Insertion (~20%): A right sectional duct drains directly into the common bile duct.
Ectopic Drainage: A right sectional branch drains into the left hepatic duct.
Hjortsjo Crook: In a majority of individuals, the right posterior sectional bile duct hooks around the origin of the right anterior sectional portal vein. This creates a risk of injury to the posterior duct during a right anterior sectionectomy if the dissection is too close to the pedicle's origin. Transection should therefore be performed as distally as possible.

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