CHAPTER 1 SURGICAL AND RADIOLOGIC ANATOMY^*

LIVER

GROSS ANATOMY

The liver lies under cover of the lower ribs, applied to the undersurface of the diaphragm, and is astride the inferior vena cava posteriorly. Most of the bulk of the liver lies to the right, where the lower border coincides with the right costal margin, but it extends as a wedge to the left of the midline between the anterior surface of the stomach and the left dome of the diaphragm. The liver is invested with peritoneum except on the posterior surface, where the peritoneum reflects onto the diaphragm, forming the right and left triangular ligaments. The posterior surface of the liver is triangular in outline, with its base to the right, and here the liver lying between the upper and lower leaves of the triangular ligaments is bare and devoid of peritoneum. Anteriorly, the convex surface of the liver lies against the concavity of the diaphragm and is attached to it by the falciform ligament, left triangular ligament, and upper layer of the right triangular ligament (Fig. 1-1).

Figure 1-1 A, Volume-rendered three-dimensional image of the external contour of the liver created from contrast-enhanced, axial CT data. Note the fissure for the falciform ligament seen en face (arrow). B, Volume-rendered three-dimensional image of the same patient rotated upward reveals the undersurface of the liver. Note the surgical clips in the gallbladder fossa and the bare area of the liver (short arrow).

Behind the liver, the inferior vena cava (IVC) is embraced in a groove on its posterior surface (Figs. 1-2 and 1-3). The right adrenal vein is a short vessel that enters the IVC behind the bare area (see Fig. 1-2). Usually there are no vena caval tributaries posteriorly.

Figure 1-2 A, The liver has two main lobes, a large right and a smaller left, and conventional description places their line of fusion on the upper surface of the liver along the attachment of the falciform ligament at the inferior extent of which the ligamentum teres enters the umbilical fissure. B, On the inferior surface of the right lobe is the transverse hilar fissure, which constitutes the posterior limit of this lobe. The portion of the right lobe located anterior to the fissure is called the quadrate lobe. Posterior to the hilar transverse fissure is the caudate lobe. C, The inferior vena cava (IVC) lies in a deep groove within the bare area; the hepatic veins open directly into it. The adrenal vein drains into the right of the IVC. To the left of the IVC, the caudate lobe slopes upward from the inferior to the posterior surface of the liver and is demarcated on the left by a fissure within which lies the ligamentum venosum. As the vena cava traverses upward in the groove on the posterior surface of the liver, it is shielded on the right side by a layer of fibrous tissue passing from the posterior edge of the liver backward toward the lumbar vertebrae and fanning out posteriorly, especially in the upper part. Behind the IVC, a prolongation of this fibrous layer joins a less marked fibrous extension from the lateral edge of the caudate lobe. Occasionally, the liver tissue embraces the vena cava completely so that it runs within a tunnel of parenchyma. LHV, left hepatic vein; MHV, middle hepatic vein; RHV, right hepatic vein.

Figure 1-3 Contrast-enhanced CT scan of the liver shows the intimate relationship of the caudate lobe (arrow), inferior vena cava (IVC), portal vein (p), and aorta (a).

The hepatic veins (Figs. 1-4 and 1-5) drain directly from the upper part of the posterior surface of the liver at an oblique angle directly into the vena cava. The right hepatic vein, which is larger than the left and middle hepatic veins, has a short extrahepatic course of approximately 1 cm. The left and middle hepatic veins may drain separately into the IVC, but usually they are joined after a short extrahepatic course to form a common venous channel approximately 2 cm long that traverses to the left of the anterior surface of the IVC below the diaphragm (see Figs. 1-4 and 1-5). There are other hepatic veins in addition to the three major hepatic veins. The umbilical vein is single, in most cases, running beneath the falciform ligament between the middle and left hepatic veins and emptying into the terminal portion of the left hepatic vein. Additional posterior and inferior draining hepatic veins with a short course into the anterior surface of the IVC are frequent and may be large (Figs. 1-5 to 1-7).

Figure 1-4 Transverse sonogram of the hepatic vein confluence shows the right hepatic vein (RHV), middle hepatic vein (MHV), left hepatic vein (LHV), and inferior vena cava (IVC).

Figure 1-5 Inferior accessory right hepatic vein shown by CT scan. A, The hepatic venous confluence with the left (L), middle (M), and right (R) hepatic veins. B, An additional inferior accessory right hepatic vein (arrow) enters the inferior vena cava (IVC) separately at a lower level. p, portal vein.

Figure 1-6 A, Thick-slab MIP through the portal veins reveals standard bifurcation of the main portal vein into the right (arrow) and left (arrowhead) portal veins. The anterior and posterior sectoral branches of the right portal vein are evident, as are the medial and lateral sectoral branches of the left portal vein. B, Thick-slab MIP image through the hepatic veins reveals the three major hepatic veins (arrowheads) and an accessory hepatic vein (arrow) draining into the inferior vena cava.

Figure 1-7 Volume-rendered three-dimensional model of the liver created from axially acquired CT data. The superior portion of the hepatic parenchyma has been removed to reveal the course of the hepatic veins through the liver substance as they drain into the inferior vena cava. The hepatic segments are indicated.

Hidden within the external gross appearance of the liver is a detailed internal anatomy, an understanding of which is essential to the performance of precise hepatectomy. This internal anatomy has been called the functional anatomy of the liver.

FUNCTIONAL SURGICAL ANATOMY

The internal architecture of the liver is composed of a series of segments combining to form sectors separated by scissurae containing the hepatic veins (Fig. 1-8). The internal structure has been clarified by the publications of Goldsmith and Woodburne (1957), Couinaud (1957), and Bismuth and colleagues (1982). The description by Couinaud is the most complete and the most useful for the operating surgeon, and this description is generally used in this book.

Figure 1-8 The portal vein, the hepatic artery, and the draining bile ducts are distributed symmetrically within the liver. Each segment (I-VIII) is supplied by a portal triad composed of a branch of the portal vein and hepatic artery and drained by a tributary of the right or left main hepatic ducts. The four sectors demarcated by the three main hepatic veins are called the portal sectors; these portions of parenchyma are supplied by independent portal pedicles. The hepatic veins run between the sectors in the portal scissurae; the scissurae containing portal pedicles are called the hepatic scissurae. The umbilical fissure corresponds to a hepatic scissura. The internal architecture of the liver consists of two livers, or hemilivers, the right and the left liver separated by the main portal scissura, also known as Cantlie’s line. It is preferable to call them the right and left liver rather than the right and left lobes because the latter nomenclature is erroneous, there being no visible mark that permits identification of a true hemiliver.

Essentially, the three main hepatic veins within the scissurae divide the liver into four sectors, each of which receives a portal pedicle. The main portal scissura contains the middle hepatic vein and progresses from the middle of the gallbladder bed anteriorly to the left of the vena cava posteriorly. The right and left parts of the liver, demarcated by the main portal scissura, are independent in terms of portal and arterial vascularization and of biliary drainage (Fig. 1-9). These right and left livers are themselves divided into two by the remaining portal scissurae. These four subdivisions in Couinaud’s nomenclature, (1957) are termed sectors (see Figs. 1-8 to 1-10).

Figure 1-9 The functional division of the liver and of the liver segments according to Couinaud’s nomenclature. A, As seen in the patient. B, In the ex vivo position.

Figure 1-10 Corrosion cast of the segmental anatomy of the liver.

(Courtesy of Dr. B. Kekis, Athens, Greece.)

The right portal scissura separating the right liver into two sectors—anteromedial or anterior and posterolateral or posterior—is almost in the frontal plane with the body supine. The right hepatic vein runs within the right scissura. The left portal scissura divides the left liver into two sectors. The left portal scissura is not within the umbilical fissure because this fissure is not a portal scissura and contains a portal pedicle. The left portal scissura is located posterior to the ligamentum teres and within the left lobe of the liver along the course of the left hepatic vein. The anterior sector of the left liver is composed of a part of the right lobe (segment IV) that is to the left of the main portal scissura and of the anterior part of the left lobe (segment III) (see Figs. 1-8 to 1-10). The left posterior sector is the only sector composed of one segment (segment II) (Fig. 1-11).

Figure 1-11 Normal hepatic segmental and vascular anatomy on CT. A, On cephalad sections, the three hepatic veins are seen to enter the inferior vena cava (IVC). B, The lines of the hepatic veins divide the liver into sectors. The right hepatic vein divides the right liver into an anterior and posterior sector; the middle hepatic vein separates the right from the left liver (and represents the line of the interlobar scissura); the left hepatic vein separates the segments of the left lobe (segments II and III). C, Approaching the midpoint of the liver, the left portal vein is seen. The fissure for the ligamentum venosum (arrows) divides the caudate lobe from the left lateral segments. D, The next section shows the horizontal portion of the right portal vein. The fissure for the ligamentum teres is now seen (large arrows), and this structure divides the lateral segments of the left liver from the quadrate lobe (segment IV). E, On the last section, the gallbladder has come into view, and a line drawn along the axis of the gallbladder to the IVC represents the inferior extent of the interlobar scissura. c, caudate lobe; GB, gallbladder; ivc, inferior vena cava; L, left hepatic vein; M, middle hepatic vein; R, right hepatic vein; pvr, right portal vein; pvl, left portal vein.

At the hilus of the liver, the right portal triad pursues a short course before entering the substance of the right liver (Figs. 1-6 and 1-12). In some cases, the right anterior and posterior pedicles arise independently, and their origins may be separated by 2 cm (Figs. 1-12 and 1-13). Indeed, it may appear as though the left portal vein arises from the right anterior branch (see also Fig. 1-48) On the left side, however, the portal triad crosses over approximately 3 to 4 cm beneath the quadrate lobe embraced in a peritoneal sheath at the upper end of the gastrohepatic ligament and separated from the undersurface of the quadrate lobe (segment IV) by connective tissue (hilar plate). This prolongation of the left portal pedicle turns anteriorly and caudally within the umbilical fissure giving branches of supply to segments II and III and recurrent branches to segment IV (see Figs. 1-8, 1-9, 1-14, and 1-15). Beneath the quadrate lobe, the pedicle is composed of the left branch of the portal vein and the left hepatic duct, but it is joined at the base of the umbilical fissure by the left branch of the hepatic artery.

Figure 1-12 A, Transverse sonogram at the level of the portal vein bifurcation. The main portal vein (MPV) bifurcates into the left (LPV) and right portal veins. The right portal vein bifurcates shortly into the right anterior (RAPV) and right posterior (RPPV) branches, but the left portal vein has a longer horizontal course within the hilar plate. The inferior vena cava (IVC) is seen posteriorly. B, Coronal view of CT angioportography. Reconstruction shows the right hepatic vein (large open arrow), and the portal vein (black arrow); anterior and posterior sectoral branches of the right portal vein (white arrows) are seen to arise independently from the main portal trunk.

Figure 1-13 Variant portal venous anatomy. Thick-slab MIP image reveals that the portal venous branch perfusing the anterior sector of the right hepatic lobe (arrow) shares a common trunk with the left portal vein (arrowhead).

Figure 1-48 CT of common variant of portal vein branching. The right posterior portal vein (arrow) has a separate early origin from the main portal vein. The right anterior sectoral portal vein (R) and the left main portal vein (L) share a common trunk. Fissure of the ligamentum teres is seen anteriorly (arrowhead) (see also Figs. 1-12 and 1-46).

Figure 1-14 Transverse sonogram shows the branching pattern of the left portal vein (p), which courses horizontally and into the umbilical fissure. The umbilical portion of the left portal vein (u) gives branches to the left hepatic segments (2, 3, and 4). The left hepatic vein (arrow) and inferior vena cava also are shown.

Figure 1-15 A, Contrast-enhanced CT of the portal vein bifurcation. L, left portal vein; R, right portal vein; RA, right anterior portal vein; RP, right posterior portal vein. B, Three-dimensional reformatted image reveals the course of the left portal vein. The left portal vein ascends in the umbilical fissure before looping anteriorly and inferiorly (black arrow) to branch into the medial (arrowhead) and lateral (long thin arrow) sectoral branches.

The branching of the portal pedicle at the hilus (Figs. 1-8, 1-12, 1-14, and 1-15), the distribution of the branches to the caudate lobe (segment I) on the right and left side, and the distribution to the segments of the right (segments V-VIII) and left (segments II-IV) hemilivers follow a remarkably symmetric pattern and allow separation of segment IV into segment IVa superiorly and segment IVb inferiorly (see Fig. 1-8). This arrangement of subsegments mimics the distribution to segments V and VIII on the right side. The umbilical vein provides drainage of, at least, parts of segment IVb after ligation of the middle hepatic vein and is important in the performance of segmental resection.

The caudate lobe (segment I) is the dorsal portion of the liver lying posteriorly and embracing the retrohepatic IVC. The lobe lies between major vascular structures. On the left, the caudate lies between the IVC posteriorly and the left portal triad inferiorly and the IVC and the middle and left hepatic veins superiorly (Figs. 1-16 and 1-17). The portion of the caudate on the right varies, but is usually quite small. The anterior surface within the parenchyma is covered by the posterior surface of segment IV, the limit being an oblique plane slanting from the left portal vein to the left hepatic vein. Thus, there is a caudate lobe (segment I) with a constantly present left portion and a right portion of variable size (see Figs. 1-16 and 1-17).

Figure 1-16 The main bulk of the caudate lobe (segment I) (shaded) lies to the left of the inferior vena cava (IVC)—the left and inferior margins being free in the lesser omental bursa. The gastrohepatic (lesser) omentum separates the left portion of the caudate from segments II and III of the liver as it passes between them to be attached to the ligamentum venosum. The left portion of the caudate lobe inferiorly traverses to the right between the portal vein (LPV) and IVC as the caudate process, where it fuses with the right lobe of the liver. Note the position of the middle hepatic vein (MHV).

Figure 1-17 The caudate lobe—segments II and III rotated to the patient’s right. Superiorly, the left portion of the caudate lobe is linked by a deep anterior portion, which is embedded in the parenchyma immediately under the middle hepatic vein (MHV), reaching inferiorly to the posterior margin of the hilus of the liver and fusing anterolaterally to the inferior vena cava (IVC) on the right side to segments VI and VII of the right liver. The major blood supply arises from the left branch of the left portal vein (LPV) and the left hepatic artery close to the base of the umbilical fissure of the liver. The hepatic veins (MHV, LHV) are short in course and drain from the caudate directly into the anterior and left aspect of the vena cava. LHV, left hepatic vein; RPV, right portal vein; PV, main trunk of portal vein.

The caudate lobe is supplied by blood vessels and drained by biliary tributaries from the right and left portal triads. Small vessels from the portal vein and tributaries joining the biliary ducts also are found, usually two on the left side and one on the right. The right portion of the caudate lobe, including the caudate process, predominantly receives portal venous blood from the right portal vein or the bifurcation of the main portal vein, whereas on the left side the portal supply arises from the left branch of the portal vein almost exclusively. Similarly, the arterial supply and biliary drainage of the right portion is most commonly associated with the right posterior sectoral vessels or pedicle and the left portion with the left main vessels. The hepatic venous drainage of the caudate is unique in that it is the only hepatic segment draining directly into the IVC. These veins sometimes can drain into the posterior aspect of the vena cava if there is a significant retrocaval caudate component.

The posterior edge of the caudate lobe on the left has a fibrous component, which fans out and attaches lightly to the crural area of the diaphragm, but extends posteriorly behind the vena cava to link with a similar component of fibrous tissue from the posterior surface of segment VII and embraces the vena cava (see Figs. 1-2C and 1-16). This ligament may be replaced, in whole or in part, by hepatic tissue, and the caudate may completely encircle the IVC and contact segment VII on the right side. A papillary process of the caudate lobe can be mistaken for an enlarged lymph node on computed tomography (CT) scan (Fig. 1-18). To summarize:

1. The liver is divided into two hemilivers by the main hepatic scissura within which runs the middle hepatic vein.

2. The left liver is divided into two sectors by the left portal scissura within which the left hepatic vein runs (see Fig. 1-8). The posterior sector comprises only one segment (segment II), which is the posterior part of the left lobe. This is the only sector that comprises one segment (this is referred to as the left posterior section according to Strasberg et al [2000]). The anterior sector is divided by the umbilical fissure into two segments—a medial segment (the quadrate lobe) (segment IV) and a lateral segment (segment III), which is the anterior part of the left lobe.

3. The right liver is divided into two sectors by the right portal scissura containing the right hepatic vein. Each of these two sectors is divided into two segments—an anterior sector (segment V inferiorly and segment VIII superiorly) and a posterior sector (segment VI inferiorly and segment VII superiorly) (see Figs. 1-8 and 1-9).

4. Segment I (the caudate lobe) lies posteriorly embracing the vena cava, its intraparenchymal anterior surface abutting the posterior surface of segment IV and merging with segments VI and VII on the right (Figs. 1-16 and 1-19).