Retrohepatic Inferior Vena Cava

The inferior vena cava (IVC) runs on the right of the aorta on the bodies of the lumbar vertebrae, diverging from the aorta as it passes upward. Below the liver, the IVC lies behind the duodenum and head of the pancreas as a retroperitoneal structure passing upward behind the foramen of Winslow posterior to the right hilar structures of the liver. The renal veins lie in front of the arteries and join the IVC at almost a right angle on the left and obliquely on the right. Behind the liver, the IVC is embraced in a groove on its posterior surface (Figs. 1B.1 and 1B.2). The IVC comes to lie on the right crus of the diaphragm, behind the bare area of the liver; it extends to the central tendon of the diaphragm, which it pierces on a level with the body of T8, behind and higher than the beginning of the abdominal aorta. As the IVC courses upward, it is separated from the right crus of the diaphragm by the right celiac ganglion and, higher up, by the right phrenic artery. The right adrenal vein is a short vessel that enters the IVC behind the bare area (see Fig. 1B.1). There may be a small accessory right adrenal vein on the right that enters into the confluence of the right renal vein and the IVC. The lumbar veins drain posterolaterally into the IVC below the level of the renal veins, but above this level, there are usually no vena caval tributaries posteriorly.

FIGURE 1B.1 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, limited on the left by the umbilical fissure, on the right by the gallbladder fossa. Posterior to the hilar transverse fissure is a fourth lobe, the caudate lobe, which hugs the inferior vena cava (IVC) and extends upward on its left side. The liver comprises two main lobes and two smaller lobes, separated by visible, well-defined fissures on the liver surface. C, The IVC lies snugly in a deep groove within the bare area; the hepatic veins open directly into it. Within this bare area, the right suprarenal gland lies adjacent to the IVC, and the adrenal vein drains into the right of the IVC. The remainder of the bare area of liver is directly in contact with the diaphragm. 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. The gastrohepatic omentum is attached to the ligamentum venosum, placing the caudate lobe within the lesser sac of the peritoneum; but the left lobe of the liver is situated anteriorly in the supracolic compartment of the peritoneal cavity. The posterior surface of the left lobe is narrow; there is a very fine bare area on this side. 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 that passes from the posterior edge of the liver backward toward the lumbar vertebrae and fans 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. This layer of fibrous tissue, sometimes called the ligament of the vena cava, must be divided on the right, to allow surgical exposure of the IVC and the hepatic veins, and on the left, to allow mobilization 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 1B.2 Contrast-enhanced computed tomographic scan of the liver shows the intimate relationship of the caudate lobe (arrow), inferior vena cava (Ivc), portal vein (p), and aorta (a).

Hepatic Veins

The hepatic veins (Figs. 1B.3 to 1B.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 are usually joined, after a short extrahepatic course, to form a common venous channel approximately 2 cm in length that traverses to the left part of the anterior surface of the IVC below the diaphragm (see Figs. 1B.3 and 1B.5). In addition to the three major hepatic veins, there is the umbilical vein, which is single in most cases and runs beneath the falciform ligament between the middle and left hepatic veins; it empties into the terminal portion of the left hepatic vein, although rarely it drains into the middle hepatic vein or directly into the confluence of the middle and left hepatic veins. Additional posteriorly and inferiorly draining hepatic veins, with a short course into the anterior surface of the IVC, are frequent and may be large (see Fig. 1B.4). Hepatic venous drainage of the caudate lobe is directly into the IVC, as described below.

FIGURE 1B.3 Transverse ultrasound image of the hepatic vein confluence shows the left (L), middle (M), and right (R) hepatic veins as they join the inferior vena cava (IVC).

FIGURE 1B.4 Two inferior accessory right hepatic veins. A, Contrast-enhanced computed tomographic (CT) image of the hepatic vein confluence. R, right hepatic vein; M, middle hepatic vein; IVC, inferior vena cava. B, A small right inferior accessory vein (arrow) enters the IVC below the hepatic venous confluence. C, The second, larger right inferior accessory right hepatic vein (arrow) is seen more inferiorly. PV, portal vein. D, CT coronal reconstruction image shows the right hepatic vein (R) and one right inferior accessory vein (arrow); A, aorta.

FIGURE 1B.5 The anterior surfaces of the major extrahepatic veins and the inferior vena cava are retroperitoneal and masked behind the layers of the falciform ligament, as it splits and passes to the right and left triangular ligaments.

This classic description of the anatomy of the liver is sufficient for gross appreciation and for mobilization of the liver to allow access for repair of injuries, liver transplantation, or the placement of probes onto or into the liver substance. Hidden within this external gross appearance is a detailed internal anatomy; however, 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 that combine to form sectors separated by scissurae that contain the hepatic veins (Fig. 1B.6). Together or separately, these constitute the visible lobes described previously. The internal structure has been clarified by the publications of McIndoe and Counseller (1927), Ton That Tung (1939, 1979), Hjörtsjö (1931), Healey and Schroy (1953), Goldsmith and Woodburne (1957), Couinaud (1957), and Bismuth and colleagues (1982); however, the description by Couinaud is the most complete, exact, and useful for the operating surgeon, so it is generally used here. An alternative terminology suggested by a committee of the International Hepato-Pancreatico-Biliary Association (Strasberg et al, 2000) adds little to the understanding or practicality of Couinaud’s description. The main difference is that in the alternative terminology, Couinaud’s sectors are referred to as sections, particularly in describing the anatomy of the left liver (see Chapters 90A to 90F for differences in the terminology of the various hepatic resections).

FIGURE 1B.6 The portal vein, hepatic artery, and draining bile ducts are distributed within the liver in a beautifully symmetric pedicular pattern, which belies the asymmetric external appearance. Each segment (I to 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 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 is 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, with alternation between the hepatic veins and portal pedicles. 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 biliary drainage (Fig. 1B.7). These right and left livers are themselves divided into two by the remaining portal scissurae. These four subdivisions are referred to as segments in the description of Goldsmith and Woodburne (1957), but in Couinaud’s nomenclature (1957), they are termed sectors (see Figs. 1B.6 and 1B.7).

FIGURE 1B.7 The functional division of the liver and its segments according to Couinaud’s nomenclature. A, As seen in the patient. B, In the ex vivo position.

The right portal scissura separates the right liver into two sectors: anteromedial (anterior) and posterolateral (posterior). With the body supine, this scissura is almost in the frontal plane. The right hepatic vein runs within the right scissura. The left portal scissura divides the left liver into two sectors, but 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—the left medial section, in the terminology of Strasberg and others (2000)—is composed of a part of the right lobe (segment IV), to the left of the main portal scissura, and of the anterior part of the left lobe (segment III; see Figs. 1B.6 and 1B.7). The left posterior sector is the only sector composed of one segment (segment II; the left posterior section in terminology of Strasberg et al).

At the hilus of the liver, the right portal triad pursues a short course of approximately 1 to 1.5 cm before entering the substance of the right liver (Fig. 1B.8A). In some cases, the right anterior and posterior pedicles arise independently, and their origins may be separated by 2 cm (see Fig. 1B.8B). In some cases, it appears as if the left portal vein arises from the right anterior branch (see also Fig. 1B.40). 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 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 (Fig. 1B.9; see also Fig. 1B.6). 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 1B.8 A, Transverse sonogram at the level of the portal vein bifurcation. The main portal vein (MPV) bifurcates into the left and right portal veins (LPV and RPV). The RPV bifurcates shortly into the right anterior (RAPV) and right posterior (RPPV) branches, but the LPV has a longer horizontal course within the hilar plate. The inferior vena cava (IVC) is seen posteriorly. B, Coronal view of computed tomographic angioportography. Reconstruction shows the right hepatic vein (open arrow) and the portal vein (large arrow); anterior and posterior sectoral branches of the RPV (small arrows) are seen to arise independently from the main portal trunk.

FIGURE 1B.9 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 (II to IV). The left hepatic vein (arrow) and inferior vena cava (IVC) also are shown.

The branching of the portal pedicle at the hilus (Fig. 1B.10; see also Figs. 1B.6, 1B.8, and 1B.9), the distribution of the branches to the caudate lobe (segment I) on the right and left sides, and the distribution to the segments of the right (segments V through VIII) and left (segments II through IV) hemiliver follow a remarkably symmetric pattern and, as described by Scheele (1994), allow separation of segment IV into segment IVa superiorly and segment IVb inferiorly (see Fig. 1B.6). 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 it is important in the performance of segmental resection.

FIGURE 1B.10 Contrast-enhanced computed tomographic image of the portal vein bifurcation. L, left portal vein; R, right portal vein; RA, right anterior portal vein; RP, right posterior portal vein.

The caudate lobe (segment I) is the dorsal portion of the liver lying posteriorly and embracing the retrohepatic IVC. This 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. 1B.11 and 1B.12). This portion of the caudate is sometimes referred to as segment IX.

FIGURE 1B.11 The main bulk of the caudate lobe (segment I; dark area) lies to the left of the inferior vena cava (IVC); the left and inferior margins are 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 left 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 1B.12 The caudate lobe (shaded) and 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, 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 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. 1B.11 and 1B.12).

The caudate lobe is supplied by blood vessels and drained by biliary tributaries from the right and left portal triad. 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 from 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 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 that drains directly into the IVC. These veins can sometimes drain into the posterior aspect of the vena cava, if a significant retrocaval caudate component is present.

In the usual and common circumstance, 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 it extends posteriorly, behind the vena cava, to link with a similar component of fibrous tissue that protrudes from the posterior surface of segment VII and embraces the vena cava (see Figs. 1B.1C and 1B.11). In 50% of patients, this ligament is replaced by hepatic tissue, in whole or in part, and the caudate may completely encircle the IVC and may contact segment VII on the right side; a significant retrocaval component may prevent a left-sided approach to the caudate veins. The caudal margin of the caudate lobe has a papillary process that occasionally may attach to the rest of the lobe via a narrow connection. It is bulky in 27% of cases and can be mistaken for an enlarged lymph node on computed tomography (CT) scan (Fig. 1B.13).

FIGURE 1B.13 Computed tomographic image of the caudate lobe with papillary process. A, Caudate lobe (asterisk) positioned between the left portal vein (arrow) and inferior vena cava (v); a, aorta. B, Papillary process of the caudate (p) represents the lower medial extension of the caudate (asterisk) and may mimic a periportal lymph node.

To summarize:

FIGURE 1B.14 Hepatic segmental anatomy as shown by computed tomography. A, At the level of the hepatic veins. B, At the portal vein bifurcation. C, Below the hepatic hilus.

Further details of segmental anatomy important in sectoral or segmental resection are described in Chapter 90A, Chapter 90B, Chapter 90C, Chapter 90D, Chapter 90E, Chapter 90F, Chapter 92 .

Surgical Implications and Exposure

All methods for precise partial hepatectomy depend on control of the inflow vasculature and draining bile ducts and of the outflow hepatic veins of the portion of liver to be excised, which may be a segment, a subsegment, or an entire lobe. The remnant remaining after partial hepatectomy must be provided with an excellent portal venous and hepatic arterial supply and biliary drainage and an unimpeded hepatic venous outflow. Under such circumstances, hepatic regeneration is usually prompt. The classification of the various partial hepatic resection procedures, incisions and exposure, necessary mobilization of the liver, and the methods of control of the structures within the portal triads and of the hepatic veins are described in detail in Chapter 90A, Chapter 90B, Chapter 90C, Chapter 90D, Chapter 90E, Chapter 90F, Chapter 92 .

Intrahepatic Bile Duct Anatomy

The right and left livers are drained by the right and the left hepatic ducts, whereas the dorsal lobe (caudate lobe) is drained by several ducts that join both the right and left hepatic ducts. The intrahepatic ducts are tributaries of the corresponding hepatic ducts, which form part of the major portal triads that penetrate the liver, invaginating the Glisson capsule at the hilus. Bile ducts usually are located above the corresponding portal branches, whereas hepatic arterial branches are situated inferiorly to the veins. Each branch of the intrahepatic portal veins corresponds to one or two bile duct tributaries that join to form the right and left hepatic ductal systems, converging at the liver hilus to constitute the common hepatic duct. The umbilical fissure divides the left liver, passing between segment III and segment IV, where it may be bridged by a tongue of liver tissue. The ligamentum teres passes through the umbilical fissure to join the left branch of the portal vein (see Fig. 1B.1).

The left hepatic duct drains the three segments—II, III, and IV—that constitute the left liver (Fig. 1B.15). The duct that drains segment III is located slightly behind the left horn of the umbilical recess. It is joined by the tributary from segment IVb to form the left duct, which is similarly joined by the duct of segment II and the duct of segment IVa, where the left branch of the portal vein turns forward and caudally. The left hepatic duct traverses beneath the left liver at the base of segment IV, just above and behind the left branch of the portal vein; it crosses the anterior edge of that vein and joins the right hepatic duct to constitute the hepatic ductal confluence. In its transverse portion, it receives one to three small branches from segment IV.

FIGURE 1B.15 A, Biliary drainage of the two functional hemilivers. Note the position of the right anterior and right posterior sectors. The caudate lobe drains into the right and left ductal system. B, Inferior aspect of the liver. The biliary tract is represented in black, and the portal branches are represented in white. Note the biliary drainage of segment IV (segment VIII is not represented because of its cephalad location). C, T-tube cholangiogram shows the most common arrangement of hepatic ducts.

The right hepatic duct drains segments V, VI, VII, and VIII and arises from the junction of two main sectoral duct tributaries (Fig. 1B.16). The posterior or lateral duct and the anterior or medial duct are each accompanied by a corresponding vein. The right posterior sectoral duct has an almost horizontal course and constitutes the confluence of the ducts of segments VI and VII (see Figs. 1B.15 and 1B.16). The duct then runs to join the right anterior sectoral duct, as it descends in a vertical manner. The right anterior sectoral duct is formed by the confluence of the ducts draining segments V and VIII. Its main trunk is located to the left of the right anterior sectoral branch of the portal vein, which pursues an ascending course. The junction of these two main right biliary channels usually occurs above the right branch of the portal vein. The right hepatic duct is short and joins the left hepatic duct to constitute the confluence lying in front of the right portal vein and forming the common hepatic duct.

FIGURE 1B.16 A, Biliary and vascular anatomy of the right liver. Note the horizontal course of the posterior sectoral duct and the vertical course of the anterior sectoral duct. B, Transtubal cholangiogram shows a common normal variant: the right posterior sectoral duct drains into the left hepatic duct. In this case, the posterior duct is anterior to the posterior sectoral duct. Frequently in this variant, the posterior duct passes posteriorly to the anterior sectoral pedicle.

The caudate lobe (segment I) has its own biliary drainage (Healey & Schroy, 1953). The caudate lobe is divided into right and left portions and a caudate process. In 44% of individuals, three separate ducts drain these three parts of the lobe, whereas in 26% a common duct lies between the right portion of the caudate lobe proper and the caudate process and an independent duct that drains the left part of the caudate lobe. The site of drainage of these ducts varies. In 78% of cases, drainage of the caudate lobe is into the right and left hepatic ducts, but in 15% drainage is by the left hepatic ductal system only. In about 7%, the drainage is into the right hepatic system.

Extrahepatic Biliary Anatomy and Vascular Anatomy of the Liver and Pancreas

The extrahepatic bile ducts are represented by the extrahepatic segments of the right and left hepatic ducts, joining to form the biliary confluence and the main biliary channel draining to the duodenum. The accessory biliary apparatus, which constitutes a reservoir, comprises the gallbladder and cystic duct (Figs. 1B.17 and 1B.18). The confluence of the right and left hepatic ducts occurs at the right of the hilar fissure of the liver, anterior to the portal venous bifurcation and overlying the origin of the right branch of the portal vein (see Fig. 1B.17). The extrahepatic segment of the right duct is short, but the left duct has a much longer extrahepatic course. The biliary confluence is separated from the posterior aspect of the quadrate lobe of the liver by the hilar plate, which is the fusion of connective tissue enclosing the biliary and vascular elements with the Glisson capsule (Fig. 1B.19). Because of the absence of any vascular interposition, it is possible to open the connective tissue constituting the hilar plate at the inferior border of the quadrate lobe and, by elevating it, to display the biliary confluence and left hepatic duct (Fig. 1B.20).

FIGURE 1B.17 Anterior aspect of the biliary anatomy and of the head of the pancreas: right hepatic duct (a); left hepatic duct (b); common hepatic duct (c); hepatic artery (d); gastroduodenal artery (e); cystic duct (f); retroduodenal artery (g); common bile duct (h); neck of the gallbladder (i); body of the gallbladder (j); fundus of the gallbladder (k). Note particularly the position of the hepatic bile duct confluence anterior to the right branch of the portal vein, the posterior course of the cystic artery behind the common hepatic duct, and the relationship of the neck of the gallbladder to the right branch of the hepatic artery. Note also the relationship of the major vessels (portal vein, superior mesenteric vein, and artery) to the head of the pancreas (see also Figs. 1B.29, 1B.35, and 1B.45).

FIGURE 1B.18 Endoscopic retrograde choledochopancreatogram showing the pancreatic duct (arrow), gallbladder, and biliary tree.

FIGURE 1B.19 Anatomy of the plate system. A, Cystic plate, above the gallbladder. B, Hilar plate, above the biliary confluence and at the base of the quadrate lobe. C, Umbilical plate, above the umbilical portion of the portal vein. Large, curving arrows indicate the plane of dissection of the cystic plate during cholecystectomy and of the hilar plate during approaches to the left hepatic duct.

FIGURE 1B.20 A, Relationship between the posterior aspect of the quadrate lobe and the biliary confluence. The hilar plate (arrow) is formed by the fusion of the connective tissue enclosing the biliary and vascular elements with the Glisson capsule. B, Biliary confluence and left hepatic duct exposed by lifting the quadrate lobe upward after incision of the Glisson capsule at its base. This technique, lowering of the hilar plate (Hepp & Couinaud, 1956), generally is used to display a dilated bile duct above an iatrogenic stricture or hilar cholangiocarcinoma. C, Line of incision (left) to allow extensive mobilization of the quadrate lobe. This maneuver is of particular value for high bile duct stricture and in the presence of liver atrophy or hypertrophy. The procedure consists of lifting the quadrate lobe upward (see A and B), then not only opening the umbilical fissure but also incising the deepest portion of the gallbladder fossa. Right, Incision of the Glisson capsule to gain access to the biliary system (arrow).

Main Bile Duct and Sphincter of Oddi

The main bile duct (see Fig. 1B.17), the mean diameter of which is about 6 mm, is divided into two portions: the upper is called the common hepatic duct and is situated above the cystic duct, which joins it to form the lower portion, the common bile duct (see Fig. 1B.18). The common duct courses downward anterior to the portal vein, in the free edge of the lesser omentum; it is closely applied to the hepatic artery, which runs upward on its left, giving rise to the right branch of the hepatic artery, which crosses the main bile duct usually posteriorly, although in about 20% of cases, it crosses anteriorly. The cystic artery, arising from the right branch of the hepatic artery, may cross the common hepatic duct posteriorly or anteriorly. The common hepatic duct constitutes the left border of the triangle of Calot, the other corners of which were originally described as the cystic duct below and the cystic artery above (Rocko et al, 1981). The commonly accepted working definition of the triangle of Calot recognizes, however, the inferior surface of the right lobe of the liver as the upper border and the cystic duct as the lower border (Wood, 1979). Dissection of the triangle of Calot is of key significance during cholecystectomy, because in this triangle runs the cystic artery, often the right branch of the hepatic artery, and occasionally a bile duct, which should be displayed before cholecystectomy. If there is a replaced or accessory common or right hepatic artery, it usually runs behind the cystic duct to enter the triangle of Calot (Fig. 1B.21).

FIGURE 1B.21 Hepatic artery variations shown by angiography. A, Replaced common hepatic artery arises from the superior mesenteric trunk. B, Angiogram. Left, The hepatic artery (large arrowhead) arises from the celiac axis. The small arrowheads indicate a drainage catheter in the bile duct. Right, An accessory right hepatic artery (large arrowhead) is arising from the superior mesenteric artery and lies lateral to the catheter (small arrowheads) in the common bile duct. C, The accessory right hepatic artery usually courses upward in the groove posterolateral to the common bile duct (CBD), appearing on the medial side of the triangle of Calot, usually running just behind the cystic duct (CD). This common variation occurs in about 25% of individuals. HA, hepatic artery; RHA, right hepatic artery.

The common variations in the relationship of the hepatic artery and origin and course of the cystic artery to the biliary apparatus are shown in Fig. 1B.22. Ignorance of these variations may provoke unexpected hemorrhage or biliary injury (Champetier et al, 1982) during cholecystectomy and may result in bile duct injury during efforts to secure hemostasis. The union between the cystic duct and the common hepatic duct may be located at various levels. At its lower extrahepatic portion, the common bile duct traverses the posterior aspect of the pancreas, running in a groove or tunnel. The retropancreatic portion of the common bile duct approaches the second portion of the duodenum obliquely, accompanied by the terminal part of the pancreatic duct of Wirsung.

FIGURE 1B.22 The main variations of the cystic artery: typical course (a); double cystic artery (b); cystic artery crossing anterior to main bile duct (c); cystic artery originating from the right branch of the hepatic artery and crossing the common hepatic duct anteriorly (d); cystic artery originating from the left branch of the hepatic artery (e); cystic artery originating from the gastroduodenal artery (f); cystic artery arising from the celiac axis (g); cystic artery originating from a replaced right hepatic artery (h).

Gallbladder and Cystic Duct

The gallbladder is a reservoir located on the undersurface of the right lobe of the liver, within the cystic fossa; it is separated from the hepatic parenchyma by the cystic plate, which is composed of connective tissue closely applied to the Glisson capsule and elongating the hilar plate (see Fig. 1B.19). Sometimes the gallbladder is deeply embedded in the liver, but occasionally it occurs on a mesenteric attachment and may be susceptible to volvulus. The gallbladder varies in size and consists of a fundus, a body, and a neck (Fig. 1B.23). The tip of the fundus usually, but not always, reaches the free edge of the liver and is closely applied to the cystic plate. The cystic fossa is a precise anterior landmark to the main liver incisura. The neck of the gallbladder makes an angle with the fundus and creates the Hartmann pouch, which may obscure the common hepatic duct and constitute a real danger point during cholecystectomy.

FIGURE 1B.23 Longitudinal sonogram shows the relationship of the liver, gallbladder (GB), portal vein (PV), inferior vena cava (IVC), hepatic artery (curved arrow) and common bile duct (arrow).

The cystic duct arises from the neck or infundibulum of the gallbladder and extends to join the common hepatic duct. Its lumen usually measures about 1 to 3 mm, and its length varies, depending on the type of union with the common hepatic duct. The mucosa of the cystic duct is arranged in spiral folds known as the valves of Heister (Wood, 1979). Although the cystic duct joins the common hepatic duct in its supraduodenal segment in 80% of cases, it may extend downward to the retroduodenal or retropancreatic area. Occasionally, the cystic duct may join the right hepatic duct or a right hepatic sectoral duct (Fig. 1B.24).

FIGURE 1B.24 A, T-tube cholangiogram shows a very low insertion of a right sectoral duct into the common hepatic duct (arrow). B, Endoscopic retrograde choledochopancreatogram shows a low right sectoral duct (large arrow), into which is draining the cystic duct (small arrow), an uncommon but important normal variant.

Biliary-Vascular Sheaths and Exposure of the Hepatic Bile Duct Confluence

Fusion of the Glisson capsule with the connective tissue sheaths surrounding the biliary and vascular elements at the inferior aspect of the liver constitute the plate system (see Figs. 1B.19 and 1B.20), which includes the hilar plate above the biliary confluence, the cystic plate related to the gallbladder, and the umbilical plate situated above the umbilical portion of the left portal vein (Couinaud, 1957). Hepp and Couinaud (1956) described a technique whereby lifting the quadrate lobe upward and incising the Glisson capsule at its base offers a good exposure of the hepatic hilar structures (see Fig. 1B.20A and B). This technique was referred to as lowering of the hilar plate. It can be carried out safely because only exceptionally (in 1% of cases) is there any vascular interposition between the hilar plate and the inferior aspect of the liver. This maneuver is of particular value in exposing the extrahepatic segment of the left hepatic duct, because it has a long course beneath the quadrate lobe. It is not as effective in exposing the extrahepatic right duct or its secondary branches, which are short. The technique is of major importance for the identification of proximal biliary mucosa during bile duct repair after injury. Basically, an incision is required at the posterior edge of the quadrate lobe, where the Glisson capsule is attached to the hilar plate (see Fig. 1B.20B and Chapter 29). The upper surface of the hilar plate can be separated from the hepatic parenchyma and, by lifting the quadrate lobe upward, display of the hepatic duct convergence, which is always extrahepatic, is effected. Bile duct incision allows performance of a mucosa-to-mucosa anastomosis. Rarely, it may be hazardous to approach the biliary confluence in this manner, especially when anatomic deformity has been created by atrophy or hypertrophy of liver lobes and in patients in whom there appears to be a very deep hilus that is displaced upward and rotated laterally. Frequently, by a simultaneous opening of the deepest portion of the gallbladder fossa and the umbilical fissure (see Fig. 1B.20C), good exposure of the biliary duct confluence, and especially the right hepatic duct, can be obtained without the necessity for full hepatotomy.

Umbilical Fissure and Segment III (Ligamentum Teres) Approach

The round ligament, which is the remnant of the obliterated umbilical vein, runs through the umbilical fissure to connect with the left branch of the portal vein. The round ligament is sometimes deeply embedded in the umbilical fissure. At the junction of the round ligament and the termination of the left portal vein, elongations containing channels that are elements of the left portal system course into the liver. The bile ducts of the left lobe of the liver (Figs. 1B.30 and 1B.31A) are located above the left branch of the portal vein and lie behind these elongations, whereas the corresponding artery is situated below the vein. Dissection of the round ligament on its left side and division of one or two vascular elongations of segment III allow display of the pedicle or anterior branch of the duct of segment III (see Fig. 1B.31B). In the event of biliary obstruction with intrahepatic biliary ductal dilatation, the segment III duct is generally easily located above the left branch of the portal vein. It is often preferable to split the normal liver tissue just to the left of the umbilical fissure to widen the fissure further, which allows access to the ductal system without having to divide any elements of the portal blood supply to segment III (Fig. 1B.32; see Chapter 29).

FIGURE 1B.30 Biliary and vascular anatomy of the left liver. Note the location of the segment III duct above the corresponding vein. The anterior branch of the segment IV duct is not represented.

FIGURE 1B.31 A, The biliary and vascular anatomy of the left liver. Note the relationship of the left horn of the umbilical recess with the segment III ductal system: left portal vein (a); left hepatic duct (b); segment III system—note that the duct (black) lies adjacent to the portal venous branch indicated (c); ligamentum teres (d). B, Segment III ductal approach: exposure of the left horn of the umbilical recess (a); division of the left horn of the umbilical recess, including segment III portal vein branches (b); exposure and opening of segment III duct: hepaticojejunostomy to the segment III ductal system (c; see also Chapter 29).

FIGURE 1B.32 A, The liver is split to the left of the ligamentum teres in the umbilical fissure. It may be necessary to remove a small wedge of liver tissue (c). B, Segment III duct is exposed at the base of the liver split, above and behind its accompanying vein, and is ready for anastomosis (see also Chapter 29, Chapter 42A, Chapter 42B ).

Surgical Approaches to the Right Hepatic Biliary Ductal System

Because of the lack of precise anatomic landmarks, exposure of the right intrahepatic ductal system is much more hazardous and imprecise than that of the left. In some cases of hilar cholangiocarcinoma, the planned surgical procedure—partial hepatectomy or segment III duct bypass—seems impossible at operation. In such a critical operative situation, intrahepatic right ductal system drainage is an option. Anatomically, the anterior sectoral duct and its branches run on the left side of the corresponding portal vein. In essence, the end of the liver scissura, within which lies the right branch of the portal vein, is opened over a short distance. The anterior sectoral duct is displayed on the left aspect of the vein, and the dilated duct is opened longitudinally and anastomosed to a Roux-en-Y loop of jejunum (Fig. 1B.33). Although this technique is rarely used, it may be valuable in selected cases. An alternative method is to open into the segment V duct through the gallbladder fossa, although we seldom use this approach and prefer the anterior sectoral duct approach.

FIGURE 1B.33 A, Anterior sectoral approach. If necessary, the liver substance is opened over a short distance in the line of the right anterior sectoral pedicle. B, The duct is displayed anterior and to the left side of the corresponding vein. This can be facilitated using a posterior pedicular approach as described by Launois (see Chapters 90A to 90F).

Exposure of the Bile Ducts by Liver Resection

This chapter does not detail exposure of the bile ducts by resection of liver substance. In essence, a segment of the left lobe may be amputated to expose the segment II or III ducts, or a similar procedure may be carried out after removal of the inferior tip of the right lobe. Finally, in some instances, removal of the quadrate lobe may be carried out to effect exposure of the biliary confluence. This procedure really represents a simple extension of the mobilization of the quadrate lobe after opening of the principal scissura and the umbilical fissure as described previously.

Celiac Axis and Blood Supply of Liver, Biliary Tract, and Pancreas

The usual classic description of the arterial blood supply of the liver, biliary system, and pancreas is found in only about 60% of specimens (Figs. 1B.34 to 1B.36). The right and the left hepatic arteries, the former in the right of the hilus of the liver and the latter in the left at the base of the umbilical fissure, become enclosed in the sheath of peritoneum, forming the right and left portal triads. In this sheath, further branching to the right anterior and posterior sectors of the liver and on the left to segments II, III, and IV occurs within the respective pedicles, which also come to enclose the portal vein branches and the tributary bile ducts from these sectors and segments. The arterial supply of the common bile duct was described earlier; it arises from branches of the hepatic artery, the gastroduodenal artery, and the pancreaticoduodenal arcades.

FIGURE 1B.34 The celiac trunk is a short, thick artery originating from the aorta just below the aortic hiatus of the diaphragm and extending horizontally and forward above the pancreas, where it divides into the left gastric, common hepatic, and splenic arteries. An inferior phrenic artery, usually arising from the aorta or the splenic artery, occasionally arises from the celiac trunk. The left gastric artery curves toward the stomach and extends along its lesser curve, forming anastomoses with the right gastric artery. The splenic artery, the largest of the three celiac branches, takes a tortuous course to the left, behind and along the upper border of the pancreas and at the hilus of the spleen, where it splits into numerous terminal branches. The splenic artery usually approaches and runs superiorly to the splenic vein. An uncommon but dangerous abnormality can occur when the splenic artery runs inferiorly and behind the splenic vein, close to the splenic vein–mesenteric vein confluence. The left gastroepiploic artery and the short gastric arteries originate from one of these terminal branches. The common hepatic artery passes forward into the retroperitoneum then curves to the right to enter the right margin of the lesser omentum, just above the pancreas, and ascends; it approaches the common bile duct on its left side and runs usually anterior to the portal vein. As it turns upward just above the pancreas, it gives rise to the gastroduodenal artery, which also may originate from the right hepatic artery. This descends to supply the anterior, superior, and posterior surfaces of the first inch of the duodenum. The gastroduodenal artery can be duplicated and often has a small branch running with it toward the pylorus. The right gastric artery passes to the left along the lesser curve of the stomach, and anastomosis is to the left gastric artery. The continuation of the common hepatic artery, beyond the origin of the gastroduodenal artery and right gastric artery, is known as the proper hepatic artery and usually soon divides into a right and a left branch. The left branch extends vertically, directly toward the base of the umbilical fissure, and usually gives off a branch known as the middle hepatic artery (MH), which is directed toward the right of the umbilical fissure and is destined to supply the quadrate lobe (segment IV) of the liver. A further branch of the left hepatic artery (LH) courses to the left to supply the caudate lobe, and further smaller caudate branches arise from the left and right hepatic artery. The right hepatic artery (RH) usually passes behind the common hepatic duct and enters the cystic triangle of Calot; in some cases it passes in front of the bile duct, which is important in surgical exposure of the common bile duct. The cystic artery usually arises from the right hepatic artery but has many variations.

FIGURE 1B.35 The primary arteries supplying the pancreas are the gastroduodenal artery (GDA), which arises usually from the common hepatic artery (HA) as it crosses the portal vein (PV) above the pancreas proper, and the dorsal pancreatic artery (DP), arising from the splenic artery (SA). The superior pancreaticoduodenal arteries (SPDAs) arise from the GDA and join the inferior pancreaticoduodenal arteries (IPDAs) from the superior mesenteric artery (SMA), forming two arcades along the anterior and posterior aspects of the head of the pancreas. The GDA, after giving rise to the pancreaticoduodenal artery (PDA), passes forward and to the left as the right gastroepiploic artery (GEA). The GDA is a good landmark for the identification of the portal vein above the pancreas, and surgical division of the GDA just at its origin from the common HA gives much greater access to the anterior surface of the portal vein at this site. The right gastric artery (RGA) also usually arises from the common HA just distal to the GDA, but it can arise from various sites. The GDA commonly divides into a larger right GEA and smaller SPDA. The right GEA runs forward between the first part of the duodenum and pancreas; the SPDA divides into anterior and posterior branches. The anterior superior PDA continues downward on the anterior surface of the head of the pancreas to anastomose with the IPDA, which arises from the SMA. The posterior superior PDA behaves similarly. MCA, middle colic artery; MCV, middle colic vein; SMV, superior mesenteric vein; LGA, left gastric artery.

FIGURE 1B.36 Computed tomographic image of the main portal vein shows the hepatic artery (arrows) coursing anterior to the portal vein (p). The interlobar fissure (open arrow), splenic vein (s), celiac axis (c), aorta (a), and inferior vena cava (IVC) are also shown.

For practical surgical issues, the most important relationships in the anatomy of the pancreas concern the arterial blood supply and the venous drainage. The dorsal pancreatic artery is a major branch, usually arising from the splenic artery, but it can arise directly from the hepatic artery. When splenectomy is performed, it is important to establish the site of origin of the distal pancreatic artery by proximal arterial ligation to avoid distal pancreatic ischemia. The superior mesenteric artery (SMA) arises from the aorta posteriorly behind the pancreas and runs forward and upward to run first behind and then to the left of the superior mesenteric vein (see Fig. 1B.35).

Variations in the Hepatic Artery

As a result of the complex embryologic development of the celiac axis and SMA, wide variations in the arterial supply of the liver are found (Fig. 1B.37). These variations are important to the angiographer and the surgeon. Failure to show all arteries feeding the liver at angiography may not only result in errors of diagnosis but may also seriously mislead the surgeon or the interventional radiologist. In most cases, the hepatic artery arises from the celiac axis as described earlier, but it may be entirely replaced by a common hepatic artery taking origin from the SMA. In this instance, the hepatic artery passes lateral to the portal vein and lies posterior and lateral to the common bile duct in the hepatoduodenal ligament, where it is susceptible to operative injury if not recognized. This applies to a replaced or an accessory hepatic artery. Other variations in the origin of the common hepatic artery include its origin from the aorta and the persistence of a primitive embryologic link between the celiac and superior mesenteric systems. These variations are of considerable importance in controlling the arterial blood supply to the liver during hepatic resection or enucleative procedures, in the performance of devascularization of the liver, in the placement of intraarterial hepatic infusion devices, and in the resection of the head of the pancreas.

FIGURE 1B.37 In approximately 25% of individuals, the right hepatic artery arises partially or completely from the superior mesenteric artery (A, C, E); in a similar proportion of patients, the left hepatic artery may be partially or completely replaced by a branch arising from the left gastric artery, coursing through the gastrohepatic omentum to enter the liver at the base of the umbilical fissure (D, F). Rarely, the right or left hepatic arteries originate independently from the celiac trunk or branch after a very short common hepatic artery origin from the celiac, and the gastroduodenal artery may originate from the right hepatic artery (B, C).

Portal Vein

The portal vein (Fig. 1B.38) is formed behind the neck of the pancreas by confluence of the superior mesenteric and splenic veins (Fig. 1B.39). The venous drainage of the pancreas runs in the main parallel to the arterial supply. There are anterior and posterior and superior and inferior pancreaticoduodenal veins that drain to the portal vein and the superior mesenteric vein (SMV). The left gastric vein and the inferior mesenteric vein (IMV) usually drain into the splenic vein, but they can drain directly into the portal vein, whereas the various small splenic tributaries drain directly to the splenic vein.

FIGURE 1B.38 A, The superior mesenteric vein (SMV) at the root of the lesser omentum is usually a single trunk; two or sometimes even three branches may unite as the vessel enters the tunnel beneath the neck of the pancreas (shaded) to form a superior mesenteric trunk. This trunk ascends behind the neck of the pancreas and is joined by the splenic vein (SV), which enters it from the left to form the portal vein (PV), which emerges from the retroperitoneal upper border of the neck of the pancreas and ascends toward the liver within the free edge of the lesser omentum, lying behind the bile duct and the hepatic artery and surrounded by the lymphatics and nodes of the lesser omentum. During this course, it receives blood through the coronary vein (CV), which communicates with esophageal venous collaterals, which connect with the gastric vein and the esophageal plexus. Sometimes a separate right gastric vein enters the PV in this area. A superior pancreaticoduodenal vein often enters the PV just above the level of the pancreas, and several smaller veins enter the SMV and PV from the right side beneath the neck of the pancreas. As the PV ascends behind the common bile duct and common hepatic duct, it approaches the hilus of the liver and bifurcates into two branches, a larger right (RPV) and a smaller left portal vein (LPV). The branch on the left courses below the left hepatic duct to enter the umbilical fissure, in company with the left hepatic artery, and subsequently branches to supply the left liver segments (II-IV). Just before its entry into the umbilical fissure, it gives off a major caudate vein, segment I, which runs posteriorly and laterally to the left. Sometimes this vein consists of two or more branches; the right portal branch, which is much shorter in length before its entry into the liver, divides at the extremity of the hilus into the right anterior (RAS) and posterior (RPS) sectoral branches and is accompanied by the respective arterial branches and biliary tributaries. B, The division of the portal vein may arise more proximally, however, and the right anterior and posterior sectoral portal veins may arise independently from the portal venous trunk. C, See also Figs. 1B.8B, 1B.40, and Chapters 90 A through F.

FIGURE 1B.39 Magnetic resonance imaging of the splenoportal confluence: postcontrast, T1-weighted, three-dimensional gradient-echo coronal maximum intensity projection. Shown are the splenic vein (s); portal vein (p); superior mesenteric vein (sm).

The anatomic relationship of the pancreas to the SMV, the splenic vein, and the portal vein (see Fig. 1B.38) is important in pancreaticoduodenectomy (see Chapter 62A, Chapter 62B ). The uncinate process can extend behind the SMV to well behind the SMA (see Fig. 1B.35). Access to the portal vein behind the pancreas usually is obtained from below by elevating the pancreas from the surface of the SMV just before it joins the splenic vein. With the exception of the inferior pancreaticoduodenal veins, which enter the SMV at the inferior border of the pancreas, it is uncommon to see branches from the pancreas run directly posteriorly into the SMV. Fixation here is usually by some inflammatory or neoplastic process. Superiorly, the portal vein runs behind the pancreas and is identified first in the gap between the curvature of the splenic vein, splenic artery, common hepatic artery, and gastroduodenal artery. Division of the gastroduodenal artery provides much greater access to the superior surface of the portal vein. If difficulty is encountered in this area, division of the common bile duct, usually above the cystic duct, can provide excellent access to the right lateral aspect and anterior surface of the portal vein. The SMA can be approached behind the pancreas above the point at which it is embraced by the uncinate process at the origin from the aorta. This allows dissection of the most proximal part of the SMA from behind.

Occasionally, the middle colic artery and other vessels of supply to the colon can arise from the more proximal SMA, such that they pass through the pancreas; this abnormality should be searched for carefully. Division of the middle colic artery is usually not a problem, however, because the colon is well supplied, and ischemia typically does not occur.

Of special importance to the surgeon is the direct relationship of the head of the pancreas to the duodenum and posteriorly to the right renal vein and the anterior surface of the IVC, and of the neck and body of the pancreas posteriorly to the SMA and the splenic vessels and their branches, the left renal vein, and, more laterally, the left kidney. The right gastroepiploic vein commonly drains into the anterior surface of the SMV just at the inferior border of the pancreas; this can often be involved by tumor, as can the anterior branch of the inferior pancreaticoduodenal vein; the middle colic vein may also join at this point. In mobilizing the SMV, these vessels are ligated so as to avoid bothersome hemorrhage. Abnormalities of the IVC are uncommon, with duplication of the vena cava and a left-sided vena cava seen rarely.

Several variations in anatomy and rare congenital anomalies of the portal vein are of surgical significance (Figs. 1B.40 to 1B.43). For example, performance of right hepatic resection, with division of what appears to be the right portal vein in a patient with absence of the left portal vein (Fig 1B.42), can deprive the entire liver of blood; this surgical error is usually fatal. Agenesis of the right branch of the portal vein is associated with agenesis of the right hemiliver and left liver hypertrophy. This may be associated with biliary and hepatic venous anatomic changes, which can compromise surgical approaches to the liver and to biliary repair (Fields et al, 2008).

FIGURE 1B.40 Contrast-enhanced computed tomographic scan of variant portal vein branching with trifurcation pattern. M, main portal vein; L, left portal vein; RA, right anterior portal vein; RP, right posterior portal vein.

(From Covey AM, et al, 2004: Incidence, patterns, and clinical relevance of variant portal vein anatomy. Am J Roentgenol 183:1055-1064.)

FIGURE 1B.41 A, The portal vein anterior to the head of the pancreas and the duodenum may be in an abnormal position. B, Another rare but interesting anomaly is the entrance of the portal vein into the inferior vena cava. C, Very rare, the entrance of a pulmonary vein into the portal vein.

FIGURE 1B.42 In a congenital absence of the left branch of the portal vein as described by Couinaud, the right branch courses through the right lobe of the liver supplying it and curves within the liver substance to supply the left lobe, which in such instances is usually smaller than normal.

FIGURE 1B.43 Computed tomographic scan in a patient with Caroli disease shows a large right portal trunk. The left branch of the portal vein is absent, with findings confirmed at operation for left hepatic lobectomy.

Portal venous blood is derived from the venous drainage of the stomach, small bowel, spleen, and pancreas, and this drainage is important when considering surgery of the pancreas and in patients with portal hypertension; it is described in detail along with the description of the anatomy of the pancreas.

Pancreatic Duct

The duct of Wirsung, beginning in the distal tail as a confluence of small ductules, runs through the body to the head, where it usually passes downward and backward in close juxtaposition to the common bile duct (see Fig. 1B.45). The sphincter of Oddi (Fig. 1B.47) has been thoroughly studied (Boyden, 1957; Delmont, 1979) and consists of a unique cluster of smooth muscle fibers distinguishable from the adjacent smooth muscle of the duodenal wall. The papilla of Vater at the termination of the common bile duct is a small, nipplelike structure that protrudes into the duodenal lumen and is marked by a longitudinal fold of duodenal mucosa. The duct of Wirsung runs downward and parallel to the common bile duct for approximately 2 cm and joins it within the sphincter segment in 70% to 85% of patients; it enters the duodenum independently in 10% to 13% of patients and is replaced by the duct of Santorini in 2% of patients (Fig. 1B.48; see also Fig. 1B.45). Rarely, the duct of Santorini and the duct of Wirsung are separate, which is known as pancreas divisum (see Figs. 1B.45Cii and 1B.48B). The islands or islets of Langerhans, which provide the endocrine component of the gland, are scattered throughout the pancreas.

FIGURE 1B.47 Schematic representation of the sphincter of Oddi: notch (a); biliary sphincter (b); transampullary septum (c); pancreatic sphincter (d); membranous septum of Boyden (e); common sphincter (f); smooth muscle of duodenal wall (g).

FIGURE 1B.48 A, Magnetic resonance imaging (MRI) cholangiography, T2-weighted coronal image at the level of the ampulla, shows the duodenum (D) and the pancreatic head with common bile duct (curved arrow) and pancreatic duct (straight arrow). B, MR cholangiopancreatography (MRCP) shows pancreas divisum. Anterior projection shows variant anatomy with the duct of Santorini (vertical arrow) between the duodenum above the duct of Wirsung (angled arrow). The two ducts are separate; the duct of Santorini drains mainly the neck and body of the pancreas, and the duct of Wirsung drains mainly the uncinate process portion of the head of the pancreas.

Annular Pancreas

Annular pancreas is the development of a ring of pancreatic tissue that surrounds and often embraces the duodenum. This ring may contain a large duct and can be firmly affixed to the duodenal musculature. The duodenum beneath this annulus is often stenosed, such that dividing this ring does not always relieve chronic duodenal obstruction. This accounts for the common process of applying duodenojejunostomy to relieve strictures caused by such an annulus.

Liver and Pancreas

The lymphatic drainage of the liver and gallbladder is mainly to nodes in the hepatoduodenal ligament and along the hepatic artery; this is shown in Fig. 1B.49A. The lymphatic drainage of the pancreas is predominantly to the nodes that lie in juxtaposition to the arteries and veins (see Fig. 1B.50B).

FIGURE 1B.49 A, The liver drains principally to hepatoduodenal nodes at the hilus and along the hepatic artery and portal vein. The gallbladder drains partly to the liver, but it also drains via the cystic node to nodes of the hepatoduodenal ligament and to suprapancreatic nodes. B, Numerous nodes (i) lie along the superior mesenteric vein along the borders of the pancreas, draining back into the splenic hilar nodes; along the superior border of the pancreas to the superior pancreatic nodes; and to the celiac trunk and nodes at the base of the common hepatic artery. A large node commonly lodges in intimate association with the surface of the superior border of the pancreas and the right side of the common hepatic artery. This node often needs to be dissected and elevated to gain access to the anterior surface of the portal vein. Removal of this node often improves access, as does division of the gastroduodenal artery. Posterior pancreaticoduodenal nodes (ii) lie along the posterior pancreatic duodenal arterial arcade. BD, bile duct; HA, hepatic artery; IMV, interior mesenteric vein; PV, portal vein; SA, splenic artery; SMA, superior mesenteric artery; SMV, superior mesenteric vein; SV, splenic vein.

FIGURE 1B.50 Note the distribution of sympathetic and parasympathetic nerves to the liver and pancreas from the celiac ganglion, mainly in association with major arteries.

Lymph Node Metastasis and Carcinoma of the Head of the Pancreas

Most patients who have carcinoma of the head of the pancreas have nodal positivity in the infrapyloric and common hepatic nodes, in the nodes along the splenic artery, or in those in the hepatoduodenal ligament. The most common are posterior pancreaticoduodenal lymph nodes, constituting 50% to 60% of all lymph nodes positive for carcinoma of the head of the pancreas. Other common sites are along the SMA and the paraaortic and anterior pancreaticoduodenal areas. In order of frequency, the anterior and posterior duodenal lymph nodes are most commonly involved.

In carcinoma of the distal bile duct or of the ampulla of Vater, the two most common sites for nodal involvement are the suprapyloric and posterior pancreatic lymph nodes. It is important to maximize staging so that at the time of resection, an adequate dissection of the lymph nodes is performed posterior to the pancreas. This is best done by dissection that begins on the anterior surface of the right renal veins and elevates the tissue in front of the vena cava and the left renal vein across to the aorta. The delivery of this soft tissue is not difficult, and it maximizes the likelihood of identifying nodes that can be expected to be positive.