Hepatic and Portal Venous Anatomy Relative to the Transjugular Intrahepatic Portosystemic Shunt Procedure

Chapter 12: Hepatic and Portal Venous Anatomy Relative to the Transjugular Intrahepatic Portosystemic Shunt Procedure

Nael E. Saad and Kathryn J. Fowler


Portal hypertension (PHT) is a condition that results from portal venous flow obstruction. Transjugular intrahepatic portosystemic shunt (TIPS) is an artificial channel created between the portal venous inflow and the hepatic vein outflow of the liver. This channel acts as a conduit through which the venous flow of the splanchnic circulation can bypass the liver parenchyma in a way that obviates the risk of life-threatening hemorrhage that can result from variceal rupture. TIPS has become the mainstay of management of PHT complications and has supplanted surgical shunt creation.

Many factors affect the success of TIPS. Anatomy plays an essential role in preprocedural planning and ultimate success. The size of the shunt is important for ensuring adequate reduction of portal pressures. Hence, the hepatic vein selected for TIPS must be of a suitable size to allow sufficient functional diameter of the TIPS. In addition to size, distance and angulation of the shunt tract are vital to successful decompression and long-term patency. An appropriate trajectory from hepatic vein to portal vein must be planned for creating a smoothly curved TIPS.1 A thorough understanding of the standard liver, hepatic vein, and portal vein anatomy as well as common anatomic variants is paramount.

Liver Morphology and Anatomy

The liver is the largest solid organ in the body, weighing between 1400 and 1600 g in men and between 1200 and 1400 g in women.2 The liver is located in the right upper quadrant; the upper margin is at the approximate T9 level, and the inferior border extends to the 11th rib (images Fig. 12.1). The size of the liver is subject to great variation, especially in patients with end-stage liver disease. Even in the healthy subjects, there are common variants of Riedel’s lobe (right lobe extends into the right lower quadrant) and high variability of left lobe size (the left border of the liver may be to the right of the spine or extend several centimeters to the left). Common morphologic changes associated with cirrhosis include right lobe atrophy with left lobe or caudate hypertrophy, widening of the preportal space, a small shrunken liver, and displacement of the liver from the right abdominal wall caused by large-volume ascites (images Fig. 12.2).

Adjacent organs are at risk for inadvertent needlestick and injury. The liver is bordered inferiorly by the right kidney and hepatic flexure of the colon. The kidney is located within the retroperitoneum separated from the peritoneal cavity and liver surface by an investment of peritoneal fascia. The hepatic flexure may extend anterior and superior to the liver margin, creating the potential for inadvertent injury from needlestick. The gallbladder is located within a fossa along the anterior inferior visceral surface of the liver between the medial left and anterior right hepatic sections. The duodenum and stomach together border the anterior-inferior margin of the left hemiliver.

Liver segmental and sectional anatomy is dictated by portal venous territories for surgical and radiological purposes. On the largest scale, the liver can be divided into right and left hemiliver along a boundary between the gallbladder fossa (interlobar fissure) and right margin of the middle hepatic vein–inferior vena cava (IVC) junction (Cantlie line).3 The right hepatic artery and portal vein supply the right hemiliver, and the left hepatic artery and portal vein supply the left hemiliver. Each hemiliver can be further divided into two sections: right anterior, right posterior, left medial, and left lateral. The right sections are divided by the right hepatic vein and the left section by the falciform ligament/left hepatic vein. Each section is supplied by a corresponding major portal venous branch. The caudate lobe is considered separately from the right and left hemilivers because it is invested by its own fascial covering and has independent portal and hepatic venous flow as well as variable arterial supply from either the right or left hepatic arteries. Furthermore, the liver may be divided into eight separate segments, first described in 1957 by Couinaud4,5 (images Fig. 12.3).

Finally, a closer look at the hepatic parenchyma shows that the portal veins are located within the portal triads accompanied by arterial branches, bile ducts, and lymphatics. The close proximity of the hepatic arteries and bile ducts to the portal veins makes inadvertent sticks common during a TIPS procedure. The portal veins become progressively diminutive within the peripheral parenchyma supplying the inflow to the sinusoidal channels, the capillary network of the liver parenchyma (images Figs. 12.4 and images 12.5).6 On the other side of the sinusoidal channel or network, the blood drains into the terminal hepatic venules. The hepatic veins course independently from other vasculature with these small peripheral tributaries joining to form larger trunks more centrally that eventually drain into the IVC.

Hepatic Venous Anatomy

The hepatic veins constitute the only venous drainage of the liver. The right, middle, and left hepatic veins are the three largest hepatic veins and drain into the anterior surface of the IVC 1 cm below the diaphragm and 2 cm below the inferior border of the right atrium7 (images Fig. 12.6).

Right Hepatic Vein

The right hepatic vein is the largest of the three main veins and drains the entire right hemiliver (segments V, VI, VII, and VIII). The diameter of the right hepatic vein is largest at the confluence with the IVC, measuring approximately 1 cm.8 It can be challenging to differentiate the right from the middle hepatic vein during venography. The insertion of the right hepatic vein on the IVC is lateral and slightly superior to that of the middle hepatic vein. The marginal tributary characteristically helps identify the right hepatic vein as it arcs through the superior aspect of the right hemiliver to join the right hepatic vein centrally (images Fig. 12.7).


Fig. 12.4 Schematic diagram showing the microvascular bed of the liver parenchyma. The liver is histologically divided into lobules (see images Fig. 12.5). The sinusoidal inflow is an admixture of “nutritive” blood from both the hepatic artery and the portal vein.

Middle Hepatic Vein

The middle hepatic vein commonly drains segment IV (left medial section) and often receives blood supply from the anterior right hepatic section (segments V and VIII). The middle hepatic vein ostium on the IVC is caudal to the right hepatic vein and located along the left anterior aspect of the IVC. The common trunk formed by the middle and left hepatic vein measures approximately 1 cm in length.8 The middle hepatic vein may be a suitable alternative to the right hepatic vein for TIPS.

Left Hepatic Vein

The left hepatic vein is a short trunk formed by the union of drainage veins from segments II and III (left lateral section). The left hepatic vein often forms a common trunk with the middle hepatic vein before draining to the IVC.8 The size of the left hepatic vein is variable because of the variability in size of the left hemiliver. It is least commonly used for TIPS.

Variant Anatomy

In addition to the three main veins, numerous other smaller veins drain the inferior portion of the right lobe and the caudate. Variations are encountered in up to 30% of patients.7,911 Supranumerary left hepatic veins are frequently present. An accessory inferior right hepatic vein is also frequently seen and is the largest accessory vein, potentially providing the dominant drainage of the right hemiliver. An accessory right inferior hepatic vein usually drains the inferior portion of the posterior right hepatic section via a sizable trunk connecting to the midportion of the retrohepatic IVC.4 Additional common variants include multiple accessory right hepatic veins, absent right hepatic vein, a separate umbilical segment vein, and the accessory segment VIII branch draining into the middle hepatic vein. Helpful tips for differentiating the right from the middle hepatic vein during venography include the following:

• The right hepatic vein ostium is lateral and slightly superior.

• The marginal tributary arcs superior to join the right hepatic vein.

• The right hepatic vein is more horizontal in course (lateral projection may help).

• There may be an inflow artifact along the left lateral aspect of the middle hepatic vein from left vein drainage.

• A wedged hepatic venogram through the right hepatic vein will opacify the right portal vein first, but through the middle hepatic vein, the left and right portal veins opacify simultaneously.

In the setting of parenchymal fibrosis, there may be attenuation or “pruning” of the hepatic veins. In addition, hepatic vein-to-hepatic vein collaterals may become prominent. As fibrosis progresses, the size of the central hepatic veins may decrease, and the shrunken liver morphology and presence of ascites may alter the relationship of the hepatic veins with the IVC. An acute angle between the IVC and hepatic veins may make catheterization from a transjugular approach very difficult. Paracentesis and removal of large-volume ascites can improve this angle and facilitate cannulation for TIPS.

In Budd-Chiari syndrome, impedance of venous outflow may occur at the level of the small hepatic venules, the larger hepatic veins, or the IVC.9,1215 Thrombosis and obliteration at the level of the main hepatic veins is most common. Long-standing obstruction results in collateral pathways and development of the so-called spider-web appearance16 (images Fig. 12.8). The caudate venous drainage is often spared, and venous collateralization and drainage of the entire liver may occur through the caudate lobe veins. As a result of venous outflow obstruction, the liver becomes enlarged, and compression of the intrahepatic IVC is typically present (images Fig. 12.9). When Budd-Chiari syndrome is caused by suprahepatic IVC obstruction, the hepatic veins are engorged and enlarged with many veno-venous collaterals present (images Fig. 12.10). Further discussion of TIPS creation in the difficult setting of Budd-Chiari syndrome is provided in Chapter 17.

Portal Venous Anatomy

The main blood supply to the normal liver is the portal vein. The portal venous inflow is formed by four major contributors: the splenic vein, superior mesenteric vein (SMV), inferior mesenteric vein (IMV), and coronary vein.7,9 images Figures 12.11 and images 12.12 demonstrate normal portal venous anatomy. The splenic vein drains the spleen and greater curvature of the stomach, the SMV drains the small bowel and right and transverse colon, the IMV drains the left and rectosigmoid colon, and the coronary vein drains the distal esophagus and lesser curvature of the stomach. The portal vein is formed posterior to the neck of the pancreas, passing behind the duodenum and along the free edge of the lesser omentum to the porta hepatis. The main portal vein is located at the approximate T11 to L1 vertebral level in healthy patients.17,18 The main portal vein is approximately 7 to 8 cm in length and just more than 1 cm in diameter in normal patients.17,19

The main portal vein bifurcates into a left and right branch, denoted as the portal bifurcation. The portal bifurcation may be extrahepatic in about half, intrahepatic in about a quarter, and located right at the entrance to the liver in a quarter of patients.2,20 The hepatic artery and common hepatic duct travel alongside the main portal vein in the hepatic hilum. The typical spatial relationship at the porta hepatis is that the portal vein lies posterior to both the bile duct and artery.8,21 This spatial relationship is often maintained within the hepatic parenchyma with the bile duct and artery located anterior to the portal vein within the portal triads.

Oct 29, 2018 | Posted by in CARDIOLOGY | Comments Off on Hepatic and Portal Venous Anatomy Relative to the Transjugular Intrahepatic Portosystemic Shunt Procedure

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