JULIAN BRITTON, KENNETH I. BICKERSTAFF, AND ADRIAN SAVAGE

 

 

INTRODUCTION

Benign diseases of the biliary tract are one of the most common surgical problems in the world. Gallstones affect millions of people in the West, while oriental cholangitis is common in the East. Surgery plays an important part in treatment: over half a million cholecystectomies are performed each year in the United States of America. New percutaneous techniques avoid the need for a conventional abdominal incision; they are playing an increasing role in treatment but a thorough understanding of the basic anatomy, physiology, and pathology of the biliary tract is required. Footnote 5

 

ANATOMY

Development

The liver and the biliary tract are derived from the foregut. The liver first appears in the 3-week embryo as a hollow endodermal bud from the distal foregut. This bud, the hepatic diverticulum, consists of rapidly proliferating cells that penetrate into the ventral mesogastrium. These cells eventually develop into the liver; the connection between the hepatic diverticulum and the foregut is preserved to form the bile duct. A ventral outgrowth of the bile duct gives rise to the gallbladder and the cystic duct. As the intestine rotates the entrance from the bile duct into the duodenum moves to a posterior position and the common bile duct comes to lie behind the duodenum and pancreas.

 

Within the developing liver the bile ducts are distributed in a segmental fashion. Bile is secreted by the liver cells into bile canaliculi. The canaliculi drain into ductules and on into larger segmental bile ducts which are tributaries of either the left or the right hepatic ducts. The left hepatic duct drains segments II, III, and IV; segments V, VI, VII, and VIII drain into the right hepatic duct. The caudate lobe (segment I) lies astride the inferior vena cava posteriorly and drains into both the right and the left hepatic ducts. This segmental anatomy of the liver and its ducts is important in liver and biliary tract surgery (Fig. 1) 1224 and is discussed in more detail in Section 22.1.

 

Extrahepatic bile ducts

The right and left hepatic ducts join to form the common hepatic duct at the hilum of the liver. The confluence usually lies outside the liver itself and in front of the right portal vein. The left hepatic duct has a relatively long extrahepatic course on the posterior aspect of the quadrate lobe (segment IV) where it is accessible to the surgeon, whereas the right hepatic duct enters liver tissue almost immediately. In fact this normal arrangement only occurs in 60 per cent of individuals. There are a large number of anatomical variants. The most common (20 per cent) is for one of the main tributaries of the right duct, usually the right anterior duct, to enter the common hepatic duct directly (Fig. 2) 1225. In 12 per cent of individuals there is a triple confluence formed by the right posterior, right anterior, and left hepatic ducts. One important variation is the presence of an anomalous subvesical duct, the duct of Luschka, which runs in the gallbladder fossa. It is found in 12 to 50 per cent of individuals, drains a variable portion of the right liver and is potentially vulnerable during a cholecystectomy.

 

The main bile duct runs from the confluence of the hepatic ducts to the papilla of Vater (Fig. 3) 1226. It is normally 10 to 12 cm in length and about 6 mm in diameter in anatomical specimens. In life, the upper limit of normal diameter on ultrasound is 7 mm. On direct cholangiography, when the duct is deliberately distended, it is up to 12 mm. The entrance of the cystic duct divides the bile duct into the common hepatic duct above the entrance and the common bile duct below. The supraduodenal portion of the bile duct lies in the free edge of the lesser omentum, anterior to the portal vein and to the right of the hepatic artery. The right hepatic artery normally crosses the common hepatic duct posteriorly, but occasionally it lies in front of the duct. Inferiorly the bile duct curves laterally away from the portal vein and passes behind the first part of the duodenum. It then runs across the posterior part of the head of the pancreas, either in a groove or in a tunnel within the gland. As the bile duct traverses obliquely through the wall of the duodenum it is joined by the main pancreatic duct of Wirsung. The exact arrangement of this junction is variable. Normally both ducts unite to form a common channel of variable length and enter the bowel through the papilla of Vater on the posteromedial wall of the second part of the duodenum. In about 10 per cent of individuals there is no common channel and each duct enters separately. There are very few muscle fibres in the wall of the bile duct, but the proximal bile and pancreatic ducts and the common channel are surrounded by circular and longitudinal smooth muscle. This muscle complex is known as the sphincter of Oddi and the muscle fibres are structurally, embryologically, and functionally distinct from the musculature of the duodenum (Fig. 4) 1227.

 

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