363-379 Embryology, Anatomy, And Surgical Applications of the Extrahepatic Biliary System(Autosaved)
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SURGICAL ANATOMY AND EMBRYOLOGY 0039-6109/00 $8.00 + .OO
EMBRYOLOGY, ANATOMY, AND SURGICAL APPLICATIONS OF THE EXTRAHEPATIC BILIARY
Robert Benton Adkins, Jr, MD, William C. Chapman, MD, and V. Sreenath Reddy, MD
EMBRYOLOGY OF THE GALLBLADDER AND BILIARY SYSTEM
At the fourth week of embryologic development, a diverticulum develops on the ventral surface of the foregut just cephalad to the yolk sac and just caudad to the fusiform dilation that is the gastric precursor (Fig. 1). This ventral diverticulum grows more ventrally into the septum transversum. Two buds of solid epithelial cells develop at its tip and create the right and left lobes of the liver by developing into hepatic cylinders and forming a meshlike network with rich vascular channels? The early developing liver is like a vascular sponge attached to the duodenum by the original hepatic diverticulum, which soon becomes the bile duct system. The bile duct system starts out as a solid out- growth, from which another bud arises to become the cystic duct and gallblad- der. As the distal portion of the bile duct branches into right and left limbs and enters the developing right and left lobes of the liver, it vacuolates and then canalizes and forms into one continuous epithelial-lined lumen. The same type of canalization occurs in the cystic duct and finally in the gallbladder at about 3 months gestation. The right and left ducts, which also begin as solid outgrowths from the original diverticulum, likewise canalize and drain the liver of its bile.3 A migration across the right face of the foregut brings the origin of the bile duct toward the dorsal mesentery of the second portion of the duodenum, where it is joined with the ventral pancreatic duct, another bud from the proximal portion
From the Departments of Surgery (RBA, WCC, VSR) and Cell Biology (RBA) and Divisions of Hepatobiliary Surgery and Liver Transplantation (WCC) and General Surgery (VSR), Vanderbilt University Medical Center, Nashville, Tennessee
SURGICAL CLINICS OF NORTH AMERICA
VOLUME 80 - NUMBER 1 FEBRUARY 2000 363
Common duct- C
Figure 1. Development of the gallbladder, pancreas, and biliary tract. A, At 5 weeks (6 mm). 6, Sixth week (8 mm). C, At the end of the sixth week (12 mm). D, At the end of the seventh week (16 mm). , At birth. Note right to left migration of the common bile duct and the ventral pancreatic primordium. (From Brainerd Avery L: The digestive tube and associ- ated glands. Arey LB: Developmental Anatomy, ed 7. Philadelphia, WB Saunders, 1965, p 260; with permission.)
THE EXTRAHEPATIC BILIARY SYSTEM 365
of the hepatic diverticulum. After its migration, the entrance of the bile duct passes through the sphincter of Oddi and finally by the ampulla of Vater, where it empties into the second part of the duodenum of the fully developed embryo (Fig. 1) .12
This simplified story represents a remarkable series of complicated events. Mishaps of development occasionally occur. That all people do not have some type of biliary tract defect of embryologic origin seems impossible. The complete developmental history of the biliary system is beautifully told in the second edition of Embryology for Surgeons by Skandalakis et a1.I2
COMMON DEVELOPMENTAL ANOMALIES
Common anomalies of the biliary system and gallbladder include variations of number and location of the gallbladder. Ductal and arterial anomalies must also be considered by surgeons in all biliary tract procedures.
Multiple gallbladders may have separate cystic ducts, or two or more may share one cystic duct. These extra gallbladders may lie beneath the right or left lobe of the liver or within the liver or gastrohepatic ligament. They may arise from the common bile duct (CBD), hepatic duct, or right or left hepatic duct (Fig. 2). In some cases, a separate duct from the liver enters the gallbladder, cystic duct, or junction of the cystic duct and CBD. These ducts have become known as Luschkas ducts. In the era of laparoscopy, these extra ducts should be treated by ligation, suture, clipping, cauterization, or exclusion when they are recognized.
The gallbladder may be absent if a separate bud failed to develop from the hepatic diverticulum or when failure of vacuolization and canalization of the gallbladder occurred at its solid embryonic stage at approximately 2 or 3 months gestation.
SURGICAL IMPLICATIONS OF THE VARIATIONS IN THE VASCULAR SUPPLY OF THE EXTRAHEPATIC BILIARY SYSTEM
The usual arterial supply of the gallbladder and the extrahepatic biliary tree is from branches of the celiac trunk. This trunk gives rise to the hepatic artery and one of its branches, the gastroduodenal artery. The hepatic artery further branches into the right gastric and right and left hepatic arteries. The gastroduo- denal artery has anterior and posterior pancreaticoduodenal arteries.
The gallbladder receives its primary blood supply from the cystic artery. It is usually a branch of the right hepatic artery or of the gastroduodenal artery. The cystic artery is usually anterior to the CBD and superior to the cystic duct. It is sometimes a paired artery. It may be immediately adjacent to the cystic
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A 1 2 3
B 1 2 c 1
D 1 2
Figure 2. Main variations in gallbladder and cystic duct anatomy: bilobed gallbladder (A), septum of the gallbladder (B), diverticulum of the gallbladder (C), and variations in cystic ductal anatomy (0). (From Smadja C, Blumgart LH: The biliary tract and the anatomy of biliary exposure. In Blumgart LH (ed): Surgery of the Liver and. Biliary Tract, ed 2. London, Churchill Livingstone, 1994, p 19; with permission.)
duct. Paired cystic veins course along either side of the artery, and they usually empty into the right portal vein.
The extrahepatic portion of the biliary ductal system has multiple sources of blood supply. The arteries supplying the ductal system, in their descending order of participation, are: posterosuperior pancreaticoduodenal (PSPD), right hepatic, posteroinferior pancreaticoduodenal, right gastric, hepatic, anteroinfer-
THE EXTRAHEPATIC BILIARY SYSTEM 367
ior pancreaticoduodenal, cystic, and superior pancreaticoduodenal arteries (Fig. 3) .
Numerous variations and anomalies of the arterial supply to the gallbladder and extrahepatic biliary tree occur. These anomalies can represent significant challenges to surgeons. The hepatic artery can have an accessory right hepatic artery from the superior mesenteric artery. An abnormal course for the hepatic artery occurs when it crosses anterior to the hepatic duct or when the right branch is located anterior to the right hepatic duct. One should be aware of possible venous varicosities or aneurysmal dilations of the right hepatic artery, either of which may occur in Calots triangle.
In some cases, an accessory cystic artery arises from the main hepatic artery or from the right hepatic artery. During open cholecystectomy or laparoscopic cholecystectomy, incomplete visualization before dissection of the cystic artery can inadvertently lead to damage of these other major vessels. The course and location relative to other structures of the cystic artery can be highly variable (Fig. 4). The cystic artery can be found between the hepatic ducts or even behind the common hepatic duct.
In 95% of cases, the cystic artery arises from the right hepatic artery and runs parallel and medial to the cystic duct. If the cystic artery arises more proximally, it arises from the common hepatic artery (in 33% of cases) or, rarely, from the celiac trunk.14 In these instances, the artery runs more parallel to the CBD. This abnormality poses obvious problems to surgeons, who must clearly identify this vessel in preparation for and during cholecystectomy.
At or near the region of the neck of the gallbladder, the cystic artery divides into anterior and posterior divisions. Double cystic arteries exist in 8% to 15%
Figure 3. The bile duct blood supply. Note the axial arrangement of the vasculature of the supraduodenal portion of the main bile duct and the rich network enclosing the right and left hepatic ducts: right branch of the hepatic artery (a), 9-oclock artery (b), retroduodenal artery (c), left branch of the hepatic artery (d), hepatic artery (e), 3-oclock artery (f), common hepatic artery (g), gastroduodenal artery (h). (From Smadja C, Blumgart LH: The biliary tract and the anatomy of biliary exposure. ln Blumgart LH (ed): Surgery of the Liver and Biliary Tract, ed 2. London, Churchill Livingstone, 1994, p 19; with permission.)
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A B C
D E F
Figure 4. 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 (), and cystic artery originating from the gastroduodenal artery (F). (From Smadja C, Blumgart LH: The biliary tract and the anatomy of biliary exposure. In Blumgart LH (ed): Surgery of the Liver and Biliary Tract, ed 2. London, Churchill Livingstone, 1994, p 16; with permission.)
of patients, and a few (0.3%) patients have a triplicate arterial supply to the gallbladder. The third vessel may be of diminutive size. In 12% of patients, accessory cystic arteries are present.I9
For routine cholecystectomy and for procedures involving exploration of the biliary tree