CHAPTER 7
Gallbladder and biliary tract: anatomy and structural anomalies

Theodore H. Welling

NYU Langone Health, New York, USA

Anatomy

The gallbladder lies in a depression along the inferior surface of the liver in a plane dividing the liver into its anatomical right and left lobes. The gallbladder is intimately attached to the liver by loose connective tissue that contains small veins and lymphatic vessels. The rest of the gallbladder, which is not in direct contact with the liver, is covered with peritoneum reflected from the liver and is in contact with the duodenum and hepatic flexure of the colon (Figure 7.1).

The gallbladder is divided into four anatomical areas: fundus, body, infundibulum, and neck. The neck tapers into the cystic duct, which joins the common hepatic duct to become the common bile duct. Although the cystic duct typically joins the common hepatic duct directly, it may join the extrahepatic biliary tract anywhere from the right hepatic duct down to the level of the ampulla (Figures 7.2 and 7.3). The blood supply to the gallbladder and cystic duct is usually from a single artery arising from the right hepatic artery, although variations in this configuration are common (Figure 7.4). The gallbladder is innervated by branches of both the sympathetic and parasympathetic nervous systems (Figure 7.5), which play a role in modulating gallbladder contractility.

The gallbladder has five layers: epithelium, lamina propria, muscularis, perimuscular connective tissue, and serosa. The gallbladder mucosa is lined with columnar epithelial cells that are covered with abundant microvilli and joined by tight junctions.

Bile drains from the liver into the right and left hepatic ducts, which usually join outside the liver to form the common hepatic duct. The cystic duct then joins the common hepatic duct to become the common bile duct. The common bile duct lies anterior to the portal vein and to the right of the hepatic artery. The common bile duct is divided into four segments: supraduodenal, retroduodenal, pancreatic, and intraduodenal. The intraduodenal common bile duct joins the main pancreatic duct to form the ampulla of Vater, which empties into the lumen of the duodenum. The intraduodenal common bile duct and ampulla of Vater are surrounded by a sheath of smooth muscle fibers referred to as the sphincter of Oddi (Figure 7.6). Regulation of bile flow is controlled primarily by the sphincter of Oddi.

Embryology

The biliary tract is first apparent during the fifth week of gestation and develops as a ventral sacculation in the distal foregut (Figure 7.7). This sacculation grows into the ventral mesentery, which divides into two buds: the cranial bud develops into the liver and intrahepatic bile ducts, and the caudal bud develops into the gallbladder and cystic duct (Figure 7.8). Another small bud arises from the inferior aspect of the caudal bud and ultimately develops into the ventral pancreas (Figure 7.9). The ventral pancreatic bud rotates 180° from right to left, fusing with the dorsal pancreatic bud to form the complete pancreas. Because the lower end of the common bile duct is attached to the ventral pancreatic bud, it also rotates and fuses with the duodenum along its posteromedial wall (Figure 7.10). Variations in this developmental process give rise to structural anomalies in the biliary tract (Figure 7.11). In addition, viral etiologies along with host response may result in various forms of atresia (Figure 7.12

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