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Gallbladder and biliary tree
The biliary tree comprises the system of ducts that collect and deliver bile from the liver to the descending (second) part of the duodenum. It is conventionally divided into intrahepatic and extrahepatic biliary trees. The intrahepatic ducts are formed from bile ductules that join to form segmental ducts. These merge to form right and left hepatic ducts close to the porta hepatis. The extrahepatic biliary tree comprises the extrahepatic segments of the right and left hepatic ducts, the common hepatic duct, the cystic duct and gallbladder, and the bile duct ( Fig. 67.1 ).
The overall arrangement of the intrahepatic and extrahepatic biliary tree. The segmental ducts often branch just before they enter the main ducts, or are multiple as they enter the main ducts, but for clarity are shown here as single ducts. Note that segment I often drains via both right and left hepatic ducts. The level of the liver at the porta hepatis is shown by the dashed line.
Gallbladder
The gallbladder is a pear-shaped, blind-ending diverticulum attached to the bile duct by the cystic duct ( Fig. 67.2 ). It stores and concentrates bile. In life it is grey–blue in colour and is usually firmly attached by connective tissue to the inferior surface of the right lobe of the liver, between segments IV and V at the lower limit of the principal plane. In the adult the gallbladder is between 7 and 10 cm long, with a resting volume of about 25 ml and a capacity of up to 50 ml ( ). It usually lies in a shallow fossa (fossa for the gallbladder) on the visceral surface of the right lobe of the liver, covered by peritoneum continued from the surface of the liver. This attachment can vary widely. Rarely, the gallbladder is almost completely buried within the liver (intrahepatic gallbladder; ), or suspended from the liver by a mesentery (when it is at risk of torsion; ), or connected to the duodenum by a variant component of the lesser omentum, the cystoduodenal ligament (which has been found in up to 35% of dissections; ).
An oblique groove on the inferior surface of the liver posterior to the fossa for the gallbladder is present in 70–80% of livers. It is variously known as the fissure of Gans, Rouvière’s sulcus or the incisura hepatis dextra ( Ch. 66 ). It overlies the division of the right posterior (lateral) portal pedicle, where it gives off the inferior segment VI branch. It has been increasingly recognized as a useful anatomical landmark during hepatic resection and in laparoscopic cholecystectomy (since the cystic duct and artery lie anterosuperior to the sulcus while the bile duct lies posteroinferior) ( ).
The gallbladder is described as having a fundus, body, infundibulum and neck. The neck lies at the medial end, close to the porta hepatis, and almost always has a short peritoneal attachment (see above) (mesentery) to the liver, which usually contains the cystic artery. The mucosa at the medial end of the neck is obliquely ridged, forming a crescentic fold that is continuous with the spirally arranged mucosal folds in the cystic duct ( ). The neck usually lies anterior to the descending part of the duodenum. The body of the gallbladder normally lies in contact with the visceral surface of the liver. The body lies anterior to the descending part of the duodenum and the proximal end of the transverse colon. The bulbous fundus lies at the lateral end of the body and usually projects past the inferior border of the liver to a variable extent. Here it frequently lies in contact with the anterior abdominal wall deep to the ninth costal cartilage, where the lateral edge of the right rectus abdominis crosses the costal arch. This is where enlargement of the gallbladder is best sought on clinical examination. The fundus commonly lies adjacent to the transverse colon. The infundibulum is a tapered and sometimes angulated part of the gallbladder between the body and neck of the gallbladder.
The gallbladder varies in size and shape. The fundus can be elongated and highly mobile. Rarely it is folded back on the body of the gallbladder, the so-called Phrygian cap; on ultrasound, this can be wrongly interpreted as an apparent septum within an otherwise normal gallbladder. Other anatomical variants of the gallbladder include duplication, with or without a double cystic duct; agenesis; internal septation; and an ectopic location (most commonly left-sided) ( , , ). Although rare, these congenital anatomical variations are particularly important if the patient requires surgery for gallbladder or gallstone disease ( , , , ).
Hartmann’s pouch
A pouch-like structure (Hartmann’s pouch) may occasionally project from the neck of the gallbladder at its junction with the body of the gallbladder ( , ). It is thought to be produced by adhesions between the neck of the gallbladder and the cystic duct: once these adhesions are separated and the cystic duct is mobilized, Hartmann’s pouch disappears. A significant association between the presence of a Hartmann’s pouch and gallstones has been reported, but the aetiology is unclear ( , ).
Intrahepatic Biliary Tree
Segmental and sectoral ducts
The segmental ducts of the left part of the liver have a relatively constant pattern, although more than one segmental duct can drain each particular segment. The left hepatic duct is formed by the union of segments II and III ducts, most often deep to or to the left of the umbilical part of the left branch of the hepatic portal vein (see Fig. 67.1 ). The biliary drainage of segment IV is more variable but is usually by a single duct into the left hepatic duct. The right hepatic duct is formed by the union of the right anterior (medial) and posterior (lateral) sectoral ducts. The right anterior (medial) sectoral bile duct drains segments V and VIII, and the right posterior (lateral) sectoral duct drains segments VI and VII. The right posterior sectoral duct usually curves around the posterior aspect of the right anterior duct before fusing with its medial aspect; this is known as Hjortsjö’s crook and is an important technical consideration when the liver is resected ( Fig. 67.3 ). The right posterior sectoral duct (and associated blood vessels) is frequently located in Rouvière’s sulcus (see below), which is a reasonably constant cleft 2–3 cm in length on the liver surface to the right of the porta hepatis anterior to the caudate lobe. An average of three small ducts drain the caudate lobe (segment I) at the hilar plate; the right-sided duct usually drains to the right hepatic duct or the posterior sectoral branch whereas the left-sided duct frequently crosses over to drain into the right posterior sectoral duct ( ). FLOAT NOT FOUND
The right hepatic duct and its branches are more often subject to variation than the left ductal system ( , ). These variations have been classified into seven main types ( Table 67.1 , Fig. 67.4 ) ( ), although additional very rare variants have also been described ( , Stringer 2016). Left intrahepatic ductal variations mostly relate to the drainage pattern of segment IV; this segmental bile duct usually drains into the left hepatic duct but in some cases it opens into a segment II or III bile duct, the right anterior sectoral duct, or even the common hepatic duct ( ).
TABLE 67.1
Major variations of the intrahepatic duct drainage patterns
Data from , , , .
| Type | Approximate % of population | Description |
|---|---|---|
| 1 | 60 ∗ | ‘Normal’ anatomy |
| 2 | 10–15 | No right hepatic duct. The common hepatic duct is formed by the union of right anterior sectoral, right posterior sectoral and left hepatic ducts (trifurcation pattern) |
| 3 | 10–15 | One of the right sectoral ducts (more often the posterior) joins the left hepatic duct |
| 4 | 5–10 | Low drainage of one of the right sectoral ducts (more often the posterior) into the common hepatic duct |
| Rare | <10 | The segment V duct or the right posterior sectoral duct drains into the cystic duct or gallbladder |
∗ This figure is higher in males and lower in females, who are more likely to have variant intrahepatic bile duct anatomy. NB The percentages of different types vary among populations.
A small, rare bile duct known as a subvesical duct from segment V of the liver can traverse the fossa for the gallbladder and join the right hepatic duct or its anterior sectoral branch or the common hepatic duct ( ). This duct is important because it can be injured during cholecystectomy, causing a postoperative bile leak ( ). These ducts are more likely to be injured if the gallbladder is not dissected close to its wall. A subvesical duct may also drain directly into the gallbladder (cholecystohepatic duct) or cystic duct (cystohepatic duct) and should not be confused with a hepatocystic duct (which is present when the bile duct is absent and both hepatic ducts drain directly into the gallbladder, which in turn drains via the cystic duct into the duodenum) ( ) ( Figs 67.5 - 67.7 ).
Extrahepatic Biliary Tree
Cystic duct
The cystic duct drains the gallbladder into the bile duct. In adults it is usually 2–4 cm long and has a luminal diameter of 2–3 mm ( ). Occasionally it is very short, which makes its division during cholecystectomy potentially hazardous. It passes posteriorly and medially from the neck of the gallbladder, often in a tortuous fashion, to unite with the common hepatic duct and form the bile duct. The anatomy of the junction between the cystic duct and common hepatic duct is variable (see Fig. 67.4 ). In most individuals the cystic duct joins the middle third of the combined lengths of the common hepatic and bile ducts ( ), but it can also drain into the distal bile duct (‘low insertion’) or into a more proximal duct such as the proximal common hepatic duct or right hepatic duct. It usually joins the right lateral aspect of the common hepatic duct but can merge medially, anteriorly or posteriorly; and it usually forms an oblique angle with the common hepatic duct but can spiral around it or run parallel to it in the hepatoduodenal ligament for a variable distance before merging ( , , Stringer 2016) ( Fig. 67.8 ). Irrespective of the site or type of union, the terminal part of the cystic duct is frequently fused to the common hepatic duct for a variable distance.
Rarely, the cystic duct is double or absent (when the gallbladder drains directly into the bile duct), or receives an anomalous hepatic duct from segment V of the liver. These variations in cystic duct anatomy are of considerable importance during surgical excision of the gallbladder (cholecystectomy). The cystic duct must be identified passing to the neck of the gallbladder and must be occluded some distance away from the bile duct to prevent injury to the latter ( Fig. 67.8 ). A preliminary operative cholangiogram is essential if the anatomy is unclear or anomalous.
The mucosa of the cystic duct has 2–10 crescentic folds that project into the lumen and form a spiral; these are continuous with those in the neck of the gallbladder. The function of these spiral folds (of Heister) is unknown but they could help to preserve the patency of this narrow, tortuous duct rather than regulate the flow of bile, as is commonly stated ( ).
Hepatic ducts
The right and left hepatic ducts emerge from the liver and unite near the right end of the porta hepatis to form the common hepatic duct. The extrahepatic segment of the right hepatic duct is short (0.5–2.0 cm in adults) and nearly vertical, while the left hepatic duct is longer (1.5–3.5 cm) and more horizontal, and lies along the inferior border of segment IV of the liver. The accessibility of the extrahepatic segment of the left hepatic duct is exploited when performing a surgical biliary bypass in patients with benign extrahepatic biliary duct strictures ( ).
In adults, the common hepatic duct descends approximately 3 cm before being joined obliquely on its right by the cystic duct to form the bile duct. The common hepatic duct lies to the right of the hepatic artery and anterior to the hepatic portal vein in the hepatoduodenal ligament. In healthy adults the luminal diameter of the common hepatic duct, as measured by ultrasound, is less than 5 mm.
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