Gallbladder and biliary tree

Gallbladder

A pear-shaped viscus that stores and concentrates bile secreted by the liver
Embryology
- See 'liver'
Gross anatomy
- Usually about 10cm long and 3-5cm wide
- Holds 30-60mL of bile as a reservoir
- Covered by peritoneum, which is continuous with the visceral surface of the liver
- Slate-blue appearance through peritoneum when not inflamed; more greenish when peritoneum is removed
- Repeated attacks of inflammation lead to thickening of the wall and fat deposition, becoming whitish-yellow in appearance
Zones
- Fundus
  - Usually projects just beyond the liver edge anteriorly
  - When the fundus is folded on itself, it is described as a phrygian cap
  - Classically, the fundus is said to lie against the abdominal wall at the point where the outer edge of the rectus sheath crosses the costal margin, but the position is quite variable in truth
- Body
  - Within GB fossa
  - Ascends towards hilum
- Infundibulum/Hartmann pouch
  - Expansion of Hartmann's pouch is probably pathological, with the presence of stones
- Neck
  - The part in between infundibulum and cystic duct
  - Adjacent to porta hepatis
  - Typically has a mesentery to liver containing CA
Relations
- GB fossa - between segments IVb and V
  - Cystic plate intervenes between GB and liver, with no peritoneal covering. It is attached by a layer of loose fibroareolar tissue
  - Ducts of Luschka may traverse this plate (<1mm in size) - can be ligated safely
  - 5% of patients have large bile ducts deep to cystic plate, which can cause bile leakage - beware of ligating, which can compromise a draining duct
- Hepatocystic triangle
  - Borders: CHD to left, margin of right lobe of liver superiorly, and proximal GB/cystic duct to right (larger than original Calot's triangle)
  - The size and shape of the triangle changes quite a lot depending on direction of retraction
  - Contents: lymphatics (Calot node), autonomic nerves, connective tissue, CA, occasionally an accessory bile duct
  - Don't use 'Calot's triangle' - it's imprecise, because it relies on the location of cystic artery
- Critical view of safety:
  1. Complete clearance of the hepatocystic triangle of fat and fibrous tissue
  2. Identification of only two structures connected to GB (CA and CD)
  3. Elevation of one-third of the base of GB off the cystic plate
- Rouvier's sulcus (fissure of Gans) - just posterior and inferior to GB
  - To the right of the hilum
  - Present in 70-80% of livers
  - Overlies the point at which the right posterior pedicle gives off the inferior segment 6 branch
  - CD and CA course anterosuperiorly to sulcus, whereas CBD is posteroinferior
Lymphatic drainage
- Usually a prominent lymph node overlying the anterior branch of the cystic artery near its insertion onto the GB - cystic node/Calot's node
- Most lymph flows into a chain on hepatoduodenal ligament between CBD and PV, which joins with pancreaticoduodenal nodes and drains to aortic nodes
- Other group into coeliac nodes via a chain between hepatic artery and PV
- Lymphadenectomy for GB cancer should involve skeletonisation of the hepatic vessels, CBD and PV, as well as removing nodes along the upper border of the duodenum
- Sometimes lymphatics can also traverse segments IV or V, which is why some surgeons advocate for their removal with GB cancer
Relevant structures
- Cystic duct
  - Usually 2-4cm, entering CHD under a layer of soft tissue surrounding porta hepatis
  - 2-10 crescenteric folds - creates an internal spiral - 'folds/valves of Heister' which are mucosal duplications, and regulate the filling and emptying of the GB
  - Three major variations:
    - Angular (75%)
    - Parallel with more distal entry (20%) - risk of injury, risk of Mirizzi if a large stone gets stuck here
    - Spiral (either anteriorly or posteriorly to CHD, and enter left side) (5%)
  - Joins RHD/RPSD in 2% - particularly at risk in cholecystectomy
- Blood supply - cystic artery
  - Usually (70%) arises from RHA, in hepatocystic triangle, before coursing onto left surface of GB
  - Usually divides into an anterior and posterior branch
  - 2-3% don't really have a cystic artery, because it divides early into small branches
- Venous drainage
  - Multiple small veins in the gallbladder bed
- Innervation
  - Sympathetic - coeliac ganglion (T7-9) which inhibits contraction
  - PNS - hepatic branch of anterior vagal trunk, which stimulates contraction of the GB and relaxation of the ampullary sphincter
  - Hormonal control (CCK from enteroendocrine cells of the upper small intestine) is more important than neural
  - Afferent pain fibres run with right-sided sympathetic fibres (T7-9), but some runs with right phrenic nerve
Variant anatomy:
- Ductal:
  - Double or absent cystic duct
  - Cystic duct receiving anomalous hepatic duct from segment 5
- Arterial supply from:
  - RHA 70%
    - Caterpillar hump 10% - passes close to GB, can be mistaken for cystic artery in Calot's
  - CHA 10%
  - LHA 10%
  - Aberrant RHA from SMA - 5-10% - RHA passes through Calot's posteriorly and parallel to the cystic duct and can be mistaken for a posterior branch of cystic artery
  - GDA <2.5%
- Gallbladder/cystic duct anatomy (variations in GB itself are less common):
  - Morphology
    - Phrygian cap - fundus folded on itself
    - Internal septations
    - Completely invested in peritoneum with a mesentery
  - Number
    - Rarely agenesis
    - Duplication/triplication
  - Ectopic
    - Left-sided 0.2%
    - Intra-hepatic

Extrahepatic biliary tree

Consists of three hepatic ducts (right, left, common), the gallbladder, the cystic duct and the bile duct
Hepatoduodenal ligament
- Located within lesser omentum
- Lateral boundary forms the anterior boundary of the epiploic foramen
- Runs between liver and duodenum
- Contains HA, PV and CBD (HA to left, CBD to right, PV posterior)
- Pringle manoeuvre: isolation and compression of the hepatoduodenal ligament (see separate topic)
Common hepatic duct
- Formed by the uniting of two major hepatic ducts, usually within 2cm of the exit of the right hepatic duct from liver parenchyma
- ~4cm long, 4mm diameter
- Lies in the free edge of the lesser omentum, in front of PV and to the right of HA
- RHA usually passes behind the CHD
- Note usual variations (Couinead classification), but primarily affecting right duct
CBD
- Right and left hepatic ducts leave the liver and unite to form common hepatic duct, and then becomes CBD from the point where cystic duct enters
  - Right duct is typically shorter and more vertically oriented
  - Can see a few subsegmental branches from segment IV going into LHD
- CBD is usually 10-15cm in length and 6-9mm in diameter (Last says 12cm long, 8mm wide)
  - Variation in length is due to variability in cystic duct entry
  - Increasing diameter with older age. Dogma states that the diameter also increases after cholecystectomy, but evidence is lacking.
- Three portions:
  - Supra-duodenal - free edge of lesser omentum, most accessible
  - Retro-duodenal - behind D1, sloping to the right away from PV
  - Pancreatic - slopes further to the right in the palpable groove between HoP and D2, in front of renal vein and to the right of GDA

Intra-pancreatic distal CBD joins with the main pancreatic duct (of Wirsung) 1.5-2cm proximal to the ampulla of Vater, with or without a common channel, then enters D2 through the major papilla of Vater
- Occasionally, the two ducts open separately into the ampulla
At the choledochoduodenal junction, the sphincter of Oddi regulates bile flow and prevents reflux
- Main parts:
  - Sphincter choledochus - circular muscle that regulates bile flow and GB filling
  - Pancreatic sphincter, present to variable degrees, which surrounds the intra-duodenal pancreatic duct
  - Sphincter ampullae, made up of longitudinal muscle, preventing duodenal reflux
- Opening is medially-placed, mostly posterior on the wall of the duodenum at about the junction of the upper two-thirds and lower third of D2
- Keep the sphincterotomy incision in the superior part of ampulla to avoid damaging pancreatic duct, and do not extend >1.5cm proximal to the orifice, since an anterior branch of pancreaticoduodenal artery crosses the duct here

Arterial supply
- Typically has a network of vessels at 3 o'clock and 9 o'clock
- Choledochotomy should be performed longitudinally to minimise risk of hitting these vessels
- Some authors state that major supply is from below, so it is prudent to divide as high possible
- Superior blood supply - quite variable - from RHA and cystic artery. RHA typically passes posterior to CHD to supply the right lobe of liver, entering the hepatocystic triangle, then giving off the cystic artery
- Inferior blood supply - retro-duodenal and pancreatic sections are not as well vascularised - prone to ischaemic strictures. Supplied by branches of the posterosuperior pancreaticoduodenal and gastroduodenal arteries.
- Note - posterior branch of superior pancreaticoduodenal artery courses anteriorly to CBD at the superior border of the pancreas, prior to twisting around the right side of CBD, and travelling to posterior surface of head of pancreas. This branch can be damaged during dissection of duct.
Venous drainage
- Parallels arterial supply, then into portal vein
Innervation
- From the coeliac plexus along hepatic artery, with both SNS and PNS contributions
- Efferent - SNS/PNS
- Afferent - SNS
- Fibres from right phrenic nerve may enter the plexus, which may explain the shoulder-tip pain from GB pathology
Lymphatic drainage
- All eventually back to coeliac axis
- Upper ducts drain into porta hepatis nodes
- Lower parts drain into nodes along the hepatic artery, and also along the superior pancreaticoduodenal nodes behind the pancreas into the retroduodenal nodes
See 'Strasberg classification' of CBD injury, under 'Cholecystectomy' topic

Microscopic anatomy

Gallbladder
- Wall composed of fibromuscular tissue with non-striated muscle cells arranged in circular, oblique and longitudinal fashion
- Layers
  - Mucosa - single layer cuboidal epithelium
  - Lamina propria (no submucosa or muscularis mucosae)
  - Muscularis externa - thin but strong fibromuscular layer
  - Serosa - derives from peritoneum, completely invests the fundus but covers the body and neck only on the opposite side to liver
Bile duct
- Walls are composed of fibro-areolar tissue and contain no muscle within their walls apart from the occasional myocytic cell
- Lined by columnar epithelium which contains mucus-secreting glands

Physiology

Gallbladder
- Serves as an extra-hepatic bile storage
  - Back-fills from CBD when there is increased sphincter of Oddi tone
  - Capable of storing up to 300mL of daily bile production
- Absorbs water and concentrates bile in an osmotic process via active sodium transport
- Bile concentration leads to increased cholesterol and composition, which leads to decreased stability of phospholipid cholesterol vesicles, which allows nucleation of stagnant cholesterol particles, and hence stone formation
- CCK (and to a lesser extent, vagal activity) induces GB contraction and secretion, and relaxes the sphincter of Oddi