106. Embryology & Anatomy of GB [SKF]

Anatomy, Embryology, Anomalies, and Physiology of the Biliary Tract

Introduction

• Cholelithiasis:
  • Affects 10–15% of the adult population.
  • Corresponds to 20–25 million Americans.
  • Laparoscopic cholecystectomy is the most common surgery in the U.S.
• Importance:
  • Understanding the anatomy, embryology, and anomalies of the biliary tract is crucial for surgeons.
  • Enhances decision-making in biliary surgery.

Anatomy and Embryology

Embryonic Development

• 4th Week of Development:
  • A projection appears in the ventral wall of the primitive midgut at the level of the primitive duodenum.
  • At the 3-mm stage, three buds are recognized:
    • Cranial Bud:
      • Develops into the two lobes of the liver.
    • Caudal Bud:
      • Becomes the gallbladder and extrahepatic biliary tree.
      • Forms the cystic diverticulum by day 26, leading to the cystic duct (CD) and gallbladder.
      • Also develops into the ventral pancreas (head and uncinate process).
    • Third Primitive Bud:
      • Originates from the dorsal surface of the midgut.
      • Forms the dorsal pancreas (neck, body, tail).
• 5-mm Stage:
  • Appearance of the primitive gallbladder and common bile duct (CBD).
• 7-mm Stage:
  • Formation of liver, hepatic ducts, gallbladder, CD, and ventral pancreas.
  • Stomach begins to form.
  • Ventral pancreas develops from the dorsal mesogastrium.
• 12-mm Stage:
  • Ventral pancreatic bud rotates 180 degrees clockwise around the duodenum.
  • Fusion of ventral and dorsal buds forms the complete pancreas (6th–7th week of gestation).
  • Annular pancreas:
    • Occurs if rotation is abnormal, leading to a ring around the duodenum.
  • Ductal Systems:
    • Ventral and dorsal ducts interconnect.
    • Dorsal duct usually degenerates, leaving the ventral pancreatic duct as the main duct.

• By 12th Week of Fetal Life:

  • Liver secretes bile.
  • Pancreas secretes fluid into the duodenum via the biliary tree.

  

Intrahepatic Ducts

• Liver Segmentation:

  • Determined by branching of the portal vein, hepatic artery, and biliary tree at the hilum.

  • Couinaud Classification:

    • Segment I: Caudate lobe.
    • Segments II–IV: Left lobe.
    • Segments V–VIII: Right lobe.

    

• Biliary Drainage:

  • Left Hepatic Duct:
    • Drains segments II–IV.
    • Crosses base of segment IV to join the right hepatic duct, forming the common hepatic duct (CHD).
  • Right Hepatic Duct:
    • Drains segments V–VIII.
    • Formed by union of right posterior and right anterior segmental ducts.
    • Right Posterior Segmental Duct:
      • Drains segments VI and VII.
      • Courses horizontally before descending vertically.
    • Right Anterior Segmental Duct:
      • Drains segments V and VIII.
• Variations:
  • 15–20%: Right posterior duct drains into the left hepatic duct.
  • Caudate Lobe (Segment I):
    • 80%: Drains into both right and left hepatic ducts.
    • 15%: Drains only into the left hepatic duct.
    • 5%: Drains exclusively into the right hepatic duct.

Extrahepatic Ducts

• Common Hepatic Duct (CHD):
  • Formed by union of right and left hepatic ducts.
  • Variations in the angle and point of union.
  • Cystic Duct (CD) enters 2–3 cm distally.
• Common Bile Duct (CBD):
  • Formed by union of the CD and CHD.
  • Length: Approximately 8 cm (varies).
  • Normal diameter: 4–9 mm; enlarged if >10 mm.
• Divisions of CBD:
  • Supraduodenal Portion:
    • Descends in lesser omentum.
    • Anterior to portal vein; right of hepatic artery.
  • Retroduodenal Portion:
    • Passes behind first part of duodenum.
    • Lateral to portal vein; anterior to inferior vena cava.
  • Intrapancreatic Portion:
    • Traverses posterior pancreas.
    • Enters second part of duodenum.
  • Intramural Portion:
    • Passes obliquely through duodenal wall.
    • Opens at the papilla of Vater.
• Relationship with Pancreatic Duct:
  • Variations:
    1. Unite outside duodenal wall (long common channel).
    2. Join within duodenal wall (short common channel).
    3. Enter duodenum separately.

  • Sphincter of Oddi:

    • Regulates flow into duodenum.
    • Composed of separate sphincters for bile duct, pancreatic duct, and ampulla.

    

    

Gallbladder and Cystic Duct

• Gallbladder:

  • Pear-shaped organ on liver's inferior surface between segments IV and V.
  • Size: 7–10 cm long; 2.5–3.5 cm wide.
  • Capacity: 50–60 mL (up to 300 mL when distended).

  • Divisions:

    • Fundus: Projects beyond liver's inferior border.
    • Body: Contacts first and second parts of duodenum.
    • Infundibulum:
      • Between neck and cystic artery entrance.
      • Dilated infundibulum forms Hartmann pouch.
    • Neck: Curves into an S-shape becoming the CD.

    

• Gallbladder Wall Layers:

  1. Epithelium (innermost).
  2. Lamina Propria.
  3. Smooth Muscle.
  4. Perimuscular Subserosal Connective Tissue.
  5. Serosa.
• Histological Features:
  • Rokitansky-Aschoff Sinuses:
    • Invaginations of epithelium.
    • Present in 40% of normal gallbladders.
    • Abundant in inflamed gallbladders.
  • Ducts of Luschka:
    • Tiny bile ducts on hepatic side.
    • Found in 10% of normal gallbladders.
• Cystic Duct (CD):
  • Length: 2–4 cm (variable).
  • Joins the CHD to form the CBD.
  • Contains valves of Heister (spiral folds without valvular function).
  • Variations in length, course, and union point with CHD.

• Calot Triangle:

  • Formed by CHD medially, CD laterally, and inferior margin of liver superiorly.
  • Contains important structures like the cystic artery (CA).
  • CA usually arises from the right hepatic artery within this triangle.
  • Accurate identification is crucial during cholecystectomy.

  

Vascular Anatomy

• Hepatic Artery:

  • Supplies 25% of liver's blood (remainder from portal vein).
  • Derived from the celiac trunk in 55% of cases.
  • Variations include origins from other vessels.

• Blood Supply to Biliary Tract:

  • Right and Left Hepatic Ducts, upper CHD:
    • Supplied by CA and right and left hepatic arteries.
  • Supraduodenal Bile Duct:
    • Supplied by branches from right hepatic, cystic, posterior superior pancreaticoduodenal, and retroduodenal arteries.
  • Axial Blood Supply:
    • Important arteries run parallel at 3 and 9 o'clock positions.
    • 60% originates inferiorly from pancreaticoduodenal and retroduodenal arteries.
    • 38% originates superiorly from right hepatic and CD arteries.
    • Injury may lead to ischemic ductal stricture.

• Cystic Artery (CA):

  • Usually arises from the right hepatic artery within Calot triangle.

  • Variations:

    • May arise from left hepatic, common hepatic, gastroduodenal, or superior mesenteric artery.
    • May pass anterior to CBD or CHD.

    

• Venous Drainage:

  • From hepatic ducts and gallbladder surface into hepatic veins.
  • Lower bile duct drains directly into the portal vein.

Lymphatic Drainage

• Hepatic Ducts and Upper CBD:
  • Drain into hepatic lymph nodes, then to celiac lymph nodes.
• Lower Bile Duct:
  • Drains into lower hepatic nodes and upper pancreatic lymph nodes.
• Gallbladder and CD:
  • Drain primarily into hepatic nodes.
  • Cystic Node located at the junction of CD and CHD.
  • Lymphatics form an "N" shape on the gallbladder surface.

Neural Innervation

• Sympathetic and Parasympathetic Fibers:
  • Derived from the celiac plexus.
  • Travel along the hepatic artery.
• Vagal Innervation:
  • Left (anterior) vagal trunk gives hepatic branches to gallbladder, bile duct, and liver.
• Sensory Innervation:
  • Visceral afferent fibers travel through greater splanchnic nerves to thoracic segments T5–T9.
  • Right phrenic nerve contributes, explaining referred shoulder pain in gallbladder disease.

• Ganglia within Gallbladder Wall:

  • Mucosal, muscular, and subserous plexuses.
  • Decreasing number of ganglion cells from subserous to mucosal layers.

  

Anomalies of the Biliary Tract

Biliary Duct Anomalies

Hepatic Ducts

• Variations in CHD Formation:
  • Standard pattern in 57–68% of patients.
  • Common variations include:
    • 12–18%: Right anterior, right posterior, and left hepatic ducts unite to form CHD.
    • 8–20%: Right posterior and left hepatic ducts unite; right anterior duct joins below.
    • 4–7%: Right posterior duct joins CHD below union of right anterior and left hepatic ducts.
• Accessory Hepatic Ducts:
  • Present in 10% of individuals.
  • May join right hepatic duct, CHD, CD, CBD, or gallbladder.
  • Risk of injury during surgery if unrecognized.

Common Bile Duct (CBD)

• Rare Anomalies:
  • Malposition or duplication.
• Variations Include:
  1. Single duct opening into pylorus or antrum.
  2. Single duct opening into gastric fundus.
  3. Independent entry into duodenum separate from pancreatic duct.
  4. Two separate ducts entering duodenum.
  5. Bifurcating duct with branches entering duodenum and stomach.
  6. Septate CBD with two openings into duodenum.
• Clinical Significance:
  • Importance lies in recognition to avoid injury during surgery.

Cystic Duct (CD)

• Variations in Length, Course, Insertion:
  • Parallel CD:
    • Runs parallel to CHD for a distance.
    • Occurs in 15% of individuals.
  • Spiral CD:
    • Spirals anterior or posterior to CHD.
    • Occurs in 8%.
  • CD may join:
    • Right hepatic duct or right segmental duct.
    • Form a trifurcation with right and left hepatic ducts.
  • Short or Absent CD:
    • Gallbladder may join CHD directly.
  • Surgical Implications:
    • Risk of misidentifying ducts during cholecystectomy.

Gallbladder Anomalies

Anomalies are categorized by formation, number, and position.

Formation Anomalies

• Phrygian Cap:

  • Most common anomaly (18% of patients).
  • Infolding between body and fundus.
  • Usually asymptomatic; not an indication for cholecystectomy.

  

• Bilobed Gallbladder:

  • Completely divided gallbladder with common CD.
  • Two forms:
    1. Single gallbladder divided internally by a septum.
    2. Two separate gallbladders fused at the neck.
  • Generally asymptomatic.
• Hourglass Gallbladder:
  • Dumbbell shape due to contour alteration.
  • Congenital in children; acquired in adults (often from chronic cholecystitis).
• Diverticulum of the Gallbladder:
  • Rare congenital outpouchings.
  • Can vary in size (0.5–9 cm).
  • Hartmann Pouch:
    • Acquired diverticulum at the infundibulum.
    • Associated with gallstones and prolonged obstruction.
• Rudimentary Gallbladder:
  • Small remnant at end of CD.
  • Congenital hypoplasia in children; may result from fibrosis in adults.

Number Anomalies

• Absence of Gallbladder (Agenesis):
  • Over 200 cases reported.
  • Often associated with other biliary abnormalities.
  • Must differentiate from intrahepatic or left-sided gallbladder.
• Duplication:
  • Occurs in approximately 1 in 4,000 persons.
  • Two types:
    1. Ductular Type:
       • Each gallbladder has its own CD.
    2. Combined Ducts:
       • Two ducts merge before entering CBD.
  • Generally asymptomatic; requires no treatment.

Position Anomalies

• Floating Gallbladder:
  • Completely surrounded by peritoneum; attached by peritoneal reflection.
  • Occurs in ~5% of individuals.
  • Risk of torsion, especially in women over 60.
• Intrahepatic Gallbladder:
  • Partially or completely embedded in liver parenchyma.
  • Associated with gallstones in 60% of adults.
• Left-Sided Gallbladder:
  • Two types:
    1. Associated with situs inversus.
    2. Isolated left-sided gallbladder.
  • Usually functions normally.
• Transverse Gallbladder:
  • Positioned horizontally in the liver's transverse fissure.
  • Deeply embedded within liver parenchyma.
• Retrodisplaced Gallbladder:
  • Located outside the gallbladder fossa.
  • May be partially or completely retroperitoneal.
  • May be challenging to access during surgery.

Vascular Anomalies

• Arterial Supply Variations:
  • Present in ~50% of individuals.
• Accessory or Double Cystic Artery (CA):
  • Occurs in 15–20%.
  • May arise from right hepatic artery within Calot triangle.
• Caterpillar Hump Right Hepatic Artery:
  • Right hepatic artery courses through Calot triangle near CD.
  • Risk of injury during cholecystectomy.
• CA Anterior to CBD or CHD:
  • Occurs in 5–15%.
  • CA may be mistaken for CD during surgery.
  • Requires careful dissection to prevent injury.

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SPEED EMBRYOLOGY

• Both insulin and glucagon can be detected in the fetal circulation by the fourth or fifth month of fetal development.

Bile Duct Development Timeline (Carnegie Stages)

20 - 27 Days (Post Fertilization)

• Stage XII:
  • Hepatic diverticulum arises from the foregut.
  • Protrudes into the mesenchyme of the septum transversum.

28 - 41 Days

• Stage XVIII:
  • Completion of a "funnel-like" extrahepatic duct abutting the amorphous liver anlage.
  • Gallbladder becomes visible later.

42 - 56 Days

• Hepatoblasts identifiable in the liver.
• Early cholangiocyte transformation.

57 - 70 Days

• Formation of ductal plate and intrahepatic bile ducts.

12 Weeks Onward

• On-going selection and deletion of intrahepatic bile ducts away from the porta.
• Formation & Transport of BILE.

Speed Notes Anatomy

CBD :

• Arterial Blood supply of CBD:
  • 3 parts
    1. Hilar = rich collateral supply from both Right and Left Hepatic arteries
    2. Supraduodenal =
       1. 3 and 9 o clock vessels
       2. RHA( descending vessels), cystic, Posterior superior pancreatico duodenal artery, Retroduodenal (ascending vessels), GDA and CHA also???.
       3. BUT NOT from LHA and ?PHA
       4. 60% runs upwards and 38% runs downwards
    3. Retropancreatic = Retroduodenal artery ⇒ br of Gastroduodenal artery

• Venous Supply of CBD:

  • important for Portal Biliopathy
  • 2 plexus of veins
    • Epicholedochal plexus = SAINT
    • Paracholedochal plexus = PETREN

  

  

Variations in Biliary drainage

• Least variation in Biliary Drainage is of which liver segment (MCQ)

  • Segment 2
  • Segment 3
  • Segment 7

• MC anatomical variation of Biliary duct (MCQ)

  • RPSD draining into LHD ( 13-19%) [ref SKF 8-20%]
  • 2nd MC = Trifurcation pattern (12-18%)

Enterohepatic Circulation of Bile Salts

• Cholesterol is taken up from plasma by the liver.
• Bile acids are synthesized at a rate of 0.6 g/24 hr
• Reabsorbed in the terminal ileum **
• Nearly 95% of bile salts are reabsorbed.
• Thus, of the total bile salt pool of 2 to 4 g, which recycles through the enterohepatic cycle 6 to 10 times daily, only about 600 mg is actually excreted into the colon.
• Bile Salts
  • Primary = Cholate ; Chenodeoxycholate
  • Secondary = deoxycholate and lithocholate

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Bullet points for MCQ’s

Summary: Structure of the Sphincter of Oddi

The Sphincter of Oddi is a complex structure composed of four sphincters, each containing both circular and longitudinal smooth muscle fibers. These sphincters regulate the flow of bile and pancreatic juice into the duodenum.

Four Sphincters:

1. Superior Sphincter Choledochus
2. Inferior Sphincter Choledochus
3. Sphincter Pancreaticus
4. Sphincter of the Ampulla

These sphincters work together to control the release of bile and pancreatic secretions, playing a critical role in digestion.

(Source: Shackelford, 8th edition, page 1253)

T tube Cholangiogram showing Right Sectional Duct

Variants in Cystic Artery:

MCQ: Common Anatomical Variation of the Hepatic Duct:

Question: What is the more common anatomical variation of the hepatic duct?

Options: a) Right anterior duct draining into CHD

b) Right posterior duct draining into CHD

c) Right anterior duct draining into left hepatic duct

d) Typical anatomy of the confluence

Answer: d) Typical anatomy of the confluence

Explanation:

• Typical Anatomy of the Confluence (Option D): The normal biliary confluence, where the right and left hepatic ducts unite, occurs in approximately 72% of patients, making it the most common anatomical configuration.
• Other Variations:
  • Triple confluence [2nd MC] (12%): Involves the right anterior and posterior sectional ducts along with the left hepatic duct.
  • Right sectional duct joining the main bile duct (20%): An anatomical variation where a right sectional duct directly joins the common hepatic duct (CHD). RASD [1st MC] = 16% and RPSD =4%
  • Right sectional duct joining the left hepatic duct (6%): Occurs in fewer cases, with the right posterior duct involved in 5% and the anterior duct in 1% of cases.
  • Absence of hepatic duct confluence (3%): Leads to unusual variations, such as the right posterior sectional duct joining the neck of the gallbladder or being entered by the cystic duct.

MCQ: Most Common Anomaly of Gallbladder Formation

Question: What is the most common anomaly of gallbladder formation?

Options: a) Diverticulum of gallbladder

b) Bilobed gallbladder

c) Hourglass gallbladder

d) Phrygian cap

Answer: d) Phrygian cap

Explanation:

• Option A (Diverticulum of gallbladder): Although diverticula can occur in various parts of the gallbladder, they are generally clinically insignificant unless they lead to complications like stones or inflammation.
• Option B (Bilobed gallbladder): A rare anomaly where the gallbladder is completely divided, either by a septum or appearing as two fused gallbladders. It is typically asymptomatic.
• Option C (Hourglass gallbladder): A congenital or acquired anomaly where the gallbladder takes on a dumbbell or hourglass shape. It may result from chronic cholecystitis in adults.
• Option D (Phrygian cap): The most common gallbladder anomaly, caused by an infolding between the body and fundus. It is typically asymptomatic and does not require surgical intervention.

Correct Answer: D) Phrygian cap

MCQ: True Statements About Gallbladder Anatomy Except

Question: Which of the following is not true about the anatomy of the gallbladder?

Options: a) Average capacity of gallbladder is 30-50 ml

b) Body of gallbladder contains most of the smooth muscle

c) Most of the elastic tissue is present in the body of the gallbladder

d) Convexity of gallbladder neck enlarges to form Hartmann's pouch

Answer: b) Body of gallbladder contains most of the smooth muscle

Explanation:

• Option A (Average capacity of gallbladder is 30-50 ml): The gallbladder typically holds about 30-50 ml, but can distend to hold up to 300 ml when obstructed.
• Option B (Body of gallbladder contains most of the smooth muscle): This statement is not true. The fundus of the gallbladder, not the body, contains most of the smooth muscle.
• Option C (Most of the elastic tissue is present in the body of the gallbladder): The body of the gallbladder is the main storage area and contains most of the elastic tissue.
• Option D (Convexity of gallbladder neck enlarges to form Hartmann's pouch): The neck of the gallbladder may form an enlargement known as Hartmann's pouch. The neck lies in the deepest part of gb fossa and extends into the free portion of HDL.

Correct Answer: B) Body of gallbladder contains most of the smooth muscle

Source: (Schwartz 10th edition page no. 1309)