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Liver, Extrahepatic Biliary System, Pancreas & Spleen - Complete Revision Answers

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QUADRANTS OF THE ABDOMEN

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LIVER

1. Surfaces, Related Structures & Indentations

• Covered by peritoneum except the "bare area" (between the two layers of coronary ligament - directly in contact with diaphragm)
• Fossa for IVC posteriorly

• H-shaped arrangement on visceral surface: left limb = fissures, right limb = IVC groove & gallbladder fossa, crossbar = porta hepatis

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2. Lobes of the Liver

• Right lobe (largest)
• Left lobe
• Caudate lobe (between IVC and ligamentum venosum) - posterior
• Quadrate lobe (between fossa for GB and ligamentum teres) - anterior

• Right surgical lobe: Couinaud segments V, VI, VII, VIII
• Left surgical lobe: Couinaud segments I, II, III, IV

Key exam point: The falciform ligament does NOT mark the boundary between surgical lobes. Cantlie's line (from gallbladder fossa to IVC) is the true boundary.

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3. Peritoneal Attachments

Bare area: Directly adherent to diaphragm; portal vein drains directly here - hence liver metastases can spread to pleura/diaphragm directly.

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4. Fissures of the Liver

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5. Blood Supply of the Liver

• Proper hepatic artery (from common hepatic artery from coeliac trunk) divides into right and left hepatic arteries at porta hepatis
• Right hepatic artery gives cystic artery to gallbladder
• Provides ~25% of hepatic blood but ~50% of O2

• Portal vein forms behind neck of pancreas by union of superior mesenteric vein + splenic vein
• Provides ~75% of hepatic blood but ~50% of O2

• Right, middle, and left hepatic veins drain into IVC just below the diaphragm

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6. Segments of the Liver (Couinaud)

• Left hepatic vein: separates II+III from IV
• Middle hepatic vein (Cantlie's line): separates right from left surgical lobes
• Right hepatic vein: separates V+VIII from VI+VII

Surgical relevance: Couinaud segments allow anatomical resections (segmentectomy, lobectomy) with minimal blood loss.

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7. Porta Hepatis

• Definition: Transverse fissure on visceral surface; the "gate" of the liver
• Size: ~5 cm long

1. Bile ducts - most anterior (left medial, right lateral)
2. Hepatic arteries - middle (left medial, right lateral)
3. Portal vein - most posterior (divides into right and left)
4. Lymph nodes, nerves, lymphatics

Memory aid: "BAPS" - Bile duct, Artery, Portal vein (front to back) - or "Portal trio" from back to front: Vein, Artery, Duct.

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8. Porto-Systemic Anastomoses

Exam focus: Know the 4 main sites: oesophagus, umbilicus, rectum, retroperitoneum. Oesophageal varices carry the highest mortality.

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9. Hepatic Lobule (Classic)

• Central vein (terminal hepatic venule) at centre
• Portal triads at 6 corners (portal vein branch, hepatic artery branch, bile ductule)
• Hepatocytes arranged in plates radiating from central vein to periphery
• Sinusoids between plates: blood flows from portal triads → central vein
• Bile flows in opposite direction: from centre → peripheral bile ductules

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10. Hepatic Acinus (Rappaport's Acinus)

• Functional unit of the liver (vs. classic lobule which is morphological)
• Shaped like a diamond/rhomboid - centred on a terminal portal tract (terminal portal venule + hepatic arteriole)
• Extends between two adjacent central veins
• Zones are numbered 1, 2, 3 from the portal tract outward (the reverse of classic zone orientation in a lobule)
• Zone 1 = best oxygenated (nearest portal blood); Zone 3 = poorest oxygenation (nearest central vein)

Key distinction: Classic lobule is centred on central vein; Acinus is centred on portal tract. The acinus better explains zonal patterns of liver disease.

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EXTRAHEPATIC BILIARY SYSTEM

1. Parts & Relations (Line Diagram in Text Form)

Right hepatic duct + Left hepatic duct
            ↓
      Common Hepatic Duct (CHD)
            ↓ ← Cystic duct joins here
      Common Bile Duct (CBD)
            ↓
    Ampulla of Vater → opens into 2nd part duodenum

• Fundus, body, Hartmann's pouch (infundibulum), neck → cystic duct
• Fundus projects at tip of 9th costal cartilage (intersection of right lateral margin of rectus with costal margin) - Murphy's sign point
• Peritoneum covers fundus and body; neck is retroperitoneal

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2. Blood Supply of the Gallbladder

• Variations (surgically important):
  • Double cystic artery
  • Cystic artery from left hepatic artery, common hepatic artery, or gastroduodenal artery
  • Cystic artery may cross anterior to CBD

Key point: Bleeding during cholecystectomy is common due to anatomical variation of the cystic artery. Identifying the node of Calot helps locate the cystic artery.

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3. Calot's Triangle

• Cystic artery (and its branches)
• Node of Calot (Lund's node) - used as landmark
• Occasionally: accessory right hepatic artery or aberrant right hepatic duct

Surgical significance: The hepatocystic triangle (a safer modern term) must be cleared of all fat to achieve the "Critical View of Safety" before dividing any structures during laparoscopic cholecystectomy. This prevents bile duct injury.

Classic definition (Calot 1891) had cystic artery as the superior boundary - modern anatomists replaced it with the liver edge.

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4. Parts of the Common Bile Duct

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5. Boundaries of the Epiploic Foramen (Foramen of Winslow)

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PANCREAS

1. Structure & Relations

• Main pancreatic duct (Wirsung) runs from tail to head → joins CBD at ampulla of Vater → opens into 2nd part duodenum at major papilla
• Accessory pancreatic duct (Santorini) opens at minor papilla (2 cm above major papilla)

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2. Peritoneal Ligaments Attached to Pancreas

The tail of the pancreas is invested within the splenorenal (lienorenal) ligament - this is why the tail is at risk during splenectomy.

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3. Blood Supply of the Pancreas

• Superior pancreaticoduodenal artery (from gastroduodenal artery → hepatic → coeliac)
• Inferior pancreaticoduodenal artery (from SMA)
• These form anterior and posterior arcades with the duodenum

• Splenic artery (gives dorsal pancreatic, great pancreatic (arteria pancreatica magna), caudal pancreatic arteries)

Exam pearl: The splenic vein runs posterior to the body of the pancreas - pancreatitis can cause splenic vein thrombosis → left-sided (sinistral) portal hypertension → gastric varices without oesophageal varices.

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4. Microscopic Structure of the Pancreas

• Acinar cells: pyramid-shaped, basophilic cytoplasm (rich in RER), apical zymogen granules; secrete digestive enzymes (amylase, lipase, trypsinogen, chymotrypsinogen)
• Centroacinar cells: pale cells at centre of acinus; secrete watery HCO3-rich fluid
• Intercalated ducts → intralobular ducts → interlobular ducts → main duct

Histological stain: H&E; beta cells most centrally located in islets; alpha cells are peripheral.

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5. Embryological Basis of Annular Pancreas

• Pancreas develops from two endodermal buds of the foregut at 5th week: dorsal bud (from dorsal duodenum) + ventral bud (from hepatic diverticulum)
• Ventral bud rotates clockwise around duodenum (along with CBD) to fuse with dorsal bud posteriorly
• Fusion at ~7th week

• The ventral pancreatic bud becomes fixed/bilobed before rotation, or rotates in both directions simultaneously
• This results in pancreatic tissue encircling the 2nd part of the duodenum as a ring
• The ring compresses the duodenum → duodenal obstruction

• May present at birth (bilious vomiting) or adulthood
• "Double bubble" sign on X-ray (air in stomach + proximal duodenum) - also seen in duodenal atresia
• Associated with Down syndrome, duodenal atresia, other congenital anomalies
• Treatment: duodenoduodenostomy (bypass, NOT resection of the ring - risk of pancreatitis/fistula)

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SPLEEN

1. Surfaces & Related Structures

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2. Peritoneal Attachments of the Spleen

All peritoneal ligaments of spleen are derived from the dorsal mesentery (dorsal mesogastrium).

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3. Blood Supply of the Spleen

• Splenic artery also gives: short gastric arteries (via gastrosplenic lig.), left gastroepiploic artery

Key point: Splenic artery is tortuous (reduces pulse pressure to the spleen). Splenic infarcts cause severe left upper quadrant pain - splenic artery embolism used therapeutically for hypersplenism.

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4. Surface Marking of the Spleen

• Lies obliquely along the 9th, 10th, 11th ribs in the left hypochondrium
• Long axis parallel to the 10th rib
• Medial end: T10 vertebral level (1 inch from midline)
• Lateral end: Mid-axillary line (left 9th-11th ribs)
• Notched superior border (1-4 notches)

Normal size: ~12 cm × 7 cm × 4 cm ("1, 3, 5, 7, 9, 11 rule" - weighs ~150-200g, not palpable normally, lies between 9th-11th ribs) Palpable below left costal margin only when enlarged to at least 2-3× normal size.

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5. Histology of the Spleen

• Lymphoid tissue arranged around central artery (periarteriolar lymphoid sheath - PALS)
• PALS contains T lymphocytes
• Lymphoid nodules (Malpighian corpuscles) = B cell follicles with germinal centres (at periphery of PALS)

• Splenic sinuses: wide vascular channels lined by elongated endothelial cells
• Splenic cords (cords of Billroth): reticular meshwork between sinuses containing macrophages, RBCs, platelets
• Old/damaged RBCs are trapped and destroyed here (extravascular haemolysis)

Key functions to link with histology:

• Filtration/destruction of old RBCs → red pulp (cords + sinuses)
• Immune surveillance → white pulp (PALS + follicles)
• Platelets sequestered → red pulp (hypersplenism causes thrombocytopenia)

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CLINICAL ANATOMY

1. Trauma to Left Hypochondrium → Massive Haemoperitoneum

• The spleen is richly vascular (receives ~5% of cardiac output = ~350 mL/min)
• Its fibrous capsule is thin and fragile - easily torn by blunt trauma to left lower ribs (9th-11th)
• The parenchyma has no ability to contract (unlike uterus); haemostasis depends entirely on capsule integrity
• The peritoneal reflections (gastrosplenic and splenorenal ligaments) are short - do not suspend the organ well, limiting tamponade
• The spleen is the most commonly injured solid organ in blunt abdominal trauma
• Results in rapid free intraperitoneal haemorrhage (haemoperitoneum)
• Delayed rupture can occur up to 2 weeks after injury (subcapsular haematoma expands then ruptures)

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2. Pringle's Manoeuvre

• All blood supply to the liver (both portal venous and hepatic arterial) passes through the hepatoduodenal ligament (free edge of lesser omentum)
• The ligament contains: portal vein (posteriorly), hepatic artery proper (left anteriorly), CBD (right anteriorly)
• Manual compression of this ligament between thumb (in epiploic foramen) and index finger (anterior) compresses all three structures simultaneously
• Stops both arterial and portal venous inflow → temporarily arrests hepatic bleeding
• Safe for up to 15-20 minutes (or intermittently up to 60 minutes with ischaemic preconditioning)
• Bleeding from hepatic veins (which drain directly into IVC, upstream of the ligament) is NOT controlled by Pringle's manoeuvre

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3. Caput Medusae in Portal Hypertension

• The paraumbilical veins run within the falciform ligament, connecting the left branch of the portal vein → umbilical vein remnant → superficial veins of the anterior abdominal wall (superficial epigastric, thoracoepigastric, lateral thoracic veins)
• Normally, the paraumbilical veins are collapsed and non-functional
• In portal hypertension (portal pressure >12 mmHg), blood is forced retrograde through porto-systemic anastomoses
• The paraumbilical veins recanalize and dilate, connecting the portal system to systemic epigastric veins
• The dilated veins radiate outward from the umbilicus in a pattern resembling "Caput Medusae" (head of Medusa with snake hair)
• Flow is away from the umbilicus (distinguishes from obstruction of IVC where flow is upward above umbilicus)

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4. Head of Pancreas Carcinoma → Jaundice, Tea-Coloured Urine, Pale Stools

• The CBD runs in a groove on (or through) the posterior surface of the head of pancreas (infraduodenal/intrapancreatic part, ~3 cm length)
• A carcinoma of the head progressively compresses and obstructs the CBD from outside
• This causes obstructive (post-hepatic / cholestatic) jaundice:
  • Bile cannot enter the duodenum → backs up into blood → bilirubin enters urine → dark/tea-coloured urine (bilirubinuria)
  • No bile reaching duodenum → stercobilin absent → pale/acholic stools
  • Pruritus from bile salt deposition in skin
• The gallbladder distends (because it cannot empty; Courvoisier's Law: palpable, non-tender distended GB in an icteric patient suggests malignant biliary obstruction rather than stones, because chronic cholecystitis makes the GB fibrotic)
• Painless progressive jaundice in elderly = carcinoma of head of pancreas until proven otherwise

Courvoisier's Law: "In obstructive jaundice, if the gallbladder is palpable and non-tender, the obstruction is unlikely to be due to gallstones." (Gallstones cause chronic inflammation → fibrotic, shrunken, non-distensible GB)

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5. Murphy's Sign - Anatomical Basis

• The gallbladder fundus lies at the intersection of the right lateral border of rectus abdominis and the right costal margin (tip of 9th costal cartilage)
• During inspiration, the diaphragm descends, pushing the liver and gallbladder downward
• In acute cholecystitis, the gallbladder wall is inflamed and oedematous (peritoneal irritation)
• As the inflamed gallbladder descends into the examiner's fingers → sudden sharp pain → inspiratory arrest
• A positive Murphy's sign is specific for acute cholecystitis (absent in chronic cholecystitis or emphysematous cholecystitis)
• Sonographic Murphy's sign: Maximal tenderness directly over the visualized gallbladder on ultrasound

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6. Gallstone Ileus

1. A gallstone erodes through the inflamed gallbladder wall into an adjacent viscus, most commonly the 1st or 2nd part of the duodenum (cholecystoduodenal fistula) - rarely into stomach or colon
2. The stone (usually >2.5 cm) passes into the small intestine and travels distally
3. It impacts at the narrowest part of the small bowel - the terminal ileum (ileocaecal valve) - causing mechanical small bowel obstruction
4. Radiological Rigler's triad:
   • Small bowel obstruction
   • Pneumobilia (air in biliary tree via the fistula)
   • Ectopic calcified gallstone visible on plain X-ray

Occurs predominantly in elderly women; accounts for ~1-3% of small bowel obstructions. The gallbladder and biliary tree are adherent to the duodenum by its anatomical proximity (gallbladder fossa is immediately above the 1st part of duodenum).

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7. Preservation of Tail of Pancreas During Pancreatectomy

• The tail of the pancreas is the only part that has independent mobility - it is invested within the splenorenal (lienorenal) ligament (rather than being retroperitoneal)
• The tail lies free and can be retracted without disrupting the body or head
• The tail is not encased in a duodenal loop (unlike the head) - it has less surgical consequence if the head + body are resected (Whipple's procedure = pancreaticoduodenectomy)
• Endocrine sparing: The tail has a relatively higher density of islets of Langerhans - preserving it helps maintain endocrine (insulin-producing) function and reduces risk of post-operative diabetes mellitus
• The tail's blood supply (from splenic artery branches) is separate from the head (pancreaticoduodenal arcades)
• However, during splenectomy, the tail is at risk of inadvertent injury (since it lies in the splenorenal ligament near the splenic hilum)

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8. Pancreatic Pseudocyst in the Lesser Sac

• The lesser sac (omental bursa) lies directly posterior to the stomach and anterior to the pancreas
• The posterior wall of the lesser sac is formed by the anterior surface of the pancreas
• In acute or chronic pancreatitis, leaked pancreatic juice (rich in activated enzymes) and blood dissect through the posterior peritoneum
• Because the lesser sac is a closed potential space bounded by peritoneal folds, the exudate is contained within the lesser sac rather than spreading freely
• The fluid accumulates as a pseudocyst (no epithelial lining - just granulation/fibrous tissue, hence "pseudo") in this space
• The pseudocyst bulges anteriorly into the lesser sac, pushing the stomach forward
• Access for drainage is via the posterior wall of the stomach (cystogastrostomy) or via endoscopic transgastric route

Key anatomical relationships: Lesser sac is bounded by: stomach/lesser omentum anteriorly, pancreas/posterior abdominal wall posteriorly, spleen/gastrosplenic lig. laterally, epiploic foramen medially, transverse mesocolon inferiorly.

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HIGH-YIELD REVISION SUMMARY TABLE

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