Liver, Gallbladder and Biliary Tree

Surfaces:

• Diaphragmatic surface: Smooth, convex, moulded against the undersurface of the diaphragm; further subdivided into anterior, superior, posterior, and right lateral parts.
• Visceral (inferior) surface: Related to the stomach, duodenum, right colic flexure, right kidney, and gallbladder, marked by several fissures and the porta hepatis.

Borders:

• Inferior border: Sharp, separates the diaphragmatic and visceral surfaces anteriorly; normally does not extend below the right costal margin in a healthy adult (a palpable liver edge below the costal margin suggests hepatomegaly, or occasionally a normal anatomical variant such as Riedel's lobe).

Anatomical lobes:

• Right lobe (larger) and left lobe (smaller), divided on the diaphragmatic surface by the falciform ligament, and on the visceral surface by a line connecting the fossa for the gallbladder and the fissure for the ligamentum venosum.
• Two smaller anatomical lobes on the visceral surface, both technically part of the right lobe by traditional anatomical (non-functional) classification, but functionally belonging to the left lobe by vascular supply: caudate lobe (posterior, between the IVC and the fissure for the ligamentum venosum) and quadrate lobe (anterior, between the gallbladder fossa and the fissure for the ligamentum teres).

Functional lobes:

• Defined by the branching pattern of the portal triad structures (portal vein, hepatic artery, bile duct) rather than surface anatomical landmarks, the functional division between right and left lobes runs along an imaginary plane (Cantlie's line) from the gallbladder fossa to the IVC, NOT along the anatomical falciform ligament.
• By this functional classification, the caudate lobe receives blood supply from both the right and left branches of the portal vein/hepatic artery (making it somewhat independent, sometimes considered a distinct functional segment), while the quadrate lobe functionally belongs to the left lobe (supplied by the left branch of the portal triad), despite being anatomically grouped with the right lobe by the traditional surface classification, a key, frequently tested discrepancy between anatomical and functional lobar division.

Porta hepatis:

• The "gateway" of the liver, on the visceral surface, where the portal triad (portal vein posteriorly, hepatic artery proper anteriorly/left, common bile duct anteriorly/right, mnemonic "Artery Duct Vein" left to right, or the duct is most anterior/lateral) enters/exits the liver, along with hepatic lymphatics and autonomic nerve fibres.
• Located between the caudate and quadrate lobes.

Ligaments:

• Falciform ligament: Anterior, connects the liver to the anterior abdominal wall (and diaphragm), containing the ligamentum teres hepatis (obliterated left umbilical vein) in its free inferior edge.
• Ligamentum teres hepatis: Fibrous remnant of the fetal umbilical vein, running from the umbilicus to the liver within the free edge of the falciform ligament, continuing intrahepatically to join the left branch of the portal vein.
• Ligamentum venosum: Fibrous remnant of the fetal ductus venosus (which shunted oxygenated umbilical vein blood past the liver directly to the IVC in utero), lying in a fissure on the visceral surface between the caudate lobe and the left lobe.
• Coronary ligaments (anterior and posterior layers) and right/left triangular ligaments: Reflections of peritoneum connecting the liver's diaphragmatic surface to the diaphragm, enclosing the bare area between the anterior and posterior coronary ligament layers.
• Lesser omentum: Connects the liver (porta hepatis) to the lesser curvature of the stomach and proximal duodenum.

Bare area:

• A triangular region on the posterosuperior diaphragmatic surface of the liver, not covered by peritoneum, lying in direct contact with the diaphragm, bounded by the reflections of the coronary ligaments.
• Clinically relevant as a potential site of direct extraperitoneal spread of infection/malignancy between the liver and the right subphrenic/pleural space, bypassing the peritoneal cavity entirely.

Relations:

• Anterior: Diaphragm, anterior abdominal wall (right costal margin region).
• Posterior: IVC (embedded in a groove/tunnel on the posterior surface, receiving the hepatic veins directly), oesophagus (left lobe), right kidney and suprarenal gland impression, right colic flexure impression, stomach impression, duodenum impression (near the porta hepatis, related to the first part).

Portal triad:

• Portal vein: formed by the union of the SMV and splenic vein, carries approximately 75% of hepatic blood flow (nutrient-rich, but relatively deoxygenated).
• Hepatic artery proper: branch of the common hepatic artery (itself from the coeliac trunk), carries approximately 25% of hepatic blood flow but provides roughly half of the liver's oxygen supply, given its fully oxygenated arterial blood.
• Common bile duct: carries bile from the liver/gallbladder to the duodenum (see Biliary Tree below).
• All three structures travel together within the hepatoduodenal ligament (free edge of the lesser omentum) before entering the porta hepatis, each dividing into right and left branches to supply/drain the corresponding functional lobe.

Hepatic veins:

• Typically three main hepatic veins (right, middle, left), draining directly into the IVC just below the diaphragm (a short, wide, and often difficult-to-access confluence surgically, given its retrohepatic position), these veins do NOT run alongside the portal triad structures, but rather run in the planes between the liver's functional segments (intersegmental), draining venous blood in a pattern distinct from and complementary to the portal venous inflow.

Segmental anatomy (Couinaud segmentation):

• Divides the liver into eight functionally independent segments (numbered I-VIII), each with its own portal triad inflow (a branch of the portal vein, hepatic artery, and bile duct) and its own venous outflow (via tributaries draining into one of the three hepatic veins), allowing individual segments to be resected surgically without disrupting the vascular supply of adjacent segments (segmentectomy), analogous in principle to bronchopulmonary segments in the lung.
• Segment I = caudate lobe (unique, receives inflow from both right and left portal triads, and drains directly into the IVC rather than via the three main hepatic veins, making it somewhat functionally autonomous and often relatively spared in certain vascular occlusion syndromes).
• Segments II-IV = functional left lobe (II and III form the left lateral segment; IV (sometimes subdivided into IVa/IVb) corresponds to the anatomical quadrate lobe, confirming its functional left-lobe grouping).
• Segments V-VIII = functional right lobe.
• The three hepatic veins run in the planes between segment groupings (right hepatic vein between the anterior/posterior segments of the right lobe; middle hepatic vein along Cantlie's line, between right and left functional lobes; left hepatic vein between the left lateral and left medial segments), while the portal triad branches run within the centre of each segment, this reciprocal relationship (veins at segment boundaries, portal triads at segment centres) is the key organising principle of Couinaud's system, and the anatomical basis for planning safe segmental resection planes.

Parts:

• Fundus: Rounded blind end, projects slightly beyond the liver's inferior border; the part most likely to be palpable if distended, and the classic surface projection site.
• Body: The main storage portion, lying in the gallbladder fossa on the liver's visceral surface.
• Neck: Narrow, tapering portion, continuous with the cystic duct; typically S-shaped/curved.
• Hartmann's pouch (infundibulum): A common, clinically significant outpouching of the gallbladder wall at the junction of the body and neck, the classic site where gallstones become impacted, obstructing the cystic duct outflow and precipitating acute cholecystitis.

Relations:

• Sits within the gallbladder fossa on the liver's visceral surface, between the right and quadrate lobes; related inferiorly/posteriorly to the first/second parts of the duodenum and the transverse colon, relevant to the (rare) complication of gallstone ileus, where a large gallstone erodes through a cholecystoduodenal (or cholecystocolic) fistula directly into the adjacent bowel, causing mechanical small bowel obstruction (classically at the ileocaecal valve, the narrowest point of the small bowel).

Blood supply:

• Cystic artery: typically a branch of the right hepatic artery, most commonly found within (or near) the boundaries of Calot's triangle; supplies the gallbladder and cystic duct.
• Venous drainage is variable: small cystic veins may drain directly into the liver bed (portal system tributaries) or via a named cystic vein into the portal vein/right branch.

• Right and left hepatic ducts: Drain bile from the corresponding functional lobes, emerging from the porta hepatis.
• Common hepatic duct: Formed by the union of the right and left hepatic ducts, just outside the porta hepatis.
• Cystic duct: Connects the gallbladder neck to the common hepatic duct, characterised internally by the spiral valve (of Heister), a series of mucosal folds that regulate bile flow into/out of the gallbladder (rather than a true functional sphincter) and provide some structural resistance to sudden pressure changes.
• Common bile duct (CBD): Formed by the union of the cystic duct and common hepatic duct.

Parts of the common bile duct:

• Supraduodenal part: Within the free edge of the lesser omentum (hepatoduodenal ligament), anterior to the epiploic foramen, to the right of the hepatic artery proper and anterior to the portal vein.
• Retroduodenal part: Passes posterior to the first part of the duodenum.
• Paraduodenal (pancreatic) part: Passes through or along the posterior surface of the head of the pancreas (often within a groove or short tunnel of pancreatic tissue).
• Intraduodenal part: Passes obliquely through the wall of the second part of the duodenum, typically joining the main pancreatic duct just before their combined opening.

Relation to duodenum:

• The CBD's retroduodenal and intraduodenal portions place it in intimate contact with the duodenum's second part, relevant both to the shared major duodenal papilla opening and to the risk of CBD injury during duodenal surgery.

Relation to pancreas:

• The CBD's paraduodenal portion runs within a groove (or short tunnel) on the posterior surface of the pancreatic head, making it vulnerable to compression by pancreatic head pathology (tumour, chronic pancreatitis with fibrosis), a key mechanism of obstructive jaundice.

Hepatopancreatic ampulla (ampulla of Vater):

• The dilated common channel formed by the union of the common bile duct and the main pancreatic duct, just before they open together at the major duodenal papilla on the posteromedial wall of the second part of the duodenum.
• Surrounded by the sphincter of Oddi (a complex of smooth muscle fibres including sphincters around the distal CBD, the distal pancreatic duct, and the ampulla itself), regulating the flow of bile and pancreatic secretions into the duodenum and preventing reflux of duodenal contents into the ducts.

Gallstones (cholelithiasis):

• Form within the gallbladder from an imbalance in bile composition (cholesterol, bilirubin, bile salts); classically become symptomatic when they obstruct the gallbladder outflow (impacted in Hartmann's pouch or the cystic duct, causing biliary colic or acute cholecystitis) or migrate into and obstruct the CBD (choledocholithiasis, causing obstructive jaundice and risking ascending cholangitis).

Calot's triangle (cystohepatic triangle):

• Bounded by the cystic duct (inferolaterally), the common hepatic duct (medially), and the inferior border of the liver (superiorly), some descriptions use the cystic artery itself as the superior boundary rather than the liver edge, but the liver-edge definition is the more classically taught version.
• Contains the cystic artery (and often a variable lymph node, Calot's/Mascagni's node, sometimes used as a surgical landmark for the artery), making careful dissection and identification of this triangle's contents the critical step in safe laparoscopic cholecystectomy, to avoid the serious complication of inadvertent common bile duct or hepatic artery injury from misidentification of structures in this small, anatomically variable region.

Cystic artery:

• Most commonly arises from the right hepatic artery within Calot's triangle, but demonstrates considerable anatomical variation in origin and course, a major source of surgical risk during cholecystectomy if not carefully identified before division/ligation.

Obstructive jaundice:

• Results from blockage anywhere along the biliary drainage pathway distal to the confluence of the hepatic ducts, common causes include choledocholithiasis (stone in the CBD), pancreatic head carcinoma (compressing the paraduodenal CBD, given its intimate anatomical relationship), cholangiocarcinoma, and strictures (post-surgical or inflammatory).
• The level of obstruction (intrahepatic, extrahepatic-proximal, or extrahepatic-distal near the ampulla) determines the clinical and radiological pattern (e.g., isolated dilatation of intrahepatic ducts vs the entire biliary tree including the gallbladder, depending on whether the obstruction lies above or below the cystic duct's confluence).