Surfaces and lobes
The liver has a smooth diaphragmatic surface, facing up, forward and back, and a visceral surface facing down and back that carries the impressions of neighbouring organs. The two meet at the sharp inferior border in front.
Anatomically it has a large right lobe and a smaller left lobe. On the front they are separated by the falciform ligament, and on the visceral surface by the fissures for the ligamentum teres and ligamentum venosum. Two further lobes are marked out on the visceral surface of the right lobe:
- Quadrate lobe: in front of the porta hepatis, between the gallbladder fossa and the fissure for the ligamentum teres.
- Caudate lobe: behind the porta hepatis, between the groove for the inferior vena cava and the fissure for the ligamentum venosum.
The visceral surface bears gastric, duodenal, colic, renal and suprarenal impressions.
Functional segments
Surgeons divide the liver by its blood supply, not its surface. A plane from the gallbladder fossa to the inferior vena cava (Cantlie's line), containing the middle hepatic vein, separates functional right and left livers, each with its own portal vein, hepatic artery and bile duct branches. The Couinaud scheme then gives eight segments.
| Part | Segments |
|---|---|
| Caudate lobe | I (independent venous drainage to the IVC) |
| Left lateral section | II, III |
| Left medial section (includes quadrate lobe) | IV (IVa above, IVb below) |
| Right anterior section | V, VIII |
| Right posterior section | VI, VII |
The quadrate lobe therefore belongs to the functional left liver, although it lies in the anatomical right lobe.
Peritoneal ligaments and the bare area
Most of the liver is covered by peritoneum, and the lines where that covering reflects onto the diaphragm and abdominal wall form its ligaments.
- Falciform ligament: a sickle-shaped fold running from the anterior abdominal wall and diaphragm to the liver. Its free lower edge carries the ligamentum teres, the obliterated left umbilical vein, with small paraumbilical veins.
- Coronary ligament: the reflection onto the diaphragm around the back of the liver, with separate upper and lower layers.
- Right and left triangular ligaments: where the two layers of the coronary ligament meet at each end.
- Lesser omentum: from the fissure for the ligamentum venosum and the porta hepatis to the lesser curvature of the stomach and first part of the duodenum.
The bare area is the roughly triangular part of the posterior diaphragmatic surface enclosed by the layers of the coronary ligament. It has no peritoneum and lies directly on the diaphragm. The ligamentum venosum is the remnant of the fetal ductus venosus.
Porta hepatis and relations
The porta hepatis is the transverse fissure on the visceral surface, between the quadrate and caudate lobes, where the portal triad enters and the hepatic ducts leave. From front to back it contains the right and left hepatic ducts, the right and left hepatic arteries and the right and left branches of the portal vein, with hepatic nodes and nerves around them. The hepatic veins do not pass through it: they leave the back of the liver straight into the inferior vena cava.
The portal triad reaches the porta in the free edge of the lesser omentum, which forms the anterior boundary of the epiploic foramen (of Winslow), the opening into the lesser sac. The other boundaries are the inferior vena cava behind, the caudate process above and the first part of the duodenum below.
Other relations are the diaphragm and pleura above, the right kidney, hepatic flexure and duodenum below and behind, and the stomach under the left lobe.
Blood supply and innervation
The liver receives nutrient-rich portal blood and oxygenated arterial blood, which mix in the sinusoids and drain to the central veins and then the hepatic veins.
The portal vein forms behind the neck of the pancreas from the superior mesenteric and splenic veins. The hepatic artery proper is the continuation of the common hepatic artery from the coeliac trunk after it gives off the gastroduodenal artery. Arterial variants are common: a replaced or accessory right hepatic artery may arise from the superior mesenteric artery, and a left hepatic artery may arise from the left gastric artery.
The right, middle and left hepatic veins enter the inferior vena cava just below the caval opening of the diaphragm, and small caudate veins drain directly into the cava.
Autonomic fibres reach the liver in the hepatic plexus around the hepatic artery. The liver substance is insensitive, but stretching of its capsule gives dull right upper quadrant pain.
Clinical relevance
Segmental anatomy is what makes liver resection and split-liver transplantation possible.
- Resection: a right hepatectomy removes segments V to VIII; a left lateral sectionectomy removes II and III, the graft often used for a child.
- Pringle manoeuvre: clamping the free edge of the lesser omentum stops inflow from the portal vein and hepatic artery. Bleeding that continues suggests a hepatic vein or caval injury.
- Budd–Chiari syndrome: hepatic vein obstruction often spares the caudate lobe, which enlarges because it drains separately.
- Portal hypertension: the paraumbilical veins in the falciform ligament can open up to give caput medusae.
- Hepatorenal pouch (Morison's pouch): the space between the liver and right kidney where fluid collects in a supine patient.
On the specimen
This station is usually an isolated liver, so orient it before naming anything. The groove for the inferior vena cava is posterior, the gallbladder fossa is on the inferior surface to the right, and the falciform ligament is anterior.
- Quadrate or caudate lobe: the quadrate lobe lies in front of the porta next to the gallbladder fossa; the caudate lobe lies behind the porta next to the inferior vena cava.
- Bare area: the rough, non-shiny triangle on the posterior surface, outlined by the cut edges of the coronary ligament and triangular ligaments at its tips.
- Structures in the porta: the portal vein is the largest and most posterior and is thin-walled; the hepatic artery is small and thick-walled; the common hepatic duct is anterior and to the right, often bile-stained.
- Diaphragmatic or visceral surface: the diaphragmatic surface is smooth and convex; the visceral surface is flatter, with impressions and the porta.