Gross anatomy of liver

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Gross Anatomy of the Liver

Overview

The liver is the largest solid organ in the body, weighing approximately 1,500 g in adults. It sits in the right upper quadrant (hypochondrium), beneath the diaphragm, protected by the rib cage. Its surface is reddish-brown in colour and covered by visceral peritoneum (serosa), beneath which lies a fibrous sheath called Glisson's capsule. At the porta hepatis, the capsule extends along portal tracts into the parenchyma, carrying branches of the hepatic artery, portal vein, and bile ducts.

Surfaces

Surface	Relations
Diaphragmatic (superior)	Smooth, dome-shaped, related to diaphragm and separated from pleura/lung
Visceral (inferior)	Bears impressions of stomach, duodenum, right kidney, right adrenal, hepatic flexure of colon

Ligaments and Peritoneal Reflections

Hepatic ligaments suspending the liver to the diaphragm and anterior abdominal wall

Hepatic ligaments - Schwartz's Principles of Surgery, 11th Ed.

Falciform ligament - remnant of the umbilical vein; runs from the umbilicus cephalad onto the liver's anterior surface, anchoring it to the anterior abdominal wall. Divides the left lateral from the left medial segment along the umbilical fissure.
Round ligament (ligamentum teres) - the obliterated umbilical vein, located along the free edge of the falciform ligament; enters the left hepatic hilum.
Ligamentum venosum (Arantius' ligament) - the obliterated ductus venosus; lies deep between the caudate lobe and left lateral segment.
Right triangular ligament - anchors the right lobe to the right hemidiaphragm and right retroperitoneum (over the right kidney).
Left triangular ligament - anchors the left lobe to the left hemidiaphragm.
Coronary ligaments - extend anteriorly from the triangular ligaments; the right also anchors to the peritoneum over the right kidney.
Lesser omentum (gastrohepatic and hepatoduodenal ligaments) - connects the liver to the stomach and duodenum; its right free edge is the porta hepatis, containing the common bile duct (right, anterior), hepatic artery proper (left, anterior), and portal vein (posterior).

The foramen of Winslow (epiploic foramen) lies posterior to the porta hepatis and connects the greater and lesser peritoneal sacs. Clamping the hepatoduodenal ligament here controls hepatic inflow - the Pringle maneuver.

Lobes (Traditional Anatomical Division)

Classically, the liver is divided into right and left lobes by the falciform ligament on the anterior surface. Two additional smaller lobes are visible on the visceral surface:

Caudate lobe (posterior, segment I) - lies anterior to the IVC, to the left, and has three subsegments: Spiegel lobe, paracaval portion, and caudate process.
Quadrate lobe - between the gallbladder fossa and the falciform ligament anteriorly; corresponds to segment IVB.

Note: The falciform ligament does NOT separate the functional right and left halves. The true surgical (functional) division is Cantlie's line (see below).

Couinaud's Segmental Anatomy

The most important surgical framework is Couinaud's segmental anatomy (1950s), which divides the liver into 8 functionally independent segments based on portal, arterial, and biliary supply:

Couinaud's liver segments - functional division as seen in the patient and in ex vivo position

Couinaud's 8 segments - Bailey & Love's Short Practice of Surgery, 28th Ed.

Segment I - Caudate lobe (posterior, receives supply from both right and left systems)
Segments II and III - Left lateral section (left lateral segment)
Segment IV - Left medial segment (IVA = cephalad; IVB = caudad, adjacent to gallbladder)
Segments V and VIII - Right anterior section
Segments VI and VII - Right posterior section

Segments are numbered clockwise from the caudate lobe. Each segment is an independent unit with its own portal vein branch, hepatic artery branch, bile duct, and hepatic vein tributary - allowing anatomical resections.

Cantlie's Line (Principal Plane)

An imaginary parasagittal plane from the gallbladder fossa to the IVC. It contains the middle hepatic vein and divides the liver into the right half (segments V-VIII) and left half (segments I-IV) of approximately equal size. This is the true surgical midplane.

Blood Supply

The liver has a dual blood supply:

Portal vein: ~75-80% of blood flow (nutrient-rich, but less oxygen)
Hepatic artery: ~20-25% of blood flow (oxygen-rich)

Hepatic Artery

Arises from the celiac trunk (which also gives left gastric and splenic arteries)
Celiac trunk → common hepatic artery → gastroduodenal artery + hepatic artery proper
Hepatic artery proper → right and left hepatic arteries
"Classic" anatomy is present in only ~76% of individuals

Common arterial variants (24%):

Variant	Frequency
Replaced/accessory right hepatic artery from SMA	10-15%
Replaced/accessory left hepatic artery from left gastric	3-10%
Both replaced right + left hepatic arteries	~1-2%
Completely replaced common hepatic artery from SMA	~1-2%

Portal Vein

Formed by the union of the superior mesenteric vein and splenic vein behind the neck of the pancreas
Runs in the posterior aspect of the hepatoduodenal ligament
Divides into right and left portal vein branches at the hilum
Supplies nutrient-rich blood from the gut, spleen, and pancreas

Venous Drainage (Hepatic Veins)

Three main hepatic veins drain directly into the inferior vena cava (IVC) just below the diaphragm:

Vein	Fissure	Separates
Right hepatic vein	Right fissura	Right posterolateral sector (VI, VII) from right anterolateral sector (V, VIII)
Middle hepatic vein	Main fissura (Cantlie's line)	Right liver from left liver
Left hepatic vein	Left fissura	Left posterior (II) from left anterior sectors (III, IV)

The caudate lobe (segment I) drains separately via multiple small veins directly into the IVC - making it unique and surgically significant in Budd-Chiari syndrome.

Biliary Drainage

Bile flows from hepatocytes → bile canaliculi → bile ductules → right and left hepatic ducts
Right hepatic duct - Right anterior duct (enters above hilar plate) + right posterior duct (dives behind right portal vein)
Left hepatic duct - Longer extrahepatic course before giving segmental branches
Right + Left hepatic ducts → Common hepatic duct → (joined by cystic duct) → Common bile duct
30-40% of cases have a non-standard hepatic duct confluence (accessory or aberrant ducts)

The gallbladder sits adherent to segments IVB and V.

Porta Hepatis

The porta hepatis (hilum of the liver) is the transverse fissure on the visceral surface through which the following structures enter or exit:

Structure	Position
Common bile duct	Right, anterolateral
Hepatic artery proper	Left, anterior
Portal vein	Posterior (largest)
Lymphatics and autonomic nerves	Accompany the above

Innervation

Parasympathetic: Left vagus (anterior hepatic branch) and right vagus (posterior hepatic branch)
Sympathetic: Greater thoracic splanchnic nerves via the celiac ganglia
The right phrenic nerve contribution explains referred pain to the right shoulder and scapula in liver/biliary disease

Lymphatic Drainage

Superficial lymphatics drain to hepatic nodes at the porta hepatis, then to celiac nodes
Deep lymphatics follow hepatic veins upward to posterior mediastinal nodes, or downward with portal structures to porta hepatis nodes

Embryology (Brief)

Hepatic diverticulum buds from the foregut at 3-4 weeks' gestation into the ventral wall of the primitive midgut
Bipotential hepatoblasts invade the septum transversum and differentiate into hepatocytes and cholangiocytes
The umbilical vein becomes the round ligament (ligamentum teres) after birth
The ductus venosus becomes the ligamentum venosum

Summary

Feature	Key Points
Weight	~1,500 g
Position	Right hypochondrium, under diaphragm
Covering	Glisson's capsule (fibrous); visceral peritoneum
Surgical lobes	Right (60-70%): segments V-VIII; Left (+ caudate): segments I-IV
Functional division	Cantlie's line (gallbladder fossa to IVC)
Segments	8 (Couinaud), numbered clockwise from caudate
Blood supply	Portal vein (75-80%) + hepatic artery (20-25%)
Venous drainage	Right, middle, left hepatic veins into IVC
Hilum contents	CBD (right), hepatic artery (left), portal vein (posterior)
Key ligament	Falciform (ant. abdominal wall), hepatoduodenal (porta hepatis)

Sources: Schwartz's Principles of Surgery, 11th Ed. | Bailey and Love's Short Practice of Surgery, 28th Ed. | Gray's Anatomy for Students

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