Liver Lobes
The liver has four anatomical lobes and eight functional Couinaud segments. The functional division determines surgical resection planes.
✦ The Mnemonic
"Really Large Caudate Quadrate — Four Anatomical Lobes"
Right · Left · Caudate (I) · Quadrate (IV)
Clinical Breakdown
The falciform ligament divides right from left anatomically. The main portal scissura (through gallbladder fossa and IVC, containing the middle hepatic vein) is the true functional midplane. Right hepatectomy = segments V–VIII; left hepatectomy = segments II–IV.
The caudate lobe (I) drains directly into the IVC independent of the three main hepatic veins. It is spared (and hypertrophies) in Budd-Chiari syndrome — caudate hypertrophy is characteristic on CT.
Couinaud segments I–VIII: numbered clockwise anteriorly. Hepatic veins run between segments; portal pedicles run through them. This enables precise resection — e.g. segment VI resection for small peripheral HCC.
⭐ Clinical Pearl
Budd-Chiari syndrome: hepatic venous outflow obstruction. Painful hepatomegaly, ascites, jaundice. Caudate hypertrophies (independent IVC drainage). Most common aetiology: polycythaemia vera and thrombophilias. CT: absent hepatic vein opacification + caudate enlargement.