A recent question in AIPGE 2004 on this baffling term makes it a contentious topic. Lets learn a bit about it. Here is the question and the tutorial follows it:
The Couinaud's segmental nomenclature is based on the position of the:
1. Hepatic veins and portal vein
2. Hepatic veins and biliary ducts
3. Portal vein and biliary ducts
4. Portal vein and hepatic artery
The answer is '1. Hepatic veins and portal vein' although some people can argue about option 2 also. Still the differences in opinion are open to discussion at aipge.previouspapers.com
Couinaud's nomenclature is a surgically relevant system of hepatic segmental anatomy, which defines the liver segments by their relationships to vascular structures, hepatic ligaments, and the gallbladder.
It was developed by Couinaud and colleagues in France. This system shows more consideration for the hepatic venous drainage and caudate lobe but also applies to the portal, biliary, and arterial anatomy.
Instead of four, there are eight segments: four on the right, three on the left, and one corresponding to the topographic caudate lobe.
Segment I corresponds to the caudate lobe;
Segments II to IV constitute the left lobe; and
Segments V to VIII make up the right lobe.
The three main hepatic veins divide the liver into four sectors. The planes containing the right, middle, and left hepatic veins are called portal scissurae, whereas the planes containing the portal pedicles are called hepatic scissurae. The caudate lobe is its own autonomous segment in the French system.
In general, the segments described in the French classification correspond to the subsegments in the lobar anatomic classification.
The North American surgeons used the classification of liver segments described by Healey, while the Couinaud's classification was used in Europe and in Japan. Recently, a new terminology called the Brisbane 2000 Terminology of Liver Anatomy and Resections has been unanimously recommended and accepted by the scientific committee of the International Hepato-Pancreato-Biliary Association (IHPBA) in order to resolve the existing confusion.