Each functional lobe of the liver can be further subdivided into two sectors. Therefore, the liver has the following four sectors:

The right functional lobe is composed of the right posterior (lateral) and right anterior (medial) sectors.
The left functional lobe contains the left medial and left lateral sectors.

Both left sectors can be separated along the attachment line of the falciform ligament and the fissures for the ligamentum venosum and round ligament. Therefore, the left medial sector is composed of the anatomical caudate and quadrate lobes. The left lateral sector is formed by the left anatomical lobe.

In contrast, no such visible landmarks distinguish both right sectors. They are usually divided by an imaginary line that is drawn obliquely from the upper-middle aspect of the right functional lobe to the inferior border of the liver. Both right sectors are formed by the right anatomical lobe of the liver.

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Liver sectors