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SURGICAL ANATOMY OF LIVER

The liver is divided into eight major subsegments or areas (excluding the caudate lobe), with

the principal line (Cautlie's Line) of division between the right and left sides extending

cephalad and obliquely from the middle of the gallbladder fossa to the center of the inferior

vena cava between the right and left main hepatic veins (Figure 1, A–A'). The true anatomic

left lobe thus defined is divided into medial and lateral segments approximately along the line

of the falciform or round ligament, and each of these segments is then subdivided into a

superior (cephalad) area and an inferior (caudad) area (Figure 2). In contrast, the right lobe is

divided into anterior and posterior segments by a plane from the anteroinferior edge of the

liver that extends both superiorly and posteriorly. This cleavage is similar to the oblique

fissure above the right lower lobe of the lung, and it is roughly parallel to it. These segments

of the right hepatic lobe are then split into superior and inferior areas similar to those on the

left (Figure 2).

Although the segmentation of the liver appears straightforward, successful segmentectomy or

lobectomy depends upon a thorough understanding of the difference between the portal vein,

biliary duct, and hepatic artery distribution as opposed to the hepatic vein drainage. In

general, the portal triad structures bifurcate in a serial manner and ultimately lead directly into

each of the eight areas. The specific exception to this rule is the paraumbilicalis of the left

hepatic branch of the portal vein, as this structure straddles the division between the left

inferior medial and lateral segments. Thus it lies roughly under the round ligament (Figure 1,

7). The superior and inferior areas of the left lateral lobe have a portal venous supply from

either end of the paraumbilicalis (Figure 1, 9 and 10); however, special note should be made

of the paired medial supply to the superior and inferior areas of the medial segment (Figure 1,

8 and 12). It is equally important at this point to examine the biliary and arterial supply of this

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area (Figure 7). The main left hepatic duct and artery proceed with the expected bifurcations

out through the superior and inferior divisions of the left lateral segment; however, the left

medial segment duct and artery (Figure 7, 13) do not divide and send a large branch to the

superior and inferior areas, but rather send long, paired structures out in each direction from

the junction of the two areas (Figure 7, 12 and 13).

In contrast, the portal triad distribution to the right hepatic lobe is by a straightforward

arborization with major divisions first into anterior and posterior segments, followed by

secondary divisions into superior and inferior subsegmental vessels (Figure 1, 2 through 5).

Interestingly, the caudate lobe straddles the major right and left cleavage plane and simply

receives its portal supply directly from the right and left main branches of the portal vein,

hepatic arteries, and biliary ducts. Its venous return, however, is usually a single caudate lobe

hepatic vein that enters the inferior vena cava on its left side just distal to the main hepatic

veins (Figure 1, 11).

The hepatic veins, in general, run between the hepatic segments in a manner analogous to

the pulmonary veins. The right hepatic vein lies in the major cleft between the anterior and

posterior segments on that side (Figure 1, 14). The left hepatic vein (Figure 1, 15) drains

predominantly the lateral segment, while the middle hepatic vein (Figure 1, 16) crosses

between the left medial segment and the right lobe. It is imperative to know that this middle

vein is variable where it joins the main left hepatic vein within a few centimeters of the

junction with the vena cava and that this vein has two major tributaries that cross over into the

right anterior inferior and the left medial inferior areas (Figure 1, 17). Appropriate preservation

of these channels is, of course, all-important in specific segmental resections, as hepatic

venous occlusion results in necrosis of the entire area(s) involved. The two common

variations in the termination of the middle hepatic vein are shown here and in Right Hepatic

Lobectomy, where it has an entrance into the cava that is separate from the left hepatic vein.

The remaining figures demonstrate the four most common hepatic resections, whose specific

details are covered in the operative text (see Local Excision of Hepatic Tumor, Right Hepatic

Lobectomy, Left Hepatic Lobectomy, and Hepatic Trisegmentectomy). Of specific note are

the "danger points" along the paraumbilicalis of the left branch of the portal vein (Figures 4, 5

and 6). It is in these areas that the surgeon must be certain of the integrity of the hepatic

venous drainage before dividing any major venous branches. Also shown is the use of

interlocking full-thickness mattress sutures for hemostasis in the partial and total left lateral

segmentectomies, a common techique (Figures 3 and 4), as is the finger fracture technique.