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The liver is divided into eight major segments (including the caudate lobe), each with its own portal triad consisting of hepatic artery, portal vein, and bile duct branch. The right and left halves of the liver are divided along the middle scissura defined by the middle hepatic vein. This division is also known as the principal line (Cantlie’s line), which extends cephalad and obliquely from the middle of the gallbladder fossa to the center of the inferior vena cava (FIGURE 1, A–A′). The left hemiliver is further divided into medial (segment IV) and lateral sections (segments II and III) along the umbilical fissure. The left lateral section is further divided by the left scissura (marked by the left hepatic vein) into a cephalad segment 2 and a caudal segment 3 (FIGURE 2). The right hemiliver is separated into the right anterior section (segments 5 and 8) and a right posterior section (segments 6 and 7) based on the right scissura, which is defined by the right hepatic vein. Each of these sections is further divided into superior segments (VII and VIII) and inferior segments (V and VI) (FIGURE 2).

A comprehensive understanding of surgical anatomy is required to safely and successfully perform complex anatomic liver resections. Furthermore, it is important to understand and anticipate aberrancy and variations of standard arterial, portal venous, and biliary anatomy that are common. In general, the portal triad structures bifurcate in a serial manner and ultimately lead directly into each of the eight segments. The specific exception to this rule is the umbilical portion of the left portal vein, because this structure straddles the division between the left inferomedial (IVb) and lateral (III) segments (FIGURE 1, #7). Inflow to the left lateral section arises from paired portal pedicles (segments 2 and 3; FIGURE 1, #9, #10), while inflow to the left medial section arises from paired portal pedicles (segments 4a and 4b; FIGURE 1, #8, #12).

It is equally important at this point to examine the biliary and arterial supply of this area (FIGURE 6). The main left hepatic duct and artery proceed with the expected bifurcations out through the superior and inferior divisions of the left lateral section, but the left medial section duct and artery (FIGURE 6, #13) do not divide but rather send long, paired structures out to the superior and inferior segments (FIGURE 6, #12, #13). In contrast, the portal triad distribution to the right hemiliver is via a straightforward arborization with major divisions first into anterior and posterior sections, followed by secondary divisions into superior and inferior segmental pedicles (FIGURE 1, #2–#5). Interestingly, the caudate lobe straddles the major right and left cleavage planes and simply receives its portal supply directly from the right ...

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