Segment Anatomy of the Liver and Imaging

Abstract

Although in gross anatomy the liver is divided into the right and left lobes with the falciform ligament as the dividing line, the right lobe is disproportionately larger than the left; it encompasses the caudate and quadrate lobes on the posterior-inferior surface. From the circulatory and functional aspects, the dividing line for the right and left lobes proposed by Cantlie in 1989 [1], one that connects the fossa for the inferior vena cava and the gallbladder fossa, is more useful because blood supply and biliary drainage are consistent with such a division. Thus, the quadrate lobe is part of the left lobe when the Cantlie line is used. A simple segment anatomy may be to divide the right lobe into the anterior and posterior segments (supplied by the anterior and posterior portal vein) and leave the left lobe without division so that the three masses are similar in size, or to divide the left lobe into the medial and lateral segments (Fig. 18.1). The caudate lobe is independent of other segments because it receives one branch coming directly from the portal trunk and several others from the first order portal branches, and should not belong to either lobe or any segment. For advanced surgery, further division may be desirable, and currently a segment anatomy (Fig. 18.2) proposed by Couinaud [2], which is a modification of the scheme based on the bile duct anatomy [3,4], is generally used. Healey and Schroy [4] divided the medial segment, which lies between the Cantlie line and the falciform ligament/fissure for the ductus venosus, into the superior and inferior segments, but Couinaud did not divide it and called it Segment IV in his scheme in which the caudate lobe was called Segment I. Since most surgeons use Couinaud’s segment anatomy, the subsequent discussion will be based on his design.