I PART 1 Pathobiology of the Liver and Biliary Tract COPYRIGHTED MATERIAL 1 CHAPTER 1 The Liver and Biliary Apparatus: Basic Structural Anatomy and Variations Nirusha Lachman and Wojciech Pawlina Department of Anatomy, Mayo Clinic, Rochester, MN, USA Summary Understanding the anatomy of the liver may be complicated by the lack of anatomic consistency in its description. Although external observation of the liver presents a clear depiction of lobar division, appreciation of its functional anatomy is often made diffi cult by its complex intrahepatic architecture. In this chapter, the liver is approached through a clear delineation of the core features central to the clinical translation of its anatomy. The liver is described in terms of its location and surface anatomy, peritoneal relationships, surfaces and lobes, segmental anatomy, blood supply, and venous and lymphatic drainage. Descriptions combine gross anatomic features and histology with a commentary on the development and variations of the liver. Introduction matic position, the liver lies beneath the overlying ribs and cartilage. Its superior convex surface fi lls the concav- The liver is one of the largest organs in the body, occupy- ity of the right dome of the diaphragm, reaching the fi fth ing at least 2 – 3% of the total adult body weight [1 – 3] . It rib on the right and the fi fth intercostal space, 7 – 8 cm weighs roughly 1200 – 1500 g in the average adult and, from the midline, on the left. The upper margin may be although not signifi cant, reports have suggested that traced at the level of the xiphisternal joint as it arches there may be population - specifi c variations in liver upward on each side. The right lateral margin therefore weight (1800 – 2600 g) [1] . lies against the diaphragm and anterolateral thoracic wall, crossing the seventh to eleventh ribs along the Location and Surface Anatomy midaxillary line. In comparison, the inferior border is (Figure 1.1 ) sharp and may be followed just below the costal margin The liver appears wedge shaped, with its base to the right on the right extending to the left toward the fi fth inter- and its apex projecting to the left as it extends between costal space. It is formed by a line joining the right lower, the right and left upper quadrants. In its subdiaphrag- and upper left extremities [2 – 11] . Peritoneal Relationships As the liver continues to grow and enlarges during its Practical Gastroenterology and Hepatology: Liver and Biliary development, the ventral mesentery is modifi ed to form Disease, 1st edition. Edited by Nicholas J. Talley, Keith D. Lindor membranous folds that not only enclose almost the and Hugo E. Vargas. © 2010 Blackwell Publishing Ltd. entire liver but also provide diaphragmatic and visceral 3 4 PART 1 Pathobiology of the Liver and Biliary Tract (a) (b) (d) (c) Figure 1.1 CT scans of liver in situ : (a) horizontal plane; (b) coronal plane. (c) Three - dimensional image of liver; (d) anterior view of liver in abdominal cavity. (Image (d) is courtesy of RF Morreale, 2008.) attachments. At its upper pole, however, the liver makes Folds of peritoneum pass from the diaphragmatic and direct contact with the developing diaphragm and, as a visceral surfaces, connecting the liver to two main struc- result, is devoid of peritoneum. This area is referred to tures (Figure 1.2 ): (1) the diaphragm and (2) the stomach. as the “ bare area ” and persists as the only portion of the When entering the abdominal cavity during a dissection, liver surface with no membranous covering. a sickle - shaped anterior fold of peritoneum is visible. CHAPTER 1 The Liver and Biliary Apparatus: Basic Structural Anatomy and Variations 5 Coronary ligament Right triangular of the liver Left triangular ligament ligament Right lobe Left lobe Falciform ligament Round ligament of the liver Fundus of the Figure 1.2 Peritoneal ligaments. (Courtesy gall bladder of RF Morreale, 2008.) This is known as the falciform ligament. It consists of • Porta hepatis: two layers of adherent peritoneum and attaches the º two layers of lesser omentum deviate to the right and liver to the supraumbilical part of the anterior abdominal enclose the portal triad (portal vein, hepatic artery, bile wall, as well as to the inferior surface of the thoracic duct) diaphragm. Inferiorly, the falciform ligament is unat- º contains lymph nodes and nerves. tached and contains the ligamentum teres (obliterated • Gall - bladder fossa: left umbilical vein). As the falciform ligament ascends º located on the inferior slope of the visceral surface superiorly, it produces the left triangular ligament, which with cystic duct close to the right margin of porta extends toward the left tip of the liver, but stops short, hepatis about two - thirds of the way along the superior margin, º lies between the colic impression and the quadrate and is related to the lesser omentum along its posterior lobe. fold. As the falciform ligament passes superiorly and • Quadrate lobe: between the gall - bladder fossa and to the right, it gives rise to the upper layer of the coronary fi ssure for ligamentum teres. ligament, so named because it encircles the bare area • Bare area: in contact with the diaphragm and right of the liver. The inferior line of peritoneal attachment suprarenal gland. passes superiorly toward the summit of the liver, where In addition, the stomach, duodenum, hepatic fl exure it meets the leaf of the falciform ligament. These of the colon, and the right kidney form impressions on ligaments then attach to a groove, which lodges the the visceral surface. ligamentum venosum (remnant of the ductus venosus). The coronary ligament fuses at its apex to form a L o b e s small, rather insignifi cant right triangular ligament Anatomically, the liver is divided into a larger right and [2 – 11] . a smaller left lobe using the line of attachment of the falciform ligament and fi ssures for ligamentum teres and Visceral Surface ligamentum venosum. Functionally, the liver is divided The visceral surface of the liver is best observed by supe- along an oblique line that passes through the center of rior rotation so that the inferior margin lies superiorly. the bed of the gall bladder and the groove for the inferior Several key structures may be identifi ed on this surface vena cava (IVC) along the plane of the middle hepatic (Figure 1.3 ): vein [12,13] . 6 PART 1 Pathobiology of the Liver and Biliary Tract Gall bladder Anterior Round ligament of the liver Porta hepatis Right Left Ligamentum venosum Inferior vena cava (a) Posterior Colic Duodenal surface surface Renal surface Gastric surface Suprarenal surface Figure 1.3 (a) Visceral surface of liver showing portal triad; (b) liver visceral surface (b) impressions. (Courtesy of RF Morreale, 2008.) The quadrate lobe is located on the superior part of ary of the epiploic foramen. Description of the functional the visceral surface, bound by the fi ssure for ligamentum segments of the liver has been based on blood supply teres on the left and the gall - bladder fossa on the right. (systemic and portal) and venous and biliary drainage. Anatomically, it is considered part of the right lobe but Although there are several descriptions of segmental remains, functionally, part of the left lobe. anatomy, the most commonly applied nomenclature is The caudate lobe is located on the inferior part of the based on Bismuth ’ s interpretation [16] , where all hepatic visceral surface of the liver, bound by the fi ssure for liga- segments, except for the caudate lobe, are defi ned by mentum venosum on the left and by the groove for the three vertical fi ssures and a single transverse fi ssure. Of IVC on the right. The caudate lobe exhibits a complex these fi ssures, only one appears to be represented super- anatomy and is said to be embryologically and anatomi- fi cially (portoumbilical fi ssure) [12,13] , while the others cally independent of the right and left lobes of the liver are related to three large hepatic veins. The right fi ssure, [14,15] . It therefore remains a separate anatomic lying almost in the coronal plane, contains the right segment. The right portion of the caudate lobe extends hepatic vein. The median fi ssure passes from the gall - as the caudate process which forms the superior bound- bladder fossa to the left margin of the IVC. The left CHAPTER 1 The Liver and Biliary Apparatus: Basic Structural Anatomy and Variations 7 fi ssure runs from the left side of the IVC toward the The following are basic points on hepatic nomencla- left margin of the liver (a point between the dorsal third ture [2,12,13,16] : and ventral two - thirds), passing inferiorly to the start of • All hepatic segments except for the caudate lobe are the ligamentum venosum. The portoumbilical fi ssure is defi ned by three vertical divisions and a single transverse marked by the attachment of the falciform ligament [12] . division. The simplest way to understand the segmental anatomy • The middle hepatic vein divides the liver into right and of the liver is to view it in four sectors (a left medial and left hemi - livers. left lateral sector and a right anterior and right posterior • The right hemi - liver is divided by the right hepatic vein sector) which are then divided into eight segments into anterior and posterior segments. [12,13] . The left lateral sector lies to the left of the falci- • The left hemi - liver is divided by the left hepatic vein form ligament attachment and the grooves for ligamen- into medial and lateral segments. tum teres and ligamentum venosum, with the left medial • Four segments are divided by a transverse line that sector lying between these lines and the plane of the gall passes through the right and left portal branches.