Liver Review.pdf

CHAPTER 14 The Liver MARILYN DICKERSON PRINCE OBJECTIVES Identify the principal functions of the liver. Describe the location of the liver. Describe the size of the liver. Describe and identify the vasculature of the liver. Identify the ligaments, segments, and fissures of the liver. Describe the...

CHAPTER 14 The Liver MARILYN DICKERSON PRINCE OBJECTIVES Identify the principal functions of the liver. Describe the location of the liver. Describe the size of the liver. Describe and identify the vasculature of the liver. Identify the ligaments, segments, and fissures of the liver. Describe the sonographic appearance of the liver. Differentiate between carbohydrate, protein, and fat metabolism in the liver. Describe the associated physicians, diagnostic tests, and laboratory values related to the liver. KEY WORDS Bare Area — Only area of the liver not covered by peritoneum. Caudate Lobe — Smallest lobe of the liver, bordered by fossa for the inferior vena cava (IVC), falciform ligament, and lesser omentum. Common Hepatic Artery — Branch of the celiac axis that supplies the liver and divides into the GDA and PHA. Coronary Ligament — Anterosuperior surface of liver that runs superiorly, then posteri­ orly on the right to the anterior leaf of the coronary ligaments. Couinaud’s Liver Segmentation — Division of liver segments based on hepatic or portal venous anatomy; used for dividing the liver into 8 segments. Epiploic Foramen of Winslow — Communica­ tion between the greater and lesser sacs of the peritoneum. Falciform Ligament — Divides right and left lobes; ends at the ligamentum teres or round ligament inferiorly. Gastrohepatic Ligament — Portion of the lesser omentum that extends across the transverse fissure for the ligamentum venosum at the porta hepatis of the lesser curvature of the stomach. Glisson’s Capsule — Tight, fibrous capsule covering the liver. Greater Omentum — Fold of omentum that extends from the lesser curvature of the stomach and covers the intestines. Greater Sac — Protective, thin layer that encloses most of the abdominal organs. 206 Hemiliver — Right or left half of the liver; a division based on Couinaud’s liver seg­ mentation system. Hepatoduodenal Ligament — Portion of the lesser omentum that extends as the right free border of the gastrohepatic ligament to the proximal duodenum and the right flexure of the colon. Left Hepatic Vein — One of three main veins draining the liver via the IVC; drains the left lobe. Left Portal Vein — Branch of the main portal vein that marks the anterior border of the caudate lobe and carries blood from the gastrointestinal tract to the left lobe. Left Triangular Ligament — Anterosuperior surface of the liver that runs superiorly, then posteriorly on the right to the left triangular ligament. Lesser Omentum — Double layer of omentum that extends from the liver to part of the duodenum. Lesser Sac — Small sac posterior to the stomach and anterior to the pancreas and part of the transverse colon; also known as the omentum bursa. Ligamentum Venosum — Marks the left anterolateral border of the caudate lobe; travels within the transverse fissure. Main Lobar Fissure — Echogenic line con­ necting the neck of the gallbladder to the right portal vein; also referred to as the plane associated with the Rex-Cantlie (RC) line in Couinaud’s liver segmenta­ tion system. The RC line runs from the gallbladder fossa to the IVC along the plane of the main lobar fissure. Main Portal Vein — Formed by the splenic, superior, and inferior mesenteric veins; drains blood from the gastrointestinal tract to the liver to be processed. Middle Hepatic Vein — One of 3 main veins draining the liver via the IVC; drains a portion of the right and medial left lobes of the liver. Morison’s Pouch — Space between the pos­ terior subphrenic and posterior subhe­ patic space; should be free of fluid. Papillary Process — Normal variant of the caudate lobe. Process can extend distally from the lobe and mimic a lesion. Porta Hepatis — Area of the hilus where portal vein and hepatic artery enter and common bile duct exits. Portal Confluence — Union of the splenic, superior, and inferior mesenteric veins near the head of the pancreas that forms the portal vein before entering the liver. Portal Triad — Portion of the portal vein, biliary duct, and hepatic artery that are disbursed throughout the liver; can be seen microscopically. Proper Hepatic Artery — Division of the common hepatic artery that supplies the liver. Quadrate Lobe — “Fourth” lobe of the liver, which is actually the medial portion of the left lobe. Chapter 14 The Liver 207 KEY WORDS—cont’d Reidel’s Lobe — Normal variant of the right lobe in which the right lobe extends cau­ dally into the abdomen and toward the iliac crest. Right Hepatic Vein — One of 3 main veins draining the liver via the IVC; drains the right lobe of the liver. Right Lobe — Largest lobe of the liver, occu­ pying most of the right hypochondrium. Right Portal Vein — Branch of the main portal vein that carries blood from the gastrointestinal tract to the right lobe of the liver. Right Triangular Ligament — Helps form the boundary of the bare area of the liver. Round Ligament (Ligamentum Teres) — Termi­ nal end of the falciform ligament. NORMAL MEASUREMENTS Anatomy Liver Size Liver weight Right lobe Left lobe Measurement Adult males: 1400 to 1800 g Adult females: 1200 to 1400 g Midclavicular linear measurement: 13 to 17 cm Highly variable Tthehelargest liver is a powerhouse among abdominal organs, parenchymal organ in the body. Its bulky mass displaces gas-filled components of the digestive system and provides an acoustic window for visualization of upper abdominal and upper retroperitoneal structures. Liver structures include the portal veins; the hepatic veins, arteries, and ducts; and the hepatic ligaments and fissures. On ultrasound images, many of these structures help divide the liver into easily identifiable segments. Subhepatic Space — Located posteriorly and inferiorly; forms part of Morison’s pouch. Subphrenic Space — Located posteriorly and inferiorly; forms part of Morison’s pouch. Transverse Fissure — Fissure that conveys the ligamentum venosum. LOCATION The liver occupies a major portion of the right hypochondrium. Normally, it extends inferiorly into the epigastrium and laterally into the left hypochondrium. Superiorly it reaches the dome of the diaphragm, and posteriorly it borders the bony lumbar region of the muscular posterior abdominal wall (Table 14-1). The bulk of the liver lies beneath the right costal margin (Figure 14-1). The superior surface, anterior surface, and a portion of the posterior surface of the liver are in contact with the diaphragm (Figure 14-2). The anterosuperior surface of the liver fits snugly into the dome of the diaphragm, separated from the overlying pleural cavities and pericardium. On the right, it rises to the level of the fourth rib interspace on full expiration. The thin edge of the superior surface of the left lobe reaches the level of the fifth rib on full expiration. The anterosuperior surface runs superiorly, then posteriorly, to the anterior leaf of the coronary ligaments on the right. On the left, it runs posteriorly to the left triangular ligament. The right anterosuperior surface of the liver is closest to the Anterior Left portal vein branch Hepatic vein Left Right Left lobe Portal radicle Caudate lobe Inferior vena cava Diaphragm Posterior FIGURE 14-1 Transverse scanning plane image showing an axial section of the diaphragmatic undersurface and the posterosuperior liver surface. Central leaf of diaphragm 208 Section III Table 14-1 ABDOMINAL SONOGRAPHY Location of the Liver Routinely Visualized With Ultrasound Lt Medial Lobe (inferior liver surface) Caudate Lobe (posterior liver surface) Stomach, EGJ, celiac artery, lt gastric artery, proximal CHA, splenic artery, aorta, SMA, pancreas body/tail, splenic vein, lt renal vein, fissure for ligamentum venosum (on liver’s posterior surface), caudate lobe, diaphragm, spine Xiphoid process, 7th and 8th costal cartilages Porta hepatis, pylorus, superior portion duodenum, transverse colon, GDA Diaphragm Hepatic flexure, rt kidney, rt adrenal gland, descending duodenum, diaphragm Anterior liver margin 6th to 10th ribs Stomach, bowel, lt kidney, lt adrenal gland Diaphragm Stomach, lt lateral abdominal wall, spleen IVC, falciform ligament (on liver’s superior surface), liver rt lobe, fissure for ligamentum teres (on liver’s inferior surface), lt medial lobe, spine Rt kidney, rt adrenal gland Porta hepatis, fissure for ligamentum venosum, liver lt lobe Splenic vein Diaphragm IVC Diaphragm Rt lateral abdominal wall Aorta Aorta, falciform ligament (on liver’s superior surface), liver lt lobe, lt medial lobe (on liver’s inferior surface) Lt Lobe Anterior to Posterior to Superior to Inferior to Medial to Lt lateral to Rt lateral to GB, fossa Fissure for ligamentum teres, lt lateral lobe, liver Rt Lobe Rt kidney CHA, Common hepatic artery; EGJ, esophageal gastric junction; GB, gallbladder; GDA, gastroduodenal artery; IVC, inferior vena cava; PHA, proper hepatic artery; SMA, superior mesenteric artery. Inferior vena cava Diaphragm Right lobe Left lobe Falciform ligament Fundus of gallbladder Round ligament FIGURE 14-2 Anterior Liver Surface. anterolateral abdominal wall and is palpable most often when the organ is enlarged. The liver is enclosed by a tight, fibrous capsule known as Glisson’s capsule and is largely covered by the peritoneum of the greater sac. A portion of the posterior surface of the liver is without a peritoneal covering and is called the bare area. This portion is in direct contact with the diaphragm. Right Posterosuperior Surface The major relations of the right posterosuperior surface are the right posterior fibers of the diaphragm, the upper posterior abdominal wall, the right kidney, and the right adrenal gland. The inferior segment of this surface below the inferior leaf of the coronary ligament communicates with the upper end of the right lumbar paracolic gutter and the visceral surface of the liver (Figure 14-3). Chapter 14 The bony and muscular posterior abdominal wall protects the posterior surface of the liver. The border between the anterior aspect of the liver and the visceral surface is the inferior margin. Inferior (Visceral) Surface The inferior or visceral surface of the liver rests on the upper abdominal organs. The inferior (visceral) surface of the liver is marked by indentations from organs in contact with its surface, including the gallbladder, pylorus, duodenum, right colon, right hepatic flexure of the colon, right third of the transverse colon, right adrenal gland, and right kidney. Left triangular ligament Falciform ligament Inferior vena cava Caudate lobe Bare area Anterior leaf of coronary ligament Posterior leaf of coronary ligament Left lobe Lesser omentum Round ligament Right triangular ligament Hepatic artery Portal vein Gallbladder Posterior surface of right lobe Hepatic duct FIGURE 14-3 Posterior Liver Surface. Posterior liver surface outlining the boundaries of the bare area. The Liver 209 Right-Sided Inferior Indentations Right-sided inferior indentations occur at the right hepatic flexure of the colon, the right kidney and adrenal gland, the first part of the duodenum, and the gallbladder. Left Side of Inferior Surface The left side of the inferior surface contains a gastric indentation, and the posterior surface is marked by the groove that surrounds the inferior vena cava (IVC) (Figure 14-4; see also Figure 14-3). The anterior midportion of the inferior surface is the medial portion of the left lobe of the liver, which is also referred to as the quadrate lobe of the liver. The left lateral boundary of this portion is the falciform ligament, usually noted near the midline of the body (Figure 14-5; see also Figures 14-2 and 14-3). Posterior Midportion of Inferior Surface The posterior midportion of the inferior surface, below the porta hepatis, marks the location of the caudate lobe (Figure 14-6). The posterior portions of the left and caudate lobes form a portion of the anterior boundary of the lesser sac. The lesser sac lies anterior to the pancreas and posterior to the stomach. Right Lobe The right lobe of the liver lies close to the anterolateral abdominal wall (Figure 14-7 and Table 14-2; see Table 14-1). The right lobe is related to the right lateral undersurface of the diaphragm along the right midaxillary line from the seventh to the eleventh ribs. On the lateral right side, the liver is related to the diaphragmatic recess and the descending fibers of the diaphragm. Anterior Superior mesenteric vein Liver Pancreas neck Inferior vena cava Inferior Portal vein Superior Portal confluence Inferior vena cava Spine Uncinate process Liver Posterior FIGURE 14-4 Sagittal scanning plane image showing a longitudinal section of the left inferior margin of the left hepatic lobe. Note posteriorly how the liver surrounds the IVC. 210 Section III ABDOMINAL SONOGRAPHY Anterior Falciform ligament Liver Superior mesenteric vein Duodenum Branch of left portal vein Gallbladder Right Left Liver Common bile duct Right kidney Splenic vein Superior mesenteric artery Inferior vena cava Crus of diaphragm Spine Uncinate process Left renal artery Aorta Posterior FIGURE 14-5 Transverse Scanning Plane Image of the Midepigastrium. The falciform ligament appears in short axis as a triangular-shaped, bright, echogenic focus demarcating the lateral border of the quadrate (medial left) lobe. Anterior Fissure for ligamentum venosum Left lobe liver Hepatic artery Left hepatic vein Inferior Superior Caudate lobe Portal vein Pancreas head Inferior vena cava Posterior FIGURE 14-6 Parasagittal scanning plane image just to the right of the midline of the body that demonstrates the liver’s caudate lobe posterior to the left hepatic lobe and a longitudinal section of the thin, bright ligamentum venosum. The left hepatic vein is seen coursing toward the inferior vena cava. Left Lobe Caudate Lobe The left lobe of the liver is closely related to the undersurface of the diaphragm. It varies in size and shape and may extend deeply into the left upper quadrant. The free inferior margin of the left lobe is closely related to the gastric body and antrum of the stomach. It frequently lies anterior to the body of the pancreas, the splenic vein, and the splenic artery (see Tables 14-1 and 14-2). The smallest lobe, the caudate, is related to the lumbar region of the posterior abdominal wall and to the lower posterior thoracic wall (see Tables 14-1 and 14-2). The caudate lobe is covered by the peritoneum of the lesser sac. The anterior boundary of the caudate lobe is marked by the posterior surface of the left portal vein, and the posterior boundary is the IVC. The lateral margin of the caudate lobe projects into the superior recess of the Chapter 14 211 The Liver Anterior Hepatic veins Right lobe of liver Right lateral margin Superior Diaphragm Inferior Posterior-inferior margin Posterior FIGURE 14-7 Longitudinal section of the right lateral margin of the liver illustrating the base of the liver pyramid. Note by the location of the transducer how the right lobe of the liver lies close to the anterolateral abdominal wall. Table 14-2 Lobar Liver Anatomy With Landmarks Lobe Identified by … Identified by … Identified by … Comments Right RL lies close to anterolateral abdominal wall LL lies close to gastric body and antrum of the stomach RL lies close to right lateral undersurface of the diaphragm Anterior to body of pancreas Diaphragmatic recess on the right lateral side Largest lobe Anterior to the splenic vein and splenic artery Quadrate Anterior midportion of the inferior surface of the LL Medial portion of the LL Caudate Posterior midportion of the inferior liver surface, below porta hepatis, lies between RL and LL Anterior boundary marked by posterior surface of LPV. Posterior boundary marked by IVC Left lateral boundary is the left intersegmental fissure, which divides the LL into medial and lateral segments. The falciform ligament and ligamentum teres are located within this fissure Separated from LL by proximal portion of LHV and fissure for the ligamentum venosum— the fissure also contains a portion of the lesser omentum May extend deep into the left upper quadrant; can vary in size and shape Some categorizations do not consider this a lobe Left lesser sac, also called the omental bursa. The caudal border forms the cephalad margin of the epiploic foramen of Winslow, the opening between the greater sac of the peritoneal cavity in the abdomen, which encloses the abdominal organs, and the lesser sac. The omental bursa is bordered anteriorly by the stomach, posteriorly by the pancreas, and posteriorly by part of the transverse colon (Table 14-3). Smallest lobe The IVC courses through the bare area of the liver, which lies between the leaflets of the anterior inferior and posterior superior coronary ligaments. The right kidney and right adrenal gland also lie near the bare area of the liver, laterally and inferiorly. The boundaries of the bare area include the falciform ligament, right anterior inferior and right posterior superior coronary ligaments, right triangular ligament, gastrohepatic 212 Section III Table 14-3 ABDOMINAL SONOGRAPHY Peritoneal Divisions Division Also Called Functions Greater sac Abdominal cavity Lesser sac Omental bursa Epiploic of Winslow Lesser omentum Omental foramen, epiploic foramen Encloses most of the abdominal organs; enclosed organs called “intraperitoneal” Small sac bordered anteriorly by the stomach, posteriorly by the pancreas and a portion of the transverse colon Passageway between greater and lesser sacs just inferior to the liver Double peritoneum extends from liver to lesser curvature of stomach and beginning of duodenum Large fold of peritoneum that extends from stomach, passes anteriorly to the colon and small intestine Greater omentum Gastrohepatic omentum, small omentum Gastrocolic omentum ligament, left anterior and left posterior coronary liga- ments, and left triangular ligament (see Figure 14-3). SIZE In men the liver weighs between 1400 and 1800 g, and in women it weighs between 1200 and 1400 g. The length of the right lobe and the size of the lateral segment of the left lobe determine the contours of the liver. The right lobe is larger than the left, containing approximately two thirds of the parenchymal tissue. Along the midclavicular line, the normal longitudinal measurement of the right lobe is 13 cm or less, although this measurement has also been stated to be 15 to 17 cm. (Refer to the Normal Measurements box at the beginning of this chapter.) The left lobe is more varied in size. It may be atrophic if interference with the left portal venous supply occurs as the ductus venosus closes at birth. A larger left lobe helps in visualization of the pancreas and left upper quadrant. GROSS ANATOMY The liver is divided into 3 lobes: a right lobe, a left lobe, and a caudate lobe. The right and left lobes are subdivided into 4 segments: anterior and posterior segments on the right and lateral and medial segments on the left. The caudate lobe is a midline structure on the posterior aspect of the liver that separates a portion of the right and left hepatic lobes. The caudate lobe is separated from the left hepatic lobe by the proximal portion of the left hepatic vein and the fissure for the ligamentum venosum (see Figure 14-6). This fissure contains the ligamentum venosum and a portion of the lesser omentum, a double layer of peritoneum that extends from the liver to the lesser curvature of the stomach and the beginning of the duodenum. It is also called the gastrohepatic or small omentum. It is related to the greater omentum, which is a great fold of peritoneum that hangs from the stomach and covers the intestines (see Table 14-3). The anterior midportion of the inferior surface of the liver is sometimes called the quadrate lobe. It is not an anatomically distinct lobe but is more correctly identified as the medial segment of the left lobe. The left intersegmental fissure divides the medial and lateral segments of the left hepatic lobe. The falciform ligament and the ligamentum teres (round ligament) are located within this fissure. The inferior surface of the liver pre­ sents a characteristic H pattern of anatomic lobar segmentation (Figure 14-8, Table 14-4). The anterior portion of the H depicts the gallbladder on the right, dividing the anterior right lobe from the medial left lobe. On the left anteriorly, the ligamentum teres divides the medial from the lateral left lobe. Posteriorly on the right, the IVC separates the right lobe and the caudate lobe, whereas on the left the ligamentum venosum divides the caudate from the lateral left lobe. The crossbar of the H depicts the porta hepatis. The hepatic veins drain blood from the segments and lobes of the liver. They are interlobar and intersegmental. The right hepatic vein separates and drains the anterior and posterior segments of the right lobe. The left hepatic vein separates and drains the medial and lateral segments of the left lobe of the liver. The middle hepatic vein separates and drains the right and the medial left liver lobes (Figures 14-9 and 14-10, Table 14-5). The hepatic veins subdivide into superior and inferior groups. The smaller inferior veins drain the caudate lobe and the posteromedial portion of the right lobe. The portal veins course within and supply the hepatic lobes and segments. Although the hepatic veins usually divide the liver segments, the left portal vein serves as an intersegmental boundary between the medial and lateral segments of the left lobe on caudal transverse scans of the left hepatic lobe. The branching patterns of the portal triads, which consist of the portal vein, the hepatic artery, the bile ducts, and their divisions, are central to the functional segmentation of the hepatic lobes, originally described by Couinaud. One can appreciate the Chapter 14 Gallbladder The Liver 213 Medial aspect of left lobe (quadrate lobe) Ligamentum teres (round ligament) Right lobe Falciform ligament Left lobe Hepatic Ligamentum venosum Inferior Caudate veins vena cava lobe Gallbladder Common hepatic duct Cystic duct Hepatic artery Common bile duct Porta hepatis Main portal vein FIGURE 14-8 The inferior surface of the liver depicting the H pattern of lobar segmentation. Table 14-4 H Pattern of Anatomic Lobar Segmentation Table 14-5 Liver Division by Hepatic Veins Part of the “H” Depicts the … Hepatic Vein Separates and Drains the … Anterior portion of the H, toward the right Gallbladder on the right, dividing the anterior right lobe from the medial aspect of the left lobe Ligamentum teres divides the medial and the lateral portion of the left lobe IVC separates the right lobe from the caudate lobe Right hepatic vein Anterior and posterior segments of the right lobe Medial and lateral segments of the left lobe Right lobe and medial left lobe Anterior portion of the H, toward the left Posterior portion of the H, toward the right Posterior portion of the H, toward the left Ligamentum venosum divides the caudate lobe from the lateral left lobe abundant quantity of portal triads in liver parenchyma when examining a liver biopsy sample microscopically. One research study reported that from an approximate 1.8-cm liver tissue sample, an average of 11 portal triads were found. Portal dyads, which contain any 2 of Left hepatic vein Middle hepatic vein the triad structures, were also found in the samples, indicating that portion of the tissue did not capture the entire triad. The pattern of anatomic segmentation provides the basis for surgical resections of the liver. Couinaud’s liver segmentation is based on venous anatomy, with either hepatic or portal veins dividing the liver (Tables 14-6 and 14-7 and Figure 14-11). When using the portal vein as the dividing basis, there is always a central portal vein within the segment, whereas a hepatic vein will course at its periphery in the plane between adjacent portal divisions. Segments are thus defined by the portal 214 Section III ABDOMINAL SONOGRAPHY Anterior Anterior segment of right lobe Middle hepatic vein Left hepatic vein Posterior segment of right lobe Diaphragm Inferior vena cava Left Right Diaphragm Posterior Right hepatic vein FIGURE 14-9 Transverse scanning plane image demonstrating the hepatic veins draining into the inferior vena cava. Anterior and posterior segments of the right hepatic lobe are prominently displayed. Recall that the right hepatic vein separates the anterior liver segments 5 and 8 from the posterior segments 6 and 7. Anterior Medial segment of left lobe Lateral segment of left lobe Anterior segment of right lobe Diaphragm Right Left Diaphragm Inferior vena cava Posterior FIGURE 14-10 Transverse scanning plane image showing a section of the hepatic veins and inferior vena cava forming the “bunny sign.” Table 14-6 Rex-Cantlie line Right hemiliver Left hemiliver Couinaud’s Liver Segmentation Runs from gallbladder fossa to IVC and passes through portion of caudate lobe; this is the plane we refer to for the main lobar fissure Anterior and posterior segments divided into … Anterior segment only divided into … Divides liver into right and left hemiliver (liver halves); hemilivers further divided into anterior and posterior segments Inferior and superior segments Superior and inferior segments Chapter 14 215 The Liver Anterior Left portal vein Right portal vein Left lobe of liver Right Left Caudate lobe Inferior vena cava Transverse fissure for ligament venosum Posterior FIGURE 14-11 Transverse scanning plane image showing the left portal vein, demonstrating Couinaud’s liver segments 1 through 4. The umbilical portion of the left portal vein branches to liver segments 2, 3, and 4. Note the caudate lobe (segment 1) anterior to the inferior vena cava and posterior to the left portal vein at this level. Table 14-7 Couinaud’s Liver Segmentation Identification Couinaud’s Segment Liver Portion Identified by … Segment 1 Caudate Segments 2 to 4 Left hemiliver Segments 5 to 8 Right hemiliver Bordered posteriorly by IVC and anteriorly by LPV Segments 2 and 3 found to the left of the ligamentum venosum and falciform ligament Segments 5 and 8 are anterior; segments 6 and 7 are posterior Note: Each of the 8 segments has a distinct portal triad independent of the other segments. venous branches that lead into them and by the hepatic veins that separate them. The liver is divided into a right and left hemiliver via a plane known as the Rex-Cantlie line, which runs from the gallbladder fossa toward the IVC and passes through a portion of the caudate lobe. This is the plane we refer to for the main lobar fissure. Each hemiliver is further subdivided into an anterior and posterior segment. On the right, the anterior and posterior segments are each subdivided into inferior and superior segments, whereas on the left, only the left anterior segment is divided into superior and inferior segments. The caudate lobe represents segment 1 (Figure 14-12). The caudate lobe is bordered posteriorly by the IVC and anteriorly by the left portal vein. Moving in a counterclockwise direction, segment 1 is separated from segment 2 by the ligamentum venosum. The left hemi­ liver contains segments 2 through 4. Segments 2 and 3 are found to the left of the ligamentum venosum and the falciform ligament. The falciform ligament separates segment 3 from segment 4. Segment 4 is separated from segment 1 by the left portal vein, and the middle hepatic vein and the main lobar fissure separate segments 5 and 8. The right hepatic vein separates anterior segments 5 and 8 from posterior segments 6 and 7 (see Figure 14-9). Segments 5 through 8 are part of the right hemiliver. Each of these 8 segments of the liver is distinct in having a central portal triad independent of the other segments, thus providing an important factor in segmental hepatic surgical resections. The portal system supplies 75% of total blood flow to the liver and has 3 main tributaries to its confluence: the splenic vein, the superior mesenteric vein, and the inferior mesenteric vein, which may join the splenic vein on its course to the portal confluence (union of the splenic and superior and inferior mesenteric veins that form the portal vein before entering the liver). The main portal vein enters the porta hepatis and divides into left and right branches (Figures 14-13 and 14-14; see Figure 14-11). These veins then branch into medial and lateral divisions on the left and anterior and posterior divisions on the right, and they become 216 Section III ABDOMINAL SONOGRAPHY Anterior Left portal veins Falciform ligament Pancreas Left hepatic vein Hepatic artery Main portal vein Caudate lobe Superior Inferior Inferior vena cava Papillary process of caudate lobe Posterior FIGURE 14-12 Parasagittal scanning plane image just to the right of the midline of the body, demonstrating the origin of the main portal vein. Note the papillary process of the caudate lobe. Anterior Left portal vein Right lobe Left lobe Left Right Right portal vein Main portal vein Inferior vena cava Posterior FIGURE 14-13 Transverse scanning plane image showing the main portal vein entering the porta hepatis just anterior to the inferior vena cava and then dividing into right and left branches. intrasegmental. The main and right portal veins traverse and supply the bulk of the liver centrally with blood from the gastrointestinal tract for processing. The left portal vein ascends anteriorly, proximal to the falciform ligament. In patients with severe portal hypertension the left portal vein enters the falciform ligament and communicates with the recanalized ligamentum teres, which had been the postnatally obliterated umbilical vein. The caudate lobe is supplied with blood from the right and left portal veins. The liver is supplied via the common hepatic artery, a branch of the celiac axis of the aorta. The common hepatic artery pursues a horizontal course to the right and branches into the gastroduodenal (GDA) artery and proper hepatic artery (PHA). The proper hepatic artery courses superiorly, supplying the liver via the right, middle, and left hepatic arteries. The cystic artery feeds the gallbladder after it branches from the right hepatic artery. The right gastric artery, which supplies the right side of the lesser curvature of the stomach, can originate from the gastroduodenal artery, common hepatic artery, or proper hepatic artery. Peritoneal ligaments connect the liver to upper abdominal structures. The coronary ligament connects the posterosuperior surface of the liver to the diaphragm at the margins of the bare area. The bare area separates and lies between the right posterior subphrenic space above the posterior subhepatic space (Morison’s pouch) below (Figure 14-15). The upper layer of the coronary ligament extends from the superior liver surface to the inferior surface of the diaphragm. The lower layer extends from the posterior surface of the right lobe of Chapter 14 The Liver 217 Anterior Right portal branch Gallbladder Right Left Hepatic vein Inferior vena cava Liver Diaphragm Right renal artery Posterior FIGURE 14-14 Transverse scanning plane image showing the right portal vein. Note the longitudinal section of the right renal artery coursing posteriorly to the axial section of the inferior vena cava. Anterior Renal capsule Morison’s pouch Right lobe of liver Right kidney Inferior Superior Diaphragm Region of right Right adrenal triangular ligament gland Bare area Posterior FIGURE 14-15 Sagittal scanning plane image showing longitudinal sections of the right kidney and right adrenal gland in contact with the bare area of the liver. Observe how the anterior kidney surface is separated from the posterior liver surface by Morison’s pouch, a peritoneal space that is not specifically appreciated sonographically unless it is abnormally filled with fluid. The bright, thin, curved line seen between the liver and kidney is the fibrous renal capsule. the liver to the right kidney, the right adrenal gland, and the IVC. The right triangular ligament is formed by an extension of the coronary ligament inferiorly to the right. It begins at the right margin of the bare area and connects the posterior surface of the right lobe to the right undersurface of the diaphragm. The posterior subphrenic and posterior subhepatic spaces, separated by the bare area medially, become continuous, lateral to the right triangular ligament. The left triangular ligament is an extension of the falciform ligament to the left. As the falciform ligament passes over the liver dome, it divides into 2 leaflets. The left leaflet forms a portion of the left triangular ligament. The right leaflet merges with the coronary ligament. It connects the posterior surface of the left lobe to the left aspect of the diaphragm. The triangular and coronary ligaments are not normally visualized on ultrasound examinations. The falciform ligament connects the liver to the anterior abdominal wall and to the diaphragm. The attachment extends from the superior surface of the liver at the umbilical notch to the inferior surface at the porta hepatis (Figure 14-16). The right, anterior, and superior 218 Section III ABDOMINAL SONOGRAPHY Anterior Liver Duodenum Falciform ligament Pancreas Gallbladder Inferior vena cava Right Left Lack of transducer/skin contact or rib shadow Right kidney Diaphragm Acoustic shadow Posterior FIGURE 14-16 Transverse scanning plane image demonstrating a longitudinal section of the falciform ligament coursing toward the anterior abdominal wall. Observe the characteristic sickle shape. Anterior Umbilical portion of left portal vein Ligamentum venosum (transverse fissure) Right Right lobe of liver Left Inferior vena cava Caudate lobe Posterior FIGURE 14-17 Transverse scanning plane image that shows the transverse fissure (ligamentum venosum) coursing toward the left portal vein, marking the anterior border of the caudate lobe. surfaces unite to form the convex upper surface of the liver. The posterior surface is a continuation of that surface. The lesser omentum is a mesentery or double layer of peritoneum that joins the lesser curvature of the stomach and the proximal duodenum to the liver. The lesser omentum contains the gastrohepatic and hepatoduodenal ligaments. The gastrohepatic ligament is the portion of the lesser omentum that extends across the transverse fissure (fissure for the ligamentum venosum) of the liver at the porta hepatis to the lesser curvature of the stomach. The lesser omentum separates the lesser sac from the gastrohepatic recess. The ligamentum venosum marks the left anterolateral border of the caudate lobe (Figure 14-17). The lateral segment of the left lobe is separated from the caudate lobe by the fissure for the ligamentum venosum. The ligamentum venosum is a remnant of the fetal ductus venosus, which shunted oxygenated blood Chapter 14 The Liver 219 Anterior Common bile duct Hepatic artery Bowel Superior Inferior Bowel shadow Portal vein Inferior vena cava Pancreas head Right renal artery Posterior FIGURE 14-18 Sagittal scanning plane image demonstrating a longitudinal section of the common bile duct coursing inferiorly to the head of the pancreas (this is at the level of the hepatoduodenal ligament). from the umbilical vein to the IVC. The transverse fissure for the ligamentum venosum contains the gastrohepatic ligament. The hepatoduodenal ligament is the portion of the lesser omentum that extends as the right free border of the gastrohepatic ligament to the proximal duodenum and the right hepatic flexure of the colon. The hepatoduodenal ligament marks the right ventral border of the lesser omentum. Portions of the common bile duct and the hepatic artery are often visualized on transverse scanning plane images at the level of the hepatoduodenal ligament, just superior to the head of the pancreas and adjacent to the porta hepatis. The porta hepatis is the opening of the liver through which the portal veins and hepatic arteries enter and the hepatic ducts exit. The common bile duct and hepatic artery course anteriorly to the portal vein in the portal triad at this level. The common bile duct is the anterolateral vessel. It then passes posteriorly to the duodenum and enters the pancreas (Figure 14-18). PHYSIOLOGY The liver is a primary center of metabolism, supporting multiple body systems and activities. In support of the digestive and excretory systems the liver metabolizes fats, carbohydrates, and proteins and forms bile and urea. The hepatic parenchyma is composed of hepatocytes, interspersed with Kupffer cells, and organized into lobules approximately 1 by 2 mm in size. Typically, there are approximately 1 million lobules within the liver. Peripherally around each lobule are several portal triads, each containing portal venules, bile ductules, and hepatic arterioles. Portal venules carry blood from the gastrointestinal tract for cleansing and synthesis to the hepatocyte. Bile ductules carry substances including waste material from the hepatocyte. This substance will eventually comprise bile and be stored in the gallbladder until activated by food in the duodenum (see Chapter 15). Hepatic arterioles carry oxygenated blood to the hepatocyte for nourishment. Kupffer cells protect the hepatocytes by engulfing toxic or harmful substances, including ethanol from alcohol ingestion. The importance of this cell function is still being studied. One research study reports that the activation of Kupffer cells may reduce liver damage from hepatocarcinoma, ethanol ingestion, or other toxic agents. The amazing durability of the liver, despite the repeated onslaught of harmful substances or presence of disease, may be due in part to the activity of the Kupffer cells. Principal functions of the liver may be categorized as metabolic, protective, secretory, formative, or miscellaneous. Metabolic Functions of the Liver Metabolic functions of the liver involve uptake of body nutrients, such as carbohydrates, amino acids or proteins, fats, and vitamins. The liver serves as a storage site for these substances, performs metabolic conversions of these substances into nutrients, and subsequently releases them into the blood and bile vessels. The liver absorbs intestinal splanchnic and venous blood received from the portal veins—which drain the digestive tract, the pancreas, and the spleen—and receives a second supply of arterial blood from the hepatic artery and a branch of the superior mesenteric artery. The liver is a dual circulatory system, receiving blood from the gastrointestinal tract via the portal vein for processing and receiving blood for organ function from the proper hepatic artery and its branches. 220 Section III ABDOMINAL SONOGRAPHY The venous blood contains products of digestion, such as amino acids and glucose. The liver uses glucose to metabolize carbohydrates. For carbohydrate metabolism, the liver breaks down, stores, and manufactures simple sugars, which the body uses as a primary source of energy. • Carbohydrate metabolism in the liver involves the processes of glycogenesis, the formation and storage of glycogen, a polysaccharide; glycogenolysis, the conversion of glycogen into its essential nutrient, glucose; and the release of glucose into the bloodstream. Diabetes mellitus is a commonly identified disease characterized by high levels of glucose measured in the blood. • Protein metabolism results in the synthesis of amino acids into proteins. Proteins serve a variety of functions in the structure and metabolism of the body. Structural proteins are found in hair, muscle, and connective tissue. Enzymes such as those that act as biologic catalysts in metabolic reactions are proteins, as are molecules such as hemoglobin, which transport vital nutrients. • Fat metabolism in the liver is a process involving the synthesis of fatty acids from carbohydrates. Fat is absorbed from fatty acids and desaturated in the liver. Ketones are intermediary products formed during this process. Fat metabolism results in the formation of cholesterol and phospholipids. Phospholipids are structural components of cell membranes that protect a cell’s contents from its environment. Cholesterol is a major component of the bile that is secreted by the liver and serves to emulsify fats. Cholesterol is a steroid present in many food products, such as eggs, dairy products, oils, fats, and meats; it is present in all tissues, most abundantly in nervous and glandular tissue and the brain. The presence of cholesterol in the bile is a result of its solubility in the presence of bile salts and the phospholipid lecithin. These substances, along with the bile pigments bilirubin (reddish) and biliverdin (greenish), are the primary components of bile. If either the lecithin or bile salts are deficient, cholesterol may precipitate, or separate, out of the solution and form gallstones, which may accumulate in the gallbladder or obstruct the common bile duct. In patients with bile duct obstruction, excessive bile pigments may appear in the blood and result in jaundice, a yellow discoloration of the skin, sclerae of the eyes, and mucous membranes. Approximately 1 pint of bile is secreted each day. The secretion of bile is a major secretory function of the liver. Bile is secreted continuously by the liver and passes from the liver through the hepatic ducts into the common bile duct and empties into the duodenum as food is digested. When the duodenum is empty, bile backs up into the gallbladder, where the organic substances are concentrated and stored. Additional metabolic functions of the liver include the storage of minerals and vitamins, formation of vitamin A, metabolism of steroid hormones, and degradation and detoxification of drugs such as alcohol and barbiturates. Detoxification of Poisonous and Harmful Substances Another protective function of the liver is the detoxification of poisonous and harmful substances absorbed by the intestine. This process may include the conversion of harmful substances, such as ammonia, a waste product of protein metabolism, into useful or excretable substances, such as the amino acid arginine and urea. Arginine is a useful amino acid, and urea is a waste product that is excreted. Synthesizing Blood Proteins The liver synthesizes the blood proteins albumin, fibrinogen, prothrombin, and globulins. The synthesis of blood plasma proteins, which include albumin and various globulins, is a formative function of the liver. Prothrombin and fibrinogen are blood-clotting factors. The synthesis of heparin, an anticoagulant, also takes place in the liver. Additional Liver Functions The liver stores vitamins and other metabolic substances. It also regulates blood volume and acts as a reservoir for blood that is released as it regulates blood volume and blood flow through the body. Additionally, the liver serves as a major source of body heat as a result of the many hepatocellular chemical reactions that take place within it. SONOGRAPHIC APPEARANCE The normal liver should appear homogeneous and moderately echogenic throughout. A boundary between the left and right hepatic lobes can be imagined along a line coursing posteriorly from the gallbladder fossa to the groove for the IVC. This line is the main lobar fissure. This fissure is identified sonographically along a right lateral, sagittal oblique scanning plane and extends a short but variable distance between the long axis section of the neck of the gallbladder and the axial or short axis section of the right portal vein. The main lobar fissure appears as a thin, bright line connecting the gallbladder neck to the portal vein (Figure 14-19). Many landmark structures are visible on a sagittal scanning plane image showing the long axis of the IVC. Cephalad (superiorly) to caudad (inferiorly), one should see, anterior to the IVC, the following structures: the right atrium, the central leaf of the diaphragm superior to the left hepatic lobe, the middle hepatic vein as Chapter 14 The Liver 221 Anterior Main lobar fissure Gallbladder Right portal vein Right lobe of liver Upper pole of right kidney Inferior Superior Diaphragm Bare area Posterior FIGURE 14-19 Sagittal scanning plane image that shows how the longitudinal section of the main lobar fissure appears as an echogenic line connecting the neck of the gallbladder to the right portal vein. Anterior Falciform ligament Splenic vein Right Left Hepatic artery Stomach Common bile duct Pancreas Inferior vena cava Spine Aorta Left renal artery Superior mesenteric artery Posterior FIGURE 14-20 Transverse scanning plane image of the midepigastrium. Note the axial section of the falciform ligament and its characteristic pyramidal shape. This echogenic focus is also referred to as the round ligament or ligamentum teres at this level. it enters the vena cava, the caudate lobe of the liver separated from the lateral left lobe by the ligamentum venosum, the extrahepatic main portal vein in crosssection, and the head of the pancreas in cross-section. The superior mesenteric vein may be seen coursing toward its junction with the splenic vein at the portal confluence. The left portal vein may be visualized on its C-shaped superior course, proximal to the falciform ligament. Ligaments and fissures are demonstrated as highly echogenic because of the presence of collagen and fat within and around these structures. The attachment of the falciform ligament from the upper surfaces of the liver to the diaphragm and the upper abdominal wall appears to divide the right and left lobes. It represents the lower margin of peritoneum surrounding the ligamentum teres, or round ligament, of the liver. The falciform ligament is highly echogenic, appearing sickle shaped in longitudinal sections and pyramidal in axial sections (Figure 14-20). The round ligament (ligamentum teres) is the obliterated umbilical vein, a fibrous cord that extends upward from the diaphragm to the anterior abdominal wall. On transverse scans, it most often is identifiable coursing within the lower margin of the falciform ligament. These structures lie close to the anterior midline surface 222 Section III ABDOMINAL SONOGRAPHY of the body and within the near field of the transducer. They are displayed on the upper midportion of the screen. The echogenic falciform ligament courses anteroinferiorly from the left portal vein toward the umbilicus. Transverse scans through the liver frequently demonstrate an echogenic focus in the area of the falciform ligament. This structure correlates the sonographic appearance of the falciform ligament with its appearance on computed tomographic (CT) scans, although it may be prominent enough to raise the suspicion of a solid mass. The presence of a recanalized umbilical vein within the falciform ligament should be looked for in patients with portal hypertension. The main portal vein is visualized at its origin, posteroinferior to the neck of the pancreas. Identification of the porta hepatis is possible by identifying the main portal vein anterior to the IVC and then moving slightly cephalad. The main portal vein can be seen entering the porta hepatis, where it divides into a smaller, more anterior and more superior left portal vein and a larger, more posterior and more inferior right portal vein. Portal veins are surrounded by bright echogenic walls due to the thick collagenous tissue in the walls. Portal veins decrease in size as they approach the diaphragm. The Doppler flow signal of a portal vein is normally continuous, monophasic, and exhibits low velocity, usually between 20 and 40 cm/s. Abnormally prominent pulsatility may be observed in patients with right heart failure, tricuspid regurgitation, fistula between a hepatic and portal vein, or portal hypertension. The junction of the right and left portal veins is noted on a superiorly angled transverse scanning plane image just inferior to the plane that demonstrates the convergence of the 3 hepatic veins on the IVC. This level also identifies the location of the union of the left and right hepatic ducts to form the proximal portion of the common duct, the common hepatic duct. The common hepatic duct can be followed medially, anterior to the right portal vein. This is the recommended location for measuring the common hepatic duct. Any measure­ ment greater than 5 mm raises the possibility of biliary obstruction. The hepatic veins increase in size as they drain toward the diaphragm and IVC. Any large vein in the liver near the diaphragm may be considered a hepatic vein. Normal Doppler flow signals in the hepatic veins demonstrate a triphasic waveform. There are several (additional) features that distinguish hepatic veins from portal veins. Hepatic veins course between lobes and segments, whereas portal veins course within segments. Hepatic veins drain toward the right atrium and usually have indistinct, anechoic borders, except near the IVC, where the venous walls appear more reflective. The positions of the hepatic veins can therefore be used to identify the segments of the liver and provide precise descriptions of focal abnormalities. Identification of hepatic segments is important in localizing potentially resectable lesions of the liver. Lesions of this type include primary hepatic neoplasms, single metastatic lesions, and some nonmalignant hepatic abnormalities (Figure 14-21). Posterior to the IVC on parasagittal scans, the anechoic right renal artery is seen in short axis, anterior to the right linear crus of the diaphragm noted with very low-level echoes. Any other solid-appearing mass Anterior Anterior segment of right lobe Medial segment of left lobe Right Left Posterior segment of right lobe Diaphragm Inferior vena cava Posterior Lateral segment of left lobe FIGURE 14-21 Transverse scanning plane image demonstrating longitudinal sections of the hepatic veins draining into the axial section of the inferior vena cava; providing sonographic segmentation of the hepatic lobes. Chapter 14 The Liver 223 Liver Portal vein 35 .80 m/s .20 FIGURE 14-22 Color-flow Doppler image showing the characteristic waveform of a normal portal vein. Note that the blood flow is in the direction of the liver toward the transducer. posterior to the IVC and inferior to the liver suggests the presence of enlarged lymph nodes or adrenal lesions. SONOGRAPHIC APPLICATIONS Ultrasound examinations of the liver are indicated for the following: • Suspected liver enlargement • Suspected hepatic or perihepatic masses • Suspected abscesses • Suspected obstructive or metastatic lesions • Cystic, solid, and complex masses, which are routinely identifiable because they can distort the smooth contour of the liver • Abnormal lesions, which are usually hyperechoic or hypoechoic compared with the appearance of normal liver parenchyma • Pleural effusions, which may be visualized in the subdiaphragmatic (subphrenic) region superior to the liver capsule • Ascites, identifiable when fluid collects in the sub­capsular or intraperitoneal spaces surrounding the liver Duplex abdominal and color-flow Doppler are used to assess the following: • Vascular structures of the liver and porta hepatis, such as the portal vein, hepatic arteries and veins, and the splenic artery and vein (Figures 14-22 and 14-23). The presence, direction, and blood flow velocity in a sample volume are evaluated with these examinations. • Portal hypertension • Portal or hepatic vein thrombosis • Preoperative and postoperative hepatic surgery. For example, in some patients with cirrhotic liver disease and variceal hemorrhages, interventional FIGURE 14-23 Color-flow Doppler image demonstrating the characteristic arterial waveform of the normal hepatic artery. radiologists surgically place a permanent shunt between the hepatic vein and intrahepatic portal vein to prevent bleeding of gastroesophageal varices. This placement is designed to divert blood around the liver, thereby relieving portal hypertension by reducing portal vein pressure. The procedure is known as placement of a TIPS (transjugular intrahepatic portosystemic) shunt. Color Doppler ultrasound evaluation of the direction and flow of the portal vein in a patient with a TIPS shunt is commonly performed before and after the procedure (Figures 14-24 to 14-26). Preoperative screening helps determine whether a patient is a candidate for a TIPS shunt. The portal vein, hepatic artery, and hepatic veins are evaluated for patency and flow direction. A TIPS shunt is contraindicated in any patient with portal vein 224 Section III ABDOMINAL SONOGRAPHY Right lobe of liver TIPS shunt Portal vein Inferior vena cava FIGURE 14-24 Oblique transverse scanning plane image of a liver section to evaluate the proximal portal end of the TIPS shunt after placement. Hepatic veins Right lobe of liver 68 Hepatic vein Liver Portal vein 68 cm/s Liver FIGURE 14-25 Color Doppler evaluation of a TIPS shunt connecting the hepatic vein to the intrahepatic portal vein. Note that the color blue represents flow away from the transducer (hepatic vein) and the color red represents flow moving toward the transducer (portal vein). thrombosis. The postoperative evaluation assesses how well the patient responds to the treatment. • Tumor invasion of the portal vein, which may be observed in cases of hepatocellular carcinoma and with metastases. To differentiate tumor invasion from portal vein thrombosis, color Doppler can be used to demonstrate tumor vascularity presenting with low-resistance arterial signals within the portal vein lesion. • Donors for partial liver transplant and in patients before and after liver transplant. Complications in complete and partial liver transplant patients can include hepatic artery thrombosis, pseudoaneurysm and rupture, and/or hepatic vein stenosis. Acute liver Chapter 14 The Liver 225 Anterior Liver Middle hepatic vein Right Left Left hepatic vein TIPS shunt in right hepatic vein Portal vein Hepatic vein branch Ascites (abnormal fluid collection) Inferior vena cava Posterior FIGURE 14-26 Transverse scanning plane image showing an axial section of the liver at the level of the hepatic veins draining into the inferior vena cava. Observe the highly reflective terminal end of the TIPS shunt within the right hepatic vein. Anterior Portal vein Right lobe of liver (Reidel's lobe) Inferior Superior Right kidney Posterior FIGURE 14-27 Sagittal scanning plane image of a woman with Reidel’s lobe, a tongue-like extension of the right lobe of the liver. This Reidel’s lobe extends inferiorly to the iliac crest. failure can be caused by acute rejection or hepatic artery thrombosis. Biliary complication has also been noted in up to 10% of adult liver transplant patients; it is more frequent in pediatric liver transplant patients. Other complications include fluid collections and post-transplant lymphoproliferative disorder. NORMAL VARIANTS • Reidel’s lobe: A tongue-like inferior extension of the right lobe, as far caudally as the iliac crest (Figure 14-27). It has the same sonographic appearance as normal liver parenchyma. On ultrasound this variant can be identified when liver tissue extends well below the inferior pole of the right kidney during normal respiration. • Distal papillary process of the caudate lobe: May be confused with an enlarged lymph node or another extrahepatic lesion. This process appears as a rounded prominence on the anteroinferior aspect of the caudate, or it may appear as a separate structure. It has the same sonographic appearance as normal liver parenchyma. • Elongated left lobe: Has a tip that can extend left laterally, all the way to the spleen. The sonographic appearance is the same as the normal liver. 226 Section III ABDOMINAL SONOGRAPHY REFERENCE CHARTS ASSOCIATED PHYSICIANS • Gastroenterologist: Specializes in treating diseases of the gastrointestinal tract, including the stomach, small and large bowel, gallbladder, and bile ducts. • Internist: Specializes in studying the physiology and pathology of internal organs and diagnosing and treating disorders of those organs. • Oncologist: Specializes in the study and treatment of tumors and malignancies. • Radiologist: Specializes in the diagnostic interpretation of imaging modalities that assess the liver. • Surgeon: Utilizes operative procedures to treat diseases, trauma, and organ deformity. • Vascular specialist: Studies and treats disorders of blood vessels. COMMON DIAGNOSTIC TESTS • Computed tomography (CT): This x-ray examination utilizes a narrow collimated beam of x-rays that rotate around the patient in a continuous 360-degree arc in order to image the body in cross-sectional slices. The image is created by a digital computer that calculates attenuation or tissue absorption of the x-ray beams. Very small differences in density of body structures may be demonstrated and are displayed on x-ray film. The examination is performed by radiologic technologists who specialize in computed tomography and is interpreted by radiologists. • Angiography: This examination utilizes x-rays to visualize the internal structure of the heart and blood vessels after the injection of a contrast medium into an artery or vein. The contrast material is inserted into a peripheral artery via a catheter, which is then threaded through the vessel to a visceral site. Angiograms are performed by radiologists and assisted by radiologic technologists. The examination is interpreted by the radiologist. • Magnetic resonance imaging (MR, MRI): The MR scanner surrounds the patient with powerful electromagnets that create a magnetic field. Hydrogen atoms in the patient’s body are disturbed by this field. The atoms’ protons become aligned in the direction of the magnetic field’s poles. The computers process and measure the speed and volume with which the protons return to their normal state and display a diagnostic image of striking clarity on a monitor. Intravenous contrast materials may be given to enhance image definition. MR produces cross-sectional and sagittal soft tissue images. The examinations are performed by registered radiologic technologists and interpreted by radiologists. Physicists assist radiologists in the MR laboratory because of the complexity of the MR equipment. • Radionuclide scintigraphy: Scintigraphy utilizes a gamma camera to detect radioactive substances given intravenously or by mouth. Scintigraphy commences when the radioisotope reaches optimum activity in the part being examined. For liver studies this begins immediately after injection. A technetium sulfur colloid is the radionuclide used in liver studies. Recording devices convert voltage impulses received from the scanner into a paper or x-ray film record of a series of dots that reflect the radiation intensities received. Abnormalities are indicated by an absence of activity. The examinations are performed by certified nuclear medicine technologists. They are interpreted by radiologists or nuclear physicians. • Liver biopsy: A needle is inserted into the RUQ to remove a sample of liver tissue for microscopic evaluation. This examination assesses severity of liver cell damage and is performed by a radiologist. LABORATORY VAL