Biliary System Review PDF

CHAPTER 15 The Biliary System YONELLA DEMARS, REVA ARNEZ CURRY, AND BETTY BATES TEMPKIN OBJECTIVES Describe the gross anatomy of the biliary system. Describe the basic function of the biliary system. Describe the ultrasound appearance of the biliary system. Describe diagnostic tests that may be u...

CHAPTER 15 The Biliary System YONELLA DEMARS, REVA ARNEZ CURRY, AND BETTY BATES TEMPKIN OBJECTIVES Describe the gross anatomy of the biliary system. Describe the basic function of the biliary system. Describe the ultrasound appearance of the biliary system. Describe diagnostic tests that may be used to examine the biliary system. KEY WORDS Ampulla of Vater (Hepatopancreatic Ampulla) — Dilatation or opening formed by the common bile duct and pancreatic duct(s) as they enter the duodenum, where they empty bile and pancreatic enzymes that assist in the digestive process. Bile Ducts — Drain the liver of bile. Bilirubin — A bile pigment. Green when oxidized. Body — Refers to the middle and main portion of the gallbladder. Cholecystectomy — Surgical removal of the gallbladder. Cholecystitis — Condition in which the gallbladder is inflamed. Presents sono­ graphically with edematous, thickened gallbladder walls. Cholecystokinin (CCK) — Peptide hormone that stimulates the gallbladder to contract and the sphincter of Oddi to relax and increases hepatic production of bile. An injectable form can be used to stimulate the gallbladder during sonographic exam­ ination for a type of function test. Choledochal (Choledochus) Cyst — Normal, localized dilatation of the common bile duct. Choledocholithiasis — Presence of gallstones in the biliary tract. Cholelithiasis — Formation or presence of gallstones, which are calcifications in the gallbladder or biliary duct. Common Bile Duct (CBD) — Distal portion of the biliary duct or common duct. Trans­ ports bile from the level of the cystic duct, inferomedially toward the head of the pancreas, and then enters the duode­ num and empties the bile to aid in digestion. 228 Common Duct (CD)/Biliary Duct — Formed by the union of right and left intrahepatic ducts. Serves to transport bile (fluid that aids digestion; manufactured in the liver) from approximately the level of the liver hilum, inferiorly to the gallbladder (stores and concentrates bile) and duode­ num to assist digestion. Its proximal portion is called the common hepatic duct; distal portion is called the common bile duct. Common Hepatic Duct (CHD) — Proximal portion of the biliary duct or common duct. Transports bile (fluid that aids diges­ tion; manufactured in the liver) inferiorly to the cystic duct that directs the flow of bile it receives directly into the gallblad­ der. Continues inferiorly as the distal portion of the common duct known as the common bile duct. Cystic Duct — Directs the flow of bile it receives from the common hepatic duct directly into the neck of the gallbladder. Extrahepatic — Outside of or not enclosed by liver tissue. Fundus — Refers to the inferior, widest portion of the gallbladder. Gallbladder — Bile reservoir on the postero­ inferior surface of the liver. Has three descriptive divisions: fundus, body, and neck. The fundus is the “bottom” of the pouch. The middle and main portion of the gallbladder is the body, and the nar­ rower area leading into the cystic duct is the neck. Gallbladder Fossa — Indentation located on the posteroinferior portion of the right lobe of the liver where the gallbladder is situated. Hartmann’s Pouch — A small sacculation (outpouching) in the area of the gallblad­ der neck. Named after Henri Hartmann, a French surgeon (1860–1952). The term infundibulum is also applied to this sacculation, which some consider an abnormality and others consider just an oddity. Hepatic Ducts (Right, Left) — Right and left intrahepatic ducts or tubules that direct the bile produced in the liver to the biliary duct. The ducts join at approximately the level of the liver hilum to form the biliary duct or common duct (CD). Hepatic Portal System — System responsible for venous drainage of the gastrointestinal tract, including the spleen, pancreas, and gallbladder. Blood is conveyed from these organs via the portal vein to the liver. The portal vein subdivides until the blood reaches the hepatic sinusoids. Blood there­ fore passes through two sets of “exchange” vessels: the capillaries within the organs of the gastrointestinal tract, the spleen, pan­ creas, and gallbladder, and the hepatic sinusoids. From the sinusoids, blood con­ verges into hepatic veins and finally the inferior vena cava (IVC) before returning to the heart. Hilum — Indention, depression, or pit on an organ forming a doorway or area of entrance and exit for vessels, ducts, and nerves; sometimes called hilus. Infraduodenal Common Bile Duct — Portion of the common bile duct inferior to the duodenum. Intraduodenal Common Bile Duct — Portion of the common bile duct within the duodenum. Chapter 15 The Biliary System 229 KEY WORDS—cont’d Intrahepatic — Completely or partially enclosed in liver tissue. Liver Function Tests — A collection of labora­ tory tests that indicates how the liver is functioning or performing. Neck — Refers to the narrow portion of the gallbladder that is connected to the cystic duct. Polyps — Protruding growth or mass from a mucous membrane. Porta Hepatis — Also known as the liver hilum or doorway giving entrance and exit to hepatic vessels, ducts, and nerves. Portal Triad — Intrahepatic bile ducts run alongside portal veins and hepatic arter­ ies in a portal triad, surrounded by connective tissue and radiating through the lobes and segments of the liver. Intra­ hepatic ducts join to form right and left hepatic ducts that join near the porta hepatis to form the biliary duct or common duct. The distal portion of the common duct, the common bile duct along with the main portal vein and proper hepatic artery, form an extrahepatic portal triad. Portal Vein — The gateway through which blood returning from the gastrointestinal tract and accessory organs passes before returning to the heart. Proper Hepatic Artery — Branch of the common hepatic artery; supplies the gall­ bladder and the liver. NORMAL MEASUREMENTS Anatomy Measurement Gallbladder 8 to 12 cm long 3 to 5 cm diameter 3 mm thick 0.5 to 2.5 cm long (left is longer than right) 0.1 to 0.2 cm diameter 2.0 to 6.5 cm long 0.1 to 0.2 cm diameter 5 to 15 cm long 0.1 to 0.7 cm diameter 0.5 to 0.8 cm long 0.1 to 0.4 cm diameter Gallbladder wall Right and left hepatic ducts Common hepatic duct Common bile duct Cystic duct Tandhe pancreas. biliary system is intimately associated with the liver It consists of the , acting as a gallbladder reservoir for bile, and the bile ducts that drain the liver of bile. The bile duct and pancreatic duct(s) may join and form one duct or remain separate and enter the duodenum together, where they empty bile and pancreatic enzymes to assist the digestive process. The pancreas and associated ducts are the focus of Chapter 16. The basic function of the biliary system is to drain the liver of bile and then store the bile until it is needed to aid digestion. As mentioned, the gallbladder acts as the storage receptacle for bile, and the various ducts provide a place to which the bile flows. The gallbladder concentrates the bile by secreting mucus and absorbing water. For a review of bile production, see the discussion of the liver in Chapter 14. Retroduodenal Common Bile Duct — Portion of common bile duct that runs behind the duodenum. Sphincter of Oddi (Oddi’s Muscle) — A muscle sheath surrounding the CBD (joined at times by the pancreatic duct) at the ampulla of Vater. Aids in regulating bile flow into the duodenum. Spiral Valves of Heister — A series of mucosal folds within the lumen of the cystic duct. Supraduodenal Common Bile Duct — Portion of common bile duct superior to the duodenum. LOCATION Gallbladder The gallbladder fossa (or indentation) is located on the posteroinferior portion of the right lobe of the liver where the gallbladder is situated (Table 15-1). This fossa or bed is closely related to the main lobar fissure of the liver (Figure 15-1). Typically, the gallbladder is not totally surrounded by hepatic tissue; however, it is possible for this to occur. An intrahepatic gallbladder will be totally (or almost totally) enclosed in liver tissue. Due to its long mesentery, the gallbladder will change location as the patient changes position. A gallbladder found to be just at the inferior border of the right lobe of the liver with the patient supine may then be found to have shifted closer to the midline when the patient is placed on the left side with the right side raised. This patient repositioning is known as the left lateral decubitus (LLD) or left lateral oblique (LLO) positions. Some imagers believe that by simply bending the right arm 90 degrees at the elbow and then placing that hand over the midline, the location of the gallbladder may be estimated—with the gallbladder being in the area of the wrist. This method is not particularly accurate but it does give a rough idea of the location of the gallbladder. Bile from the liver reaches the gallbladder through the hepatic ducts, the proximal portion of the common duct (the common hepatic duct), and the cystic duct. Hepatic Ducts The left and right intrahepatic ducts join at approximately the level of the liver hilum (also called the porta hepatis, or doorway) to form the biliary duct or common duct (CD). The proximal portion of the CD is referred to as the common hepatic duct; the distal portion is the common bile duct (Figure 15-2). 230 Section III ABDOMINAL SONOGRAPHY Table 15-1 Location of Gallbladder and Biliary Tract Routinely Visualized With Ultrasound Anterior to Posterior to Superior to Rt and Lt Hepatic Ducts Common Hepatic Duct Cystic Duct Common Bile Duct Gallbladder (location variable) Portal vein, rt branch hepatic artery Liver, peritoneum PHA, portal vein, IVC Portal vein PHA, portal vein, IVC Superior portion rt kidney Liver, peritoneum Liver, peritoneum Liver, superior portion duodenum, peritoneum, GDA Peritoneum (inferior surface, fundus), transverse colon (fundus) CHD, CBD, cystic duct, duodenum, pancreas Cystic duct, CBD, GDA CBD Superior portion duodenum, pancreas head Rt and lt hepatic ducts, liver CHD CHA, cystic duct, superior portion duodenum Liver rt lateral lobe Cystic duct, liver rt lateral lobe Liver rt lateral lobe, GB neck Cystic duct, duodenum CHA, liver caudate lobe, duodenum, pancreas CHA, GDA CHD, CBD Pancreas head, terminal pancreatic duct, PHA, CHA, superior portion duodenum Inferior to Medial to Lt lateral to Rt lateral to Rt branch portal vein, liver’s main lobar fissure, rt lobe liver, ninth costal cartilage (fundus) Cystic duct (neck), rt branch portal vein CBD, Common bile duct; CHA, common hepatic artery; CHD, common hepatic duct; GB, gallbladder; GDA, gastroduodenal artery; IVC, inferior vena cava; PHA, proper hepatic artery. Anterior Common hepatic duct Superior Main lobar fissure Liver Inferior Gallbladder Right portal vein Hepatic vein Proper hepatic artery Inferior vena cava Posterior FIGURE 15-1 Main Lobar Fissure. Note the location of the gallbladder and how it relates to the main lobar fissure. Chapter 15 The Biliary System Right hepatic bile duct Left hepatic bile duct Gallbladder Common hepatic duct Common bile duct Cystic duct Pancreas Area of the ampulla of Vater with sphincter of Oddi Pancreatic duct (duct of Wirsung) Duodenum Gallbladder and biliary tract, including the pancreatic duct, and the duodenum. FIGURE 15-2 Biliary System Biliary Structure Location Gallbladder (GB) • • • • • • • • • • Cystic duct (CD) Right and left hepatic ducts • Common hepatic duct (CHD) • • • Common bile duct (CBD) • • • • • On posteroinferior surface of the liver Right kidney may be noted posterior to GB Near main lobar fissure Follow main portal vein toward the right to help locate Easier to locate when distended Extends from GB neck and meets CHD where CBD begins Located on posteroinferior surface of liver Intrahepatic Drain right and left lobes of the liver Located on posterior medial surface of the liver toward the liver hilum Join at the level of the liver hilum (also known as porta hepatis) to form the biliary duct or common duct Proximal portion of the common duct Located on posterior surface of liver Becomes the common bile duct after receiving the cystic duct from the gallbladder Distal portion of the common duct Extends inferiorly from the union of the CHD and cystic duct to enter the duodenum near the head of the pancreas Parts of CBD can be described in relationship to the duodenum (i.e., supra-, retro-, infra-, and intraduodenal portions) Enters duodenum at the ampulla of Vater through sphincter of Oddi muscle Pancreatic duct from the pancreas can join the CBD in entering the duodenum at the ampulla of Vater 231 232 Section III ABDOMINAL SONOGRAPHY Liver Anterior Gallbladder Right portal vein Superior Inferior Common hepatic duct Proper hepatic artery Inferior vena cava Posterior FIGURE 15-3 Common Hepatic Duct and Right Portal Vein Relationship. Sagittal scanning plane image demonstrating a longitudinal section of the common hepatic duct seen just anterior to the longitudinal section of the right portal vein and axial section of the proper hepatic artery. The common hepatic duct is often mistaken as the common bile duct, which is located more inferiorly and is more closely associated with the main portal vein. Common Hepatic Duct (CHD) The common hepatic duct (CHD) extends inferiorly from the liver hilum to the level of the gallbladder neck, where it meets the cystic duct (see Figure 15-2). It is anterior to the right portal vein and proper hepatic artery (Figure 15-3). Cystic Duct The cystic duct connects the gallbladder to the CHD. It directs the flow of bile it receives from the CHD, directly into the gallbladder. Common Bile Duct (CBD) The common bile duct (CBD) is the distal or inferior potion of the common duct. It is a continuation of the CHD but decribed separately based on its location and association with adjacent anatomy that is different from the anatomy associated with the CHD. From its origin at the level of the CHD and cystic duct, the CBD runs inferiorly along the right border of the lesser omentum, along the hepatoduodenal ligament; passes posterior to the first portion of the duodenum; passes through or lies on the back of the posterolateral portion of the pancreas head; and enters the posteromedial aspect of the descending portion of the duodenum and terminates. It is anterior and slightly right lateral to the main portal vein and right lateral to the proper and common hepatic arteries (Figure 15-4; see also Figure 15-2). When referring specifically to the CBD, anatomists use terms that relate its location to the duodenum: supraduodenal, retroduodenal, infraduodenal, intraduodenal. The part of the CBD superior to the duodenum is the supraduodenal section. As the name implies, the portion posterior to the duodenum is the retroduodenal section; the infraduodenal portion is inferior to the duodenum; and the part of the CBD within the duodenum is the intraduodenal portion (Figure 15-5, A and B). The infraduodenal portion of the CBD is the portion previously mentioned that may be located within a groove on the posterolateral portion of the head of the pancreas or pass directly through the head. At this point the CBD either joins the pancreatic duct(s) to form a single duct or remains separate and enters the ampulla of Vater (or hepatopancreatic ampulla, an opening into the duodenum), where the intraduodenal CBD empties bile to assist in the digestive process. A muscle sheath—known as the sphincter of Oddi, or Oddi’s muscle—surrounds the CBD at the ampulla of Vater. The sphincter of Oddi aids in regulating bile flow into the duodenum. SIZE Gallbladder The overall length of the normal gallbladder is highly variable, depending on the amount of bile within and any existing normal variant. There are times when the gallbladder is simply difficult to see, not because of some structural variation, but because of physiology. For example, a patient who has fasted (not eaten) since midnight prior to an ultrasound examination may present with a bile-filled, easily visualized gallbladder. A patient who has eaten, causing the gallbladder to partially or completely empty to aid digestion, may present with a partially bile-filled, small gallbladder or, a collapsed, bile-free gallbladder, that may appear as nonexistent at first. However, when a patient has fasted correctly for the exam and a bile-filled gallbladder is Chapter 15 Right hepatic duct 233 Left hepatic duct Left portal vein Common hepatic duct Right portal vein Proper hepatic artery Cystic duct Common hepatic artery Main portal vein Gallbladder A The Biliary System Common bile duct Common bile duct Proper hepatic artery Main portal vein B C Anterior Liver Right Left C H P D Posterior FIGURE 15-4 Portal Vein, Hepatic Artery, and Common Duct Relationship. A, Observe how the common duct (common hepatic duct and common bile duct) is anterolateral to the proper hepatic artery. Notice that the proximal common duct, the common hepatic duct, is anterior to the right portal vein branch, and the distal portion of the common duct, the common bile duct, is anterior to the main portion of the portal vein. B, In an oblique transverse scanning plane image at approximately the angle of the solid line (approximately the same level as the right costal margin angle), one should see the relationship demonstrated in C. C, Note that the common bile duct and proper hepatic artery have approximately equal diameter. D, Oblique transverse scanning plane image demonstrating “Mickey’s Sign,” formed by the appearance of the axial sections of the extrahepatic portal triad. C, Common bile duct; H, proper hepatic artery; P, main portal vein. 234 Section III ABDOMINAL SONOGRAPHY Anterior First portion of the duodenum Liver Superior Inferior Portal vein Common hepatic artery A Retroduodenal portion of the common bile duct Supraduodenal portion of the common bile duct Posterior Anterior Pancreas neck Liver Ligamentum teres Stomach Pancreas head Portal splenic confluence Inferior vena cava Superior Inferior Portal vein Spine Infraduodenal portion of the common bile duct Right renal vein B Posterior FIGURE 15-5 Common Bile Duct and Duodenum Relationship. A, Obliqued sagittal scanning plane image showing a longitudinal section of the supraduodenal and retroduodenal segments of the common bile duct. B, Longitudinal section of the infraduodenal segment of the common bile duct in an oblique sagittal scanning plane. visualized, it is found to have a normal length of approximately 8 to 9 cm in the majority of patients, although some reports have cited gallbladder length as much as 12 cm as measured from the neck to the fundus. Figure 15-6 shows a fully distended gallbladder. The normal gallbladder is approximately 3 to 5 cm in diameter and holds up to approximately 40 mL of bile. To put this amount in perspective, a teaspoon typically holds approximately 5 mL of fluid; therefore the gallbladder holds approximately 8 teaspoons of fluid. Recall that 2.5 cm equals 1 inch; this provides a better picture of the sizes involved when visualizing the biliary system. With experience, the sonographer discovers that the gallbladder has a wide variety of shapes, sizes, and locations. The walls of the gallbladder are generally only a few millimeters thick, up to approximately 3 mm. This wall thickness is important to note. Certain conditions, such as cholecystitis (inflammation of the gallbladder), may cause the walls to appear edematous and perhaps even greatly thickened. Localized thickening of the gallbladder wall may indicate the presence of a mass or other condition that would call for further investigation. As would be expected, the wall thickness is slightly less when the gallbladder is full or distended (the walls are Chapter 15 235 The Biliary System Anterior Fundus Liver Hepatic vein Inferior Superior Portal vein Inferior vena cava A Posterior Anterior Gallbladder body Bowel Liver Bowel shadow Superior Inferior Portal vein B Gallbladder neck Right kidney Posterior FIGURE 15-6 Distended Gallbladder. A, Gallbladder fundus. Sagittal scanning plane image demonstrating a longitudinal section of the fundus. Notice the proximity of the axial section of the portal vein and longitudinal section of the inferior vena cava; B, Gallbladder body and neck. Longitudinal section of the body and neck seen in a sagittal scanning plane. Note the long section of the right kidney seen immediately posterior to the gallbladder. stretched) as compared with an empty gallbladder, when the walls are slightly thicker. Common Hepatic Duct (CHD) The length and inside diameter of the CHD are variable. Schwartz reports a CHD length of 3 to 4 cm, whereas Oikarinen gives a length of 2 to 6.5 cm for the common hepatic duct and 0.5 to 2.5 cm for the right and left hepatic ducts, with the left hepatic duct typically longer than the right. The diameter of the right and left hepatic ducts has been reported at between 0.1 and 0.2 cm. A fairly widely accepted upper limit for the inner diameter of the CHD is 4 mm. One study has reported the diameter to range from approximately 1 to 7 mm in the normal patient, depending on age, previous surgery, and gallbladder function or disease. It is typical for an individual sonographic practice to set an acceptable upper limit on duct size based on criteria used by referring physicians, especially surgeons. Soto and Castrillon report that the CHD should be measured at the level of the right hepatic artery where it crosses between the CHD and the portal vein. They also report that it’s a good rule of thumb to consider it normal for the extrahepatic duct to dilate approximately 1 mm per decade of life. Thus, the upper limits of a CHD in a geriatric patient is 10 mm. 236 Section III ABDOMINAL SONOGRAPHY Anterior Liver Bowel filled gallbladder fossa Right Left Right kidney Bowel shadows A Posterior Anterior Liver Bowel filled gallbladder fossa Superior Inferior Bowel shadows Right kidney B Posterior FIGURE 15-7 Gallbladder Fossa. Transverse (A) and sagittal (B) scanning plane images showing an empty gallbladder fossa after cholecystectomy. Notice how bowel has filled the space where the gallbladder would normally be located. Cystic Duct The diameter of the cystic duct is approximately 3 mm. The length is highly variable, ranging from 1.0 to 3.5 cm. An average length of 4 cm has been reported at surgery. The apparent large difference in these figures is common and holds little significance on sonography. Common Bile Duct (CBD) The length of the CBD is also highly variable. A range in length of 8 to 11.5 cm has been suggested, although lengths of up to 17 cm have been reported. The diameter has been reported to be 1 to 7 mm in the normal patient and up to 10 mm in a patient after cholecystectomy (surgical removal of the gallbladder), although larger diameters have been reported. As discussed, individual practices will set an upper limit that is appropriate to their particular patient population. Figure 15-7 shows the fossa of a patient who has undergone a cholecystectomy. GROSS ANATOMY Gallbladder The gallbladder is perfused by the hepatic artery, a branch of the celiac artery, which is a branch of the Chapter 15 Anterior gallbladder wall The Biliary System 237 Anterior Gallbladder fundus Gallbladder body Right Left Gallbladder neck Posterior FIGURE 15-8 Gallbladder Fundus, Body, and Neck. Transverse oblique scanning plane image showing all three gallbladder sections in a longitudinal orientation. The fundus is the bottom portion; the body the middle; the neck the narrow portion adjacent to the body. abdominal aorta. The hepatic artery, or common hepatic artery, as it is often called, divides into the proper hepatic and gastroduodenal arteries. The proper hepatic artery supplies the gallbladder and the liver. The cystic artery may, on occasion, originate directly from the common hepatic artery or, rarely, from the gastroduodenal artery, but it usually originates from the right branch of the proper hepatic artery. It passes posterior to the CHD and anterior to the cystic duct. At this point, it travels inferiorly and divides into superficial and deep branches. Venous drainage of the gallbladder is by way of the hepatic portal system. The gallbladder is drained by tributaries of the hepatic portal venous system, which carry blood to the inferior vena cava. The portal circulatory route is the term used to describe venous blood that passes through two capillary exchange systems before reaching the heart. “Portal” comes from the Latin word porta, which means “gateway.” The portal vein is the gateway through which blood returning from the gastrointestinal tract and accessory organs passes before returning to the heart. This system includes all the veins draining the gastrointestinal tract, including the spleen, pancreas, and gallbladder. Blood is conveyed from these organs via the portal vein to the liver. The portal vein subdivides until the blood reaches the hepatic sinusoids. Blood therefore passes through two sets of “exchange” vessels: the capillaries within the organs of the gastrointestinal tract, the spleen, pancreas, and gallbladder, and the hepatic sinusoids. From the sinusoids, blood converges into hepatic veins and finally the inferior vena cava before returning to the heart. There are three distinct layers to the gallbladder wall: the inner mucosa; the middle fibromuscular layer; and the outer serous layer. Inside the gallbladder are many minute, inward folds or rugae. These folds aid in concentrating the bile through absorption of water and secretion of mucus. The gallbladder may be descriptively divided into three major sections: fundus, body, and neck. The shape of the normal gallbladder has been likened to that of a pear, which has a narrow “neck” and a round “bottom” (Figure 15-8). The fundus is the bottom portion (refer to Figure 15-6, A). The middle and main portions of the gallbladder are called the body, and the narrower area leading into the cystic duct is the neck (refer to Figure 15-6, B). Hepatic Ducts Surrounded by a sheath of connective tissue, intrahepatic bile ducts and hepatic arteries accompany portal veins in portal triads that radiate throughout the lobes and segments of the liver. The intrahepatic ducts unite to form the right and left main hepatic ducts. As noted, the right and left main ducts join at approximately the level of the liver hilum to form the CHD, the proximal portion of the CD (refer to Figure 15-2). Biliary Ducts The cystic duct, CBD, and part of the CHD are extrahepatic biliary ducts (not enclosed by liver tissue). They are lined with subepithelial connective tissue and some smooth muscle fibers. 238 Section III ABDOMINAL SONOGRAPHY Cystic Duct The lumen of the cystic duct contains a series of mucosal folds, the spiral valves of Heister. Even though this area of folds is called a valve, it is a misnomer. There does not seem to be any valve or flow control action; bile flows freely in both directions through the cystic duct. Pressure differences in the biliary system, along with the stimulated contraction of the gallbladder, seem to govern the flow of bile. The spiral valves of Heister prevent the cystic duct from overdistending or collapsing. PHYSIOLOGY Bile is produced by the liver and carried to the gastrointestinal system by the biliary tract. The sphincter of Oddi, located in the duodenum, regulates the passage of bile into the duodenum and at the same time prevents reflux of gastrointestinal fluids into the biliary system. When closed, the sphincter of Oddi forces the gallbladder to fill with bile. When fats and amino acids are ingested, the duodenal mucosa releases cholecystokinin (CCK), a peptide hormone. CCK stimulates the gallbladder to contract and the sphincter of Oddi to relax, and it increases hepatic production of bile. An injectable form of CCK has been used to stimulate the gallbladder during sonographic examination for a type of function test. The gallbladder is actually more than just a storage area for bile. Related blood vessels and lymphatics concentrate the stored bile through absorption of water and inorganic salts. Bile in the gallbladder is much more concentrated than hepatic bile. Bile is composed mostly of water (82%) and bile acids (12%). The remaining constituents include cholesterol, bilirubin (bile pigment), proteins, electrolytes, and mucus. SONOGRAPHIC APPEARANCE Much of the biliary system is readily appreciated on sonography. It is especially common for the gallbladder, CHD, and CBD to be imaged. In the absence of disease, the other portions of the biliary system may prove difficult to appreciate because they are so small. Gallbladder The sonographic appearance of a longitudinal section of the normal, distended gallbladder is that of an anechoic or nearly anechoic pear-shaped structure with thin, bright walls in the right upper quadrant of the abdomen. As mentioned, there is variation in shape and size of the gallbladder. The longitudinal appearance of the normal gallbladder has also been compared to a partially filled water balloon because it is slightly more oval than round (Figure 15-9, A). An axial view of the normal gallbladder at the level of the body will show an almost round to oval-shaped, anechoic structure with reflective walls (Figure 15-9, B and C). An axial section of the gallbladder should not be mistaken for axial sections of the inferior vena cava or aorta. It is important to identify whether or not the gallbladder is distended. A nonfasting patient will not have a distended gallbladder. The nondistended gallbladder may be mistaken for bowel or pathology (Figure 15-10, A and B). In the “empty” gallbladder the walls are thicker and may appear more irregular, with the central portion containing a few random echoes. The walls of a distended gallbladder tend to be well defined, regular, and echo-dense (Figure 15-10, C). As mentioned, normal gallbladder wall thickness is usually 3 mm or less (Figure 15-11). The wall may be difficult to measure when the gallbladder is in a partially distended, normal state or if pathology is present. Inadequate examination may lead to a false diagnosis of thickened walls or cholecystitis (the presence of a thickened gallbladder wall). Four landmarks may be helpful in locating the gallbladder: the portal vein, right kidney, duodenum, and main lobar fissure. • Portal vein. From its origin posterior to the pancreas neck, the longitudinal main portal vein can be followed as it courses toward the liver (Figure 15-12). It will reveal the gallbladder to be just inferior to the level of the right portal vein branch. Moreover, the right portal vein must be located to visualize the CHD (see Figure 15-1). In a transverse scan of the midepigastrium, finding the main portal vein (or portalsplenic confluence) and following it to the right will reveal (in typical order of appearance) the anechoic longitudinal portal vein; mid-gray longitudinal pancreas head section; anechoic to reflective and gassy long section of the duodenum; mid- to low-gray axial section of liver; longitudinal or axial (depending on its position) anechoic gallbladder section; and again, axial liver (Figure 15-13). This common relationship is important because during a scan, each anechoic structure can be eliminated as a possible gallbladder. • Right kidney. An axial section of the superior/midportion of the right kidney may also be typically noted with the gallbladder immediately anterior and to the left (see Figure 15-9). Further, the anechoic, axial section of the inferior vena cava can be visualized just posterior to the head of the pancreas and could be mistaken for an extremely posteriorly lying (or floating) gallbladder. • Duodenum. Whether anechoic or gassy, the duodenum serves as an excellent landmark because it is usually sandwiched between the gallbladder (laterally) and pancreas head (medially) (see Figure 15-13). • Main lobar fissure. The thin, reflective, main lobar fissure may be demonstrated between the portal Text continued on p. 242 Chapter 15 The Biliary System 239 Anterior Superior Inferior Liver Gallbladder Bowel Posterior A Anterior Anterior GB Liver Liver Right Right Left Left GB IVC Rt kid C Posterior B Posterior IVC FIGURE 15-9 Gallbladder Shape. A, Sagittal scanning plane image; longitudinal section of the gallbladder. Notice its oblong shape. B, Oblique transverse scanning plane image; axial body/middle section of the gallbladder (GB) anterior, and the right kidney and inferior vena cava (IVC), posterior. C, Another axial section of the body of the gallbladder (GB) in a different patient. Notice the shape of the gallbladder and its anechoic, bile-filled lumen. Observe the posterior through transmission. Also note the similarly shaped, anechoic, axial sections of the inferior vena cava (IVC) and aorta (AO), which should not be confused with the gallbladder. AO 240 Section III ABDOMINAL SONOGRAPHY Anterior Superior Inferior Liver Gallbladder Duodenum A Posterior Anterior Liver Left Right Gallbladder Duodendum Right kidney B Posterior Liver GB PV IVC C FIGURE 15-10 Nondistended/Distended Gallbladder. A, Sagittal scanning plane image; longitudinal section of the gallbladder that is nondistended or contracted. B, Transverse scanning plane image; axial body/middle section of the same nondistended gallbladder. Observe how the walls are prominent and could appear thickened due to its contracted state. Note that it’s slightly more oval than round. C, Sagittal scanning plane image; longitudinal section of a distended gallbladder (GB). Notice how the walls of a normal, distended gallbladder appear well-defined, smooth, and echo dense. IVC, Inferior vena cava; PV, portal vein. Chapter 15 The Biliary System A B FIGURE 15-11 Gallbladder Wall Thickness. The thickness of the normal gallbladder wall is usually less than 3 mm. Cholecystitis and carcinoma are just two examples of pathologic states that may alter the thickness and appearance of the gallbladder wall. Care must be taken when adjusting technique to resolve actual wall thickness and not misrepresent the walls by setting the gain or power settings too high. Image A shows an oblique transverse scanning plane image demonstrating the correct place to measure the anterior gallbladder wall. Note measurement caliper placement. Image B shows a sagittal scannning plane image also demonstrating the anterior gallbladder wall measurement. 241 242 Section III ABDOMINAL SONOGRAPHY vein and the gallbladder. It helps to form the “bed” in which the gallbladder lies (Figure 15-14). The main lobar fissure is considerably more difficult to consistently appreciate than the portal vein, but it is of value. Reference to all the landmarks will make locating the gallbladder easier. Anterior Right RPV SV MPV IVC SMA Left AO Posterior FIGURE 15-12 Main Portal Vein. The main portal vein (MPV) is a useful landmark when locating the gallbladder. This transverse scanning plane image shows that following the longitudinal MPV from its origin to the liver will reveal the right portal vein (RPV) branch, which is typically at a level just superior to the gallbladder. AO, Aorta; IVC, inferior vena cava; SMA, superior mesenteric artery; SV, splenic vein. At times, regardless of scanning technique, the gallbladder simply will not be visualized. Nonvisualization may occur for a number of reasons: • If the gallbladder fails to develop (agenesis), there will be nothing to image. However, this cause of nonvisualization is rare. • A small, tubelike (vermiform or wormlike) gallbladder may appear as a bile duct and be missed on sonography. • As previously noted, an empty or contracted gallbladder may be small and can be overlooked. • The gallbladder is obscured or hidden by bowel gas. The fundus of the gallbladder can be challenging to visualize because of its close proximity to bowel. Bowel often creates a shadow that partially obscures the fundus (Figure 15-15). Thus, changing patient position or transducer position may be necessary to examine the entirety of the fundus. Floating gallstones, polyps (protruding masses from the inner wall of the gallbladder), and other masses may be present in the fundus of the gallbladder and easily missed on casual examination. A small sacculation (outpouching) may be seen in some patients in the area of the gallbladder neck (Figure 15-16). This has been called Hartmann’s pouch after Henri Hartmann (1860–1952), a French surgeon. The term infundibulum is also applied to this dilatation of the gallbladder neck area. Some consider this sacculation an abnormality, whereas others consider it an oddity. It must be carefully screened to detect coexisting abnormalities, such as cholelithiasis (gallstones). Shadows and other minor distortions related to the edge of the gallbladder walls and distal to the spiral Anterior Pancreas head Pancreas neck Pancreas body Round ligament Stomach Shadow cast by ligament Liver Right Left Pancreas tail Gallbladder Duodenum Inferior vena cava Spine Common bile duct Superior mesenteric artery Aorta Portal splenic confluence Posterior FIGURE 15-13 Relationship of Gallbladder, Duodenum, and Pancreas. A transverse scanning plane image through the mid-epigastrium may reveal the above relationship. Notice how the gallbladder is lateral to the duodenum, which is just lateral to the head of the pancreas. Chapter 15 The Biliary System 243 Anterior Main lobar fissure Hepatic vein Superior Inferior Gallbladder Portal vein Inferior vena cava Posterior FIGURE 15-14 Main Lobar Fissure and Gallbladder Relationship. The main lobar fissure helps to form the “bed” in which the gallbladder lies and serves as a useful landmark to help locate the gallbladder. Gallbladder fundus Gallbladder neck Cystic duct S Common hepatic duct F Gallbladder body Common bile duct Hartmann's pouch FIGURE 15-15 Bowel Shadows. The fundus of the gallbladder can be challenging to examine because of its close proximity to bowel. Bowel often creates a shadow (S) that partially obscures the fundus (F). Changing patient position or transducer position can help visualize the entirety of the fundus. valves of Heister are common. High-frequency sound produces a particularly striking shadow from these areas because it is more easily reflected than the lower frequencies (Figure 15-17). Each shadow must be explored to determine whether it is natural or associated with disease. An acoustic shadow should be followed to its origin to learn whether it begins slightly more anteriorly and interrupts the representation of the wall. If it interrupts the wall, the shadow may indicate abnormal anatomy and deserves further study. FIGURE 15-16 Hartmann’s Pouch. A dilatation located in the area of the neck of the gallbladder is called Hartmann’s pouch. This slight sacculation is also known as the infundibulum. Ductal System In the average patient, bile ducts other than the common duct are small and usually not appreciated sonographically. The common duct is larger in diameter and can be seen on ultrasound closely associated with the portal venous system. Its longitudinal section may be noted as two bright, parallel lines separated by just 1 mm or so of anechoic bile. Because of its small diameter, axial sections of the common duct appear very small, round, and anechoic with reflective walls. 244 Section III ABDOMINAL SONOGRAPHY s s FIGURE 15-17 Wall Shadowing. Shadows and other minor distortions related to the edge of the gallbladder walls and distal to the spiral valves of Heister are common. High-frequency sound produces a particularly striking shadow from these areas because it is more easily reflected than the lower frequencies. S, Shadowing. Anterior Common duct Bowel Superior Inferior Common bile duct Liver Right Proper hepatic portal vein Common artery hepatic duct Posterior FIGURE 15-18 Relationship of Right Portal Vein, Proper Hepatic Artery, and Common Hepatic Duct. Slightly oblique, sagittal scanning plane image showing a longitudinal section of the common duct. An axial section of the proper hepatic artery is seen between the common hepatic duct portion of the common duct (anteriorly) and right portal vein (posteriorly). As previously discussed, the proximal common duct, the CHD, is located anterior to the right portal vein; it is not uncommon to see a portion of the proper hepatic artery running between them (Figure 15-18). The CHD is often mistaken for the CBD, which is generally more closely associated with the main portal vein than the right branch. However, there are always variations, so it is possible to see the CBD and the right portal vein at the same time. As noted, the distal CBD is located anterior and slightly right lateral to the main portal vein. In an oblique sagittal scanning plane, a longitudinal section of the supraduodenal CBD can be seen coursing superior to inferior, between an axial section of the common Chapter 15 hepatic artery and the first portion of the duodenum. The small, round, anechoic axial section of the common hepatic artery is visualized at the superoanterior edge of the CBD, and the duodenum is seen inferiorly (see Figure 15-5, A). Depending on the contents of the duodenum, it may be possible to follow the supraduodenal CBD inferiorly and visualize a long section of the retroduodenal CBD. In some cases, patients drink water to fill up the duodenum (obliterating any reflective gas) to make a passable window for the sound waves and expose the retroduodenal portion of the duct. A longitudinal section of the infraduodenal CBD can be seen medial to the first portion of the duodenum, running inferiorly to the posterolateral edge of the axial section of the pancreas head (see Figure 15-5, B). In many cases the long section of the gastroduodenal artery can be visualized running parallel and anterior to the long section of the infraduodenal CBD. Generally, the intraduodenal CBD is not routinely visualized. In a transverse scanning plane, an axial section of the infraduodenal CBD is routinely noted on the posterolateral border of the pancreas head, posterior to a small axial section of the gastroduodenal artery. The contrast between the small, round anechoic duct and artery and the midgray appearance of pancreatic parenchyma makes it easier to detect the small diameter structures (Figure 15-19). 245 The Biliary System Because of the appearance of the shape that its axial sections form together, the extrahepatic portal triad has become known as “Mickey’s Sign” or the “Mickey Mouse Sign.” The CBD is the right “ear” of the famous mouse, the proper hepatic artery the left “ear,” and the larger main portal vein is the “face” (see Figure 15-4, C and D.) SONOGRAPHIC APPLICATIONS For most physicians, sonography is the method of choice for examining the biliary system. Some specific applications of sonographic examination of the biliary system include: • Assessment for possible obstruction of the biliary ductal system • Presence of stones in the gallbladder (cholelithiasis) • Presence of stones in the ductal system (choledocholithiasis) • Ruling out masses associated with the biliary system • Postsurgical follow-up evaluation (e.g., cholecystectomy) Indications for Examinations Clinical indications that are normally used as reasons for an ultrasound examination of the biliary system and right upper quadrant (RUQ) include: • RUQ pain • Positive Murphy’s sign (RUQ pain) on physical examination Portal splenic confluence Anterior Pancreas neck Pancreas body Gastroduodenal artery Splenic vein Superior mesenteric artery Pancreas head Common bile duct Right Left renal vein Pancreas tail Liver Aorta Spine Right renal artery Inferior vena cava Posterior FIGURE 15-19 Relationship of Infraduodenal Common Bile Duct, Pancreas Head, and Gastroduodenal Artery. Transverse scanning plane image of the mid-epigastrium demonstrating an axial section of the infraduodenal common bile duct on the posterolateral border of the pancreas head, posterior to an axial section of the gastroduodenal artery. Left 246 • • • • • • Section III ABDOMINAL SONOGRAPHY Nausea Vomiting Pain radiating to the right shoulder or scapula Jaundice or abnormal liver function tests (LFTs) Loss of appetite Intolerance to fatty foods or dairy products NORMAL VARIANTS The biliary system may not develop normally, which can cause different types of deviations to occur. Deviations are of special interest to the sonographer because they may challenge adequate examination. For example, what appears to be a septated gallbladder (a gallbladder with divisions or septations) may simply be a gallbladder folded onto itself. If the patient’s position is changed, the gallbladder may unfold to reveal no septation (Figure 15-20). Other variations may be considered pathologic or may contribute to the development of disease. For instance, a gallbladder attached to the liver by a parti­ cularly long mesentery can mimic a “floating” gall­ bladder that is prone to torsion (twisting) as opposed to a gallbladder that is partially embedded in liver tissue. Gallbladder Congenital abnormalities of the gallbladder are relatively common: • Floating gallbladder: low position in the abdomen • Hypoplasia: underdevelopment; relatively rare but must be ruled out as possible reason for nonvisualization on sonography and other imaging modalities • Agenesis: complete failure of the gallbladder to develop; relatively rare but must be ruled out as possible reason for nonvisualization on sonography and other imaging modalities • Duplicated gallbladder: with or without duplication of the cystic duct • Double gallbladder (rare): two gallbladders are present; however, only one is functioning Variations in gallbladder shape are very common: • Bilobed: hourglass-shaped • Septated: characterized by one or more internal divisions of the gallbladder; septations tend to be associated with gallstone formation resulting from the stasis of gallbladder contents; they may make it difficult to identify cholelithiasis (gallstones) • Junctional fold: fold seen at the body and neck. Hartmann’s pouch may fold back on itself at the neck, creating a pouch for stones to collect, which could cause obstruction. • Phrygian cap: the most common variation in gallbladder shape. In this case, the gallbladder fundus is partially folded onto itself, so that it appears similar to the Phrygian cap worn by the early Roman freed slaves and later by French revolutionaries as a symbol of liberty. This looks similar to a Smurf’s hat (Figure 15-21). Anterior Gallbladder Bowel Liver Superior Inferior Posterior Right kidney FIGURE 15-20 False Appearance of a Gallbladder Variation. In this sagittal scanning plane image, it appears that a septation is present in the gallbladder. However, when the patient’s position was changed, the gallbladder was observed folded onto itself (a normal variation) and not abnormally septated. Clearly, it is imperative that the patient be placed in at least two different positions during sonographic examination of the gallbladder and biliary tract to rule out normal variations from abnormalities. Chapter 15 The Biliary System 247 Portal vein A B C D Gallbladder septation Anterior Liver Superior Inferior Gallbladder E Posterior FIGURE 15-21 Typical Gallbladder Shape Variations. A, Bilobed gallbladder. B, True septated gallbladder. C, Gallbladder folded onto itself in what has been called the Phrygian gallbladder, named after the shape of a Phrygian cap seen in D. D, The Phrygian cap was worn by early Roman freed slaves and later by French revolutionaries as a symbol of liberty. E, Example of a gallbladder septation. Biliary Ducts • Variations in the extrahepatic biliary ducts are frequently seen and may appear in almost any combination. For example, the cystic duct may join the CHD at almost any point from the porta hepatis to the duodenum. With a low juncture, the cystic duct may run parallel to the CHD for some distance. • Accessory hepatic ducts are also fairly common; on sonographic examination, they may present as an “extra” tubular structure. Such variations should not be an obstacle; following them to their origin will differentiate them from similar appearing structures. • A more easily recognized variation is the choledochal (or choledochus) cyst. Of the three types—congenital cystic dilation, intraduodenal (choledochocele), and congenital diverticulum—the first is the most common. A choledochal cyst is a localized dilatation of the CBD. When caused by a congenital diverticulum, it may appear as a separate or loosely connected structure to the CBD. The choledochocele (or intraduodenum) is formed by a section of the CBD that has entered the duodenum and enlarged. This is similar to the process involved in the formation of a ureterocele. • Biliary atresia (congenital closure) may be diffuse or focal in the extrahepatic ducts, or it may be intrahepatic. Diffuse extrahepatic biliary atresia is the most common. REFERENCE CHARTS ASSOCIATED PHYSICIANS • Surgeon: Involved in the diagnosis of biliary disease, as well as surgical intervention. • Internist: Involved in the diagnosis and medical treatment of biliary disease. • Radiologist: Performs and interprets the various imaging tests used to diagnose biliary disease. 248 Section III ABDOMINAL SONOGRAPHY DIAGNOSTIC TESTS • Oral cholecystogram (OCG): A contrast material (dye) is ingested by the patient the night before the test. Information on structure and function of the gallbladder is obtained. This test is performed by a radiologist assisted by a radiologic technologist and is interpreted by the radiologist. • Nuclear medicine (HIDA scan): A minute amount of a radiopharmaceutical is injected. It passes through the bloodstream to the liver, then to the biliary system, and eventually into the duodenum. Functional information is the primary focus of this test, and some structural information is also obtained. This test is performed by a nuclear medicine technologist and interpreted by the radiologist. • Computed axial tomography (CT scan): A radiologic examination in which cross-sectional x-ray images of the biliary system and other abdominal structures are obtained. A contrast medium may be administered to differentiate between disease and normal anatomy. Structural information is the primary focus of this test, but some functional information may be obtained. It is performed by a radiologic technologist and interpreted by the radiologist. • Cholangiography: A contrast material is injected into the biliary system either by catheter (i.e., T-tube cholangiogram) or by needle (transhepatic cholangiogram) under radiographic guidance. This yields structural information about the entire biliary system, especially about obstruction. It may be performed before, during, or after surgery. Surgeons, radiologists, and radiologic technologists are involved in the procedure, and it is interpreted by the radiologist. • Endoscopic retrograde cholangiopancre­atography (ERCP): In this endoscopic, radiographically guided examination, the ampulla of Vater is cannulized through a tube inserted into the patient’s upper gastrointestinal tract. Contrast material is then injected to fill and delineate the pancreatic and bile ducts. Information on obstructive processes is the objective. This type of endoscopy is usually performed by the gastroenterologist, who is assisted by the radiologist. The gastroenterologist interprets the endoscopic results, and the radiologist interprets the radiologic findings. • Hepatobiliary scintigraphy: A radionuclide imaging study that evaluates both liver function and the biliary sytem. It traces the production of bile and its pathway through the biliary system into the small intestine. It detects bile leaks, biliary atresia, and/or neonatal hepatitis. Hepatobiliary scintigraphy also provides functional information that US, CT, or MR cannot. • Endoscopic ultrasonography (EUS): Involves an endoscope and ultrasound probe to visualize the GI tract. EUS requires expert skills and specific equipment. This test is usually only available at tertiary care facilities. This is commonly used for patients with biliary obstruction, to stage malignancies affecting the biliary tracts and to assist in image-guided interventions. LABORATORY VALUES Direct (conjugated): <0.5 mg/dL Indirect (unconjugated): ≤1.1 mg/dL Urine: negative Elevated if there is obstruction, excess amount of red blood destruction, or malfunction of liver cells 1 to 12 mg/dL Serum bilirubin (infant) Urobilinogen Fecal: 50 to 300 mg/24 hours Urine: Men: 0.3 to 2.1 Ehrlich units/2 hours Serum alkaline Elevated in cases of hepatic phosphatase jaundice, abscess, cirrhosis, carcinoma, or obstruction Alanine aminotransferase Elevated in cases of acute (ALT) cirrhosis, hepatic metastasis, and pancreatitis White blood cell count Elevated in cases of infection (cholecystitis, cholangitis, etc.) Aspartate Elevated with liver cell injuries aminotransferase Carcinoembryonic Cancer indicator antigen Lactic acid Elevated in cases of hepatitis, dehydrogenase cirrhosis, and obstructive jaundice Prothrombin time (PT) Clotting time is longer in patients with acute cholecystitis, cancer, cirrhosis, and obstruction Serum bilirubin (adult) Collectively, these laboratory tests or liver function tests are used to help in the diagnosis of hepatobiliary diseases. These tests are a great indicator for physicians to determine how the liver is functioning. Elevations in certain labs allows for a quick and more accurate diagnosis. VASCULATURE BLOOD SUPPLY Common hepatic artery → proper hepatic artery → cystic artery → gastroduodenal artery VENOUS DRAINAGE Cystic veins → hepatic veins → IVC The gallbladder neck is drained via the cystic veins. The gallbladder body and fundus are drained via hepatic sinusoids. AFFECTING CHEMICALS Nonapplicable