Diseases of the Gallbladder and Bile Ducts - part 3 pdf

80 Section 2: Diagnostic and therapeutic approaches for the biliary tree and gallbladder Figure 4.6 Axial contrast-enhanced CT shows acute cholecystitis with evidence of calculi and gallbladder wall thickening greater than 3 mm. Figure 4.7 Axial contrast-enhanced CT shows gangrenous cholecystitis with massive distension and gallbladder wall thickening greater than 3 mm. gradient echo images with fat suppression are commonly used to define the extent of invasion into the liver, pancreas, or duodenum [39]. On PET or PET/CT scan, gallbladder cancer shows up as specific FDG accumulation in the gallbladder area with pos- sible extension into the liver. Advanced tumors may impose as large FDG-positive mass with infiltration into the liver or adjacent abdominal organs (Plate 1, facing p. 84). PET and PET/CT scan have a high sensitivity to detect gallbladder can- cer regardless of the primary or recurrent nature of the tumor (Table 4.1). Although the study population is relatively small, the three series which use PET scans to detect gallbladder cancer report a sensitivity of 75 to 80% and a specificity of 87 to 82% [40–42]. Furthermore, the PET scan proved to be an accurate method to differentiate benign disease such as cho- lecystitis, gallstone disease, and cholesterol polyp from gall- bladder cancer [40,42]. Our experience in Zürich with the integrated PET/CT scanner even demonstrated a sensitivity Chapter 4: Noninvasive imaging of the biliary system 81 Figure 4.8 Coronal T2-weighted (A), unenhanced axial T1-weighted (B), and gadolinium-enhanced axial T1-weighted (C) images in a patient with acute cholecystitis. Note the wall thickening and the pericholecystic fluid (arrows). Edema within the pericholecystic fat is best appreciated on MRCP image (D). of 100% with a high median maximum standardized uptake value (SUV max ) of 9.9 [43]. We also found PET/CT very help- ful in detecting distant metastases which were not visible by standard imaging. Bile ducts The intrahepatic bile ducts may not be visualized by ultra- sound when they are normal in caliber. When dilated, they often have a “tram track” appearance because the biliary rad- icals parallel the portal veins. Color Doppler ultrasound is helpful in discerning which tubular structure is the bile duct (Fig. 4.10, Plate 2, facing p. 84). When they are markedly di- lated, the ducts can be quite tortuous. The wall of the bile duct is normally very thin, measuring less than 1 mm. CT has the advantage of high spatial resolution, which allows depiction of both the lumen and the wall of the bile ducts, but has the disadvantage of imaging only in the axial plane. This is offset by multidetector helical CT with which a high-quality volu- metric data set can be acquired and then rendered or dis- played in a multiplanar or three-dimensional fashion. CT is very sensitive to ductal dilatation and on occasion even non- dilated bile and pancreatic ducts can be visualized. The de- piction of ductal structures is markedly reduced, however, (A) (B) (C) (D) 82 Section 2: Diagnostic and therapeutic approaches for the biliary tree and gallbladder when intravenous iodinated contrast material is not used. Furthermore, CT cholangiography can also be performed noninvasively by acquiring a thin-section spiral CT within the first hour after the intravenous administration of 20 mL of iodipamide meglumine 52% (Cholografin; Bracco Diag- nostics, P ri nceton, NJ) d iluted in 80 m L of normal sal ine via a 30-min infusion [44,45]. This data set can be reconstructed in three dimensions to evaluate the bile ducts in a fashion similar to direct cholangiography or MR cholangiography (MRC) (Fig. 4.11). Unfortunately, there must be reasonable liver function in order for the ducts to be adequately opacified. Like MRI of the intrahepatic and extrahepatic bile ducts, MRC relies on heavily T2-weighted sequences on which sta- tionary fl uid within the ducts is of very high signal intensity relative to the adjacent liver [46–49] (Fig. 4.12). Gradient- echo sequences were originally used to produce these images but more recently fast spin echo sequences have been shown to yield better visualization of the ducts without long breath holds or magnetic susceptibility artifacts [50]. The data ob- Figure 4.9 Axial unenhanced (A) and contrast- enhanced (B) C T imag e s show carcino m a of t h e gallbladder. While this tumor is hardly visualized on unenhanced imaging (A), it shows subtle perfusion after contrast administration (B). (A) (B) Chapter 4: Noninvasive imaging of the biliary system 83 tained from these sequences can be manipulated on a com- puter workstation and displayed like the images obtained in an ERCP. In addition, it is also possible to obtain physiological information on the gallbladder ejection fraction utilizing cholecystokinin-stimulated magnetic resonance cholangi- ography [51]. Currently, even nondistended second order biliary branches are seen on a regular basis on MRC, inde- pendent of the patient’s liver function (Fig. 4.12). Choledocholithiasis Ultrasound is usually the initial imaging choice in patients with jaundice to determine the integrity of the bile ducts. Al- though ultrasound does not reliably visualize the bile ducts at their extremes (i.e. the peripheral intrahepatic ducts at one end and the distal common bile duct at the other), the central intrahepatic ducts and especially the common hepatic duct are well visualized. Either CT or MRI better delineate the ex- treme portions of the ductal system. The normal common he- patic duct courses just anterior to the main portal vein and measures 5 to 6 mm in diameter. A duct measuring more than 6 mm yet not obstructed is a condition seen in elderly patients, in a minority of patients following cholecystectomy, and in patients with previous long-standing ductal obstruc- tion. For elderly patients in particular, the upper limit of nor- Figure 4.10 Grey-scale (A) and color Doppler (B) ultrasound of a patient with intrahepatic biliary ductal dilatation. Color Doppler ultrasound is particularly helpful in discerning which tubular structure is the bile duct. (See also Plate 2, facing p. 84). Figure 4.11 Three-dimensional CT cholangiogram obtained 25 min after the intravenous administration of a biliary secreted contrast agent. This method offers excellent delineation of the segmental biliary branches. (Courtesy of F. Yang, M. D. and SG Ruehm, M.D., University Hospitals of Essen, Germany.) (A) (B) 84 Section 2: Diagnostic and therapeutic approaches for the biliary tree and gallbladder mal in duct caliber can increase by 1 mm for every decade after the age of 60 (i.e. 7 mm after age 70, 8 mm after 80, and so on) [52]. Most patients with choledocholithiasis have di- lated ducts, and on occasion the calculi themselves will be visualized as echogenic intraluminal foci, with or without acoustical shadowing. In general, CT is very sensitive to dilatation of the biliary tree, including both intrahepatic and extrahepatic ducts. Al- though ultrasound is superior to CT for detecting stones in the gallbladder, CT is superior to ultrasound for detecting stones in the bile ducts [53–55]. This is mainly because there is better visualization of the distal common bile duct by CT and the level of dilatation or obstruction is better depicted. Even when a stone is not readily apparent, the diagnosis may be entertained when there is no evidence of a mass at the level of obstruction. However, this combination of findings is not specific for choledocholithiasis, because both a benign stric- ture and ampullary stenosis may have a similar appearance. There is some evidence that a preliminary CT prior to the ad- ministration of either oral or intravenous contrast material may increase the sensitivity for detecting stones [56]. In general, ERCP remains the technique of choice when evaluating patients with a high probability of having com- mon bile duct stones, as the diagnosis can be made and then treatment applied in the same setting [57]. However, in cer- tain clinical settings — for example where ERCP is contrain- dicated or there is a moderate to low probability of common bile ducts stones — MRC is the imaging modality of choice [57]. MRC has greater than 90% sensitivity and specificity in the detection of choledocholithiasis [58–62]. These percent- ages are superior to both ultrasound and CT. With MRC, cal- culi are seen as low-signal intensity defects within high-signal intensity bile (Fig. 4.13). It must be remembered, however, that both air bubbles and blood clots can have a similar low- signal intensity appearance. Cholangitis Infl ammation of the bile ducts is caused by a number of conditions including infection, such as acute suppurative cholangitis, recurrent pyogenic cholangitis, or sclerosing Figure 4.12 MRCP using a respiratory triggered three-dimensional T2- weighted data set in a patient postcholecystectomy. Arrow marks a duodenal diverticulum. Note the exquisite image quality with depiction of nondilated biliary segmental branches. Figure 4.13 MRCP using a respiratory triggered three-dimensional T2-weighted data set in a patient with calculi in the distal common bile duct. Maximum intensity projection (MIP) (A) and source image (B) show intraluminal filling defects within the distal common bile duct. (A) (B) Chapter 4: Noninvasive imaging of the biliary system 85 cholangitis. In acute cholangitis, the bile ducts are often di- lated and there may be thickening of the ductal wall. If bili- ary gas is present it will be seen as foci of indistinct or “dirty” acoustical shadowing on ultrasound. Occasionally, intrahe- patic abscesses develop, which are usually multiple and relatively small (less than 2 cm), with their distribution de- pending on the site and level of ductal obstruction. Gas bub- bles may also be noted within these abscesses. Abscesses tend to be multilocular and hypoechoic on ultrasound, hypoat- tenuating on CT, and hyperintense on T2-weighted MRI (Fig. 4.14). CT and MRI can also demonstrate marked enhancement of the ductal walls [63,64]. In sclerosing cholangitis, chronic obliterative fibrotic in- fl ammation involves the wall of the intrahepatic and extra- hepatic bile ducts resulting in chronic obstructive jaundice. The patients are predominantly men under the age of 45. Sec- ondary associations include infl ammatory bowel diseases, cirrhosis, pancreatitis, retroperitoneal fibrosis, Peyronie’s disease, Riedel’s thyroiditis, and retro-orbital pseudotumor [65] . C hola ng iocarci noma develops i n up to 12% of patients with sclerosing cholangitis [66]. Other complications in- clude biliary cirrhosis and portal hypertension. Ultrasound can detect the segmental biliary dilatation and the morphologic changes of primary sclerosing cholangitis, although the irregularity of the ducts noted on either direct cholangiography or MRC is difficult to appreciate. When the infl ammation is chronic, such as in primary sclerosing chol- angitis, the CT and MRI findings are much different than in acute cholangitis. Although segmental and scattered intra- hepatic duct dilatation is apparent, the degree of dilatation is Figure 4.14 Patient with liver abscess, which appears hyperintense on axial T2-weighted imaging (A) and hypointense with rim enhancement on contrast-enhanced T1-weighted axial imaging (B). Also note intrahepatic ductal biliary dilatation. (A) (B) 86 Section 2: Diagnostic and therapeutic approaches for the biliary tree and gallbladder relatively mild. Intrahepatic calculi may be seen on ultra- sound and CT [67]. The segmental narrowing and irregular- ity of the bile ducts inherent to this disease, however, are difficult to appreciate with these two techniques. The most striking changes relate to the morphology of the liver. First, the caudate lobe is enlarged and in some cases may account for the vast majority of liver parenchyma. Sec- ond, there are deep lobulations in the capsular surface owing to profound segmental atrophy, particularly in the anterior segment of the right hepatic lobe and the medial segment of the left hepatic lobe. Furthermore, there are often enlarged lymph nodes in the porta hepatic and paraduodenal region. While ERCP has been the initial diagnostic technique in the past, improvements in spatial resolution have increased t h e d i a g no s t ic c ap a b i l it y o f M RC , a nd m a ny i n s t i tu t ion s no w consider MRC as the initial imaging modality of choice [68]. The biliary tree can be depicted on MRI by using both MRC and multiphasic gadolinium-enhanced T1-weighted images. Common findings include intrahepatic bile duct dilatation (77%) and intervening bile duct stenoses (64%), giving the ducts a “beaded” appearance [69,70] (Fig. 4.15). Other find- ings include periportal edema, enhancement and thickening of the wall of the extrahepatic bile ducts, and increased enhancement of the periphery of the liver during the hepatic arterial phase. Cystic dilatation of the bile duct Congenital biliary cysts occur not only in the extrahepatic biliary ductal system but also everywhere in the biliary tree, and are frequently accompanied by pancreatobiliary mal- union. In 1959, Alonso-Lej and colleagues classified chole- dochal cysts into three types [71]. Due to the recognition of intrahepatic involvement, in 1977, Todani and colleagues re- fined their classifi cation into six types, and this has become the reference [72]. These diseases are rare and the patients often present with colicky right upper quadrant pain and jaundice [73]. The incidence of cholangiocarcinoma is in- creased in these patients [74]. Because ultrasound tends to depict only a portion of the biliary tree, it is not the modality of choice for diagnosing or characterizing choledochal cysts [75]. The diagnosis should be considered, however, when- ever focal dilatation of either an intrahepatic or extrahe- patic bile duct is detected. On CT, a choledochal cyst should be considered for any unilocular cystic mass that occurs in the region of the extra- hepatic bile duct. At times there may be calculi within these cysts, which are typically thin-walled and can be quite large, on the order of several centimeters [76]. In the normal pa- tient, the common hepatic duct may dilate focally as it exits the liver parenchyma, so it is more difficult to make the diag- nosis of a choledochal cyst in this region. If the cystic mass projects into the duodenal lumen, a choledochocele (=chole- dochal cyst ty pe I I I accord ing to the Todani c lassifi cation) is suspected. A history of pancreatitis may confuse the picture because a pseudocyst in the head of the pancreas may have a similar appearance on ultrasound and CT. Only a few studies have used MRC to evaluate choledochal cysts (Figs 4.16 and 4.17). These studies compared the find- ings of ERCP with MRC and concluded that both modalities provide similar information [77,78]. MRC readily demon- strates the various types of choledochal cysts including Caro- li’s disease (=choledochal cyst type V according to the Todani classifi cation), where cystic dilation of the intrahepatic ducts in a segmental manner and with no intervening stenotic re- gions is usually seen [79]. Cholangiocarcinoma Patients with cholangiocarcinomas commonly present with painless jaundice. The majority of cholangiocarcinomas originates from the extrahepatic bile ducts and often unre- sectable at the time of diagnosis because the tumor has al- ready spread to regional lymph nodes or infiltrated adjacent liver parenchyma [80]. Tumors occurring at the confluence of the right and left intrahepatic ducts are termed Klatskin tumors. The natural history of the untreated Klatskin tumor is dismal, and results in exceptional 5-year survivors [81]. ERCP is often required to obtain cytologic proof and for stent placementbuthaslimited value for determining the extent of the disease because the tumors tend to form strictures, there- by limiting opacifi cation of more peripheral ducts. In this clinical scenario, MRI in conjunction with MRC can provide valuable information concerning both the size and extent of the tumor and potential resectability [82,83]. However, de- spite the good visualization of the biliary ductal system by MRC, its accuracyand reliability to assessthe borders of chol- angiocarcinoma are clearly inferior to PTC [84]. On ultrasound, cholangiocarcinoma may be suspected when there is thickening or nodularity of the duct wall [85]. Although the cause of biliary obstruction is not always ap- parent by ultrasound, following the dilated biliary radicals from the periphery to the porta hepatis and down into the ex- trahepatic ducts may reveal a soft tissue mass. Intraluminal debris and even calculi may be seen within these proximally dilated ducts. The atrophic changes associated with long- standing biliary obstruction may be difficult to appreciate with ultrasound. Furthermore, some cholangiocarcinomas have a similar echo pattern to that of normal hepatic paren- chyma and may not be apparent sonographically. On CT, cholangiocarcinomas are seen as irregular or well- defined soft tissue masses found along the course of the intra- hepatic ducts, the extrahepatic ducts, or both [86]. Although many tumors are centrally located, others are peripheral and mimic a liver metastasis. They may be multifocal or seen as a subtle infiltrative mass extending along the course of the bili- ary tree. At times, the tumor is so obscure that the only evidence for a mass is proximal duct dilatation. If ductal ob- Chapter 4: Noninvasive imaging of the biliary system 87 struction is severe or long-standing there may be associated lobar atrophy [87]. Cholangiocarcinomas are relatively vas- cular tumors, although they uncommonly demonstrate hy- perenhancement during the hepatic arterial phase of a multiphasic CT. Furthermore, about a third of the tumors will demonstrate a unique phenomenon whereby there is slow wash-in and delayed wash-out of contrast material [88]. As a result, they will be isoattenuating to subtly hypoattenu- ating during the portal venous phase of enhancement and then hyperattenuating during a delayed phase, about 15 to 20 min later. Although CT remains the initial imaging modality for tumor characterization, MRI in conjunction with MRC ap- pears superior in determining tumor extension [84,89]. Cholangiocarcinomas typically present as poorly defined, and at times subtle, masses that may be of low signal intensity on T1-weighted images and of high signal intensity on T2-weighted images (Fig. 4.18). Common findings also in- Figure 4.15 Patient with inflammatory bowel disease and primary sclerosing cholangitis. While the MRCP MIP image (A) provides an immediate excellent overview, details such as intrahepatic bile duct dilatation and intervening bile duct stenoses (arrows) are better appreciated on the source image (B). (A) (B) 88 Section 2: Diagnostic and therapeutic approaches for the biliary tree and gallbladder clude markedly dilated ducts with thickening of the wall measuring greater than 5 mm. T1-weighted multiphasic gad- olinium-enhanced three-dimensional gradient echo se- quences with fat suppression typically show peripheral enhancement of the liver during the hepatic arterial phase and delayed or incomplete central fi ll-in on later phases [90,91]. Delayed images are also useful in showing the extent of tumor infiltration along the biliary tree. On a PET or PET/CT scan, intrahepatic (peripheral) chol- angiocarcinoma shows up as intrahepatic specific FDG accu- mulation which may be also observed in colorectal liver metastases and less frequently in hepatocellular carcinoma. Extrahepatic cholangiocarcinoma are visible as specific FDG in the liver hilus or along the extrahepatic bile duct. Hiliar cholangiocarcinomas (Klatskin tumors) that infiltrate into the liver may be difficult to differentiate from intrahepatic cholangiocarcinomas in this hepatic region. A PET series [92] and our series with the integrated PET/CT scanner [43] reported a high detection rate of 95 and 93% for intrahepatic cholangiocarcinoma. These favorable data are not applicable to extrahepatic tumors where PET and PET/CT had a signifi - cantly lower sensitivity (Table 4.1). However, there is one study that reported a high FDG uptake rate of 92% in a popu- lation of 26 Klatskin tumors [93]. These encouraging data could not be reproduced by other studies including our expe- rience. In our series of 33 extrahepatic cholangiocarcinomas, PET/CT identified the primary tumor site in only half of the cases (55%). On the other hand, PET and PET/CT seem to be very helpful to identify biliary distant metastases which were detected in 83 and 70%, respectively (Plate 1, facing p. 84) [43,93]. In addition, we could demonstrate that PET/CT was superior to the contrast enhanced CT scan in detecting dis- tant metastases. This is of paramount importance, especially for hepatobiliary surgeons and hepatologists, since the pres- ence of distant metastases has a signifi cant impact on the treatment decision. In contrast to distant metastases, PET and PET/CT is not suitable for the detection of regional lymph nodes, which were detectable in only 13 to 19% of patients with biliary malignancies [43,93]. Cholescintigraphy Cholescintigraphy is a nuclear medicine examination used in a number of clinical scenarios related to the hepatobiliary system. The exam uses a 99mTc-labeled iminodiacetic acid Figure 4.16 MRCP in a patient with type 1 choledochal cyst. Figure 4.17 A 25-year-old patient with history of choledochal cyst and status posthepaticojejunostomy at the age of 5. MRCP demonstrates remnant of a type 1 choledochal cyst which contains a stone. Also note the hepaticojejunostomy. Chapter 4: Noninvasive imaging of the biliary system 89 analogue (IDA) radiopharmaceutical that shares the same hepatocyte uptake, transport, and excretion pathways as bil- irubin. This technique not only provides images of the biliary tree but also yields functional information about the liver, gallbladder, and bile ducts, a major advantage of cholescin- tigraphy over other imaging modalities. For example, it can detect obstruction to bile flow without relying on secondary signs such as ductal dilatation [94,95]. Function can even be quantitated in the form of gallbladder ejection fractions and biliary transit times [96,97]. The main disadvantage of cholescintigraphy is the low spa- tial resolution. Compared to CT, which has 0.7 line pairs/mm and MRI, which has 0.3 line pairs/mm, cholescintigraphy has less than 0.1 line pairs/mm. Other disadvantages include the presence of ionizing radiation (approximately a third less than CT), the limited availability of the radiopharmaceutical agent at some sites (which must be prepared just prior to the examination), the cost of the examination (greater than ul- trasound but less than CT or MRI), the need for adequate pa- tient preparation (nothing by mouth for greater than 4 hours but less than 24 hours), and the fact that certain medications such as morphine sulfate can interfere with the test [98]. Figure 4.18 Patient with Klatskin tumor, which appears slightly hyperintense on axial T2-weighted imaging (A), hypointense on T1-weighted axial imaging (B), and hyperintense on gadolinium-enhanced delayed T1-weighted imaging (C). MRCP (D) demonstrates intrahepatic biliary ductal dilatation within both lobes. (A) (B) (C) (D) [...]... Malignancies of the bile duct are also classified according to their location Upper 1 /3 tumors involve the common hepatic duct and confluence, middle 1 /3 tumors arise from the common bile duct between the cystic duct and the upper border of the duodenum, and lower 1 /3 tumors arise from the common bile duct between the upper border of the duodenum and the ampulla of Vater For endoscopists, the Bismuth... biliary tree through the main papilla (Fig 5.2) provides excellent anatomic detail In the majority of cases, the following structures can be identified: the common bile duct (CBD), the common hepatic duct, the cystic duct leading to the gallbladder, the gallbladder itself, the liver hilum with right and left main intrahepatic ducts, and secondary and tertiary ducts leading from these Due to the patient’s prone... Release of bile into the duodenum is not continuous but regulated by the activity of the sphincter of Oddi, a ring of smooth muscle at the level of the ampulla of Vater So dysfunction may be associated with a syndrome of recurrent biliary pain with or without abnormal liver function tests and/ or dilatation of the bile duct In most individuals, the CBD is joined by the main pancreatic duct at the ampulla,... delay in excre- 92 Section 2: Diagnostic and therapeutic approaches for the biliary tree and gallbladder tion of the labeled isotope agent, giving the appearance of SOD or biliary obstruction This results in delayed biliary-tobowel transit time, and gives the appearance of common bile duct obstruction The administration of CCK will cause gallbladder contraction, which increases the pressure in the biliary... 1980; 136 : 437 –8 92 Kim YJ, Yun M, Lee WJ, et al Usefulness of 18F-FDG PET in intrahepatic cholangiocarcinoma Eur J Nucl Med Mol Imaging 20 03; 30:1467–72 76 Araki T, Itai Y, Tasaka A CT of choledochal cyst Am J Roentgenol 1980; 135 :729 34 93 Kluge R, Schmidt F, Caca K, et al Positron emission tomography with [(18)F]fluoro-2-deoxy-D-glucose for diagnosis and staging of bile duct cancer Hepatology 2001 ;33 :1029 35 ... Bilateral intrahepatic bile duct spread or multifocal disease 2 Involvement of the main trunk of the portal vein 3 Involvement of both branches of the portal vein or bilateral involvement of the hepatic artery and portal vein 4 Vascular involvement on one side of the liver with extensive bile duct involvement on the other Biliary stenting Endoscopic stenting is now a well-established form of palliative treatment... from the second portion of the duodenum, whereas the proximal CBD and the common hepatic duct are viewed from the duodenal bulb The CBD can be completely inspected in 96 to 100% of cases [26,27 ,30 ] However, anatomic limitations such as postBillroth II gastrectomy reconstruction and significant stenoses may preclude the use of EUS to examine the extrahepatic bile duct The sensitivity and specificity of. .. the thickened gallbladder wall retains its normal multilayered appearance as viewed with EUS Indeed, EUS adds little to the investigation of a thickened gallbladder wall, unless gallbladder cancer is considered a possible diagnosis The integrity of the gallbladder wall is a key factor in the diagnosis of depth of invasion of gallbladder cancer The normal gallbladder wall generally appears as a two-... enables examination of the entire extrahepatic bile duct and the right and left hepatic ducts The main advantage of this technique is that staging can be performed during the initial diagnostic and/ or therapeutic ERCP Additionally, IDUS can assess portal vein invasion at the liver hilum and invasion of the right hepatic artery It is difficult to image the liver hilum with EUS; in one study, bile duct tumors... hepatoma, and gallbladder cancer Secondary malignancies cause biliary strictures by extrinsic compression of the bile ducts; they include pancreatic tumors (e.g., adenocarcinoma and lymphoma) and metastatic malignancy (e.g., of the colon, breast, or bronchus) As the management of each type of these malignancies is unique, a vigorous effort must be made to identify the tissue of origin A minority of tumors . and thickening of the wall of the extrahepatic bile ducts, and increased enhancement of the periphery of the liver during the hepatic arterial phase. Cystic dilatation of the bile duct Congenital. has the advantage of high spatial resolution, which allows depiction of both the lumen and the wall of the bile ducts, but has the disadvantage of imaging only in the axial plane. This is offset. ducts. Al- though ultrasound does not reliably visualize the bile ducts at their extremes (i.e. the peripheral intrahepatic ducts at one end and the distal common bile duct at the other), the central