18 Heptobiliary Surgery 1 Fig. 1.12. Normal and aberrant sectoral ductal anatomy. (A) Typical ductal anatomy, (B) triple confluence, (C) ectopic drainage of a right sectoral duct into the common hepatic duct (C1), right anterior duct draining into the common hepatic duct; (C2), right posterior duct draining into the common hepatic duct, (D) ectopic drainage of a right sectoral duct into the left hepatic ductal system (D1, right posterior sectoral duct draining into the left hepatic ductal system; D2, right anterior sectoral duct draining into the left hepatic ductal system, (E) absence of the hepatic duct confluence, (F) absence of right hepatic duct and ectopic drainage of the right posterior duct into the cystic duct. Reprinted with permission from: Surgery of the Liver and Biliary Tract (3rd Edition), Blumgart LH, Fong Y (Eds.) W.B. Saunders, London, UK (2000). 19 Essential Hepatic and Biliary Anatomy for the Surgeon 1 Fig. 1.13. Normal and aberrant segmental ductal anatomy. (A), variations of Segment V, (B) variations of Segment VI, (C) variations of Segment VIII, (D) variations of Segment IV. Note there is no variation of drainage of Segments II, III, and VII. Reprinted with permission from: Surgery of the Liver and Biliary Tract (3rd Edition), Blumgart LH, Fong Y (Eds.) W.B. Saunders, London, UK (2000). CHAPTER 2 Hepatobiliary Surgery, edited by Ronald S. Chamberlain and Leslie H. Blumgart. ©2003 Landes Bioscience. Imaging of the Liver, Bile Ducts and Pancreas Douglas R. DeCorato, Lawrence H. Schwartz Imaging of the upper abdomen including the liver, biliary tree and pancreas has evolved rapidly over the past ten years. Fast imaging techniques using both com- puted tomography (CT) and magnetic resonance imaging (MRI) permit dynamic contrast-enhanced imaging in seconds. Similarly, ultrasonography (US), an integral part of hepatobiliary imaging for both benign and malignant disease, has seen marked advances due to improved technology. Modalities such as nuclear medicine and angiography play a more specialized role in the identification and characterization of pathology. For example, although nuclear medicine is limited in its evaluation of hepatic lesions, it is a physiologic examination that can aid in detecting disease of the gallbladder, biliary tree, and postoperative complications such as bile leaks. These three imaging modalities, which are utilized most commonly, have certain characteristics that are unique to each. A detailed discussion of the physical proper- ties and principles underlying each imaging technique is beyond the scope of this chapter, and interested readers are referred to the additional reading section at the end of the chapter. Basic principles will be outlined below. US is based on the transmission or reflection of sound waves (echoes) as they pass through tissue. Structures are described with regard to their relative echogenicity compared with surrounding structures. A hyperechoic lesion has more echoes than its surroundings and thus appears slightly brighter than the adjacent tissue. A hypoechoic mass has fewer echoes and thus appears darker. CT is based on the absorption of x-ray by structures. This absorption undergoes a mathematical calculation to generate specific attenuation values in Hounsfield units (HU). Structures are referred to as high or low attenuation or hyper- or hypodense lesions. A hyperdense or high attenuation lesion appears brighter than background structures or has been enhanced; a low attenuation or hypodense lesion is darker than background structures. It cannot be assumed that a low attenuation lesion has not been enhanced, or a high attenuation lesion has been enhanced. Spe- cific criteria exist for enhancement by CT based on an increase of 10 HU from a noncontrast study to a contrast study. MRI uses a strong magnetic field to image innate protons within organs. Signal intensity is based on sequence parameters and the relative abundance of protons. Commonly used terms for MR sequences include T1, T2, and gradient echo. Similar to US and CT, structures are described as hypointense and hyperintense. T1-weighted images will display fluid as dark (hypointense), and are classically thought of as 21 Imaging of the Liver, Bile Ducts and Pancreas 2 displaying anatomic information. Certain MR contrast agents, such as gadolinium chelates, are administered with T1-weighted images (mostly gradient echo images, a sequence that can be adjusted to generate rapid T1-weighted images). T2-weighted images generate bright (hyperintense) fluid and are generally used to identify patho- logic processes. Imaging of the hepatobiliary system is dependent on the suspected underlying disease, pretest likelihood of a positive study, and clinical suspicion of concurrent underlying disease process (for example, cirrhosis). The initial study, if chosen prop- erly, may be able to both identify the underlying disease process and provide staging information at the same time. In a patient with a low pretest likelihood of disease, initial screening of the liver is best accomplished with US due to its wide availability and relatively low cost. A patient with a negative ultrasound, and low pretest likeli- hood of disease, may need no further workup. However, patients with a high pretest likelihood of disease may require a different initial examination. Once a lesion or unsuspected underlying parenchymal disease is identified on US, a second imaging test may be necessary. A comparison between the three main imaging modalities is summarized in Table 2.1. Test Selection The choice of initial imaging test is influenced by several factors, including patient population, prevalence of certain disease processes, test availability, cost restraints, radiologic equipment and the pretest likelihood of a positive study. For example, US is an excellent screening test for many patients; however, body habitus, underlying hepatic disease, and overlying bowel gas can limit an otherwise diagnostic examina- tion. CT with contrast routinely delivers images of diagnostic quality; however, precontrast images, as well as arterial dominant phase images, are not always obtained. Significant limitations arise in patients in whom intravenous contrast is contraindi- cated or not administered for other reasons. A noncontrast CT scan markedly limits identification of small lesions and hinders characterization. MRI routinely acquires multiple sequences that aid in lesion identification and characterization. MRI has a set of absolute contraindications for scanning (Table 2.2). Additionally, since no radiation is administered, precontrast images are routinely obtained. MRI scanners are variable in both speed and quality. Low field strength systems and “open” mag- nets may not afford the resolution necessary for preoperative planning. Contrast administration is an important aspect of both CT and MRI. CT scans principally use iodinated contrast material, while MRI has a variety of contrast agents available of which gadolinium is the most common. Patients allergic to iodine will usually not cross-react with gadolinium-based agents and, thus, may be safely referred for MRI. A variety of newer MRI contrast agents, including tissue specific antigens, are currently under investigation. A more detailed analysis of the best test for each specific hepatic, biliary and pancreatic abnormality is beyond the scope of this Chapter, but general guidelines are discussed below and summarized in Table 2.3. Evaluation of the liver is best done with MRI, as it provides improved lesion detection and characterization. In addition, MRI can precisely define underlying liver processes, such as fatty infiltration, which can sometimes be confused with other diagnoses on both CT and US. An additional advantage of MRI is the development of 22 Heptobiliary Surgery 2 Table 2.1. Comparison of imaging modalities MRI CT Ultrasound Resolution Superior contrast Superior spatial Spatial resolution resolution resolution dependent on transducer selected Contrast material Superior safety High safety profile No contrast profile than CT of nonionic administered and lower volumes contrast. Requires are administered relatively high doses of iodinated contrast for study Radiation None Ionizing radiation None used Speed Rapid imaging Rapid imaging Imaging time time available time. Entire exam operator dependent may be performed in under a minute Technique Variable depending More uniform than Standard images on hardware and MR, while still with additional software somewhat variable images acquired depending on the clinical situation Cost Relatively high High Moderate Availability Less than CT Readily available, Generally available, usually 24 hrs/day but may be limited at certain periods due to staffing Table 2.2. Contraindications for MR imaging* Absolute contraindications Relative contraindications Pacemaker Pregnancy Neurostimulator Recent intravascular stent Cerebral aneurysm clip of unknown composition. Claustrophobia Possible metallic foreign body in the globe. Critically ill patients * Note: This table is not meant to be a complete list of all contraindications and any question should be referred to an MR imaging specialist. new contrast agents, such as ferumoxides (Feridex), which have been shown to im- prove lesion detection in certain cases. The selection of an ideal imaging technique for abnormalities of the biliary tree is somewhat more complex. In the evaluation of cholelithiasis or choledocholithiais, US is clearly first choice due to its low cost, availability and accuracy. If an evalua- tion is performed for suspected malignant disease, MRI is superior to both CT and 23 Imaging of the Liver, Bile Ducts and Pancreas 2 US since bowel gas will not interfere with evaluation of the distal common bile duct or the identification of periportal and retroperitoneal adenopathy (Fig. 2.5). Pancre- atic imaging is best obtained with CT if contrast administration is not contraindi- cated. If iodinated contrast cannot be administered, or the CT is equivocal, MRI is the next test of choice. MRI and CT are equivalent with regard to vascular encase- ment and adenopathy in the setting of pancreatic adenocarcinoma. Microcystic adenomas may be better delineated with MRI, as the small cysts are more easily depicted (Fig. 2.6). Pancreatitis is best evaluated with CT especially if the patient is unstable or in critical condition. The next section will review the more commonly encountered lesions of the liver, biliary tree and pancreas and their associated imaging features. Hepatic Lesions Hepatic cysts are commonly encountered on all imaging studies. On US, they are hypoechoic, with increased through transmission and thin or imperceptible walls. If these criteria are met, the lesion is considered a simple cyst (Fig. 2.1A). On CT, a cyst is a nonenhancing lesion with low HU typically under 10 (Fig. 2.1B). On MRI, cysts are hyperintense on initial T2-weighted imaging and remain hyperintense on heavily T2-weighted images (TE> 180). The lesion is typically hypointense on T1-weighted images and, as with CT, does not enhance with contrast administration. Hemangiomas are the most common benign hepatic tumors. These lesions are typically hyperechoic on US and are either well defined or have lobulated borders (Fig. 2.2A). Hemangiomas typically reveal low attenuation on the noncontrast CT study and peripheral nodular enhancement following contrast administration (Fig. 2.2B). On MRI, hemangiomas display similar signal intensity to cysts and are hyperintense on T2 and heavily T2-weighted images (Fig. 2.2C). Initial peripheral nodular enhancement is seen after contrast administration, and the lesion may or may not completely fill on delayed contrast imaging. The enhancement patterns of particular lesions are often critical to their charac- terization. Specific lesion types enhance during the arterial dominant phase (hypervascular) while others do not (Fig. 2.3A). The most common lesions demon- strating arterial dominant phase enhancement include hepatocellular carcinoma, hepatic adenomas, focal nodular hyperplasia, and metastatic disease. Other condi- tions include coexistent hepatic disease. For example, patients with underlying cirrhosis and a hypervascular lesion are considered to have hepatocellular carcinoma (HCC) until proven otherwise (Fig. 2.3B). In addition to arterial dominant Table 2.3. Test selection based on body part CT MR Imaging Ultrasound Liver 2 1 3 Biliary Tree 3 1 1 Pancreas 1 2 3 Ranking is in order of preference (1 being the most preferred). When two modalities are ranked first, it depends on the clinical indication for the study as to, which is chosen as discussed in the text. 24 Heptobiliary Surgery 2 Fig. 2.1A. Hepatic cyst. A) Ultrasound image through the left lobe of the liver dem- onstrates a lesion (arrow) which is hypoechoic and thin walled with increased through transmission. Fig. 2.1B. A CT image of the same patient demonstrates two lesions. Although these lesions are low attenuation, Hounsfield units were greater than 10 and thus nondiagnostic for a cyst. (Note a noncontrast CT was performed prior to the con- trast-enhanced scan to evaluate for enhancement.) 25 Imaging of the Liver, Bile Ducts and Pancreas 2 Fig. 2.2A. Hepatic hemangioma: Ultrasound examination demonstrates a hyperechoic mass (arrows) in the liver. Although hemangiomas are hyperechoic, a definitive diagnosis is often difficult. Fig. 2.2B. A CT examination of the same patient demonstrates a lesion (arrow) with peripheral nodular enhancement (curved arrow), characteristic for a hemangioma. 26 Heptobiliary Surgery 2 Fig. 2.2C. An MRI examination in a different patient demonstrates a mass (m) which is hyperintense on T2 weighted images. The fluid is bright (please note CSF arrow). Gadolinium enhanced MRI (not shown) will also demonstrate the classic periph- eral nodular enhancement pattern when present. Fig. 2.3A. Metastatic disease ultrasound examination of a patient with a prior hepatic resection demonstrating a mass (arrow) in the residual left lobe. The mass demon- strates a partial hypoechoic rim (arrowhead), a slightly hyperechoic portion, and a central region which is hyperechoic (target). 27 Imaging of the Liver, Bile Ducts and Pancreas 2 Fig. 2.3B. A T2-weighted image demonstrates a mass (m) with a peripheral portion that is slightly hyperintense to liver, and a central portion that is markedly hyperintense. Fig. 2.3C. Contrast enhanced T1-weighted MRI demonstrates heterogeneous enhancement (arrow) consistent with metastatic disease. [...]... 31 2 Fig 2. 5B Axial image from a T2-weighted MRI demonstrates eccentric soft tissue (curved arrow) surrounding a narrowed common bile duct Note the plastic stent is not appreciated as it is on the ultrasound Fig 2. 6 Pancreatic mass: Ultrasound examination demonstrates a normal appearing pancreatic head with a hypoechoic mass in the body/tail region (curved arrows) 32 Heptobiliary Surgery 2 Fig 2. 7A... lesion (arrows) biopsy proven to be HCC Fig 2. 4B An axial T2-weighted image with fat suppression from an MRI exam performed 9 months earlier demonstrates the same lesion (curved arrow) 30 Heptobiliary Surgery 2 Fig 2. 4C Equilibrium phase postcontrast T1-weighted image demonstrates the lesion (arrow) but also demonstrates significant underlying siderotic nodules Fig 2. 5A Hilar cholangiocarcinoma (Klatskin... accurately depicted by these less invasive means Interventional Radiology in Hepatobiliary Surgery 45 4 Fig 4.1B Non-contrast CT image shows a 1.5 cm mass in Segment V Fig 4.1C Non-contrast CT image shows a 22 gauge notched needle within the mass The notch is directed anteriorly at the edge of the lesion 46 Hepatobiliary Surgery CT Arterial Portography There are some surgeons who still feel that CT... retained common bile duct stones Am J Gastroenterol 1998 Apr;93(4): 52 7-3 1 van Der Velden JJ, Berger MY, Bonjer HJ, Brakel K, Lameris JS Percutaneous treatment of bile duct stones in patients treated unsuccessfully with endoscopic retrograde procedures Gastrointest Endosc 20 00 Apr;51(4 Pt 1):41 8 -2 2 Welbourn CR, Mehta D, Armstrong CP, Gear MW, Eyre-Brook IA Selective preoperative endoscopic retrograde cholangiography... normal liver Core specimens are Hepatobiliary Surgery, edited by Ronald S Chamberlain and Leslie H Blumgart 20 03 Landes Bioscience Interventional Radiology in Hepatobiliary Surgery 43 4 Fig 4.1A Percutaneous biopsy Representation of two biopsy needles also often helpful in classifying sarcomas and lymphomas Cores of tissue can be obtained with needles as small as 22 gauge, although these biopsies... noninvasive imaging should not routinely have a preoperative ERCP Endoscopic Management of Hepatobiliary and Pancreatic Disorders 41 Selected Reading 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Park AE, Mastrangelo MJ Jr Endoscopic retrograde cholangiopancreatography in the management of choledocholithiasis Surg Endosc 20 00 Mar;14(3) :21 9 -2 6 Erickson RA, Carlson B The role of endoscopic retrograde cholangiopancreatography... sphincterotomy N Engl J Med 1996 Sep 26 ;335(13):90 9-1 8 Mehta SN, Pavone E, Barkun JS, Bouchard S, Barkun AN Predictors of postERCP complications in patients with suspected choledocholithiasis Endoscopy 1998 Jun;30(5):45 7-6 3 Nelson DB, Freeman ML Major hemorrhage from endoscopic sphincterotomy: risk factor analysis J Clin Gastroenterol 1994 Dec;19(4) :28 3-7 Sharma VK, Howden CW Meta-analysis of randomized controlled... 1999 Nov;94(11): 321 1-4 3 CHAPTER 4 Interventional Radiology in Hepatobiliary Surgery Lynn A Brody and Karen T Brown Introduction The interventional radiologist performs many procedures which facilitate the diagnosis and treatment of patients being cared for by the hepatobiliary surgeon Procedures may be diagnostic, therapeutic, or palliative A close working relationship between the hepatobiliary surgeon... Jul;109(1) :25 2- 6 3 Cotton PB Endoscopic retrograde cholangiopancreatography and laparoscopic cholecystectomy Am J Surg 1993 Apr;165(4):47 4-8 Johnson AS, Ferrara JJ, Steinberg SM, Gassen GM, Hollier LH, Flint LM The role of endoscopic retrograde cholangiopancreatography: sphincterotomy versus common bile duct exploration as a primary technique in the management of choledocholithiasis Am Surg 1993 Feb;59 (2) :7 8-8 4... images and are typically hyperintense on T2 weighted MR images Cystic neoplasms of the pancreas may also demonstrate characteristic appearances (Figs 2. 7A, 2. 7B) Calcifications, while seen on MRI are better appreciated on CT images The size and nature of the cystic components are better delineated on MRI Imaging of the Liver, Bile Ducts and Pancreas 29 2 Fig 2. 4A Hepatocellular cancer Arterial dominant . (Fig. 2. 1A). On CT, a cyst is a nonenhancing lesion with low HU typically under 10 (Fig. 2. 1B). On MRI, cysts are hyperintense on initial T2-weighted imaging and remain hyperintense on heavily T2-weighted. noncontrast CT was performed prior to the con- trast-enhanced scan to evaluate for enhancement.) 25 Imaging of the Liver, Bile Ducts and Pancreas 2 Fig. 2. 2A. Hepatic hemangioma: Ultrasound examination. difficult. Fig. 2. 2B. A CT examination of the same patient demonstrates a lesion (arrow) with peripheral nodular enhancement (curved arrow), characteristic for a hemangioma. 26 Heptobiliary Surgery 2 Fig. 2. 2C.