103 Hepatobiliary Imaging

Abdominal Plain Films doned as other modalities such as ultrasound, computed tomography (CT), and magnetic resonance imaging Abdominal plain films are usually used in the initial eval- (MRI) have improved. uation of disease. Specific information concerning hepa- tobiliary disease cannot generally be gained from plain films. This being said, important information can be gained from plain films. This information includes calci- Radionuclide Imaging fications and gas shadowing. Calcifications can be asso- ciated with hemangiomas, granulomatous disease, and Liver scintigraphy is used to evaluate a variety of metastatic neoplasms. Chronic cholecystitis can be asso- hepatic diseases, ranging from malignancy to cholecysti- ciated with gallbladder wall calcification, called porcelain tis. The technique is limited by its lack of resolution gallbladder. The risk of gallbladder cancer is greater with and its higher cost. Other modalities, such as CT, MRI, a porcelain gallbladder. and ultrasound, are less time consuming and less expen- 99m Overlying gas shadowing can indicate a number of sive. Technetium-labeled sulfur colloid can be used to hepatic conditions. Portal venous gas can indicate an evaluate for hepatic metastases. Hemangiomas may be 99m ischemic process such as bowel infarction, necrotizing visualized with tagged red cell scans ( Tc-labeled red enterocolitis, hemorrhagic pancreatitis, or ulcerative blood cell). Hepatobiliary iminodiacetic acid (HIDA) colitis. The portal venous system is generally demon- scans can provide some important information concern- strated in the periphery of the liver as branching linear ing gallbladder function when evaluating patients for gas shadows. Abscesses can appear as large collections of suspected biliary colic or cholecystitis. These scans overlying gas. Pneumobilia can be the result of an incom- involve the administration of iminodiacetic acid labeled 99m petent sphincter of Oddi or a gastroduodenal ulcer or can with Tc (such as diisopropyl IDA or DISIDA). This occur after enteric anastomosis. radionucleotide is taken up in the liver and excreted within the biliary system. The test is commonly used to evaluate the contractibility of the gallbladder, the gall- bladder ejection fraction (normal is 55% to 75%), and Oral Cholecystography the patency of the biliary system. Failure to opacify the gallbladder signifies biliary obstruction, and decreased Oral cholecystography is an older imaging technique ejection fractions (<55%) suggest biliary dyskinesia. that requires the patient to drink oral contrast. Once There are many factors that can cause false-positive ingested, the contrast material is absorbed through the results, including hepatitis, cirrhosis, pancreatitis, pro- intestines and excreted into bile. The gallbladder con- longed fasting, and hyperalimentation. The study is also centrates the contrast material contained in the bile. This helpful for evaluating for postoperative bile leaks and method allows for visualization of stones or wall abnor- congenital disorders such as biliary atresia. Radionu- malities that appear as filling defects. Gallbladder dys- cleotide imaging is also helpful in the workup of malig- function is evident through the failure to opacify the nant diseases. Neuroendocrine tumors can be located gallbladder and failure to contract. The accuracy of using radioactive somatostatin analogues (111-indium oral cholecystography for diagnosing gallbladder disease octreotide). This is especially useful for localizing gastri- approaches 100%. The technique has largely been aban- nomas preoperatively.

240 103. Hepatobiliary Imaging 241

Ultrasound systolic velocity, and finally to the entire loss of arterial waveforms.

Ultrasound is the most common noninvasive test of the liver. Ultrasound is close to 100% accurate for evaluat- Computed Tomography ing gallbladder and biliary disease. Gallstones are intra- luminal in ultrasound images. Characteristics commonly Parenchymal imaging of the liver is better with CT than associated with acute cholecystitis include a thickened with ultrasound. The specifics and background of CT are gallbladder wall, pericholecystic fluid representing discussed in Chapter 16. Computed tomography scans of edema, distention, gallstones, sludge, and sonographic the liver can be done as noncontrasted or as single-, dual- Murphy’s sign. In addition, the biliary tree (intra- and , or triple-phase intravenous contrast studies. The type of extrahepatic) can be evaluated for signs of obstruction study needed is determined by the specific disease and dilation. Common bile duct dilatation (<6mm) can process being evaluated. Diffuse hepatic diseases may be be seen with ultrasound, although the cause may not better detected with noncontrast imaging. Intravenous always be identified (i.e., common duct stones or malig- contrast can obscure diseases such as hemochromatosis nancy). Ultrasound is quite good for evaluating gallblad- and choledocholithiasis. der and biliary disease but begins to lose accuracy when Single-phase studies are done to visualize focal hepatic examining hepatic masses, especially with cirrhosis. lesions (e.g., trauma, malignancy). Single-phase studies Hepatic metastasis can be overlooked in 50% of cases. acquire images approximately 1 minute after contrast is Therefore, ultrasound of the liver is a poor tool for administered (peak enhancement of the liver). Intrahep- excluding liver metastasis. When a focal mass is seen in a atic masses enhance at a lower intensity than does the cirrhotic liver, the chance of malignancy is about 98%. normal surrounding liver tissue. Single-phase studies are Doppler ultrasound is a useful tool for evaluating the used for demonstrating biliary dilatation. hepatic vascular system. Its use is indicated for conditions In dual-phase studies, images are acquired before and such as portal vein thrombosis, evaluation after liver after intravenous contrast enhancement. This allows for transplant, and follow up after transjugular intrahepatic imaging of the liver during hepatic artery enhancement portal-systemic shunt (TIPS) placement. Portal vein and portal venous enhancement.This technique is helpful thrombosis is diagnosed by the absence of flow through for staging malignancies and determining the resectabil- the portal vein seen on Doppler ultrasound. Other asso- ity of hepatic lesions. The evaluation of hepatocellular ciated findings include dilation of the vein or the pres- carcinoma is easier than more laborious methods such as ence of echogenic material within the lumen. In some iodized oil CT (poppy seed oil uptake by hepatocellular instances the portal vein is replaced by venous collater- carcinoma) and CT arterial portography. Triple-phase als when thrombosis is long standing. Pulsatile blood flow studies involve capturing images before and during arte- from within the venous thrombosis can be a sign of neo- rial and portal venous phases of enhancement. plastic invasion. Computed tomography can also be useful for detect- Doppler ultrasound helps exclude extrahepatic portal ing abnormalities of the biliary system. Dilated bile ducts vein obstruction and determine baseline flow velocities can be clearly seen with single-phase contrast imaging. before TIPS placement is attempted. The function of the Primary sclerosing cholangitis is associated with beaded TIPS is evaluated at regular intervals (every 3 months for dilations of the intrahepatic ducts. Cholangiocarcinoma 1 year) with Doppler ultrasound to monitor for hepatic often appears with central duct obstruction along with vein stenosis. Velocities less than 60cm/sec suggest steno- intrahepatic ductal dilation. sis. Many institutions implement routine Doppler ultra- sound evaluation of hepatic vasculature after liver transplantation. In particular, the hepatic artery is exam- ined for signs of stenosis caused by the associated mor- Magnetic Resonance Imaging bidity and mortality. The most common indication of stenosis is an intrahepatic tardus parvus waveform (i.e., Magnetic resonance imaging is used primarily as an prolonged systolic acceleration time [>0.1 second] and adjunct to other imaging modalities. The basic concepts low resistive index [>0.5 second]). Thrombosis of the behind MRI are discussed in greater detail in Chapter 16. hepatic artery is indicated by the absence of arterial Magnetic resonance imaging relies on the variations in waveforms in the hepatic artery and liver. Postoperative water content among tissue types to differentiate them. edema can produce false-positive results. Thrombosis Hepatic malignancies tend to have higher water content may be predicted when a series of Doppler ultrasound than the surrounding liver parenchyma, which produces examinations show normal hepatic artery flow initially a relatively low signal on T1-weighted images. Unfortu- that progresses to loss of diastolic flow, then to decreased nately, the liver parenchyma also tends to produce a low 242 Part XII. Gastrointestinal Disorders signal on T1 images, making the distinction between examined in detail. Additional information concerning normal and neoplastic tissue difficult to resolve. T2- the spread of the tumor can be obtained, which is useful weighted scans are generally done following T1 to for staging the malignancy. provide better contrast between the two tissues (i.e., bright signal in tumor, low signal in normal liver) and in conditions such as fatty infiltration of the liver, which can Invasive Imaging Procedures be confused with a neoplasm. Alterations in the signal frequency suppress certain tissues, such as fat, and lower Cholangiograms are indicated for the evaluation of the intensity of fat in the image. stones, tumors, strictures, and leakage. Cholangiography As with CT, MRI also has the capability of providing can be performed during surgery, through a T-tube, or intravenous contrast enhancement of images. Gadolin- via percutaneous technique. An adequate cholangiogram ium is a paramagnetic intravenous contrast agent used to consists of a scout image of the right upper quadrant accentuate MRI images. Gadolinium is commonly used before administration of contrast, images of contrast in magnetic resonance angiography (MRA) in which filling the biliary system (i.e., right and left hepatic radi- images are obtained with contrast in the vascular system. cals and common bile duct), and delayed images showing This modality is often used to image the portal venous contrast emptying into the duodenum. Intraductal stones system. The second most common use for gadolinium commonly appear as filling defects within the lumen. Pit- is with dynamic multiphase imaging of hepatic paren- falls of stone detection include air bubbles, which can be chyma. Obtaining images with administration of contrast introduced into the biliary tree and mimic filling defects is similar to that of CT (i.e., single, double, or triple and blood clots. A diluted iodinated contrast agent is phase). Contrast agents that have a specific affinity for generally used at a 1:1 ratio of contrast to saline. The use liver tissue have been developed but are rarely used of densely concentrated contrast or dilute contrast can because of their potential for causing lumbar back pain obscure the stones in the ducts. and hypotension. Operative cholangiography can be conducted during open or laparoscopic cholecystectomies. It involves the administration of iodinated contrast to the biliary system through a surgically created opening of the cystic duct or Magnetic Resonance gallbladder. The study can be done with 93% success Cholangiopancreatography and 100% accuracy in most cases. When intraoperative cholangiogram is used selectively (e.g., for patients sus- Magnetic resonance cholangiopancreatography (MRCP) pected of having choledocholithiasis or who have ele- is an excellent alternative to endoscopic retrograde vated liver function tests, dilated common bile duct, or cholangiopancreatography (ERCP) for imaging the jaundice), the risk of leaving retained stones after surgery biliary system. The complications associated with ERCP is about 1%. Intraoperative cholangiograms are also (i.e., pancreatitis, cholangitis, bleeding, and perforation) helpful for evaluating aberrant ductal anatomy before can be avoided with MRCP because it is noninvasive. It committing to ductal transection. is an attractive alternative for patients with previous A T-tube cholangiogram uses a surgically placed biliary/enteric surgery (i.e., choledochoenterostomy). biliary drainage catheter to deliver contrast media to Magnetic resonance cholangiopancreatography employs the biliary system. The study is used to evaluate for T2-weighted images gathered in volume or in slices to stones, malignancy,stenosis, to follow up on interventions, view the ductal structures. Extrahepatic ducts can be seen and to inspect biliary anastomoses. Contrast is allowed to with 100% accuracy; however, visualization of the intra- enter through the tube by gravity or by hand injection. T- hepatic ducts is limited to the outer one-third of the liver tubes generally remain in place for 4 to 6 weeks to allow with approximately 90% accuracy. Pancreatic ducts, with for maturation of a transperitoneal tract. This prevents exception of the ampulla, can be imaged in most patients. free spillage of bile into the peritoneum, which occurs Conditions such as pancreatic divisum and abnormal with premature tube removal. The development of a common channels can be visualized with MRCP.It is also mature tract is essential before an interventional proce- used for detecting choledocholithiasis in preoperative dure is undertaken. Confirmation of proper tract matu- patients. Stones as small as 2mm are detected in most ration can be made using a contrast tract-o-gram. In this cases. Obstructing gallstones causing acute pancreatitis study, the T-tube is removed over a guidewire, and con- are detected in 50% of cases. Strictures, ductal dilatations, trast is administered through the exit site at the skin. and other signs of acute and chronic pancreatitis can be Images are obtained as the contrast material travels seen on MRCP.Biliary obstructions due to cholangiocar- through the tract. Extravasation of contrast material indi- cinoma can be evaluated with MRCP. The entire biliary cates an immature tract and requires replacement of the tree proximal and distal to the level of obstruction can be T-tube. 103. Hepatobiliary Imaging 243

Percutaneous Transhepatic Table 103.1. Regimen for patients with allergic reactions to contrast agents. Cholangiography Intravenous (IV) By mouth (po) During percutaneous transhepatic cholangiography Methylprednisolone 32mg IV × 2 Prednisone 50mgpo × 3 doses (PTC) the biliary tree is accessed with a small-gauge doses (12 and 2 hours before (13, 7, and 1 hour before contrast) contrast is given) needle (21 or 22) that is passed percutaneously through Benadryl 50mgpo 1 hour before the liver parenchyma. Radiographic contrast is adminis- contrast tered through the needle to visualize the bile ducts. Non- invasive studies have largely replaced the use of PTC.The technique is now generally reserved for percutaneous bile duct dilatations, for biliary decompression proximal include biliary sepsis, bleeding, bile leak, and pneumoth- to obstructing lesions, or when noninvasive techniques orax. The technique can be performed successfully in are not feasible. Percutaneous transhepatic cholangiog- nearly 100% of patients with dilated bile ducts and about raphy is contraindicated when conditions prevent safe 90% in nondilated patients. The overall risk of major access to the liver, such as overlying loops of bowel. Rel- complications is approximately 3%. ative contraindications include ascites, coagulopathy,con- Allergic reactions to contrast agents manifest with trast allergy, and the presence of vascular tumors. The rashes, facial or glottic edema, laryngospasm, bron- procedure must be conducted using analgesia, sedation, chospasm, arrhythmias, and hypotension. Patients with a and hemodynamic monitoring. Prophylactic antibiotics history of an allergic reaction receive low-osmolar con- are given to avoid biliary sepsis. Potential complications trast and steroid prophylaxis (Table 103.1).