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Imaging is essential for accurately diagnosing biliary tract disease and is important for diagnosing focal liver lesions (eg, abscess, tumor), but it is limited in diagnosing diffuse hepatocellular disease (eg, hepatitis, cirrhosis).
Ultrasound:
Ultrasound, traditionally performed transabdominally and requiring a period of fasting, provides structural, but not functional, information. It is the least expensive, safest, and most sensitive technique for imaging the biliary system, especially the gallbladder. Ultrasound is the procedure of choice in screening for biliary tract abnormalities, differentiating intrahepatic from extrahepatic causes of jaundice, and detecting liver masses. The kidney, pancreas, and blood vessels are also often visible on hepatobiliary ultrasound. Ultrasound can be difficult in the presence of intestinal gas or obesity and is operator-dependent. Endoscopic ultrasonography incorporates an ultrasound transducer into the tip of an endoscope, which allows for greater image resolution even if intestinal gas is present.
Gallstones cast intense echoes with distal acoustic shadowing that move with gravity. Diagnostic accuracy on transabdominal ultrasound is extremely high (sensitivity > 95%) for gallstones > 2 mm in diameter. Endoscopic ultrasound can detect stones as small as 0.5 mm (microlithiasis) in the gallbladder or biliary system. Transabdominal and endoscopic ultrasound also can detect biliary sludge (a mixture of particulate material and bile) as low-level echoes that layer in the dependent portion of the gallbladder, without acoustic shadowing. Cholecystitis produces a thickened gallbladder wall (> 3 mm), pericholecystic fluid, an impacted stone in the gallbladder neck, and tenderness on palpation of the gallbladder with the ultrasound probe (ultrasonographic Murphy's sign).
On transabdominal and endoscopic ultrasound, bile ducts stand out as echo-free tubular structures. The diameter of the common duct is normally < 6 mm, increases slightly with age, and can reach 10 mm after cholecystectomy. Dilated ducts are virtually pathognomonic for extrahepatic obstruction in the appropriate clinical setting. Ultrasound can miss early or intermittent obstruction without dilated ducts. Transabdominal ultrasound may not reveal the level or cause of biliary obstruction (eg, sensitivity for common duct stones is < 40%). Endoscopic ultrasound has a better yield.
Transabdominal ultrasound detects focal liver lesions (> 1 cm in diameter) more accurately than diffuse diseases (eg, fatty liver, cirrhosis). In general, cysts are echo-free; solid lesions (eg, tumors, abscesses) tend to be echogenic. Carcinoma appears as a nonspecific solid mass. Ultrasound has been used to screen for hepatocellular carcinoma in those at high risk (eg, with chronic hepatitis B). The ability to localize focal lesions permits ultrasound-guided aspiration and biopsy. The advent of endoscopic ultrasound may further refine several of these diagnostic approaches.
Doppler ultrasound is a noninvasive method with which to assess direction of blood flow and patency of blood vessels around the liver, particularly the portal vein. Doppler ultrasound can reveal evidence of portal hypertension with collateral flow, assess the patency of liver shunts (eg, surgical portocaval, percutaneous transhepatic), and reveal hepatic artery thrombosis after liver transplantation. It also can detect unusual vascular structures, such as cavernous transformation of the portal vein.
CT:
CT is commonly used to identify hepatic masses, particularly small metastases, with an accuracy of about 80%. CT with IV contrast is accurate for diagnosing cavernous hemangiomas of the liver as well as differentiating them from other abdominal masses. Neither obesity nor intestinal gas obscures CT images. CT can detect fatty liver and the increased hepatic density associated with iron overload. CT is less helpful than ultrasound in diagnosing biliary obstruction but often provides the best assessment of the pancreas.
Cholescintigraphy:
In this procedure, IV technetium-labeled iminodiacetic compounds (eg, hydroxy or diisopropyl iminodiacetic acid [HIDA or DISIDA]) are given which are taken up by the liver and excreted in the bile, thus outlining the path of bile excretion, particularly the cystic duct.
In calculous cholecystitis, which usually is caused by impaction of a stone in the cystic duct, the gallbladder is not visible. The test has a sensitivity of 95% and a specificity of 90% but is infrequently needed to diagnose acute cholecystitis. False-positive results are common in critically ill patients.
In suspected acalculous cholecystitis, the gallbladder is scanned before and after administration of cholecystokinin (which causes the gallbladder to contract). The difference in scintigraphic count, termed the gallbladder ejection fraction, is below normal in acalculous cholecystitis.
Cholescintigraphy also detects bile leaks (eg, after surgery or trauma) and anatomic abnormalities (eg, congenital choledochal cysts, choledochoenteric anastomoses). After cholecystectomy, cholescintigraphy can quantitate biliary drainage and assist in defining sphincter of Oddi dysfunction.
Radionuclide liver
scanning:
Ultrasound and CT have largely supplanted radionuclide scanning, which has been used to diagnose diffuse parenchymal disease and mass lesions of the liver. Radionuclide scanning demonstrates the distribution of an injected radioactive tracer, usually technetium (99mTc‑sulfur colloid), which distributes uniformly within the normal liver. Space-occupying lesions > 4 cm, such as liver cysts, abscesses, metastases, and tumors, appear as defects. Generalized liver disease (eg, cirrhosis, hepatitis) decreases the liver uptake of the tracer, with more appearing in the spleen and bone marrow. In hepatic vein obstruction, liver uptake is decreased except in the caudate lobe because of its drainage into the inferior vena cava.
Oral cholecystography:
The oral cholecystogram (OCG) was once the procedure of choice for diagnosing gallstones and suspected cholecystitis. Unlike ultrasound, OCG measures the concentrating function of the gallbladder. OCG has been replaced by ultrasound, however, because OCG is less accurate, can take up to 48 h to complete, and can cause diarrhea and, rarely, a hypersensitivity reaction with kidney damage.
Plain x‑ray of
the abdomen:
The plain x‑ray is an inaccurate tool for diagnosing hepatobiliary disease, even gallstones. Rarely, it can help in gravely ill patients by revealing air in the biliary tree, which suggests emphysematous cholangitis.
MRI:
MRI images blood vessels (without using contrast) and hepatic tissues. Although expensive, its indications are still evolving. MRI is superior to CT and ultrasound for diagnosing diffuse liver diseases (eg, fatty liver, hemochromatosis), and for clarifying some focal defects (eg, hemangiomas). MRI also reveals blood flow and therefore can complement Doppler ultrasound and CT angiography in diagnosing vascular abnormalities and in performing vascular mapping before liver transplantation.
MRI of the biliary tree is magnetic resonance cholangiopancreatography (MRCP). MRCP is more sensitive than CT or ultrasound in diagnosing common bile duct abnormalities, particularly stones. Its images are comparable to those from ERCP and percutaneous transhepatic cholangiography, which are more invasive. MRCP, therefore, is a useful screening tool when biliary obstruction is suspected and before proceeding to therapeutic ERCP (eg, for simultaneous imaging and stone removal).
ERCP:
ERCP combines endoscopy through the second portion of the duodenum with contrast imaging of the biliary and pancreatic ducts. First, an endoscope is placed in the descending duodenum, then the papilla of Vater is cannulated, and the pancreatic and biliary ducts are injected with contrast. ERCP is the procedure of choice when bile duct stones are suspected but have not been found on less invasive tests. The test is especially valuable for diagnosing correctable biliary tract lesions causing persistent jaundice (eg, stone, stricture, sphincter of Oddi dysfunction). Besides providing excellent images of the biliary tract and pancreas, ERCP reveals some of the upper GI tract and the periampullary area. Biopsies and interventional procedures may be performed (eg, sphincterotomy, biliary stone extraction, placement of a biliary stent in a stricture—see Gallbladder and Bile Duct Disorders). Its sensitivity and specificity for common bile duct stones are about 95%. The morbidity from a diagnostic ERCP with only injection of contrast material is about 1%. The addition of sphincterotomy raises morbidity to 4 to 9% (mainly pancreatitis and bleeding). ERCP with manometry to measure sphincter of Oddi pressure causes pancreatitis in up to 25%.
Percutaneous
transhepatic cholangiography (PTC):
PTC involves puncture of the liver with a needle under fluoroscopic or ultrasound guidance to cannulate the peripheral intrahepatic bile duct system above the common hepatic duct into which contrast material is injected. PTC is highly diagnostic for biliary disease and can be therapeutic (eg, for decompression of the biliary system, insertion of an endoprosthesis). However, ERCP is generally preferred because PTC causes more complications (eg, sepsis, bleeding, bile leaks).
Operative cholangiography:
This is direct injection of a contrast agent at laparotomy for visualization of the cystic duct or common bile duct. Operative cholangiography is indicated when jaundice occurs and noninvasive studies are equivocal, leading to suspicion of common duct stones. It then can be followed by common duct exploration for removal of biliary stones. Technical difficulties have limited its use, particularly during laparoscopic cholecystectomy.
Last full review/revision November 2005
Content last modified November 2005
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