Section 10. Liver and Gallbladder Disorders

Chapter 134. Diagnostic Tests for Liver and Gallbladder Disorders

Topics: Introduction | Imaging Tests | Liver Biopsy

Imaging Tests

Ultrasound scanning uses sound waves to provide images of the liver, gallbladder, and biliary tract. The test is better for detecting structural abnormalities, such as tumors, than diffuse abnormalities, such as cirrhosis (severe scarring of the liver) or fatty liver (excess fat in the liver). It is the least expensive and safest technique for creating images of the gallbladder and biliary tract.

Using ultrasound, a doctor can readily detect gallstones in the gallbladder. Ultrasound of the abdomen easily distinguishes jaundice (a yellowish discoloration of the skin and the whites of the eyes) caused by bile duct obstruction from jaundice caused by liver cell malfunction; ultrasound shows that the ducts are dilated (widened) in obstruction. A type of ultrasound, called vascular Doppler ultrasound, can show the flow of blood in the blood vessels of the liver. A doctor also may use ultrasound scanning as a guide when inserting a needle to obtain a tissue sample for biopsy.

Radionuclide (radioisotope) imaging uses a substance containing a radioactive tracer that is injected into the body and taken up by a particular organ. The radioactivity is detected by a gamma-ray camera (positioned over the upper abdomen) attached to a computer that generates an image. Liver scanning is a type of radionuclide imaging that uses a radioactive substance taken up by liver cells. Cholescintigraphy (hepatobiliary scintigraphy), another type of radionuclide imaging, follows the movement of a radioactive substance through the biliary tract after it has been excreted by the liver. This technique can detect blockage of the cystic duct, which leads to acute inflammation of the gallbladder (cholecystitis (see Section 10, Chapter 140)).

Computed tomography (CT) provides excellent images of the liver. Doctors find it particularly useful for detecting tumors. It can also be used to detect diffuse disorders, such as fatty liver (excess fat in the liver), collections of pus (abscesses), and abnormally dense liver tissue caused by iron overload (hemochromatosis). Because CT involves exposure to x-rays (which are potentially harmful) and is more expensive than ultrasound, it is not as widely used, even though it often provides more information about the liver.

Magnetic resonance imaging (MRI) provides images similar to those obtained with CT. An advantage over CT is that it does not involve exposure to x-rays. Its drawbacks include being more expensive than CT and taking longer to perform than other imaging methods do. Its major use is in providing images of the biliary tract, termed magnetic resonance cholangiopancreatography (MRCP). The quality of the image produced can reduce the need for more invasive tests, in which dye is directly injected into the biliary and pancreatic ducts.

Hepatic arteriography uses a radiopaque dye (a dye that can be seen on x-rays) that is injected into the hepatic artery. X-rays then display the hepatic artery and its branches. Hepatic arteriography is particularly useful in investigating and sometimes treating a type of liver cancer called hepatoma (a cancer that begins in the liver cells (see Section 10, Chapter 139)).

Endoscopic retrograde cholangiopancreatography (ERCP) is a test in which an endoscope (a flexible viewing tube) is passed through the mouth, esophagus, and stomach and into the duodenum (the first segment of the small intestine). A fine tube is inserted through the endoscope and into the biliary tract. A radiopaque dye is then injected into the bile ducts, and x-rays are taken of the biliary tract and pancreatic duct and its tributaries. This test causes inflammation of the pancreas (pancreatitis) in 3 to 5% of the people who undergo it.

Percutaneous transhepatic cholangiography involves inserting a long needle through the skin into the liver and then injecting a radiopaque dye into one of the liver's bile ducts. A doctor uses ultrasound for guidance when inserting the needle. The x-rays clearly reveal the biliary tract, particularly any blockage within the bile ducts.

Operative cholangiography involves the injection of a radiopaque dye directly into the ducts of the biliary tract at the time of gallbladder surgery. X-rays then reveal clear images of the biliary tract.

Simple x-rays of the abdomen can often reveal a gallstone that contains calcium. Gallstones that are not calcified are not generally seen.

See the figure Diagnostic Imaging Techniques for Assessing the Biliary Tract.