15. Imaging of the liver and the hepatobiliary system. Imaging techniques, indications, information content.

From greek.doctor

Ultrasound is the primary modality for imaging of the liver and biliary system. CT and MR may also be used, but only if ultrasound does not visualise the pathology.

Magnetic resonance cholangiopancreatography (MCRP), endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiography (PTC) are also used.

Indications

Patient preparation

The patient should be fasting for 6 hours before. This is because the gallbladder contracts when eating, which makes visualisation of pathology in the gallbladder more difficult.

Interpretation

In a healthy person, the liver is isoechoic with the renal cortex, and the liver parenchyme is globally isoechoic. In case of steatosis, the liver is more echogenic (lighter on ultrasound) than the renal cortex. On CT, a steatotic liver will be less dense than the spleen.

Cholecystitis

Ultrasonographic signs of cholecystitis include thickened gallbladder wall, often with wall oedema, which makes it look like the gallbladder has a double wall.

Cirrhosis

In case of cirrhosis, some parts of the liver will be hyperechoic and some hypoechoic on ultrasound. The right lobe will be smaller than the left. On CT one can also see lobulation of the parenchyme and nodules in the liver.

Gall stone

Gall stones are visible on ultrasound as small structures that cast an acoustic shadow, as the ultrasounds cannot pass through the stone. If the stone is in the bile ducts (choledocholithiasis), the duct may be dilated proximally to the stone.


MRCP

Magnetic resonance cholangiopancreatography (MRCP) is a magnetic resonance imaging modality used to examine the biliary tree. It's a non-invasive modality that does not require contrast and is therefore frequently used in the evaluation of cholestasis and choledocholithiasis. If MRCP shows a stricture or obstruction of the biliary tract, an endoscopic retrograde cholangiopancreatography is usually indicated to treat the problem.


ERCP

Endoscopic retrograde cholangiopancreatography (ERCP) is an examination which combines upper endoscopy and fluoroscopy to visualise and treat pathology of the biliary tree and pancreatic ducts. It only rarely causes complications, but potential complications can be severe, so ERCP is mostly used for treatment of pathology rather than for diagnosis, as MRCP is usually sufficient for diagnosis.

ERCP allows for removal of any obstructing pathology, dilating and stenting strictures, and opening the sphincter of Oddi.

Indications

Procedure

An endoscope is passed through the mouth to the descending duodenum and into the ampulla of Vater. Contrast material is injected, allowing for detailed visualisation of the biliary tract with fluoroscopy. The endoscope has tools which can be used to remove pathology, take samples, dilate, and stent.

Complications

Following ERCP, pneumobilia (air in the biliary tract) is common but rarely problematic. Acute pancreatitis is a potentially severe complication which can be life-threatening, which occurs due to increased pressure in the pancreatic duct from the procedure. Other complications include:

  • Perforation of the biliary tract
  • Haemorrhage of the biliary tract
  • Cholangitis