The biliary tract

Modalities

 

Ultrasonography

The gallbladder is studied by US with a 3.5-5 mHz transducer. The organ is studied in both its longitudinal (Fig. 20) and transverse axes, with the patient lying supine. Views are also obtained with the patient turned to the left and upright views are sometimes required. Positional changes help in the diagnosis of gallstones that move with gravity. The extrahepatic biliary ducts are well seen by US, but the intrahepatic ducts are more difficult to image unless they are dilated. The most distal part of the common bile duct is not usually seen, because of interference with the image by gas in the duodenum. The overall diagnostic accuracy of US of the gallbladder is 90-95%.

Peroral cholecystography

Peroral cholecystography was the primary method for imaging the gallbladder for over 50 years (since its introduction in 1925), until ultrasonography largely replaced it in the early 1980's. In some departments, however, oral cholecystography is still employed (Fig. 21).

In peroral cholecystography the contrast medium is administered by mouth as tablets, absorbed through the intestinal mucosa, bound to albumin in the blood and transported to the liver. From the liver the medium is excreted into the biliary ducts and concentrated in the gallbladder. Sodium ipodate and calcium ipodate, however, are concentrated by the liver and are thus not dependent on the gallbladder's concentrating

	Figure 20. US of the gallbladder. The normal gallbladder (gb) is seen as a cystic structure with echo-free contents. The walls of the gallbladder are smooth. Normal liver parenchyma (L) is seen to the left of the gallbladder.
a	Figure 21. A normal cholecystogram. (a) In the initial phase the contrast medium is seen evenly filling the gal/bladder, the walls of which are smooth. (b) After a fatty meal, the gallbladder has contracted. Now both the fundus and the neck of the gallbladder, as well as the cystic duct is filled with contrast medium and the common bile duct is demonstrated (arrows).
b

capacity. When its iodine content exceeds 0.5% the gallbladder is visible on fluoroscopy and conventional radiographs. The concentration of contrast medium reaches its maximum 10-15 hours after ingestion and imaging usually takes place on the day following ingestion. Some centres advocate a scheme whereby a double dose of contrast medium is ingested on two consecutive days before the study.

Non-opacification of the gallbladder may indicate gallbladder disease, such as obstruction of the cystic duct. It may, however, also result from liver disease or disorders resulting in disturbances in the absorption of contrast medium from the gut, e.g. diarrhoea. Sometimes the patient may not even have taken the contrast medium or there may have been a previous cholecystectomy. Gallstones are seen as filling defects in the opacified gallbladder. Most gallstones contain some calcium, and in 15-20% of cases this is enough for the stones to be seen on a plain radiograph.

The gallbladder is radiographed in multiple projections including same using external compression. The study is often completed by exposing a so-called contraction film of the gallbladder 1/2-1 hour after the ingestion of a fatty meal. This may show the changes of adenomyomatosis or cholesterolosis.

The diagnostic accuracy of cholecystography in diagnosing gall-stones is 85-90%, i.e. slightly less than that of US though the methods are to some extent complementary. The use of peroral cholecystography has undergone a modest revival with the increasing popularity of non-operative methods of treating gallstones.

Cholangiography, biligraphy

Visualization of the extrahepatic biliary ducts may require the intravenous administration of contrast medium. On intravenous cholangiography the contrast medium is given intravenously as a slow infusion for approximately 1/2 hour. The contrast medium is bound to the albumin in the blood and excreted by the liver into the bile. The concentration of contrast medium in the biliary tree is usually so low that the ducts can only be demonstrated by tomography. Some contrast material is also seen in the gallbladder, but since it is immiscible with bile and forms a separate layer in the organ, the method is unsuitable for the diagnosis of gallbladder disease or stones. Allergic reactions may still occur on intravenous cholangiography, and the mortality is not insignificant. The diagnostic accuracy of the method is only 50-60% and it should be employed only when good indications exist and in those cases where other available methods (US, ERC, PTC, CT) are unhelpful. There has been some renewed interest in this technique in patients prior to laparoscopic cholecystectomy.

Percutaneous transhepatic cholangiography

Percutaneous transhepatic cholangiography (PTC) (see Fig. 35) entails the puncture of an intrahepatic biliary duct, by a percutaneously introduced needle. The procedure is performed under US guidance, and is successful in 95-98 % of subjects with dilated ducts and 80 % of those with non-dilated ducts. The biliary ducts are filled with contrast medium through the needle. The frequency of complications is not insignificant, but depends on the type of needle used. With a Chiba needle it is approximately 2 %. Through the needle a guide wire can be negotiated into the biliary ducts, for the introduction of various catheters or instruments (see Chapter 8).

Endoscopic retrograde cholangiography

Endoscopic retrograde cholangiography (ERC) (see Fig. 36) entails cannulation of the papilla of Vater through an endoscope introduced via the stomach into the duodenum. Contrast medium (low osmolar) is injected through the cannula retrogradely into the common bile duct filling the extra- and intrahepatic biliary ducts and the pancreatic duct. The contrast medium injection is performed under fluoroscopic control. Overdistension of the biliary tree and especially the pancreatic duct should be avoided; in the latter case it may cause pancreatitis. Radiographs are exposed in various projections when the injection is complete. The study requires an experienced endoscopist and has an 80-90% success rate. Care should be taken not to introduce air into the biliary tree, since air bubbles may be mistaken for stones; bubbles, however, are always round and move freely with gravity into the uppermost part of the duct when the patient is moved into an upright position.

Peroperative cholangiography

Peroperative cholangiography is performed in the operating theatre during operative procedures involving the biliary ducts, and entails the injection of contrast medium directly into the exposed biliary ducts through a needle or cannula. Several injections may be necessary during the study for maximum diagnostic benefit.
Peroperative cholangiography is performed in order to diagnose or exclude the existence of concretions in the biliary tree or to demonstrate a biliary leak. It is also occasionally used to record biliary tract anatomy. In many centres it is performed routinely during cholecystectomy. Care should be taken to avoid the introduction of air bubbles into the biliary tracts (see section on ERC).

Postoperative cholangiography

Postoperative cholangiography entails the injection of contrast medium through the T -tube used to decompress the biliary tree following operative procedures. The procedure is usually performed 7-10 days after cholecystectomy to check for any residual biliary concretions. The contrast medium should be diluted so that small stones are not obscured. The procedure is performed under fluoroscopic control and films are exposed in various projections. Care should be taken to avoid the introduction of air into the biliary tract, since this may simulate stones (see section on ERC).

Radionuclide imaging

Radionuclide imaging or gammascintigraphy is performed to evaluate biliary dynamics. The most commonly used agent is 99m Tc-HIDA which is injected intravenously, where it is bound to albumin and then excreted through the liver into the bile. The activity over the liver, biliary ducts and small intestine is sequentially recorded using a gamma camera. The study gives information on hepatic function and biliary flow. It may show reduced flow in, for example, strictures of the biliary tree or calculus obstruction, non-filling of the gallbladder in obstruction of the cystic duct, or leakage of bile from the biliary tree. In normal subjects the study takes approximately one hour, but it may take up to 24 hours if the flow of bile is retarded. Radionuclide imaging of the biliary tree has lost much of its importance with the introduction of other imaging methods, such as US, CT and MRI, but may still be useful in special cases where information on biliary dynamics is important, where direct visualization of the biliary tree with injected contrast medium is unsuccessful, or if the patient is strongly allergic to contrast medium.

Magnetic resonance imaging

The value of MRI has yet to be established in the study of the biliary ducts but newer techniques that permit so-called MRI-cholangiography may be valuable in the near future. In gallbladder cancer MRI may be important in both diagnosis and staging.

Choice of imaging method

Ultrasonography has become the primary imaging technique in the evaluation of the gallbladder. It has the advantages of being precise, easy and quick to perform. It gives information on the contents and wall of the organ, as well as the surrounding tissues. Stones, cholesterolosis, adenomyomatosis, inflammation and tumours are all diagnosed with great precision. Peroral cholecystography is still used in many centres, as being a relatively easily performed and accurate diagnostic method, especially in calculus disease. It is still a useful secondary method if the findings on US are unclear, if there is a discrepancy between the clinical assessment and the US findings, or if non-operative treatment of gallstones is planned. Computed tomography is performed if gallbladder cancer is suspected.

Ultrasound is also the primary method for studying the intrahepatic and proximal extrahepatic biliary ducts, giving information on ductal calibre. This is important when studying an icteric patient for example, when it can distinguish between extrahepatic obstruction and intrahepatic disease. CT gives additional information concerning the biliary tree and surrounding structures, PTC or ERCP direct information concerning the biliary tree.

 

David J. Allison and Carl-Gustaf Standertskjold-Nordenstam