Gallstone disease other imaging findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hadeel Maksoud M.D.[2]

Overview

There are other imaging modalities that can be useful in diagnosing gallstone disease, these include; endoscopic retrograde cholangiopancreatography (ERCP), bile microscopy and oral cholecystography. It should be noted however, that some of these have been replaced by non-invasive, more advanced and less expensive imaging techniques.

Endoscopic retrograde cholangiopancreatography

Endoscopic retrograde cholangiopancreaticogram (ERCP) is an invasive procedure that requires technical expertise and often performed by inserting a tube into the common bile duct while the patient is sedated. Contrast material is then injected to allow visualization of the biliary tree. Traditionally, ERCP was not only diagnostic but is also therapeutic, so that if a stone was detected, it could be removed in the same sitting. The sensitivity of ERCP for choledocholithiasis is estimated to be 80 - 93%. ERCP has largely been replaced by MRCP and is now reserved for patients at a high risk of having a common bile duct stone, particularly with cholangitis.

[[Image:ercp.jpg|thumb|center|500px|Source:wikiwand

Source:wikiradiography

Bile microscopy — Bile microscopy detects microcrystals of cholesterol or amorphous bilirubinate as indirect evidence for the presence of microlithiasis in the bile. It has an overall sensitivity of 65 to 90 percent for identifying patients with gallstones [43-47]. Because of the improved sensitivity of transabdominal ultrasonography for detection of small stones and sludge, there is less need for microcrystal analysis. However, it still has a role in category 4 patients with biliary colic without gallstones on transabdominal ultrasound. However, because obtaining a sample for bile microscopy during endoscopy can take over 45 minutes, we reserve the procedure for patients with a negative EUS.

The test is based upon the theory that patients with cholesterol microlithiasis have bile that is supersaturated with cholesterol and thus have cholesterol monohydrate crystals in their gallbladder bile (picture 1), while those with bilirubinate microlithiasis have amorphous reddish-brown bilirubinate granules in their gallbladders (picture 2) [48,49]. However, the methods for performing the test have not been well standardized, which has led to confusion regarding how to collect and process the bile samples for analysis and what constitutes a positive test.

The proportion of patients with suspected gallstones but negative transabdominal ultrasound found to have microlithiasis varies substantially among reports. A systematic review found that microcrystals accounted for 7 to 79 percent of cases of idiopathic pancreatitis, 83 percent of patients with unexplained biliary-type pain, and 25 to 60 percent of patients with altered biliary and pancreatic sphincter function [50].

While the presence of any cholesterol crystals is theoretically abnormal, to increase specificity, some of the newer reports presume the test to be positive only if more than three crystals are seen per high power field [51]. However, whether findings based upon this approach correlate with clinical outcomes has not been established. As a result, this presumption has not been widely accepted.

Bile collection — Most available studies describe the test as it pertains to the detection of microlithiasis in patients with idiopathic recurrent pancreatitis and have used variable techniques for bile collection, bile processing, and microscopic crystal analysis. Nevertheless, most investigators agree that crystals are formed in the gallbladder where bile is concentrated, so gallbladder bile rather than hepatic bile should be analyzed [28,44,52]. Hepatic bile is significantly less concentrated and thus has a lower yield for the detection of microlithiasis.

Gallbladder bile can be collected using the following techniques:

●Through direct percutaneous puncture of the gallbladder under ultrasound or fluoroscopic guidance. ●During endoscopic retrograde cholangiopancreatography, either through selective gallbladder cannulation or by aspirating bile from the common bile duct after stimulating gallbladder contraction with a slow intravenous infusion of the cholecystokinin (CCK) analogue, sincalide. ●During endoscopy by suctioning bile from the duodenum in the region of the ampulla after gallbladder stimulation with sincalide. In most cases, collection during endoscopy is the simplest and most practical method. Since EUS includes an endoscopic examination, bile collection can be performed during the same session as an EUS, which increases the sensitivity for detecting gallstones over that of EUS alone [40,42]. (See 'Endoscopic ultrasound' above.)

Our approach in patients with biliary colic and a negative EUS is to collect a bile sample during the same endoscopic session as the EUS. Sincalide (0.03 mcg/kg body weight) is given by intravenous drip over 45 minutes; the longer infusion is safer and more effective than a short bolus technique [53]. The tip of the endoscope is positioned next to the ampulla and the bile is aspirated. Bile flow usually starts to accelerate within five minutes of the start of the sincalide infusion. The first 5 to 10 minutes of bile flow is normally light in color and represents common bile duct and hepatic bile. Gallbladder bile is the darker bile that starts flowing several minutes later. We use a commercially available bile collecting catheter with a mushroom tip that we introduce through the working channel of the endoscope and connect to an external suction trap. Once we start to observe dark gallbladder bile being suctioned into the collecting trap, we empty the light colored bile from the trap and begin collecting the dark bile sample. When about 10 to 20 mL of bile has been collected, we stop the Sincalide infusion and conclude the procedure. This typically takes about 30 to 45 minutes from the start of the sincalide infusion to accomplish.

The collected sample of dark bile is incubated at 37°C for 24 hours and then centrifuged at 3000 G for 30 minutes [54]. The supernatant is discarded and the sediment is mixed into the liquid remaining at the bottom of the tube. A drop of that liquid is placed on a slide and examined using a polarizing microscope; a polarizing filter facilitates identification of cholesterol crystals, which exhibit birefringence (they shine against the dark background of the polarizing microscope). The test is considered positive if any cholesterol crystals or amorphous red-brick colored bilirubinate granules are seen.

Tests that are rarely done

Oral cholecystography — Oral cholecystography can diagnose gallstones and assess gallbladder function, but it has largely been replaced by more sensitive and specific tests, such as transabdominal ultrasound [33,55]. It is still occasionally used in patients in whom a high-quality ultrasound examination cannot be obtained (such as in obese patients), to confirm the presence of adenomyomatosis of the gallbladder, and to evaluate patients who are being considered for medical dissolution therapy with ursodeoxycholic acid, in whom it is important to demonstrate stone number and size, relative density of the stones to bile, cystic duct patency, and the gallbladder's concentrating ability. (See "Patient selection for the nonsurgical treatment of gallstone disease".)

An orally administered contrast agent (eg, iopanoic acid, sodium tyropanoate, or calcium ipodate) is given and is absorbed through the intestine, taken up by the liver, and secreted into bile. Gallstones appear as filling defects within the contrast on plain radiographs (image 5). Non-opacification of the gallbladder can occur due to poor absorption from the intestine, impaired liver function, or extrahepatic biliary obstruction. With the currently available oral contrast agents, it is unlikely that the gallbladder will be visualized if the serum bilirubin is greater than 2 to 3 mg/dL.

An approximation of gallbladder motor function can also be obtained using oral cholecystography. The patient is given a fatty meal and serial radiographs are obtained. If the gallbladder is functioning normally, there will be a decrease in gallbladder size over time. Evaluation of the gallbladder motor function is not recommended in patients who have known gallbladder stones since it may induce biliary colic or complications of gallstone disease.