Case #03 Discussion:

Interpretation of Findings:

These findings are consistent with cholesterol gallstones. The patient is currently asymptomatic without signs of common bile duct obstruction (i.e. jaundice or right upper quadrant pain). The normal common bile duct has a diameter up to 6 mm, hence it is clearly distended in this patient. Occasionally, patients present with dilated extrahepatic ducts with no obvious site or cause of mechanical obstruction. These patients are often elderly individuals. One theory is that dilation is due to a combination of age and/or chronic inflammation destroying elastic recoil and contractility of the duct wall. It is often difficult on either radiographic or historic grounds to exclude low-grade obstruction from prior stone passage, infection, or periampullary fibrosis. However, there exists a subgroup of patients who present with sonographic evidence of duct dilation before the development of clinical jaundice. Hence outpatient follow-up is suggested as cholelithiasis places the patient at increased risk for developing acute cholecystitis.

Diagnostic Options

Approximately 20 million Americans have gallstones. Gallstones are twice as common in women as in men and are more common in some racial and ethnic groups such as American Indians. Gallstone prevalence increases with age. In the United States, 80% of gallstones are predominantly cholesterol and 20% are pigment stones.

Cholesterol gallstones form when there is a change in bile composition. High calorie diets, obesity, malabsorption of bile acids, oral contraceptives, exogenous estrogens and Clofibrate therapy increase the likelihood of cholesterol stones.

Gallstones that are asymptomatic and incidentally discovered usually remain asymptomatic. However, symptomatic gallstones tend to produce recurrent symptoms (mild or severe biliary colic) and complications such as acute cholecystitis, hydrops, or perforation.

Plain Film Radiography

Only 10 - 15% of gallstones contain enough calcium to be detected by plain radiographs. Gallstones typically produce round or oval calcification in the right upper quadrant. Ultrasound confirmation may be necessary. The "Mercedes Benz" sign of triradiate collections of nitrogen gas filling the crevices created by shrinkage of cholesterol crystals in the stone is a useful identification.

Ultrasound

The procedure of choice for gallstone diagnosis is real-time ultrasonography, replacing oral cholecystography. Accuracy of detection is greater than 95%. The gallbladder is normally an echo-free structure on the undersurface of the liver. Characteristic findings of gallstones include moveable, discrete, echogenic foci within the dependent portion of the gallbladder and acoustic shadows emanating directly below the echogenic foci. Stones usually sink to the dependent portions of the gallbladder, but cholesterol stones may float. Occasionally collections of weaker echoes without acoustical shadowing are found within the gallbladder lumen, representing biliary sludge. Sludge can be found in fasting patients, nonambulatory patients, patients on total parenteral nutrition. and patients with cirrhosis or extrahepatic biliary obstruction.

Computed Tomography

Noncalcified stones can be difficult to detect despite CT being more sensitive than plain film. Noncalcified stones can be recognized as subtle areas of slightly lower or higher attenuation within the bile.

Magnetic Resonance Imaging

Stones can be observed as areas of low signal intensity within the higher signal intensity of the gallbladder bile. The accuracy of this technique relative to other imaging modalities is currently unknown.

Treatment

Cholecystectomy is the standard therapy for cholelithiasis. Alternative therapies for cholesterol stones include oral therapy with bile acids (cheno-/ursodeoxycholic acid), percutaneous gallbladder catheterization with methyl-tertiary-butyl ether perfusion for stone dissolution, and lithotripsy in patients where surgery is contraindicated.