Biliary lipid mass in the gallbladder in health and in cholesterol gallstone disease

Abstract

Objectives: A high cholesterol saturation index of gallbladder bile is an essential prerequisite for cholesterol gallstone formation. This could be due to a high cholesterol mass, or to a low bile acid and/or phospholipid mass in gallbladder bile, or to a combination of these abnormalities. The conventional method of measuring the saturation index cannot distinguish between these alternatives. Our aim was to distinguish between these alternatives in patients with cholesterol gallstones by measuring biliary lipid masses, and to study the effect of gender and obesity within this gallstone population. Methods: We have developed a simple technique for the measurement of total biliary lipid masses in the gallbladder. This involves a combination of 99mTcHIDA cholescintigraphy and of nasoduodenal intubation with intravenous cholecystokinin infusion to obtain a bile sample. We validated this technique by comparing it with direct measurement of biliary lipid masses following cholecystectomy; we studied 19 male non-obese healthy controls and a total of 45 gallstone patients, who were further subdivided into male non-obese (n = 13), female non-obese (n = 17) and obese (n = 15) gallstone patients. Results: The validation studies showed close agreement for all three biliary lipids between our technique and the direct measurements. The male non-obese gallstone patients had a significantly higher saturation index than the male non-obese healthy controls. This was due to a reduction in bile acid mass (2.73 versus 4.79 mmol, P < 0.005), with no difference in the masses of phospholipid or cholesterol. There were no differences between male and female non-obese gallstone patients; and obese patients had a reduced phospholipid mass as well as a reduced bile acid mass. There was no increase in cholesterol mass within the gallbladder in any of the groups. Conclusions: We conclude that 99mTcHIDA scintigraphy together with nasoduodenal intubation provides a simple valid technique for measuring biliary lipid masses in the gallbladder; that the main defect in gallstone disease is a reduction in bile acid mass; that within the gallstone population, gender has no effect on biliary lipid masses, but that obese gallstone patients have a reduction in phospholipid mass also. There was no increase in cholesterol mass in the gallbladder in any of the gallstone groups, presumably because this was prevented by the low bile acid mass.