Normally a balance of bile salts, lecithin and cholesterol keep gallstones from forming. If there are abnormally high levels of bile salts or, more commonly, cholesterol, stones can form. Symptoms usually occur when the stones block one of the biliary ducts or gallstones may be discovered upon routine x-ray or abdominal CT study.
Review Date 11/2/2020
Updated by: Michael M. Phillips, MD, Clinical Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.