Biliary colic develops in 1 to 4% annually, and acute cholecystitis develops in about 20% of these symptomatic patients if they are left untreated. Acute cholecystitis may coexist with choledocholithiasis, cholangitis, or gallstone pancreatitis. Obstruction of the cystic duct in the presence of bile supersaturated with cholesterol can lead to inflammation, enlargement, and necrosis of the gallbladder. Bacterial super-infection may also occur.