Cholecystitis is inflammation of the gallbladder, most commonly caused by gallstones obstructing the cystic duct. There are three main types: acute calculous cholecystitis (90% of cases), acute acalculous cholecystitis (10% of cases), and chronic cholecystitis. Acute calculous cholecystitis results from chemical irritation and inflammation due to obstruction by gallstones. Acalculous cholecystitis is thought to result from ischemia. Chronic cholecystitis may develop after repeated acute attacks or in the absence of attacks, and is associated with gallstones in over 90% of cases.