The causes of acute cholecystitis can be grouped into two main categories:
- calculous cholecystitis, where the inflammation of the gallbladder is caused by a blockage in the cystic duct, usually by a gallstone
- acalculous cholecystitis, where the inflammation is unrelated to gallstones or a blocked cystic duct
Each of these types is discussed in more detail below.
Calculous cholecystitis
Calculous cholecystitis is the most common, and usually less serious, type of acute cholecystitis. It accounts for around 90% of all cases.
Calculous cholecystitis develops when the main opening to the gallbladder, called the cystic duct, gets blocked by a gallstone or by a substance known as biliary sludge. Biliary sludge is a mixture of bile and small crystals of cholesterol and salt.
The blockage in the cystic duct results in a build-up of bile inside the gallbladder, which causes the pressure inside the gallbladder to increase. For reasons that are still unclear, the rise in pressure inside the gallbladder causes the gallbladder to become inflamed and swollen.
In around one in five cases, the inflamed gallbladder becomes infected by bacteria. This can trigger the more serious complications of acute cholecystitis, such as gangrenous cholecystitis (tissue death inside the gallbladder).
Acalculous cholecystitis
Acalculous cholecystitis is usually a much more serious type of acute cholecystitis. It often requires admission to an intensive care unit (ICU) for treatment.
Acalculous cholecystitis usually develops as a complication of a serious illness, infection or injury that damages the gallbladder. Possible causes for acalculous cholecystitis include:
- accidental damage to the gallbladder during major surgery
- serious injury or burns
- blood poisoning (sepsis)
- severe malnutrition
- HIV or AIDS
Risk factors
Factors that increase the risk of getting acute cholecystitis include:
- being very overweight, with a body mass index of 30 or more
- being female, as women are three times more likely to get acute cholecystitis than men, although the symptoms tend to be more severe in men
- being middle-aged, as rates of acute cholecystitis are highest in people who are 40 to 60 years of age
- being of East Asian origin, as rates of acute cholecystitis are higher in people of Japanese and Chinese origin
