Cholecystitis is inflammation of the gallbladder. The gallbladder is a pear-shaped organ that lies beneath the liver on your right side. It stores bile, which is a fluid produced by the liver to help to digest fats.

Acute cholecystitis is usually caused by a gallstone blocking the outlet from the gallbladder, so that bile cannot get out. The bile becomes thicker and sometimes stagnant and infected. This irritates and inflames the inside of the gallbladder, causing severe pain. Sometimes there are other causes, such as injury, surgery, or body-wide infection.

The gallbladder may also become inflamed because of sludging of the fluid in it. Sludging is the formation of thickened fluid that has not yet formed stones. The sludge is thick enough to prevent a normal flow of bile so it has the same effect as gallstones.