Acalculous cholecystitis is a form of cholecystitis caused by dysfunction or hypokinesis of gallbladder emptying. The more commonly encountered condition of cholecystitis is caused by a mechanical blockage of the gallbladder outlet at the cystic duct, usually by a gallstone. Duncan first described the condition of acalculous cholecystitis in 1844. Although it can present acutely, acalculous cholecystitis typically presents more insidiously. The condition is more common in ill patients in the ICU. Acalculous cholecystitis is a life-threatening disorder that has a high risk of perforation and necrosis compared to the more typical calculous disease.