<prompt> Which of the following are causes for cholecystitis wxcept?EstrogenOCPDiabetes mellitusObesity  <response>: acalculous cholecystitis is not an uncommon entity, but can be commonly missed. It is common in patients who have undergone major surgeries, trauma, burns, or any other stress or in cases of cholecystoses. Common in ICU patients. ACUTE CHOLECYSTITIS Commonly it occurs in a patient with pre-existing chronic cholecystitis but often also can occur as a first presentation. Usual cause is impacted gallstone in the Hamanns pouch, obstructing cystic duct. ref : SRB;s manual of surgery,3 rd ed,pg no 576 