**4.1 Acute calculous cholecystitis**

Obstruction of the cystic duct by stones lead to inflammation of the gallbladder resulting in acute calculous cholecystitis. The obstruction causes gallbladder swelling followed by bile acid concentration, ischemia of gall bladder wall and occasionally, bacterial infection. Symptoms include pain similar to biliary colic with increased vomiting and fever. Patients usually have right upper quadrant tenderness on clinical examination and sometimes a palpable mass. Ultrasound can identify cholecystitis by presence of stone or sludge with gallbladder wall thickening and edema [double-wall sign], and pericholecystic fluid.
