Acute cholecystitis represents inflammation of the gallbladder that develops over hours usually due to a gallstone obstructing the extrahepatic biliary tree duct, as shown in this case. 

Ultrasound is the first imaging modality of choice when assessing acute biliary tree pathologies. This patient was referred to CT before the blood results, with a broad differential for acute abdomen. As cholecystitis was not specifically suspected, the patient was not initially guided to ultrasound assessment.