Why can you not diagnose cholecystitis from the CT appearances?
GB wall thickening and oedema can be due to acute cholecystitis, but can also be due to cirrhosis, hepatitis, right heart failure, renal failure or pancreatitis. Acute cholecystitis is usually due to obstruction by an impacted calculus which is best evaluated by dynamic ultrasound: patient positioning demonstrates whether calculi are mobile or impacted. If calculi are impacted, US can demonstrate distension and non-compressibility of the gall bladder. Transducer pressure gives anatomical correlation for the site of maximum tenderness.
Full gall bladder with oedematous wall. No radiopaque calculi. Non-distended ducts. Trace ascites in the RUQ and pelvis (not shown).