Acute Cholecystitis

Most acute cholecystitis begins when a gallstone obstructs the cystic duct. The gallbladder continues to secrete mucus and concentrate bile behind the obstruction, so intraluminal pressure rises. Distension compromises mucosal perfusion, while stagnant bile promotes bacterial overgrowth. The result is inflammation of the gallbladder wall. Pain is usually steady rather than colicky once inflammation is established. It commonly localizes to the right upper quadrant and may radiate to the right shoulder or scapula because diaphragmatic irritation refers pain through the phrenic nerve. Persistent obstruction can progress to ischemia, necrosis, empyema, gangrene, or perforation with peritonitis. Not every patient has stones. Acalculous cholecystitis occurs without gallstones, usually in critically ill patients with prolonged fasting, severe trauma, sepsis, major burns, or total parenteral nutrition. Bile stasis and poor gallbladder perfusion drive the process. In an ICU patient who cannot report pain, unexplained fever, leukocytosis, abdominal distension, or worsening sepsis may be the only warning.