In this radiology lecture, we review the ultrasound appearance of acute cholecystitis, including gangrenous and emphysematous cholecystitis! Key teaching points include: * Acute cholecystitis = Acute gallbladder inflammation. * Most often (95%) caused by an impacted, obstructing gallstone in the cystic duct or gallbladder neck = Acute calculous cholecystitis. * Clinically presents as persistent RUQ pain that may radiate to right shoulder, often with N/V and fever. * Ultrasound findings of uncomplicated acute cholecystitis: Gallstones, sonographic Murphy sign, gallbladder wall thickening (greater than 3 mm) and edema, gallbladder distention (greater than 4 cm short axis), and pericholecystic fluid. * Sonographic Murphy sign = Maximal abdominal tenderness from transducer pressure over gallbladder. PPV of gallstones and a positive sonographic Murphy sign = 92%. * Pericholecystic fluid occurs in less than 20% of patients with acute cholecystitis, usually seen in more advanced cases. * Gangrenous cholecystitis = Most common complication of acute cholecystitis. Ischemia with necrosis of gallbladder wall. Increased mortality compared to uncomplicated acute cholecystitis. * Ultrasound findings of gangrenous cholecystitis: Wall disruption, ulceration, mucosal irregularity, and/or focal bulge, sloughed mucosal membranes, pericholecystic fluid, less likely to have positive Murphy sign, and increased risk of perforation (usually at fundus). * Emphysematous cholecystitis = Gallbladder wall necrosis with gas formation in wall and/or lumen. More common in elderly men with underlying diabetes. Higher risk of perforation, rapid progression, and increased mortality compared to uncomplicated acute cholecystitis. Emergent surgical intervention typically required. * Ultrasound findings of emphysematous cholecystitis: Bright reflectors from nondependent portions of gallbladder wall, dirty posterior acoustic shadowing, and ring-down artifact. CT can confirm if necessary. To learn more about the Samsung RS85 Prestige ultrasound system, please visit: https://www.bostonimaging.com/rs85-prestige-ultrasound-system-4 Click the YouTube Community tab or follow on social media for bonus teaching material posted throughout the week! Spotify: https://bit.ly/spotify-rhq Instagram: https://www.instagram.com/radiologistHQ/ Facebook: https://www.facebook.com/radiologistHeadQuarters/ Twitter: https://twitter.com/radiologistHQ Reddit: https://www.reddit.com/user/radiologistHQ/