An elderly man presented with upper abdominal pain. A diagnosis of cholecystitis was initially suspected. Just prior to the ultrasound being performed his pain became much worse.
Free gas is seen over the liver. Small locules of gas are seen immediately adjacent to the liver and gallbladder, but are not within the duodenum.
Ultrasound is frequently thought of as unable to diagnose free intraperitoneal air, but can show signs if looked for. Air over the liver must be distinguished from lung (watch for respiratory movement). Bowel interposition (Chiliaditti's anomoly) can also result in gas over the liver, but will be contained within the lumen, which may be seen. If there is doubt then repositioning the patient onto their side may help distinguish the two conditions.
For another example of pneuoperitoneum, see this case also