Free intraperitoneal gas – CT

Free intraperitoneal gas. This patient presented with acute abdominal pain, localizing to the right iliac fossa. CT was requested and showed free gas anterior to the liver (arrows). When searching for extra-luminal gas in the abdomen, it is often very useful to switch to lung windows (right-hand image), which can make the gas much more obvious. The cause in this case was perforated acute appendicitis.