Abdominal x rays made easy: abnormal extraluminal gas
This month Ian Bickle and Barry Kelly look at identifying abnormal extraluminal gas on plain abdominal films, in the third part of our series on abdominal radiographs
Extraluminal gas is gas outside the sealed gastrointestinal tract.
A most important and potentially devastating finding is that of free intraperitoneal gas, which is known as pneumoperitoneum. Emergency surgical intervention is likely to be necessary, as pneumoperitoneum usually indicates a perforated viscus. The supplementary plain radiograph should be an erect chest radiograph that visualises gas collecting beneath the diaphragm. Depending on the volume of gas in the peritoneum, it may be apparent under one or both hemidiaphragms. As you may recall from the first part of the series (normal radiographs) a gastric air (“gas”) bubble is usually seen in the left hypochondrium on the erect film. This can make distinguishing free air on this side problematic. For this reason, identification of free gas on the right side is more straightforward. The air is trapped between the underside of the diaphragm and the upper surface of the liver (fig 1). A