Expansion
Gas on both sides of the bowel wall makes it visible as a thin line
Expansion
Normally only the inner surface of the bowel wall is outlined by gas, so the wall itself is not visible. When free gas is present in the peritoneal cavity, the outer surface is outlined too and the wall appears as a thin white line, Rigler’s (double wall) sign.
Other signs of pneumoperitoneum:
- Gas under the diaphragm on an erect chest radiograph - the classic sign; can detect as little as a few millilitres
- Football sign - a large oval lucency filling the abdomen
- Falciform ligament sign - the ligament outlined by surrounding gas
- Triangle sign - small triangular gas collections between loops
The commonest cause is a perforated viscus, most often a duodenal ulcer. Remember the important exception: free gas is expected for some days after laparotomy or laparoscopy, and its presence then does not imply perforation.