47 y/o female PMH appendectomy presents with three days of worsening abdominal pain and constipation. Over the past day she has had persistent vomiting. She appears ill and has a diffusely tender abdomen. You quickly order labs and an obstructive series with upright chest XR with concern for a perforated viscus. To your surprise the CXR shows no signs of air under the diaphragm. Are there other signs of pneumoperitoneum could you look for on abdominal films?

Look for air where it shouldn’t be!

  1. Rigler’s sign– In radiology, things become visible due to a change in density. When there is air in both the lumen of the intestine and on the outside, the bowel will have a 3D, well-defined wall.


  1. Falciform ligament sign– The falciform ligament connects the anterior abdominal wall to the liver. Normally it’s not visible because its the same density as the liver. But with free air surrounding it, it becomes visible.