Free Air: Signs to Watch Out for In Abdominal Imaging Part III

Pneumoperitoneum must be diagnosed promptly when it occurs, which is often abruptly and without warning.

Author: Stephen R. Baker, MD. Special Presentation for Practical Reviews in Radiology

Other Signs of Free Air on Radiography

This third section of the review on diagnosing pneumoperitoneum considers supine plain film signs of abdominal free air outside the right upper quadrant.

In the anterior paramedian superior position of the abdomen, the most common manifestation is the cupola sign, which is much more frequent than the presence of air in the lesser sac.

Like a cupola, free air in this location is well delimited superiorly, but indistinctly bordered inferiorly.

Occasionally, the only evidence of pneumoperitoneum can be found in the left upper quadrant.

In the mid-abdomen, the classic finding is Rigler’s sign, otherwise known as the bas-relief sign.

It is, unfortunately, insensitive and non-specific, requiring for its presence almost a liter of extraluminal air and accompanying ascites.

However, in patients with intestinal perforation and intra-abdominal adhesions, Rigler’s sign may be encountered even though the more subtle right upper quadrant patterns of free air are absent, because the rostral migration of free air is retarded by the presence of adhesions.

Summary
In patients with intestinal perforation and intra-abdominal adhesions, Rigler’s sign may be encountered even though the more subtle right upper quadrant patterns of free air are absent, because the rostral migration of free air is retarded by the presence of adhesions.