Pneumoperitoneum (summary)

Dr Jeremy Jones et al.

Pneumoperitoneum describes gas within the peritoneal cavity and is often the harbinger of a critical illness, often perforation of a hollow viscus. Pneumoperitoneum is distinct from pneumoretroperitoneum (much rarer) and may be mimicked by other causes (pseudopneumoperitoneum).

Reference article

This is a summary article; read more in our article on pneumoperitoneum.

  • pathophysiology
    • gas within the peritoneal space
    • most common cause is bowel perforation
    • other causes include gas tracking from elsewhere
      • pneumothorax
      • mechanical ventilation
  • investigation
    • erect chest radiograph best plain radiograph
    • can be detected on an abdominal radiograph
    • CT much more sensitive than any plain radiograph

On plain radiographs, structures can be seen when they neighbour structures of different density. Looking for gas within the peritoneal cavity relies on identifying lucency where it shouldn't be.

Usually performed after sitting erect for 10 minutes. Look for gas beneath the diaphragm, but don't misinterpret gas within bowel or the stomach for free gas.

Performed supine. Gas can be seen when it outlines certain structures. The most apparent is often when gas within the peritoneum lies adjacent to a bowel loop full of gas making the bowel wall appear particularly prominent - Rigler's sign.

Much more sensitive than plain film. Can identify even tiny amounts of free gas. Look for low-density gas outwith bowel, particularly anteriorly in the abdomen (almost all patients will be scanned supine).

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Article information

rID: 47266
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Cases and figures

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    Case 1: pneumoperitoneum
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    Case 2: pneumoperitoneum
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    Case 3: free gas on AXR - Rigler sign
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    Case 4: pneumoperitoneum on CT
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    Case 5: free gas triangles on CT lung windows
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