Pneumoperitoneum (summary)

Last revised by Daniel J Bell on 2 Apr 2018
This is a basic article for medical students and other non-radiologists

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

AP erect chest x-ray | abdominal CT

  • role of imaging
    • confirm pneumoperitoneum
    • determine the cause of pneumoperitoneum
  • radiographic features
    • erect chest x-ray
      • sitting erect for 10 minutes
      • gas will rise to the top of the peritoneal cavity
        • seen beneath (outlining) the diaphragm
    • abdominal x-ray
      • may be challenging to detect free gas
      • many signs of pneumoperitoneum
      • gas on both sides of the bowel wall - Rigler sign
    • abdominal CT
      • much more sensitive than plain film
      • gas tends to sit anteriorly
      • gas tends to form small triangles between bowel loops
      • CT also useful to try to determine the cause

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Cases and figures

  • 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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