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).
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Reference article
This is a summary article; read more in our article on pneumoperitoneum.
Summary
-
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
Imaging
AP erect chest x-ray | abdominal CT
-
role of imaging
- confirm pneumoperitoneum
- determine the cause of pneumoperitoneum
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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
- erect chest x-ray
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