Abdominal X-ray
Abnormal bowel gas pattern
Free gas mimics
Stomach bubble
The normal stomach bubble should not be confused with free intra-abdominal gas.
The stomach bubble forms a round/ovoid shape under the left hemidiaphragm. As the stomach has a thick wall, there is a thick line separating gas in the stomach from air in the lungs.
In contrast to this, free intra-abdominal gas forms a crescent under the diaphragm, and is separated from the lungs only by the thin membrane of the diaphragm.
Key points
- Certain normal structures can mimic pneumoperitoneum
Normal stomach bubble - erect chest X-ray
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Normal stomach bubble - erect chest X-ray
Normal stomach bubble may be identified by -
- Round/ovoid - 'bubble' shape
- Thick upper wall
- Fluid level or food contents
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Chilaiditi's phenomenon
In patients who have small livers (cirrhosis), or flattened diaphragms due to lung hyperexpansion (emphysema), a void is created within the upper abdomen above the liver. This space may be filled by bowel. If this bowel is air filled then it may mimic free gas.
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Chilaiditi's phenomenon - example
- Gas forms a near crescent shape under the right hemidiaphragm
- There is however a thick hemidiaphragm (partly consisting of bowel wall)
- Gas can be seen to lie within bowel
- Importantly, this patient with hyperexpanded lungs, due to emphysema, did not have acute abdominal pain
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False Rigler's/double wall sign
Be careful not to mistake the gas within two adjacent bowel segments for Rigler's sign.
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False Rigler's/double wall sign
- Gas seen on both sides of the bowel wall is contained within adjacent bowel
- There are no black triangles or sharp angles on the outside of the bowel wall
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False football sign
Don't mistake normal abdominal fat for free gas.
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False football sign - example
- 1 - Perirenal fat (retroperitoneal)
- 2 - Peritoneal fat (next to the liver)
- 3 - Abdominal wall fat (separating muscles of the abdominal wall)