This PA erect chest x-ray is from a 40 year old female patient who has presented with abdominal pain. What can you deduce from the x-ray?

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The lung fields are clear and the cardiomediastinal contour is normal. However, there appears to be an air crescent under the left diaphragm. Is this pneumoperitoneum?

The patient indeed had a large pneumoperitoneum, secondary to a perforated antral ulcer; the following CT scans were obtained just an hour after the plain x-ray!

Pneumoperitoneum:

• About 76% of perforated peptic ulcers will reveal free air on erect chest x-rays.
• In patients who are unfit or too sick to stand upright, a left lateral decubitus x-ray can show a small pneumoperitoneum.
• Both erect cxr and left lateral decubitus abdominal x-rays require the patient to be in position for at least 10 mins to allow sufficient time for the air to rise.
• On the left, it can be difficult to distinguish free air from gas in the stomach/colon.
• CT is the most sensitive investigation for the detection of free peritoneal gas.

(Reference: Textbook of Radiology and Imaging by Sutton)

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