Question

Gas under the diaphragm is most commonly seen in which of the following conditions?

• A. Viscus perforation
• B. Liver abscess
• C. Spontaneous rupture of oesophagus
• D. Empyema Thorax

Hint:

Gas under the diaphragm on an erect X-ray signifies free air in the peritoneal cavity -- think of the most common cause of pneumoperitoneum.

Answer 1

The Correct Option is A

Step 1: Understand the significance of gas under the diaphragm.
Free gas (pneumoperitoneum) under the diaphragm visible on an erect chest X-ray or erect abdominal X-ray indicates the presence of air in the peritoneal cavity. This is a classic radiological sign of visceral perforation.

Step 2: Identify the most common cause.
The most common cause of gas under the diaphragm (pneumoperitoneum) is perforation of a hollow viscus, most frequently:
- Perforated peptic ulcer (duodenal or gastric) -- most common cause
- Perforated appendix
- Perforated diverticulitis
- Perforated carcinoma

Step 3: Evaluate the other options.
- Liver abscess: Can rarely cause gas in the right upper quadrant if caused by gas-forming organisms (e.g., Klebsiella), but this does not classically produce subphrenic free gas visible on erect X-ray as a first-line finding.
- Spontaneous rupture of oesophagus (Boerhaave syndrome): Causes pneumomediastinum and pleural effusion/hydropneumothorax, not typically subdiaphragmatic free gas.
- Empyema Thorax: A pleural space infection -- it does not cause gas under the diaphragm.

Note: In 10% of cases, subdiaphragmatic gas can result from rare causes (gas-forming intra-abdominal infections, post-laparoscopy, etc.), but the most common cause remains hollow viscus perforation.

Conclusion: Gas under the diaphragm is most commonly seen in hollow viscus (viscus) perforation.