[Computed tomographic assessment of breathing-induced "pseudo" pneumoperitoneum]

The differentiation between a "pseudo" pneumoperitoneum and a pneumoperitoneum due to a perforation may be difficult in unconscious or ventilated patients. The use of CT for differentiating between extraperitoneal and intraperitoneal air is demonstrated by three examples in whom air below the diaphragm was shown by conventional radiographs. CT can prove the extraperitoneal position of an air crescent below the diaphragm in cases of "pseudo" pneumoperitoneum. CT will also show that extraperitoneal air does not rise in the way that true peritoneal air will do when the patient is supine. In this position the viscera therefore do not fall backwards in the presence of a "pseudo" pneumoperitoneum.