Misleading pneumoperitoneum.

Misleading pneumoperitoneum takes one of two forms: true pneymoperitoneum without peritonitis or pneumoperitoneum simulated by adventitious x-ray shadows. In both instances, the roentgenographic appearance of free intraperitoneal air proves to be a specious indication for laparotomy. Twenty-eight per cent of 29 patients with misleading pneumoperitoneum were subjected to operations that, retrospectively, might not seem absolutely necessary. The decisions to operate on patients with pneumoperitoneum without peritonitis were based on the amount of pneumoperitoneum roentgenographically visualized. The instances of pseudopneumoperitoneum had several common features. The diagnosis often was based only on x-ray films of the chest. Compatibility with clinical features was marginal; the radiolucency was often not truly at the apex of the diaphragm. Finally, the x-ray films, interpretation and working conditions frequently were suboptimal.