Spectrum of Signs of Pneumoperitoneum.

Pneumoperitoneum is caused by rupture of a hollow viscus that includes the stomach, small bowel, and large bowel, with the exception of those portions that are retroperitoneal in the duodenum and colon. The causes of pneumoperitoneum are numerous, ranging from iatrogenic and benign causes to more life-threatening conditions. In the absence of a benign cause of pneumoperitoneum, the identification of free intraperitoneal gas usually indicates the need for emergency surgery to repair a perforated bowel. The plain film is the primary diagnostic tool for detecting pneumoperitoneum: multiple signs of free intraperitoneal air can be found especially on supine abdominal radiographs. Computed tomography (CT) examination has been shown to be more sensitive than abdominal radiographs for the detection of free intraperitoneal air. It is important that the radiologist become familiar with the signs of pneumoperitoneum that can be discerned on abdominal radiographs, on CT scout view, and on CT scan.