Figure 59A: A supine abdominal radiograph demonstrates a large volume of free intraperitoneal air in the right hemiabdomen. The Rigler sign is identified with air present on both sides of the abdominal wall (arrowhead). The lucent liver sign is identified with increased lucency noted over the liver, which corresponds to free air anterior to the ventral surface of the liver (arrows). (Courtesy of Dr. Lauren Burke, Chapel Hill, NC, USA.) Figure 59B: A left lateral decubitus radiograph of the abdomen demonstrates a large volume of free intraperitoneal air in the nondependent abdomen between the abdominal wall and the liver, confirming pneumoperitoneum. The Rigler sign is again identified (arrowhead). There is an air-fluid level indicating fluid in the abdomen consistent with hydropneumoperitoneum (arrows). (Courtesy of Dr. Lauren Burke, Chapel Hill, NC, USA.)

Chilaiditi syndrome (colonic interposition between liver and hemidiaphragm), biliary or portal venous gas, fat within the subdiaphragmatic space or ligamentum teres, abscess, pneumatosis, gas within skin folds, properitoneal fat stripe, pneumoperitoneum.