Clinical

The most common cause of pneumoretroperitoneum is perforation of the second, third, or fourth portion of the duodenum or retroperitoneal colon secondary to trauma, diverticulitis, or ulceration.

Radiological findings

Pneumoretroperitoneum is most often seen on the right side where the air can outline the right kidney and the undersurface of the liver. In contrast to pneumoperitoneum, air in the retroperitoneum does not move freely with change in position. The gas can extend up into the mediastinum or neck because there is no barrier between them.

This plain film demonstrates pneumoretroperitoneum with gas outlining the right psoas major (arrows).