Pneumoperitoneum – Rigler Sign

History: 75 year old man with abdominal pain, nausea and vomiting. 

Pneumoperitoneum: Single frontal radiograph of the upper abdomen shows free intraperitoneal air, as evidenced by the conspicuous outline of the small bowel walls (Rigler Sign).

This is the typical appearance of a Rigler Sign, also known as a bas relief sign, which has its origin in sculpture. Look again at the image above. Notice surgical skin staples over the right lower quadrant of the abdomen. The patient was recently operated on, indicating the free air is from his open abdominal surgery, not a bowel perforation. Pneumoperitoneum typically resolves earlier after a laparoscopic abdominal surgery compared to open abdominal surgery because the high nitrogen content in room air is absorbed more slowly than CO2 used in laparoscopy.