Radiographic signs of pneumoperitoneum

The pneumoperitoneum which imply to the presence of air within  peritoneal cavity. Pneumoperitoneum mostly results from infection(e.g enteric fever), tissue ischemia(causing perforation), erosion, thermal or mechanical injury. The differential diagnosis(DDs) are wide, including, iatrogenic injury, cancer, infection, and ulcerative disease. Among these the most common cause of pneumoperitoneum is a perforation of the abdominal viscus organ most commonly, a perforated ulcer. Pneumoperitoneum may occur as a result of perforation of any part of the bowel for example a tumor, benign ulcer or trauma. The exception to this is a perforated appendix, which rarely causes a pneumoperitoneum.

The pneumoperitoneum does not, however, always imply a perforation, because there are numbers of other (nonsurgical mostly) conditions that are associated with pneumoperitoneum. Likewise, not every viscus perforation results in pneumoperitoneum; some perforations seal over, allowing little or no gas to escape. Pneumoperitoneum is also common after  surgery(abdominal or Pelvic); which usually resolves after 3-6 days of surgery, although it may sometimes persist for as long as 24 days after surgery. 

Some radiographic signs of pneumoperitoneum are given below. 

Radiographic signs of pneumoperitoneum 

Air under diaphragm. 

The most common cause of gas(air) under diaphragm is the perforation of hollow viscous organ. In less than 10% of cases it can be due to rare cause for example intra abdominal infection by gas forming organisms.

Air under diaphragm

The football sign. 

This is mostly seen in cases of massive pneumoperitoneum. In football sign the abdominal cavity is outlined by gas from the perforation of viscus. The falciform ligament and median umbilical ligament are sometimes included in the description of this radiographic sign, as representing the sutures.

The football sign 

The Rigler sign. 

This is also known as the double-wall sign, is a sign of pneumoperitoneum seen on an abdominal xray when gas is outlining both sides of the bowel wall, i.e. gas within the bowel's lumen and gas outside the bowel lumen (within the peritoneal cavity). It is mostly seen when there is large amounts of pneumoperitoneum (>1000 mL).

The Rigler sign

The inverted "V" sign. 

This is also known as the lateral umbilical ligament sign. This pneumoperitoneum sign is seen on supine view of abdominal radiographs and manifested by the visualization of an inverted "V"  shape in the pelvis. It represents free air outlining the lateral umbilical ligaments. In infants, there are umbilical arteries in the lateral umbilical ligaments while in adults, they contain the inferior epigastric vessels.

The inverted "V" sign

The telltale triangle sign.

This is also known as the triangle sign, is a radiographic sign seen on plain abdominal radiographs in a supine position, decubitus view or cross table lateral  that signifies pneumoperitoneum, of any cause. 

It illustrate the appearance of a radiolucent triangle of air formed between two loops of bowel and the abdominal wall or between three loops of bowel.

The telltale triangle sign