Rigler's sign

Clinical History

The patient presented with severe abdominal pain but no obvious signs of peritonism. In the supine abdominal film both surfaces of the wall of the colon were well delineated.

Imaging Findings

This elderly malnurished patient presented to ER complaining of severe abdominal pain for 6 hours. On examination, palpation revealed no rebound tenderness or other obvious signs of peritonism. Her abdomen was distended. Laboratory tests revealed nothing but mild leukocytosis. Supine plain abdominal X-rays demonstrated distended small and large bowel loops and on closer inspection of the film, the wall of the colon was well delineated, reminding of the Rigler’s sign. Abdominal non contrast enhanced CT showed free intraperitoneal air, perihepatic fluid and subdiaphragmatic collection as well. Laparotomy, performed the same day, confirmed diffuse peritonitis due to a perforated gastric ulcer.

Discussion

The demonstration of pneumoperitoneum in a patient with acute abdominal pain is one of the most significant signs in medicine. In over 90% of cases the cause of it will require emergency surgery. However, pneumoperitoneum following a perforated viscus, is demonstrable in only 75-80% of cases. This may be because the perforation is confined or that the perforated viscus is fluid filled. It may also result from the presence of adhensions or from simple non detection due to errors. If a perforated viscus is suspected, then a horizontal-ray radiograph, either an erect chest or decubitus abdomen, is mandatory. The patient should remain in the upright or decubitus position for at least 10 minutes before radiography is performed. Radiographic technique is important: a pneumoperitoneum can be detected in 76% of cases using an erect chest film only( free air is seen in the subdiaphragmatic spaces ) , but when a left decubitus projection is added ( free air is seen between the liver margin and right abdominal wall ), a pneumoperitoneum can be demonstrated in nearly 90% of cases. Probably the best known roentgenographic sign of pneumoperitoneum on supine films is the demonstration of air on both sides of the bowel wall, the serosal surface and the lumen, making it appear as a linear stripe. This was first described by Rigler in 1941 and it is also called the bas relief sign. However it is both insensitive and nonspecific. At least 750 ml to 1 lt of gas must be present before there is sufficient volume to outline the bowel wall. However visualization of both the inner and the outer wall of a loop, is also possible, regardless the existence of pneumoperitoneum. That is when two or more filled with air bowel loops are plased next to each other (pseudo-Rigler sign). Several studies have documented that abdominal CT is far more sensitive than plain film radiography for the detection of small pneumoperitoneum and unsuspected perforations.A balance has to considered between quick diagnosis and high radiation risk for patients with acute abdominal presentation. Conventional imaging studies are now being closely studied for clinical utility. The plain film of the abdomen occupies a middle ground, and it has undoubted value for the assessment of intestinal obstruction and pneumoperitoneum, if the entire abdomen is included. In conclusion whenever there is a case of suspected pneumoperitoneum and erect abdominal or chest films are not possible to obtain, then Rigler’s sign is one valuable indication of the underlying situation. If there is no such finding then CT imaging is the last non invasive diagnostic procedure.

Differential Diagnosis List

Final Diagnosis

Unsuspected perforation of viscus (stomach).

URL:	https://www.eurorad.org/case/1179
DOI:	10.1594/EURORAD/CASE.1179
ISSN:	1563-4086