Case 59
This radiograph shows pneumoperitoneum in the form of free air under both hemidiaphragms. Under the left hemidiaphragm, air is seen on both sides of a GI tract structure (bowel or stomach). This is known as Rigler’s sign, though typically this is most useful on supine abdominal radiograph where air under the diaphragm is not a reliable finding due to patient position. The lungs are clear.
The differential for pneumoperitoneum includes the emergent finding of perforated bowel and should always be suspected in a patient with abdominal pain. Pneumoperitoneum can also be seen in a few more benign settings. One is a history of abdominal surgery in the past few days, particularly laparoscopic surgery, as it takes time for the air introduced to the peritoneal space to be absorbed. The other is air that is inadvertently introduced by patients on peritoneal dialysis. This patient had an unremarkable abdominal exam and was on peritoneal dialysis, so the air was attributed to the dialysis.