Pseudo-Rigler’s sign | Radiology Signs

Answer:

The pseudo-Rigler’s sign is a false double wall appearance created when two dilated bowel loops lie against each other, so that gas within each loop outlines both sides of the two apposed walls and simulates the appearance of intraluminal and free intraperitoneal gas outlining a single wall. True Rigler’s sign requires gas on both sides of the same bowel wall, which is possible only when free intraperitoneal gas is present, and it is normally seen when the pneumoperitoneum is large. The distinction matters because pseudo-Rigler’s is most likely to occur in exactly the setting where free gas is being sought, a distended obstructed abdomen imaged supine. The practical rule is not to accept the sign in isolation: look for corroborating signs of pneumoperitoneum on the same film, the falciform ligament sign, the football sign, the inverted V sign of the umbilical ligaments, the triangle sign of gas in an interloop recess and gas in Morison’s pouch (the doge’s cap sign). If the question remains open, an erect chest radiograph, which can detect as little as 1 to 2 mL of free gas beneath the diaphragm, or a left lateral decubitus film in the patient who cannot sit up, resolves it, and CT is the most sensitive test and additionally shows the site and cause of perforation. Careful window review on CT with lung settings is required, since small volumes of gas are otherwise easily missed.

Why is it called so?

The sign takes its name from Rigler’s sign, which it imitates: the appearance is of a wall outlined on both sides, but the second gas collection is inside an adjacent loop rather than free in the peritoneum.

Pathophysiology

In bowel obstruction or ileus, loops distend and their walls thin and appose across the peritoneal surfaces. Where two gas-filled loops touch, the beam passes through gas, two thin walls and gas again, so the projected image shows a single soft tissue stripe with lucency on both sides, indistinguishable at a glance from a single wall outlined by luminal and free gas. The apposed wall stripe is usually slightly thicker than a single wall and can often be traced to where the two loops diverge, which is the anatomical cue that separates the artefact from a genuine Rigler’s sign; on a supine film free gas instead collects anteriorly in the midabdomen and produces the corroborating signs listed above.

Alternative names: False Rigler’s sign; pseudo double wall sign

Other associated named signs: Rigler’s sign, the falciform ligament sign, the football sign, the cupola sign and the triangle sign

References

1. Levine MS, Scheiner JD, Rubesin SE, Laufer I, Herlinger H. Diagnosis of pneumoperitoneum on supine abdominal radiographs. AJR Am J Roentgenol. 1991;156(4):731-5. PMID: 2003436.