An erect abdominal radiograph of an asymptomatic 55-year-old man undergoing routine screening shows a curvilinear lucency beneath the right hemidiaphragm. On careful review, haustral markings are continuous through this lucency and it lies below the diaphragm rather than above the liver edge. The patient has no pain, guarding or fever. What is the most likely explanation?
- A Chilaiditi sign, colonic interposition between liver and diaphragm ✓
- B Pneumoperitoneum from silent perforation
- C Subphrenic abscess with gas formation
- D Free air from recent laparotomy
Correct answer: A. Chilaiditi sign, colonic interposition between liver and diaphragm
Explanation
The findings describe the Chilaiditi sign, hepatodiaphragmatic interposition of colon. Distinguishing features are continuity of haustral folds across the lucency and absence of peritoneal signs. True free air forms a smooth crescent that changes with patient position and lacks haustral markings. Subphrenic abscess would show an air-fluid level with systemic upset, and recent surgery is excluded by history. This distinction matters because misreading Chilaiditi as perforation can lead to unnecessary laparotomy.
Reference: Grainger and Allison's Diagnostic Radiology, 7th ed.
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