Chilaiditi sign mimicking pneumoperitoneum with ischemic sigmoid volvulus: CT diagnosis of a surgical emergency.

Chilaiditi syndrome involves the abnormal position of bowel between the liver and diaphragm, causing symptoms in the patient, which can mimic pneumoperitoneum on plain X-rays. Although sigmoid volvulus associated with Chilaiditi syndrome has been previously reported, the principal educational value of the present case lies in demonstrating how contrast-enhanced computed tomography (CT) can simultaneously distinguish pseudopneumoperitoneum from true pneumoperitoneum and identify ischemic volvulus requiring urgent surgical management. We describe a 45-year-old man who came to the hospital with acute large-bowel obstruction and visible gas under the right diaphragm. An upright X-ray showed subdiaphragmatic gas along with haustral markings. A contrast-enhanced CT scan confirmed the Chilaiditi sign and showed a sigmoid volvulus with mesenteric whirling and reduced enhancement, indicating ischemia. Subtle peripheral hepatic enhancement was also noted, likely reflecting adjacent inflammatory change. Emergency surgery found a gangrenous 720° sigmoid volvulus trapped between the liver and the diaphragm; a sigmoid colectomy and Hartmann's procedure were performed, followed by a successful colostomy reversal. The patient remained well at 12-month follow-up. This case highlights how CT can help distinguish between pseudopneumoperitoneum and true pneumoperitoneum while also identifying ischemic volvulus that needs urgent surgery. The case further emphasizes the value of CT in directing timely operative management in patients with apparent subdiaphragmatic free air and suspected bowel ischemia.