The cupola sign of pneumoperitoneum in the supine patient.

Free air within the peritoneal cavity can be recognized on supine abdominal films by identification of the median subphrenic space. We have termed this the "cupola sign." In a review of 100 patients with pneumoperitoneum, this sign was seen in 6 patients. In 3 instances it was the only manifestation of a pneumoperitoneum and in 3 instances it was seen in association with air below the right and left diaphragmatic leaves.