Depiction of diaphragmatic muscle slips on supine plain radiographs: a sign of pneumoperitoneum.

PURPOSE: To describe the diaphragm muscle slip sign, a previously unreported finding of pneumoperitoneum on plain radiographs.

MATERIALS AND METHODS: Diaphragmatic muscle slips were observed on supine plain abdominal (n = 6) or recumbent frontal chest (n = 3) radiographs in nine patients. Computed tomographic (CT) confirmation was available in six patients; free air was depicted on upright chest radiographs in the other three patients.

RESULTS: Muscle slips of the costal portion of the diaphragm were depicted in the right upper quadrant as they indented the adjacent air-filled peritoneal cavity. On supine radiographs, these discrete muscle bundles appeared as two or three large, arcuate interfaces or as bands of increased opacity of similar dimensions, with their long axes directed vertically. These smoothly marginated bundles were parallel to the dome and converged superomedially. On the CT scans, the costal muscle slips were clearly defined as bands or small peripheral triangles impinging on the parietal peritoneum.

CONCLUSION: Depiction of the undersurface of the long costal muscle slips of the diaphragm on supine plain radiographs is a sign of pneumoperitoneum.