Detection of pneumoperitoneum on chest radiographs: comparison of upright lateral and posteroanterior projections.

OBJECTIVE: This study was done to determine whether upright lateral chest radiographs were more sensitive than upright posteroanterior chest radiographs in detecting pneumoperitoneum.

SUBJECTS AND METHODS: We prospectively evaluated the ability of upright posteroanterior and lateral chest radiographs to show subdiaphragmatic air in 100 consecutive patients with known pneumoperitoneum from a variety of causes. The difference in sensitivity between the two was evaluated by means of McNemar's test.

RESULTS: The upright lateral chest radiograph showed pneumoperitoneum in 98% of the cases; the upright posteroanterior chest radiograph showed pneumoperitoneum in only 80%. The upright lateral chest radiograph was significantly better at showing pneumoperitoneum than was the upright posteroanterior chest radiograph (p < .01).

CONCLUSION: The upright lateral chest radiograph is more sensitive than the upright posteroanterior chest radiograph in detecting small amounts of pneumoperitoneum. When there is a strong clinical suspicion of a perforated hollow viscus, it may be of benefit to include an erect lateral chest radiograph as part of the acute abdominal series.