DETECTION OF PNEUMOPERITONEUM ON CHEST RADIOGRAPHS - COMPARISON OF UPRIGHT LATERAL AND POSTEROANTERIOR PROJECTIONS

OBJECTIVE. This study was done to determine whether upright lateral ch est radiographs were more sensitive than upright posteroanterior chest radiographs in detecting pneumoperitoneum. SUBJECTS AND METHODS. We p rospectively evaluated the ability of upright posteroanterior and late ral chest radiographs to show subdiaphragmatic air in 100 consecutive patients with known pneumoperitoneum from a variety of causes. The dif ference in sensitivity between the two was evaluated by means of McNem ar's test. RESULTS. The upright lateral chest radiograph showed pneumo peritoneum in 98% of the cases; the upright posteroanterior chest radi ograph showed pneumoperitoneum in only 80%. The upright lateral chest radiograph was significantly better at showing pneumoperitoneum than w as the upright posteroanterior chest radiograph (p < .01). CONCLUSION. The upright lateral chest radiograph is more sensitive than the uprig ht posteroanterior chest radiograph in detecting small amounts of pneu moperitoneum. When there is a strong clinical suspicion of a perforate d hollow viscus, it may be of benefit to include an erect lateral ches t radiograph as part of the acute abdominal series.