Sonographic detection of pneumoperitoneum in patients with acute abdomen

We describe five patients who presented with an acute abdomen in whom pneumoperitoneum was first detected by sonography. All five subsequently were proved to have a perforated viscus. In all cases, the pneumoperitoneum was seen as an echogenic line with a posterior ring-down or reverberation artifact between the anterior abdominal wall and the anterior surface of the liver. The finding was shown best in the right upper quadrant with the patient in the left lateral decubitus position. The echoes caused by the pneumoperitoneum overlapped the echoes of the lung during inspiration, but the echoes were separate during expiration. The probable cause of pneumoperitoneum was determined with sonography in four of the five patients: three had perforation of duodenal ulcer and one had perforation of gastric cancer. The fifth patient had a perforated ileum, which was not evident on the sonogram. Our experience with these patients suggests that the detection of pneumoperitoneum on sonography in patients with an acute abdomen is an important sign of a perforated viscus.