Pneumoperitoneum

Abnormal presence of free gas within the peritoneal cavity, most often due to perforation of a hollow viscus. Possible causes are perforated peptic ulcer, diverticulitis, bowel obstruction, ischemic bowel, inflammatory bowel, cancer perforation, post-operative air, endoscopy, peritoneal dialysis, mechanical ventilation, CPR, pneumothorax, and air forced into the vagina and travelling through the fallopian tubes into the abdomen.