• Free intra-abdominal gas – it usually indicates perforation of a viscus (it is often a peptic ulcer – a perforated appendix rarely demonstrates free gas)
Plain abdominal radiograph
ABNORMAL GAS DISTRIBUTION
PNEUMOPERITONEUM
DEFINITION
Plain abdominal radiograph
appendicitis 
bowel ischaemia 
diverticular disease 
post colonoscopy
do not confuse this appearance with Chilaiditi’s syndrome (where intestine is seen between the liver and diaphragm) or a subphrenic abscess
triangular collections of air are seen within the abdomen (outlining the visceral contents) 
gas is seen on either side of the falciform ligament 
scrotal air can be seen in children
a perforated sigmoid diverticular disease 
post colonoscopy
