Recognizing Free Air
© William Herring, MD, FACR
Remember
Air will rise towhatever is thehighest part of theabdomen
The 3 Signs of Free Air
Air beneath diaphragm
Both sides of bowel wall
Falciform ligament sign
ERECT
Air beneaththe diaphragmforms acrescentriclucency seenbest on theright side overthe liver
Air on both sides of the bowelwall (Rigler’s sign). Normally(see below) you do not see thebowel wall as a discrete line.
Normal
Falciform Ligament Sign
Air over theconvexity of theliver on a supineview outlines theFalciform ligament,which is usuallyinvisible.
These are the Causes of Free Air
Rupture of a hollow viscus
Perforated ulcer
Perforated diverticulitis
Perforated carcinoma
Trauma or instrumentation
Post-op 5–7 days
NOT perforated appendix
Take Home Points
3 major findings for free air:
Air beneath the diaphragm
Falciform Ligament sign
Air on both sides of bowel wall
Most common cause of free air is aperforated ulcer
For plain films, free air is best seen on anerect or left lateral decubitus (left-sidedown) film
Which of the followingpatients has free air?
Answer follows on slide after question
Quiz
Does this patient have free air?
Answer follows on next slide
Yes, There is Free Air
Both sides of thebowel wall (thestomach) arevisible
Does this patient have free air?
Answer follows on next slide
No, There is No Free Air
The stomach is dilated,but both sides of thestomach wall are notvisualized
Does this patient have free air?
Answer follows on next slide
No, There is No Free Air
None of the signs offree air is present here
Does this patient have free air?
Answer follows on next slide
Both sides of thebowel wall arevisualized here.
Yes, There is Free Air
Congratulations, You Graduate
I knowmy FreeAir