Red Flag, I found the images. This was a 32 year old male stabbed in the chest, right side antero-laterally. He was stable, no big deal, here is his first CXR (supine):
http://i55.photobucket.com/albums/g1...upinesmall.jpg
There was no obvious pneumothorax but we suspected it because of the subcutaneous emphysema you see there on the right. I can't remember what they made of the right middle and lower lobe, just that they didn't like the look of it and were thinking should we put ICD now or wait a bit? Next shot was erect:
http://i55.photobucket.com/albums/g1...Erectsmall.jpg
Still nothing obvious. No pneumo edge. Some 10cm CT cuts showed the pneumo nicely:
http://i55.photobucket.com/albums/g1...estCTsmall.jpg
Because it was mainly anterior there was reduced chance to define the pneumo in this case where the standard X-rays are 90 degrees to the coronal plane. Based on the CT they decided to err on the side of caution and place an ICD.
A historical note: this was Joburg in the late 90s. We had one single slice spiral CT scanner and a heavy workload. It wasn't like the UK and US where you could afford to just scan a guy as a matter of course. With 16,000 adult trauma patients annually, they had to have very strong indications and ambivalent clinical assessments before getting a scan.