Think breach in the diaphragm.
It is usually caused by penetrating rather than blunt injury and is easily missed clinically and radiologically.
In blunt injury, it is three times more common on the leftthe right hemidiaphragm being protected by the liverand nearly always at the weakest point, posterolaterally. Vigilance is required on CT analysis since the diagnosis can be easily missed. Both the chest X-ray (CXR) and CT images demonstrated have rather obvious injuries (see images below. Click the images to see larger versions).
Any diaphragmatic breach will not heal spontaneously (it’s about pressure gradients between chest and abdomen) — abdominal content herniation is a possibility and may be picked up years later.
Figs 6 and 7. Diaphragmatic injury