In most significant trauma, both blunt and penetrating, there will often be multiple findings and you don't want to let satisfaction of search get you. This case demonstrates a minuscule right pneumothorax, with air noted in the anterior costophrenic recess. Subpleural groudglass in the lingula is also present, representing a pulmonary contusion. Additionally, there is a SUBTLE sternal body fracture. This patient also had a couple of subtle, non-displaced rib fractures, but I didn't include those as some of the images on purpose. The things I've seen folks miss the most on trauma are small pneumothoraces, non-displaced rib, sternal, and vertebral body/transverse process fractures, and small mediastinal hematomas. Be sure to always look in these regions for abnormalities. In trauma, I always look at three things on the sagittal series - the sternum, vertebral bodies, and diaphragms looking for injury. If I see a sternal fracture, I will also look at the retrosternal space searching for a hematoma, which can be very small. Reexamining the vessels is also important to assess for underlying vascular injury. I will also run the spine on the axial and coronals looking for transverse process fractures. I've included a link to a good radiographics article for blunt thoracic trauma.
