Also, please know that I am not a doctor, just a former nurse. :)
HI, after placement of any central line that you describe, docs always do an xray to check for pneumothoraxes (collapsed lungs). They do this because the lungs are so close to the vein that they want to access, it doesn't happen too often but sometimes the lung gets nicked by the needle.
According to your CT, there was a tiny amount of air in the neck (subcutaneous emphysema) and a tiny pneumothorax (too tiny to treat, if it were large enough, docs would put a chest tube in to re expand the collapsed lung. Yours was very small and did not need it, it probably will go away on its own)
This is the best I can do, if you have any more questions you should ask your doctor who is familiar with your case.
I hope this helps...Sunny