A CT sinus scan is not an unreasonable option, particularly if you have a history of sinus disease, or if you have sinus congestion/infection currently. I can't read your physicians mind, but I highly doubt if they were getting the CT scan
to look for a cancer. Cancer within your sinuses is very rare to begin with, and a CT scan probably isn't the best imaging modality to use if that is the question one is trying to answer (MRI
would be better). More than likely what your physician is looking for is any evidence of chronic sinus disease, or chronic sinusitis. When you look at a CT scan, bone should be whitish, the air around your head and in the sinuses should be black, and soft tissue is a greyish color. Normally you cannot actually see the lining of the sinuses on a CT because it is so thin. However in chronic rhinosinusitis, the lining will be thickened and the sinuses are outlined by grey soft tissue. They may even be totally full of polyps or mucous. If your physician is thinking that post-nasal drip may be contributing to your cough/chest congestion, then this is probably more of what they are looking for. As I said, I can;t read your physicians mind however, nor do I have your medical records, so if you have more specific questions, I would recommend that you ask you physician. I hope this was helpful.