I understood your concern about the scan! the scan for sinusitis
is not to look for a tumour which is actually a rare cause of headache but to assess and diagnose the severity of sinusitis. Although the scan can also very well rule out the tumour so you don't have to worry
As I mentioned before, a CT of the PNS is the baseline investigation in any headache currently
Dry air can very well increase any type of headache, both tension and sinus headache
especially if you are not very used to the same so I would advice you to try and avoid the exposure if possible.
is primarily used to relieve nose block which you have not mentioned and thus I will assume you do not have the same. If you do have nose block then even that can cause headache and this can be treated with a combination of nasal spray and medications but even this can be started after a baseline scan has been taken
In summary what I would suggest is that if you are having a headache which is bothering you at least once a week then it is better to get it evaluated by an ENT and a scan of the sinuses
will be the basic investigation for the same. Even if the headache is happening rarely, there is no harm in ruling out any serious cause which though are rare but will at least put your mind at ease.
hope this helps
Dr Sriram Nathan