Most definitive diagnostic of sinusitis is:
Nasal endoscopy is the most definitive diagnostic of sinusitis. It is done to see the various sinus meatuses, mucopus or any other pathology. If mucopus is seen in the meatus, it is confirmatory of sinusitis.
X-ray PNS
Proof puncture
Nasal endoscopy
Transillumination test
Paranasal Sinuses