How can sinusitis be diagnosed?

By History. Most sinus infections are diagnosed by the history. Typically, if you have a "cold" that lasts for more than 7-10 days... It's most likely a sinus infection. If you see your ENT he can use a camera to look in your nose to confirm the diagnosis. A ct scan can also be helpful as well.
A good history. Often the diagnosis of sinusitis can be reached by getting a detailed history from the patient. Sometimes when the history is not clear an ear, nose, & throat doctor can perform a nasal endoscopy to get a better idea. If the diagnoses is still not clear, then a ct scan can be done.