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The diagnosis of sinusitis is based on the symptoms and their duration along with signs of disease identified by endoscopic and/or radiologic criteria. Sinusitis is classified into acute sinusitis, subacute sinusitis, and chronic sinusitis. In acute sinusitis, symptoms last for less than four weeks, and in subacute sinusitis, they last between 4 and 12 weeks. In chronic sinusitis, symptoms must be present for at least 12 weeks. In the initial evaluation of sinusitis an otolaryngologist, also known as an ear, nose and throat (ENT) doctor, may confirm sinusitis using nasal endoscopy. Diagnostic imaging is not usually needed in the acute stage unless complications are suspected. In chronic cases, confirmatory testing is recommended by use of computed tomography.