what is a sinus infection
Sinusitis (or rhinosinusitis) is defined as an inflammation of the mucous membrane that lines the paranasal sinuses and is classified chronologically into several categories: 1  Acute rhinosinusitis â A new infection that may last up to four weeks and can be subdivided symptomatically into severe and non-severe.inusitis (or rhinosinusitis) is defined as an inflammation of the mucous membrane that lines the paranasal sinuses and is classified chronologically into several categories: 1  Acute rhinosinusitis â A new infection that may last up to four weeks and can be subdivided symptomatically into severe and non-severe.