Overview. Sinusitis is an inflammation of the mucosal lining of the paranasal sinuses. As the mucosa of the sinuses is continuous with that of the nose, rhinosinusitis is a more suitable term.Sinusitis can be subdivided into acute, subacute, and chronic disease. Acute sinusitis is defined as disease lasting less than 1 month.verview. Sinusitis is an inflammation of the mucosal lining of the paranasal sinuses. As the mucosa of the sinuses is continuous with that of the nose, rhinosinusitis is a more suitable term.