Sinusitis is an inflammation of the mucosal lining of the paranasal sinuses usually related to viral, bacterial or fungal infections. Allergic sinusitis is ... common. Inflammatory response to allergens results in edema and thickening of the mucous membrane. Usually the margins of the edematous mucosa have a scalloped appearance, but in severe cases, mucous may completely fill a sinus, making it difficult to distinguish an allergic process from infectious sinusitis. Characteristically, all of the paranasal sinuses are affected and the adjacent nasal turbinates are swollen. Air-fluid levels and bone erosion are not features of uncomplicated allergic sinusitis; however, swollen mucosa in a poorly draining sinus is more susceptible to secondary bacterial infection.