The common route of drainage and ventilation of the frontal, anterior ethmoidal, and maxillary sinuses are through the osteomeatal complex. This is the most frequent site for obstruction of the mucociliary blanket, and is best visualized by endoscopy or via a CT scan. Plain films of the sinuses do no define the area well. The process of development of some forms of rhinosinusitis is as follows:

• An inciting cause such as direct irritants, viral infection, allergic edema, polyps or other masses damages the cilia and epithelial lining, or interferes with mucous flow.
• Inflammation ensues, leading to an increase in secretions, but a decreased rate of mucociliary clearance.
• Stasis of the secretions causes inflammation, swelling and ostial obstruction.
• With the ostium closed, the secretion thicken and the pH decreases.
• A secondary bacterial infection develops and becomes a “closed infection” within the affected sinus cavities.
• Recurrent/chronic bacterial infection of 3 months or longer leads to scarring and hypertrophy of the mucosa, and irreversible damage to the sinus lining.