Although small, the maxillary (behind the cheek) and ethmoid (between the eyes) sinuses are present at birth. The small anatomy combined with the enlarged tonsils and adenoids make for overall tight spaces and may predispose them to blockage and subsequent infections. Allergic rhinitis, either from foods or inhalants, can lead to further congestion worsening the problem. Once the sinus openings are blocked, the secretions just sit there and can become infected with bacteria.
The middle ear itself is essentially a sinus, that is an air containing space connected to the nose. Thus, when a child has rhinosinusitis they almost always get ear infections. These infections are especially common in early childhood. They are even more common when children suffer from allergies as well. Allergic inflammation can cause swelling of the adenoids in the nose and around the opening of the Eustachian tube (ear canal). This swelling has the potential to interfere with drainage of the middle ear. When bacterial sinusitis exists, infection can often travel up the Eustachian tube to infect the middle ear.
Tonsils and adenoids become more inflamed with allergies and infections. They not only tend to obstruct the upper airways but also have lots of crypts and crevices for viruses, bacteria and fungus to hide. Removal of tonsils and adenoids have repeatedly been shown to reduce the frequency and severity of pediatric upper respiratory infections including rhinosinusitis. In addition airway obstruction such as pediatric obstructive sleep apnea and upper airway resistance syndrome are most often cured by tonsillectomy and adenoidectomy.
There is really only one airway, from the tip of the nose to the base of the lungs. This “single airway theory” is even more evident in children. When they are sick they will have a stuffy nose with purulent rhinorhea, pus in the sinuses, fluid behind the ears, pharyngitis, and cough.