However, a eustachian tube that is blocked by swelling of its lining or plugged with mucus from a cold or for some other reason cannot open to ventilate the middle ear. The lack of ventilation may allow fluid from the tissue that lines the middle ear to accumulate. If the eustachian tube remains plugged, the fluid cannot drain and begins to collect in the normally air-filled middle ear. One more factor that makes children more susceptible to otitis media is that adenoids in children are larger than they are in adults. They are positioned in the back of the upper part of the throat near the eustachian tubes.
Enlarged adenoids can, because of their size, interfere with the eustachian tube opening.
In addition, adenoids may themselves become infected, and the infection may spread into the eustachian tubes. Bacteria reach the middle ear through the lining or the passageway of the eustachian tube and can then produce infection which causes swelling of the lining of the middle ear, blocking of the eustachian tube and the migration of white cells from the bloodstream to help fight the infection. In this process the white cells accumulate, often killing bacteria and dying themselves, leading to the formation of pus, a thick yellowish-white fluid in the middle ear. As the fluid increases, the child may have trouble hearing because the eardrum and middle ear bones are unable to move as freely as they should. As the infection worsens, many children also experience severe ear pain.