Otitis media is an infection of the middle ear. It is very common in children but can also occur in adults. The chamber of the middle ear is connected to the outside through a hollow tube, the eustachian tube, that leads down to the throat. Air may enter or leave through this tube to keep the pressure in the middle ear equal to the outside pressure. This is important because of the pressure changes that occur when one changes altitude as in a tall building elevator or in an airplane.