What Causes Fluid in the Middle Ear?

The middle ear is a space found behind the eardrum and before the inner ear. Middle ear fluid may be associated with a middle ear infection, a condition known as acute otitis media. Fluid in the middle ear can also occur without infection, in which case it is referred to as otitis media with effusion. Otitis media with effusion generally results from a problem with Eustachian tube drainage. The Eustachian tube is a passage that normally allows the middle ear space to drain into the throat, so if it becomes blocked this can lead to a buildup of fluid in the ears.

Otitis media with effusion is the more common condition associated with fluid in the middle ear. The middle ear effusion, or fluid, is almost always associated with an obstruction in the Eustachian tube. This blockage could be the result of allergy, injury, abnormal anatomical development, or infection. The fluid in the middle ear space is often mucus-like, but occasionally what is called serous otitis media occurs, where the fluid is clear and watery. Otitis media with effusion often follows an ear infection, with fluid in the middle ear remaining after the infection has resolved.

Children are more frequently affected by otitis media with effusion, as a child's Eustachian tubes are shorter and less sloping, meaning that the ear is aired and drained less effectively. Abnormal development of the Eustachian tubes in conditions such as Down syndrome or cleft palate can also increase the risk of otitis media. The resulting fluid in the middle ear causes symptoms such as loss of hearing and a feeling of fullness in the ear, but there is no fever or pain.

If otitis media with effusion persists and hearing loss is significant, surgery may be carried out. This is particularly important in children who are at risk of speech delay. In the most common procedure, tubes are inserted into the eardrum to drain the middle ear.

When fluid in the middle ear results from infection, this is usually caused by viruses or bacteria associated with existing illnesses such as colds and sore throats. During such a respiratory infection, the middle ear space, which is normally full of air, becomes filled with mucus. The mucus-filled cavity makes a suitable breeding ground for microbes, which move in to infect it.

Symptoms of ear pain, temporary hearing loss, fever, nausea, and vomiting may occur. Middle ear infections usually go away by themselves but painkillers may be needed for a few days. In some cases, the infection does not resolve and antibiotics may be required. Occasionally, the eardrum bursts, and the infected fluid in the middle ear is released, which can relieve the pain. The eardrum typically heals after the infection is gone.