One of the most important structures in your inner ear is the mastoid bone. Although it’s called a bone, the mastoid doesn’t have the typical structure associated with other bones in the human body. It’s made of air sacs and resembles a sponge, rather than being solid and rigid like most bones.

The mastoid must receive air from other parts of the ear, including the eustachian tube, to function properly. Your eustachian tube connects your middle ear to the back of your throat. If an infection develops in your middle ear and blocks your eustachian tube, it may subsequently lead to an infection in the mastoid bone. This serious infection is known as mastoid bone infection of the skull, or mastoiditis.

The most common cause of mastoiditis is a middle ear infection that has been left untreated. It can spread to your inner ear, invading the sacs of the mastoid bone, without treatment. This can cause the mastoid bone to begin to disintegrate.

Although the condition is most common in children, it can also occur in adults.

The symptoms of mastoiditis are similar to those of an ear infection. They include:

In some cases, mastoiditis may result in the development of a brain abscess or other complications involving your skull. The symptoms of these conditions include severe headaches and swelling behind your eyes. This swelling is known as papilledema.

If you have symptoms of an ear infection, your doctor will examine your ears and head to determine if the infection has spread to your mastoid bone.

The mastoid bone is located in your inner ear and may not be visible due to the infection. Your doctor may perform other tests to confirm the diagnosis. These include:

If the tests confirm a diagnosis of mastoiditis, your doctor may also perform a lumbar puncture, or spinal tap. This test will allow your doctor to determine if the infection is present in your spinal column.

Mastoiditis is a potentially life-threatening condition. Initial treatment for a severe infection may include hospitalization. You will receive antibiotic medication through a vein in your arm, or intravenously, while at the hospital. You will need to take oral antibiotics at home for several days after leaving the hospital.

If the infection doesn’t clear up after treatment with antibiotics, surgery may be necessary. Surgery may involve removing part of your mastoid bone to drain the infection. Doctors may also need to drain your middle ear of infected fluid to successfully treat the infection.

Treatment of mastoiditis can be difficult because the mastoid bone is located deep inside your ear. Serious health problems may result if treatment isn’t effective or if the infection isn’t treated before damaging the mastoid. These health problems include:

You can prevent mastoiditis by effectively treating all ear infections. Seek prompt medical attention and follow your doctor’s advice if you develop an ear infection. This may include taking oral antibiotics for 7 to 10 days.

Early intervention is necessary to prevent permanent damage if mastoiditis develops. Even if treatment is successful, the infection may return. Doctors will need to monitor those who develop mastoiditis to ensure that the infection doesn’t return or spread.