Understanding the Mastoid Bone
The mastoid is the bony prominence located just behind the ear. It contains a honeycomb of small air spaces called mastoid air cells. This hollow structure helps the middle ear regulate air pressure, and its thin walls are lined by the same kind of mucosa that lines the middle ear cavity. Because of this direct connection, any disease process that affects the middle ear can also involve the mastoid.
What Is Mastoiditis?
Mastoiditis is a bacterial infection of the mastoid air cells. The word refers to inflammation and infection of the mastoid process. Mastoiditis almost always begins as an extension of acute otitis media, an infection in the middle ear. When the infection is severe or is not treated effectively, pus and infected fluid can travel from the middle ear into the surrounding mastoid spaces, causing the bone to become infected and inflamed.
Mastoiditis can be classified as acute, subacute, or chronic. Acute mastoiditis usually develops rapidly after a recent middle ear infection. Chronic mastoiditis may cause persistent drainage and a gradual destruction of the mastoid bone.
The Relationship Between the Middle Ear, Sinus, and Mastoid
The middle ear is closely linked to several important structures. The mastoid air cells open directly into a large cavity within the mastoid bone called the mastoid antrum, which in turn connects with the middle ear space. Just behind the mastoid lies the sigmoid sinus, a major venous channel that drains blood from the brain. This sinus is separated from the mastoid air cells only by a thin layer of bone. An untreated mastoid infection can therefore erode bone and spread to the sigmoid sinus, leading to a serious condition called sigmoid sinus thrombosis. In this same region, infection can also reach other nearby venous sinuses, causing severe complications.
The term sinus can also apply to the paranasal sinuses located around the face. Viral or bacterial sinusitis can cause congestion and swelling that block the eustachian tube, leading to fluid accumulation in the middle ear. This fluid, in turn, can promote an ear infection that eventually spreads to the mastoid. For this reason, a history of a sinus infection may precede mastoiditis in some patients.
How Fluid and Pus Accumulate
The underlying problem in mastoiditis is trapped fluid. Viral infections, allergies, or sinus inflammation can irritate the lining of the eustachian tube, causing it to swell and close. When the eustachian tube is blocked, the middle ear cannot equalize pressure or drain normally. Fluid builds up behind the eardrum, and this stagnant fluid becomes a perfect place for bacteria to multiply.
As the infection progresses, the body sends white blood cells to fight the bacteria, producing pus. The pus and fluid cannot escape easily, so they fill the middle ear and then extend upward into the mastoid air cells. As pressure rises within the mastoid, the thin bony partitions separating the air cells may break down. This destruction of bone is a key feature of mastoiditis and distinguishes it from a simple ear infection.
Signs and Symptoms of Mastoiditis
The most common mastoiditis symptoms include:
- Persistent ear pain, often deep and throbbing
- Swelling, redness, and tenderness behind the ear over the mastoid area
- Ear discharge or drainage, especially if the eardrum ruptures
- Fever and general fatigue
- Hearing loss in the affected ear
- Protrusion of the outer ear, caused by swelling beneath it
A person with mastoiditis may feel ill and may complain of a full sensation in the ear. Infants and young children might be irritable, have trouble feeding, or pull at the affected ear. The symptoms usually appear one to two weeks after the onset of an untreated or undertreated middle ear infection.
Diagnosis of Mastoiditis
Doctors suspect mastoiditis when a patient shows typical symptoms alongside a history of a recent ear infection. During the physical exam, the area over the mastoid bone is examined for swelling, warmth, and tenderness. The eardrum is inspected for redness, bulging, or perforation.
Imaging tests are important for an accurate diagnosis. A computed tomography scan of the head and temporal bone can illustrate the mastoid air cells and reveal whether fluid or pus has destroyed bone tissue. Magnetic resonance imaging is particularly helpful when the infection is believed to have reached the sigmoid sinus or other intracranial structures. Routine blood tests can show elevated white blood cell counts, while a culture of the draining fluid can identify the exact bacteria causing the infection.
Complications of Mastoiditis
If mastoiditis is not treated quickly, serious complications can occur:
- Subperiosteal abscess: a collection of pus beneath the outer covering of the mastoid bone that causes visible swelling behind the ear.
- Sigmoid sinus thrombosis: a blood clot in the sigmoid sinus, which can obstruct the drainage of blood from the brain.
- Meningitis: the spread of bacteria to the protective layers covering the brain and spinal cord.
- A brain abscess: a pocket of pus inside the brain tissue.
- Facial nerve paralysis: damage to the nerve that controls facial muscles, as that nerve passes near the middle ear and mastoid.
- Permanent conductive or sensorineural hearing loss.
Certain complications of mastoiditis, such as involvement of the venous sinus or brain, are medical emergencies and require immediate attention.
Treatment for Mastoiditis
Treatment of mastoiditis usually starts with intravenous antibiotics directed against the most common bacterial causes. Because the condition prevents the infected fluid from draining properly, antibiotics alone are often insufficient if the fluid remains trapped. Medical therapy works best when the middle ear is drained at the same time.
A procedure called myringotomy is frequently performed. During this procedure, a small incision is made in the eardrum to release pus and infected fluid from the middle ear. A tube may be placed through the eardrum to keep the middle ear draining and ventilated while the infection clears.
For advanced mastoiditis that has caused bone erosion or a collection of pus, surgery becomes necessary. A mastoidectomy is a surgical procedure in which the infected air cells of the mastoid bone are removed. Depending on the location and severity of the disease, the surgeon may preserve or remove portions of the eardrum and middle ear bones. This surgery helps to eliminate the infection and to prevent further damage to nearby structures such as the sinus and the facial nerve.
Prevention and Outlook
Most cases of mastoiditis can be prevented by timely treatment of middle ear infections. Parents and caregivers should monitor young children for signs of persistent ear pain, fever, and hearing difficulty, and seek medical care when these symptoms appear.
With prompt antibiotic therapy and appropriate surgery when necessary, the outlook for mastoiditis is generally good. The infection resolves and hearing usually recovers fully if the condition is caught early. The risk of poor outcomes increases considerably if the brain, the sigmoid sinus, or other vital adjacent structures become involved. For this reason, mastoiditis is always considered a serious complication of a middle ear infection, and rapid medical evaluation is strongly advised whenever mastoid tenderness or ear swelling occurs.