Conditions: Mastoiditis
Mastoiditis is an infection of the mastoid bone behind the ear, almost always arising as a complication of a middle ear infection. It is uncommon today but important to recognize because, left untreated, it can spread to nearby structures and become serious. It occurs most often in young children.
The Mastoid Bone and How It Connects to the Ear
The mastoid is the bony bump that can be felt just behind the earlobe. It is part of the temporal bone of the skull. Rather than being solid, much of the mastoid is honeycombed with tiny air-filled spaces called the mastoid air cells.
These air cells open directly into the middle ear (the small, air-filled chamber behind the eardrum) through a narrow passage known as the aditus ad antrum. Because this connection has no valve, whatever happens in the middle ear tends to affect the mastoid as well. For this reason, nearly every ordinary middle ear infection involves some degree of inflammation in the mastoid lining, usually without causing true mastoiditis.
What Mastoiditis Is
Mastoiditis is a bacterial infection in which pus builds up within the mastoid air cells. It typically develops when swelling and inflammation block the narrow passage connecting the mastoid to the middle ear, trapping infected fluid that cannot drain. If the infection continues, it can begin to destroy the thin walls of bone separating the air cells, merging them into larger pockets of pus, a more advanced stage called coalescent mastoiditis. From there, infection can erode through bone and reach the structures around the mastoid.
Acute mastoiditis comes on over days to a few weeks and involves active, pus-producing infection with the swelling and redness described below. Chronic mastoiditis lasts longer, generally more than a month, and tends to show up as persistent ear drainage and gradual hearing loss rather than dramatic outward swelling.
An important point of confusion is that scans of the head or sinuses often show fluid or "opacification" in the mastoid air cells in people who simply have an ordinary ear infection or a cold. This incidental finding, without erosion of the bone or the outward signs of infection, is not the same as mastoiditis and usually needs no specific treatment. True mastoiditis is a clinical illness, not just a finding on a picture.
Who Gets It and Why
Mastoiditis is mainly a disease of children, with the highest rates in those under about two to three years of age. Young children are especially prone to it because their mastoid anatomy and the narrow connecting passage make it easier for infected fluid to become trapped, and because ear infections are so common at this age. Limited ability to describe symptoms in very young children can also delay recognition.
The infection is usually caused by the same bacteria responsible for ordinary ear infections, most commonly a type of pneumococcus, along with certain streptococci and staphylococci. Although antibiotics and childhood vaccination have made mastoiditis far less common than it once was, it has not disappeared, and some regions have reported modest increases in recent years.
Symptoms and Signs
The most recognizable feature of mastoiditis is a change behind the ear. The area over the mastoid bone often becomes red, swollen, warm, and tender to the touch. As the swelling grows, it can push the outer ear (the pinna) forward and outward, so that the ear appears to stick out compared with the other side. The normal crease behind the ear may be lost.
Other common features include ear pain, fever, and sometimes drainage from the ear. Because mastoiditis usually follows a middle ear infection, these behind-the-ear signs often appear a week or two after a bout of ear pain. The classic signs are not present in every case, and they may be muted in children who have already been taking antibiotics.
How It Is Diagnosed
Mastoiditis is primarily a clinical diagnosis, meaning it is recognized from the history and physical examination, particularly the tenderness, redness, and swelling behind the ear together with a protruding pinna, often alongside signs of a middle ear infection seen when the eardrum is examined.
When the picture is severe, unclear, or there is concern that the infection has spread, imaging is used. A CT scan with contrast is the most common test and can show the fluid-filled air cells and breakdown of the bony walls, as well as many complications. MRI is considered especially sensitive for detecting spread toward the brain, the inner ear, or the large veins near the mastoid, and is often chosen when there are neurological concerns. Samples of ear fluid or pus may be cultured in the laboratory to identify the exact bacteria and guide the choice of antibiotic, and blood tests are sometimes used to gauge the severity of infection.
Possible Complications
Because the mastoid sits close to many delicate structures, untreated or aggressive mastoiditis can spread beyond the bone. Complications outside the skull include a subperiosteal abscess (a collection of pus just under the covering of the bone behind the ear, the most common complication), weakness of the facial nerve causing drooping of one side of the face, hearing loss, and labyrinthitis (infection of the balance and hearing organ of the inner ear, which can cause dizziness).
More serious complications occur when infection reaches inside the skull. These include clotting of a large vein that drains blood from the brain (venous sinus thrombosis), meningitis (infection of the membranes around the brain), and brain abscess. Intracranial complications are uncommon but potentially life-threatening, and they can sometimes appear gradually with headache, vomiting, drowsiness, or other neurological symptoms. The possibility of these complications is the main reason mastoiditis is treated promptly and taken seriously. Treatment generally involves intravenous antibiotics, often combined with a small procedure to drain the middle ear, with surgery on the mastoid itself reserved for more severe or complicated cases.