Mastoiditis is the most common complication of acute otitis media (AOM), occurring at a rate of roughly 5.6 per 10,000 ear infection episodes. But it’s far from the only one. Infection from the middle ear can spread to surrounding bone, the inner ear, the facial nerve, and even the brain, producing a range of complications that fall into two categories: those that stay within the ear and temporal bone (intratemporal) and those that reach the brain (intracranial).
Intratemporal Complications
These complications develop when infection spreads from the middle ear into nearby structures within or around the temporal bone. They include mastoiditis, labyrinthitis, facial nerve paralysis, hearing loss, eardrum perforation, and petrositis. Mastoiditis is by far the most frequent, while the others are considerably rarer in the era of antibiotics.
Mastoiditis
The mastoid bone sits just behind the ear and contains small, air-filled pockets that connect directly to the middle ear. When an ear infection spreads into these spaces, the bony walls between the air cells begin to break down. In children under two, this typically shows up as irritability, fever, and ear pulling. Adults usually report severe ear pain, fever, and headache. The telltale physical sign is swelling, redness, warmth, and tenderness behind the ear, often pushing the outer ear forward and outward.
Mastoiditis is diagnosed primarily by physical exam. CT imaging can confirm it by showing fluid in the mastoid, breakdown of the bony walls between air cells, and disruption of the outer bone surface. In some cases a pocket of pus (subperiosteal abscess) forms beneath the tissue covering the bone. Treatment involves intravenous antibiotics and, when an abscess has formed, surgical drainage through a procedure called a cortical mastoidectomy. Some patients also get a small tube placed through the eardrum to drain the middle ear.
Labyrinthitis
The labyrinth is the fluid-filled structure of the inner ear responsible for both hearing and balance. When infection from the middle ear penetrates into it, the result is suppurative labyrinthitis. In a long-term study spanning 26 years, every patient with this complication developed ringing in the ears (tinnitus) and some degree of permanent hearing loss. Seventy-one percent experienced vertigo, and 57% lost hearing entirely in the affected ear. The remaining patients had moderate to severe mixed hearing loss. The vertigo eventually compensates over time, but the hearing damage is largely irreversible.
Facial Nerve Paralysis
The facial nerve runs through a bony canal in the middle ear on its way to the muscles of the face. In roughly 0.005% of acute ear infections, inflammation and swelling inside this canal compress the nerve enough to cause weakness or paralysis on one side of the face. Before antibiotics were widely available, the rate was much higher, around 0.5 to 0.7%. The main mechanism appears to be swelling that chokes off blood supply to the nerve, causing it to stop functioning. Bacterial toxins may also directly damage the nerve’s protective coating. When facial paralysis occurs alongside an ear infection, treatment typically combines antibiotics with surgical decompression of the nerve through the mastoid bone.
Intracranial Complications
These are the most dangerous outcomes of untreated or poorly controlled ear infections. They occur when infection crosses from the temporal bone into the spaces surrounding or within the brain.
Meningitis
Meningitis is the most common intracranial complication of otitis media. It develops when bacteria from the middle ear reach the membranes covering the brain and spinal cord. Warning signs include severe headache, high fever, neck stiffness, and altered consciousness. Because the ear and brain are separated by only thin bone in some areas, infection can spread quickly, making this a medical emergency.
Brain Abscess
Brain abscess is the second most common intracranial complication, though it remains rare overall, occurring in about 0.03 per 10,000 ear infection episodes. In pooled data from multiple studies, the most frequent symptoms were headache (82.5% of patients) and altered mental status (75%). Roughly half showed signs of meningeal irritation, and about a quarter experienced seizures. Treatment requires both high-dose intravenous antibiotics and surgical drainage, typically through a small opening in the skull.
Other Intracranial Complications
Less common but still serious intracranial complications include subdural empyema (a collection of pus between the brain’s protective layers), extradural abscess (pus between the skull and the outer brain lining), lateral sinus thrombosis (a blood clot in a major vein draining the brain), and otitic hydrocephalus (increased pressure inside the skull). Each of these requires urgent hospital-based treatment with antibiotics and often surgery.
How Often Complications Actually Happen
Serious complications of acute otitis media are rare. A large retrospective study published in the British Journal of General Practice found that mastoiditis occurred in about 5.6 per 10,000 AOM episodes, and brain abscess in roughly 0.03 per 10,000. The widespread use of antibiotics has dramatically reduced these numbers. Facial nerve paralysis, for instance, dropped from roughly 1 in 150 ear infections to about 1 in 20,000.
That said, complications tend to cluster in specific groups: very young children who can’t clearly communicate worsening symptoms, people with weakened immune systems, and anyone whose initial ear infection was inadequately treated or went undiagnosed.
Signs That an Ear Infection Is Getting Worse
Most ear infections resolve on their own or with a course of antibiotics. The red flags that suggest a complication is developing include swelling, redness, or tenderness behind the ear (pointing to mastoiditis), new dizziness or sudden hearing loss (suggesting labyrinthitis), facial drooping on the same side as the infected ear, and severe or worsening headache with confusion, lethargy, or high fever (raising concern for intracranial spread). In young children, watch for increasing irritability, refusal to eat, persistent vomiting, or unusual sleepiness that goes beyond what you’d expect from a simple ear infection.