Understanding Conductive Hearing Loss
Conductive hearing loss occurs when sound waves encounter an obstruction or disruption in their journey from the outer or middle ear to the inner ear. This means that while the inner ear and auditory nerve might be functioning properly, sound cannot be efficiently transmitted to them. It is distinct from sensorineural hearing loss, which involves issues with the inner ear or auditory nerve itself.
Hearing begins when sound waves travel through the air into the outer ear, collected by the auricle or pinna. These waves then move through the ear canal to the eardrum, a membrane that vibrates in response to sound. These vibrations are transferred to three tiny bones in the middle ear: the malleus, incus, and stapes, known as the ossicles.
The ossicles amplify these sound vibrations before sending them to the cochlea, a fluid-filled structure in the inner ear. Inside the cochlea, hair cells convert these mechanical vibrations into electrical signals. These electrical signals are then transmitted via the auditory nerve to the brain, which interprets them as recognizable sounds. Conductive hearing loss disrupts this process, occurring when a problem in the outer or middle ear prevents sound vibrations from efficiently reaching the inner ear.
Common Causes
Many medical conditions or issues can impede sound conduction, leading to conductive hearing loss.
Outer Ear Causes
A common cause is the accumulation of excess earwax (cerumen impaction) or a foreign object blocking the ear canal, preventing sound waves from reaching the eardrum. Outer ear infections, known as otitis externa or “swimmer’s ear,” can also cause swelling and discharge that obstruct the ear canal.
Middle Ear Causes
Middle ear problems are frequent contributors to conductive hearing loss. Middle ear infections (otitis media) can fill the middle ear space with fluid, hindering the eardrum and ossicles from vibrating effectively. This fluid buildup, sometimes called “glue ear,” is a common cause of acquired hearing loss in children. A perforated eardrum, a hole in the tympanic membrane, prevents it from vibrating properly and transmitting sound. This can result from trauma, severe ear infections, or pressure changes.
Issues with the ossicles are another significant cause. Otosclerosis is a genetic condition where abnormal bone growth occurs in the middle ear, often around the stapes bone, causing it to fuse and become fixed. This prevents the stapes from vibrating and transmitting sound to the inner ear, leading to a progressive conductive hearing loss. Trauma can also lead to ossicle discontinuity, where the tiny bones become dislodged or fractured.
Cholesteatoma, a non-cancerous skin growth that develops behind the eardrum, can also cause conductive hearing loss. These growths can expand and erode the ossicles or other middle ear structures, impairing sound conduction and potentially leading to permanent damage if untreated. This condition often arises from chronic ear infections or eardrum retraction.
Recognizing the Symptoms
Individuals experiencing conductive hearing loss often notice muffled hearing, as if their ears are plugged or they are hearing sounds from underwater. This can make soft sounds or whispers particularly difficult to perceive. They might find themselves needing to increase the volume of televisions, radios, or other audio devices to hear adequately.
A feeling of fullness or pressure in the affected ear is a common symptom, which can sometimes be accompanied by pain or discomfort, especially if an infection is present. In some instances, there might be a discharge from the ear, indicating an infection or a perforated eardrum. While less common, severe middle ear issues can sometimes lead to dizziness or balance problems. Some individuals with conductive hearing loss report hearing better in noisy environments, as the background noise can make it easier to distinguish speech, unlike sensorineural hearing loss where noise typically worsens speech understanding.
Diagnosis and Treatment Approaches
Diagnosing conductive hearing loss involves a thorough evaluation by medical professionals. This begins with a physical examination of the ear using an otoscope, a device with a light and magnifying lens. This allows the doctor to visualize the ear canal and eardrum, checking for blockages like earwax, foreign objects, signs of infection, or a perforated eardrum.
Following the physical exam, several hearing tests are conducted. Pure-tone audiometry measures the softest sounds a person can hear at different pitches, while tympanometry assesses the eardrum’s movement and middle ear function. These tests help distinguish conductive hearing loss from other types and determine the severity. Imaging such as CT scans or MRIs may be necessary to identify underlying issues like tumors or structural damage not visible during a routine exam.
Treatment for conductive hearing loss is dependent on the underlying cause. Simple issues like earwax impaction can be resolved with professional earwax removal. Middle ear infections are often treated with antibiotics or ear drops. For conditions like a perforated eardrum that do not heal on their own, surgical procedures like tympanoplasty can repair the eardrum using a tissue graft.
Surgical interventions are common for ossicular problems. For otosclerosis, a stapedectomy may be performed, replacing the fixed stapes bone with a prosthesis to restore sound transmission. If surgery is not an option or does not fully resolve the hearing loss, hearing aids can be beneficial. These include traditional air-conduction hearing aids or bone-conduction hearing aids that transmit sound vibrations directly through the skull to the inner ear, bypassing the outer and middle ear entirely.