Hearing Loss and Deafness – Causes of Hearing Loss (Unilateral) and Modern Treatment of Anacusis

Deafness refers to the complete loss of hearing in both ears. In addition, medicine distinguishes between absolute deafness and practical deafness.

In cases of practical deafness, those affected can still perceive individual sounds or noises. In absolute deafness, however, there is no longer any auditory perception at all.

Deafness can be congenital or acquired later in life due to illness. Congenital deafness—that is, deafness occurring before the development of language skills—is referred to as prelingual deafness. Severe congenital hearing impairments can be hereditary or result from factors during pregnancy.

Hereditary deafness is characterized by the fact that parts of the auditory system, such as

• the middle ear,
• the inner ear, or
• the auditory nerve

are not formed, or are only partially formed. Children of deaf parents may therefore also be born deaf.

Many cases of hereditary hearing loss are associated with damage to other organs,

• such as the eyes,
• kidneys,
• bones,
• skin, and others

. Well-known syndromes associated with deafness include, among others,

• Usher syndrome, which involves a restricted field of vision, or
• Waardenburg syndrome, which involves pigment abnormalities in the skin, hair, or eyes, as well as
• Alport syndrome,
• Jervell-Lange-Nielsen syndrome,
• Waardenburg syndrome,
• Cockayne syndrome, and
• Pendred syndrome.

Some cases of hearing loss develop in utero, that is, before birth during pregnancy. Severe cases of hearing loss that develop in utero are usually caused by

• infections with viruses such as rubella, cytomegalovirus, or toxoplasmosis, or
• bacteria such as syphilis

Toxic damage can result from

• medications such as certain antibiotics, diuretics, or cytostatic drugs, or
• toxins such as alcohol or nicotine

.

Hearing loss can also occur perinatally, that is, during childbirth. Risk factors include

• premature birth,
• kernicterus, or
• respiratory arrest with oxygen deprivation.

Postnatal (after birth) acquired hearing loss can result from infectious brain diseases such as meningitis or encephalitis.

• infections such as mumps, shingles, measles, and tuberculosis, as well as chronic middle ear infections or
• toxic damage,
• severe accidents involving skull fractures—particularly fractures of the temporal bone—

can cause hearing loss.

The internal structures of the ear © Henrie | AdobeStock

If hearing loss occurs only after a person has learned to speak, it is referred to as postlingual hearing loss. Causes in such cases include

• brain tumors,
• brain diseases such as multiple sclerosis,
• severe traumatic brain injuries,
• acoustic accidents such as explosions or barotrauma,
• severe infections, e.g., with herpes viruses,
• cytotoxic agents and medications such as chemotherapy drugs or loop diuretics, as well as
• antibiotics such as gentamicin.

In rare cases, psychogenic hearing loss occurs in the form of a dissociative hearing disorder. Furthermore, genetically inherited predispositions to hearing loss are also known in this context.

Deaf individuals cannot perceive any sounds or noises. Communication with the hearing and speaking environment is therefore difficult in cases of unilateral deafness. In cases of bilateral deafness, those affected cannot learn language and speech, or can do so only with great difficulty.

Deafness significantly impairs social interactions and career opportunities and often leads to personality development disorders.

The first babbling period begins in deaf children as well, from the 6th week to the 6th month. Without appropriate newborn hearing screening programs, the average age at which deafness is detected is more than two years. 

In cases of congenital hearing loss, as mentioned above, damage to other organs—such as

• the eyes,
• bones,
• kidneys,
• skin

may occur.

Deafness is diagnosed through specialized hearing tests. If deafness is suspected, the first step is a medical history interview with the patient or their parents. The doctor then performs an examination of the ear, nose, and throat.

The actual hearing tests include, for example,

• a tone audiogram, which tests sounds at various frequencies, or
• the Freiburg speech audiogram, which tests numbers and words.

To determine the location of the hearing loss, the following additional tests are typically performed:

• Measurement of otoacoustic emissions (OAE) to objectively detect damage to the outer hair cells in the inner ear
• objective hearing tests such as BERA (Brainstem Evoked Response Audiometry) or CERA (Cortical Evoked Response Audiometry) to diagnose damage between the cochlea and the brain regions responsible for processing sound
• Balance testing to rule out involvement of the vestibular system
• Computed tomography (CT) and/or magnetic resonance imaging (MRI) to detect anatomical changes in the area of the cochlea or the auditory nerve
• Promontory test to assess the functionality of the auditory nerve. For this test, a small electrode is placed through the eardrum directly onto the bone (promontory), and electrical impulses are used in place of sounds. The patient perceives these impulses as sounds.

Today, the standard tests for newborns and patients who are unwilling or unable to cooperate are OAE and BERA measurements, collectively known as newborn hearing screening.

In newborn screening, the newborn’s hearing is tested one or two days after birth. This allows for the early detection of any hearing impairments, which can then be treated.

Without appropriate therapy, deafness will not improve. Treatment options include both conservative and surgical measures.

The goal of treatment for deafness is to improve patients’ abilities in everyday life.

Causal Therapy and Surgery for Deafness

In cases of acute hearing loss, causal therapy may be an option. This primarily refers to conservative treatments

• with antibiotics,
• infusions (e.g., with cortisone), as well as
• measures to improve blood circulation.

If these treatments are ineffective, surgery may also be an option. During the procedure, performed under either local or general anesthesia, the middle ear is opened, and the anatomical structures within it are examined to assess their function.

Hearing Aids for Hearing Loss

If hearing does not improve, hearing aids are used. These hearing aids can be

• in the ear canal—and thus largely out of sight—or
• behind the ear

. Their function is to amplify incoming sounds and noises. People with hearing loss can adjust the amplifier individually to suit specific situations.

In rare cases, specially adapted hearing aids, such as CROS (Contralateral Routing of Sound) hearing aids, are used if

• some residual hearing is still present or
• deafness is limited to one ear.

CROS hearing aids can transmit sound from the affected side to the healthy side via a sound conduit. In this way, they mimic directional hearing.

Cochlear Implant for Deafness

If the anatomical structures are intact, a cochlear implant may also be an option. In cases of severe bilateral hearing loss or complete deafness, the implant can replace hearing function.

The cochlear implant consists of an internal and an external component. The internal component, which contains an electrode, is implanted directly into the cochlea. The external component is a microphone with a speech processor that is worn on the outside of the head, usually behind the ear.

Cochlear implants should be implanted as early as possible so that children can develop normal speech abilities © satura_ | AdobeStock

The implant is powered by electromechanical induction through the scalp. The internal implant therefore does not require regular battery changes.

The external microphone picks up sound waves, which the speech processor converts into electrical impulses. These impulses travel via the electrodes in the cochlea directly to the auditory nerve, which transmits the sound waves to the brain

The following criteria must be met for a cochlear implant:

• Children with unilateral or bilateral hearing loss that occurred pre-, peri-, or postnatally, with existing auditory nerve conduction
• Adolescents and adults with unilateral or bilateral deafness or profound hearing loss
• A positive result on the promontorial test, if possible
• Sufficient anatomical conditions (the cochlea or cochlear turns must be present)
• No serious underlying medical conditions or recurrent inflammation
• Demonstrated ability and willingness to learn in adults
• Guarantee of appropriate rehabilitation
• An intact and supportive social environment

Brainstem implant for deafness

If there is damage to the auditory nerves, a brainstem implant may be an option. In this procedure, electrodes directly stimulate the auditory nerve nuclei in the brain.

The implantation is performed as a neurosurgical procedure. Intensive rehabilitation at specialized centers is also required.

Alternative Communication Methods for Deafness

If treatment is not possible, patients with bilateral hearing loss must learn to live with their condition. However, this does not mean they have to completely give up on communication. Lip-reading and sign language help those affected communicate with the world around them.

Deaf people can communicate effectively using sign language and lip-reading © fizkes | AdobeStock

Especially in cases of congenital hearing loss or severe hearing impairment, early diagnosis and treatment have a positive impact on language development.

Follow-up rehabilitation is crucial to the success of a cochlear implant. This process is very comprehensive and takes place in specialized centers, often referred to as CICs (Cochlear Implant Centers). Here, patients must “re-learn” how to hear and speak. Only consistent practice and the right motivation lead to good results.

For children who have been deaf since birth, the implants are inserted before they turn one year old. Early intervention in the form of speech and language therapy is a priority in these cases. This allows them to acquire language and speech skills just like healthy children. In many cases, these children can then attend a mainstream school.

For adults who have become deaf, cochlear implantation is usually promising if

• the hearing loss has not persisted for too long,
• cognitive abilities are present, and
• they are motivated to relearn how to hear.

Health insurance companies cover the costs of the surgery and follow-up care.

What is deafness?
Deafness refers to the complete loss of hearing and is medically known as anacusis. Those affected can barely perceive sounds or are unable to perceive them at all. Deafness can be congenital or acquired.

What are the possible causes of deafness?
Causes of deafness include infection, genetic deafness, injuries to the auditory nerve, or damage to the outer hair cells in the inner ear. Certain medications or conditions, such as rubella during pregnancy, can also cause deafness. In some cases, deafness develops shortly after birth.

What is the difference between hearing impairment and deafness?
Hearing impairment and deafness differ in the degree of hearing loss. While people with hearing impairment can still hear to a limited extent, deafness involves an almost complete loss of hearing. Especially in cases of unilateral deafness, the other ear often remains functional.

How is deafness diagnosed?
If deafness is suspected, objective hearing tests, audiometric tests, MRI, and CT scans are performed. Measuring otoacoustic emissions assesses the outer hair cells of the inner ear and the functionality of the auditory nerve. In addition, an examination of the auditory nerve or the cochlear portion of the vestibulocochlear nerve is often performed.

What treatment options are available?
Treatment depends on the type and cause of the condition. Hearing aids, inner-ear prostheses, or cochlear implants can improve hearing. Early intervention is particularly important in cases of prelingual deafness or unilateral or bilateral deafness to support normal language acquisition.