Sound Waves

Figure 1: The pathway from newborn hearing screening

Unilateral hearing loss, as the name suggests, refers to hearing loss in one ear while the other ear has typical hearing. The degree of hearing loss in the affected ear can range from mild to profound, where the child hears very little with that ear. UHL is relatively common, affecting approximately one in 1,000 children at birth. Furthermore, a child can acquire unilateral hearing loss at any time after birth.

The impact on your child

The good news is that your baby can hear! With appropriate monitoring and support, they will experience a similar childhood to their typically-hearing peers. UHL presents with difficulties hearing sounds and speech on the affected side. This has implications for listening to speech in noise and locating the sources of sound. However, technology, such as hearing aids, can enhance your child’s ability to hear and listen.

How common is unilateral hearing loss?

The numbers vary according to the definition of unilateral hearing loss used by researchers, but as a general guide:

• 8/1000 babies are born with unilateral hearing loss.
• Around 30% of babies identified with hearing loss through newborn hearing screening have unilateral hearing loss.
• The incidence of unilateral hearing loss increases in school-aged children, with 3-6% identified with UHL.
• Approximately 7.2% of adults have UHL—most of these are in the mild range.

Figure 2: Degree of hearing loss at diagnosis of 91 Australian children with congenital UHL¹

Challenges and considerations

While most children with UHL achieve typical developmental milestones, there are some considerations to keep in mind:

• Speech in noise: Understanding speech in noisy settings is often difficult.
• Sound localisation: Children with UHL find it difficult to know where sounds are coming from.
• Fatigue: Children with UHL can become more fatigued than typically-hearing children, even when the affected ear is aided².
• Glue ear: Some children experience persistent glue ear (otitis media), which occurs when fluid builds up in the middle ear, leading to temporary hearing difficulties. If the glue ear is present in both ears or the unaffected ear, it can result in bilateral hearing loss while the glue ear persists.
• Deteriorating hearing: A small percentage of children with UHL can lose the hearing in their unaffected ear. Any deterioration in hearing levels in one or both ears usually occurs before four years of age³.

One of the first questions parents ask when learning about their child’s hearing loss is ‘Why?’ While finding the cause for the hearing loss may not change its management, it can provide comfort and clarity for many parents. Understanding the underlying reason can help families feel more informed and prepared as they consider their child’s care.

Structural abnormalities of the temporal bone
The temporal bone houses important structures related to hearing and balance, such as the inner ear. Examples of structural abnormalities in the temporal bone that can lead to hearing loss include:

• Cochlear Malformations: Abnormalities in the structure of the cochlea, which is a part of the inner ear responsible for hearing.
• Vestibular Abnormalities: Issues with the vestibular system, which is responsible for balance. This can impact both hearing and coordination.These abnormalities can be present at birth (congenital) or develop later in life due to injury, infection, or other factors. Structural abnormalities can contribute to various types and degrees of hearing loss.

Congenital cytomegalovirus infection
Congenital cytomegalovirus (CMV) is a common virus, and most people may not even know they have it. However, if a pregnant woman gets infected with CMV, there is a risk of passing it to the developing foetus. Congenital CMV can lead to serious health issues for the newborn, including hearing loss, developmental delays, and vision problems.

Genetic factors
Congenital hearing loss may be due to genetic factors through genes inherited from both parents. Genes contain instructions for the development and functioning of the body, including the structures involved in hearing. Genetic causes are less common in unilateral hearing loss than bilateral hearing loss.

Despite an improved understanding of the causes of unilateral hearing loss, in around a quarter to a third of children with UHL, no cause will be identified⁴.

Figure 3: Distribution of causes of unilateral sensorineural hearing loss in children^{4
Note: CMV is included in acquired hearing loss in this chart.}

Acquired hearing loss
Children can develop hearing loss at any time after birth. This can be due to an illness such as meningitis, medications, recurrent severe ear infections or injury.

Medical tests are available to determine the possible cause of your child’s hearing loss. Medical tests can also help families understand what to expect in the future and, sometimes, how to minimise worsening hearing loss.

The Childhood Hearing Australasian Medical Professionals (CHAMP) Network⁶ suggests three tests for babies identified with hearing loss:

1. MRI: Magnetic Resonance Imaging
   An MRI, or Magnetic Resonance Imaging, takes detailed pictures inside the body. An MRI of the head is recommended for babies with hearing loss to check for any issues in the brain or inner ear that might be causing the hearing loss. An MRI is particularly helpful for children with UHL with the high prevalence of structural abnormalities of the temporal bone in this group. An MRI is a safe and painless procedure. It is preferable to have an MRI done when the baby is younger than 4 months, as it can be done without sedation or anaesthesia. Before the MRI, the baby is typically fed and settled to sleep, in a process called ‘feed and wrap’. The availability of this option may depend on where you live.If your child is older than 4 months, a general anaesthetic may be needed to help them stay still during the MRI. A doctor can assess whether an MRI can be postponed until your child is old enough to lie still without an anaesthetic, which is usually around school age.
2. CMV: Cytomegalovirus testing
   For babies younger than 21 days, a saliva swab from your baby’s mouth or a urine test can be taken to test for CMV. For babies older than 21 days, your doctor may request access to your child’s heel-prick card (blood sample taken soon after birth) to test for CMV.
3. Genetic testing
   Genetic testing will check for any variations or changes in genes that could cause hearing loss. There are different types of genetic tests – some are government-funded. Talk to a genetic counsellor or doctor before considering genetic testing.

For more information

• Medical assessments for children with permanent hearing loss

People with UHL experience difficulties localising sounds and hearing in noisy environments. Our ears are strategically positioned on both sides of our head to enable our brain to detect subtle sound variations between our two ears, which helps with sound localisation and listening in noisy environments.

While unilateral hearing loss presents its own set of challenges, having one typical-hearing ear provides distinct advantages over bilateral hearing loss (BHL). These advantages can make a significant difference in the child’s ability to hear, communicate, and engage in daily activities.

*In situations where children have no listening devices

There are three basic things children need to learn their first spoken language:

• They need to interact with people who speak the language fluently.
• They need to be able to hear all the words and sounds of the language.
• They need to hear how well they are saying the words, so they can learn to improve.

For hearing children of hearing parents, these three things happen naturally as they learn to talk.  However, for a deaf child of hearing parents, the second and third requirements are not met – they do not have enough access to sound to hear the words and sounds and may not get enough feedback to their own speech without appropriate listening devices.

Unlike deaf children, children with unilateral hearing loss do have access to sound, and their needs can be met when the environment is quiet, or when someone speaks on the side where the child can hear. Families can create an environment where their child with UHL has the three basic requirements for developing spoken language⁵.

Unilateral and bilateral hearing loss can have educational, social and emotional impacts on children. However, this is very variable in children with UHL.