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Conductive Hearing Loss

Posted by Rosie Dooley, BSc (Hons) Audiology, RHAD on March 30, 2020

Conductive Hearing Loss

Conductive Hearing Loss

Have you been told that you have a conductive hearing loss? Let’s unpack what that might mean. The word conductive is used to describe hearing losses which are caused by issues relating to the first few structures and mechanisms of the hearing pathway. These structures and mechanisms are responsible for conducting the sound vibrations to the cochlear, the hearing organ. The structures include:

  • The pinna (outer visible ear)
  • The ear canal
  • The tympanic membrane (eardrum)
  • The middle ear space and eustachian tube
  • The ossicles (middle ear bones)

If there is a blockage or damage at any point along this pathway, it can result in reduced sound levels reaching the cochlear and therefore a conductive hearing loss. Individuals who have both conductive and sensorineural elements to their hearing loss are described as having a mixed hearing loss.

A conductive hearing loss can be seen on an audiogram (hearing chart) when there is a gap between the air conduction and bone conduction hearing thresholds. An audiologist will carry out careful masking of one side at a time if necessary to gain the “true” level of your hearing. A tympanometry test will tell an audiologist how well the eardrum is functioning and assist in gaining a bigger picture of what might be causing a conductive hearing loss. 

 

Common Causes and their treatment options

The treatment choice for a conductive hearing loss is dependent on its cause and which element of the conductive pathway has been interrupted so we will discuss both the cause and treatment together. 

Glue ear (otitis media with effusion)

This is a condition very common in children, though it can present rarely in adults too. Fluid builds up in the middle ear space behind the eardrum inhibits its usual ability to move, dampening the sound vibrations it conducts to the rest of the hearing pathway. Usually triggered by an ear infection, glue ear can come and go and cause fluctuations of hearing, pain, tinnitus and the feeling of aural fullness. Children usually grow out of the condition, as their head structure changes in shape, allowing for more efficient draining of the middle ear space. For children or adults with recurrent glue ear, management by ENT can result in grommets, adenoidectomy and/or hearing aid management. Grommets are small tubes that are inserted through the eardrum to help equalise the pressure across it and allow it to carry out its vital role unhindered. 

A perforated eardrum 

This can cause varying levels of conductive hearing loss depending on the size and position of the perforation. Rupture of the eardrum can be caused by severe pressure differences across the tympanic membrane (barotrauma) e.g. the pressure changes associated with flying or scuba diving. An acute middle ear infection can sometimes cause enough pressure to build behind the eardrum to rupture it too. Sadly, another common cause of perforations is when foreign objects are inserted into the ear canal to clear wax e.g. cotton bud or hair grip. When the membrane is broken in any way, it cannot move as it usually does, therefore, delivering altered vibration to the ossicles. Perforated eardrums generally heal by themselves though severe or total perforations can need surgical repair (tympanoplasty). When healed, the scar tissue that remains is thicker than the original tissue and because of this, some form of conductive hearing loss can remain even though the eardrum is intact. For irreparable perforations or lingering hearing loss after a repair, different types of hearing aid can help manage the difficulties associated with these hearing losses. 

Atresia and Microtia

These are the terms used to describe malformations of a baby’s outer ear and canal developed during pregnancy. The level of hearing loss caused by these malformations will entirely depend on their severity. Microtia refers to any form and severity of differences of the pinna and ear canal, whereas Atresia is used to describe the absence of the ear canal altogether. These malformations can occur alone or with other craniofacial abnormalities or as part of a syndrome e.g. Goldenhaar or Treacher-Collins. Surgical reconstruction can correct the features of the outer ear and therefore improve hearing outcomes. Conventional hearing aids are often not appropriate for individuals with Atresia or Microtia due to the absence of the usual features on which they are worn and into which the sound is delivered. Bone conduction hearing aids can often be successfully worn on a soft band for young children. Bone anchored hearing devices and other implants are other treatment choices.

Otosclerosis

This is a disease of the three middle ear bones – the malleus, incus and stapes. Together they are called the ossicles and they transmit vibrations from the eardrum to the oval window of the cochlear. In patients with otosclerosis, they have become sclerotic and brittle, reducing their ability to vibrate together in their linked chain. Though thoroughly researched, the aetiology of otosclerosis is not yet confirmed, though both hormonal and genetic factors are assumed. Treatment options will vary depending on how progressed the condition is at diagnosis. Symptoms of mild otosclerosis can be managed with hearing aid however once the condition has worsened a stapedectomy or stapedotomy might be considered where surgery is performed to remove or modify the brittle bone and insert a prosthetic stapes bone.

Surgery

can be carried out to remove skin growths or diseased mastoid cells (mastoidectomy), caused by chronic ear infections, can result in conductive hearing loss because the acoustic properties of the ear canal are altered, sometimes radically. Mastoidectomy surgery is much less common now as ear infections are often successfully treated with antibiotics, reducing the likelihood of repercussions for the mastoid and potential skin growths. 

Amplification to manage conductive hearing loss

Hearing aids are extremely important in the management of conductive hearing loss in adults and children. Where surgery is not appropriate or wanted, traditional hearing aids provide users with the crucial amplification they need to be able to access the sounds needed for speech discrimination. As conductive hearing losses can often fluctuate, especially with glue ear in children, regular audiology contact is vital to ensure full hearing potential. For adults, the generous volume control is recommended or a hearing aid app is a handy tool if the hearing undergoes large fluctuation. Though conventional hearing aids are very efficient, bone conduction hearing aids may give better results for those with a conductive hearing loss. This is because they bypass all of the conductive elements of the hearing pathway by sending sound vibrations via the bone directly to the cochlea. In the same way, bone-anchored hearing devices utilise the bone to directly stimulate the cochlear, though surgery is required to place the titanium abutment into the skull which the device then attaches to. 

If you have a conductive hearing loss, we can talk to you more about how hearing aids can benefit you. Do not hesitate to book an appointment at any of our Hear4U centres, we are here to help. 

 

Refferences:

Picture 1 credit:https://www.nationalhearingtest.org/wordpress/?p=604#!prettyPhoto

Picture 2 credit: Osborne Head and Neck Institute, ℅ https://eardoctorla.com/stapedectomy/

https://www.guysandstthomas.nhs.uk/our-services/hearing-implant-centre/microtia-clinic.aspx

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