Hearing loss after a head injury can occur after damage to certain parts of the brain, particularly the temporal or parietal lobes. It can also be a result of problems with the ear’s mechanisms itself.
To help you navigate the various hearing problems that can occur after brain injury, this article will cover everything from diagnosing hearing loss to treating it.
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Causes of Hearing Loss After Head Injury
There are two primary ways that hearing problems can arise after a head injury or concussion: neurological damage or mechanical damage.
For example, if an injury affects the mechanical process of hearing, the ear will not transmit sound to the brain at all. This is the most common cause of hearing loss after head injury.
On the other hand, if the parts of the brain that process hearing become damaged or disrupted, the brain can no longer process sound. Therefore, even if the ear itself functions properly, a patient can still experience hearing problems.
Ear Anatomy: Every Head Injury Affects the Ear Differently
To understand how hearing loss can occur after a head injury, it will help to understand how the ear works.
The ear comprises three sections: the outer ear, the middle ear, and the inner ear. Each section plays a part in the hearing process:
- The outer ear consists of the ear lobe and ear canal and protects the rest of the ear.
- The middle ear contains the tympanic membrane (eardrum), a thin layer of tissue that vibrates when sound waves strike it. This vibration transfers to three small bones (ossicle bones) in the middle ear which in turn transfer the vibration to the fluid in the inner ear.
- The inner ear contains fluid and a spiral structure called the cochlea. The cochlea senses the movement of the fluid and changes that movement into electrical impulses.
Finally, the cochlea sends electrical impulses to the auditory nerve, which transmits those signals to the brain. If a head injury interrupts any part of this process, hearing loss can result.
For example, the blow from the injury can rupture the eardrum, dislocate the ossicle bones, or sever the auditory nerve. All of this can lead to hearing problems after head injury.
Types of Hearing Loss After Head Injury
There are many types of hearing loss that can occur after a head injury, depending on which part of the ear or brain was damaged. We shall discuss each type in more detail in the sections below:
1. Conductive Hearing Loss
This type of hearing loss can occur when sound cannot transmit to the inner ear. Conductive hearing loss typically occurs after the ossicular chain is either damaged or dislodged. When this happens, sound can no longer travel through the bones to the cochlea.
Another, less common cause of conductive hearing loss is otosclerosis, which occurs when the three small bones in the ossicular chain fuse until they are so stiff that they can no longer vibrate. This once again makes it difficult for sound waves to travel.
For reasons researchers still don’t fully understand, brain injury can trigger abnormal bone growth throughout the body, including in the ear. Doctors call this heterotopic ossification. Therefore, if bone growth occurs inside the ear it can lead to hearing loss.
Finally, if the head injury occurred directly over the ear, the force of the impact could tear the tympanic membrane, which can cause blood to accumulate in the middle ear, a condition known as hemotympanum. This collection of blood will also cause conduction problems.
2. Labyrinthine “Concussion”
This occurs when an injury damages the structures of the inner ear. Blast-induced TBIs and airbag injuries are the most common causes of this type of hearing loss.
What separates labyrinthine concussions from other types of hearing loss is that this one occurs even if there are no visible bone fractures. Instead, the extreme force of the injury itself nearly destroys the cochlea.
3. Meniere’s Syndrome
Also known as hydrops. This disorder is caused by excess pressure in the inner ear chambers that contain fluid.
The pressure causes the fluid to shift, which can impair your hearing and your balance. It’s thought to occur as a result of bleeding in the inner ear.
There is no cure for Meniere’s syndrome. However, steroids and other medications can ease symptoms.
4. Sensorineural Hearing Loss
This is the most common type of hearing loss after head injury. It occurs when there is damage to either the hair-like cells in the inner ear that transfer sound or to the auditory nerve itself. While it is difficult to damage the auditory nerve, a temporal bone fracture can sometimes sever it.
This condition rarely causes complete hearing loss. It mainly affects the loudness or clarity of certain sounds.
It can also make a person more sensitive to sound, which may seem strange at first. Noises will seem so loud that it actually causes pain.
5. Auditory Verbal Agnosia (Pure Word Deafness)
Auditory verbal agnosia is not technically a “hearing disorder.” However, it’s worth mentioning because it’s sometimes referred to as “pure word deafness.” This condition is caused by damage to the regions of the brain that process language.
Auditory verbal agnosia is similar to aphasia, in which the person loses the ability to understand spoken words. However with aphasia, the individual typically has trouble with reading and writing as well.
Contrastingly, with verbal agnosia, reading and writing typically remain intact, but these patients may describe hearing spoken language as meaningless noise. However, they typically still retain their ability to recognize other sounds.
Again, this condition is not a hearing disorder. Instead, it’s a language disorder that is best diagnosed and treated by a Speech-Language Pathologist.
6. Central Hearing Loss
Finally, hearing loss can occur after direct damage to the parts of the brain that process sound, such as the temporal lobe. This type is known as central hearing loss.
It can also develop after damage to hearing pathways that reside in the brain stem. Because the brain stem is responsible for receiving and transferring signals, including sound, to the rest of the brain, damage to the brain stem can disrupt this process and thus lead to hearing loss.
However, this type of hearing loss is exceedingly rare after a head injury, because these hearing pathways are bilateral. In other words, the pathways are present on both sides of the brain and brain stem. To cause lasting damage, an injury must take out both sides of the hearing circuitry, which is difficult to do.
Therefore, central hearing loss is typically not the culprit after a person’s head injury, and doctors usually only diagnose it when all other causes have been eliminated. It is, however, more common after brain damage caused by radiation to eliminate cancer, known as radiation necrosis.
Diagnosing Hearing Loss After Head Injury
The best way to treat hearing loss after head injury is to first determine what type of hearing loss you have. To do this, you should make an appointment with a hearing specialist known as an audiologist.
There are several ways an audiologist might diagnose your hearing loss, including:
- Physical exam. This is where your doctor might look for any structural problems that are causing your hearing loss, such as bone fractures.
- Whisper test. With this test, your doctor will ask you to cover one ear at a time to see how well you respond to words at different volumes. Its accuracy is limited, but it can be a good first step.
- Tuning fork test. A tuning fork is a two-pronged, metal instrument that produces sound when struck. It can help your doctor find out where in your ear the damage lies.
- Audiometer test. This is the most thorough hearing test. Conducted by an audiologist, the test involves wearing earphones where sounds are directed to each ear. The audiologist repeats the tones at increasingly faint levels to find the quietest sound you can hear.
Once your doctor determines which type of hearing loss you have incurred, you can get started on treatment.
Furthermore, if your doctor does not detect any hearing issues, they may refer you to a Speech-Language Pathologist to diagnose any potential cognitive or language issues.
Treatment for Hearing Loss
Fortunately, there are a variety of treatments for hearing loss available to head injury patients, such as:
- Rehabilitation: For those with neurological hearing problems, some training programs such as auditory discrimination training and interhemispheric transfer training can activate your brain’s neuroplasticity and teach you how to process sounds again.
- Surgical procedures: to remove bone growth and repair your eardrum.
- Hearing aids: to boost your hearing. For people with profound hearing loss, high power hearing aids or bone-anchored hearing devices can be especially helpful.
- Cochlear implants: that bypass damaged parts of your inner ear and directly stimulate the auditory nerve. These are great for those who have seen only small improvements from a hearing aid.
Talk to your audiologist for more information on treatments for hearing loss. They often suggest non-invasive treatments such as rehabilitation or hearing aids before exploring surgical options.
Coping with Hearing Loss After Head Injury
Hearing loss is a potential complications of brain injury that has a variety of causes. For example, it could stem from damage to the ear itself, or it could stem from damage to the areas of the brain that process sound.
Based on the cause of the hearing loss, your doctor can recommend different treatments. For example, if the ear anatomy sustained damage, a hearing aid or surgery may be the best option; or if hearing loss stems from cognitive difficulties, rehabiltiation with a Speech-Language Pathologist could be the best route.
Get the conversation with your doctor started, and they will help guide you in the best direction for your unique needs.