Enlarged Vestibular Aqueduct Syndrome

What Is Enlarged Vestibular Aqueduct Syndrome?

The vestibular aqueduct is a narrow tube filled with fluid in the inner ear. It is located in the temporal bone of the skull behind the ear and connects the inner ear to a balloon-shaped structure called the endolymphatic sac. The inner ear consists of the cochlea and vestibular apparatus, which control hearing and balance respectively. These structures send signals to the brain to help process sound and support the body’s sense of balance. Abnormalities in these structures may contribute to hearing loss, balance problems or both.

The vestibular aqueduct is considered enlarged if it larger than 1 millimeter, about the size of the head of a pin. Children with EVA may also have an enlarged endolymphatic duct (which runs through the vestibular aqueduct) and endolymphatic sac.

Causes of EVA

The exact cause of EVA is unknown but there are likely a number of contributing factors. These include a gene mutation known as SLC26A4 that can cause EVA, Pendred syndrome and hearing loss. Other genetic and environmental factors may be at play in EVA.

EVA and Hearing Loss

Most children with EVA develop some degree of hearing loss, although the timing and severity varies for each child. About 5–15 percent of children who are diagnosed with sensorineural hearing loss – or hearing loss caused by damage to the inner ear – have EVA. However, the hearing loss may be caused by an underlying anatomical defect and not the EVA itself. The identification of EVA can be an important clue to understand all causes of the hearing loss.

About 25 percent of people with EVA have Pendred syndrome, which is characterized by hearing loss and thyroid disease. The hearing loss associated with Pendred syndrome is often progressive, resulting in more severe hearing loss or deafness.

Children with EVA-related hearing loss may also have problems with their balance. Fortunately, these balance difficulties are typically brief and mild. If balance issues are more problematic, vestibular (balance) testing with vestibular rehabilitation may be required.

It is not entirely understood how abnormalities in the inner ear contribute to sensorineural hearing loss. Experts believe that the fluids in the endolymphatic duct and sac must remain in careful balance, because even minor changes may lead to hearing loss.

Diagnosing EVA

EVA is usually diagnosed while trying to determine the source of a child’s hearing loss. When hearing loss is suspected, your child’s physician will conduct an age-appropriate hearing (audiometry) test to determine the presence and severity of the hearing loss. Additionally, they may conduct auditory brainstem response testing (ABR), which uses electrodes attached to the skin to record brainwave activity in response to sound.

Once sensorineural hearing loss has been confirmed, imaging scans such as magnetic resonance imaging (MRI) and computed tomography (CT) may be recommended to evaluate the inner ear structure. Although most imaging results are normal, when there is an anatomic abnormality, EVA is the most common.

Early Diagnosis Reduces EVA’s Impact

Identifying hearing loss as early as possible is the best way to reduce EVA’s impact. The earlier hearing loss is identified in children, the sooner they can develop skills that will help them learn and communicate with others. Children with permanent and progressive hearing loss, which often is linked with EVA, will benefit from learning other forms of communication, such as sign language or cued speech, or using assistive devices, such as a hearing aids or cochlear implants.

EVA Treatment and Management

There are no routine medical or surgical treatments for EVA. In fact, research has shown that surgical procedures to drain liquid from the endolymphatic duct and sac or to remove them are not only ineffective in treating EVA, they can be harmful and worsen hearing.

There is some anecdotal evidence that a course of steroids may be helpful at restoring some hearing in cases where sensorineural hearing loss is sudden in patients with EVA. However, more research on this topic is needed.

Reducing the Risk of Hearing Loss with EVA

Certain activities are associated with increased hearing loss in children with EVA. These activities should either be avoided or proper precautions should be taken to reduce the risk of injury or trauma. These include:

• Contact sports and activities: Any activity where the participant could sustain a head injury or barotrauma (ear damage caused by pressure differences between the middle ear and the outer ear) could cause further damage and hearing loss. Activities such as contact sports, cycling and skiing should be undertaken with protective headgear or avoided altogether.
• Activities with rapid changes in air pressure: Activities such as scuba diving and hyperbaric oxygen treatments should be carefully avoided because of their risk of sudden worsening of hearing loss.
• Air travel: Pressure changes with air travel have also been reported to cause hearing loss in EVA patients. However, this is rare in commercial aircraft with pressurized cabins, and this risk may be minimized by taking a nasal decongestant before travel, particularly if there is sinus or nasal congestion.