Enlarged vestibular aqueduct syndrome

Overview

Enlarged Vestibular Aqueduct Syndrome (EVAS), also known as Large Vestibular Aqueduct Syndrome (LVAS), is a congenital condition affecting the inner ear that can lead to progressive or sudden hearing loss, usually beginning in childhood. The vestibular aqueduct is a small bony canal that houses the endolymphatic duct and sac, structures involved in maintaining inner ear fluid balance. In EVAS, this canal is abnormally wide, which disrupts normal ear function and can lead to both auditory and balance issues. EVAS is one of the most common inner ear malformations associated with pediatric sensorineural hearing loss.

Causes

EVAS is primarily a congenital condition, meaning it is present at birth. It may occur in isolation or as part of a genetic syndrome. Causes and contributing factors include:

• Genetic mutations: Mutations in the SLC26A4 gene are commonly associated with EVAS, particularly in individuals who also have Pendred syndrome (a disorder that affects hearing and thyroid function).

• Sporadic cases: In some individuals, EVAS occurs without any known genetic cause or family history.

• Associated syndromes: Most notably Pendred syndrome, but EVAS can also occur independently of other medical conditions.

Symptoms

Symptoms of EVAS can vary but generally relate to hearing and balance. These may include:

• Sensorineural hearing loss: Usually bilateral and can be stable, fluctuating, or progressively worsening. It may also occur suddenly after minor head trauma.

• Hearing loss triggered by head injury or barotrauma: Hearing may decline suddenly after activities like sports, falls, or even sneezing.

• Tinnitus: Ringing or buzzing in the ears

• Vestibular symptoms: Including imbalance, dizziness, or unsteadiness, particularly in younger children

• Speech and language delay: Due to hearing loss in early childhood

Diagnosis

EVAS is diagnosed through a combination of clinical history, audiological testing, and imaging studies. Key diagnostic steps include:

• Hearing tests: Audiometry and otoacoustic emissions (OAE) help assess the type and degree of hearing loss.

• Imaging:

  • CT scan: Shows an abnormally wide vestibular aqueduct (typically greater than 1.5 mm in width at the midpoint)

  • MRI: Used to assess the endolymphatic sac and other inner ear structures

• Genetic testing: May be done to detect SLC26A4 mutations, especially if Pendred syndrome is suspected

• Thyroid function tests: Conducted if there are signs suggestive of Pendred syndrome

Treatment

There is no cure for EVAS, but treatment focuses on preserving hearing, managing symptoms, and providing support for communication and balance. Treatment options include:

• Hearing aids: Often effective in the early stages or for mild to moderate hearing loss

• Cochlear implants: May be considered for individuals with severe or profound hearing loss who do not benefit from hearing aids

• Speech and language therapy: Especially important for children with early hearing loss to support communication development

• Vestibular therapy: To improve balance and coordination in children with dizziness or unsteadiness

• Activity modifications: Avoidance of contact sports and activities with risk of head trauma to prevent sudden hearing deterioration

• Educational support: Special education services and accommodations in school may be necessary

Prognosis

The long-term outlook for individuals with EVAS varies. Some experience stable hearing loss, while others may face progressive or sudden loss. Early diagnosis and intervention are crucial to maximizing speech, language, and cognitive development, especially in children. With appropriate hearing devices, therapies, and educational support, many individuals with EVAS can lead full and productive lives. Monitoring is essential, as hearing can decline unpredictably, and protective strategies should be implemented to reduce the risk of trauma-induced hearing loss.