Enlarged vestibular aqueduct

Symptoms

Although large vestibular aqueducts are a congenital condition, hearing loss may not be present from birth. Age of diagnosis ranges from infancy to adulthood, and symptoms include fluctuating and sometimes progressive sensorineural hearing loss and disequilibrium. It is possible that a small portion of those with large vestibular aqueducts will not exhibit auditory symptoms such as hearing loss. While this is uncommon, hearing loss can progress later in life, especially after head trauma. Hearing loss can be unilateral or bilateral and can be sensorineural, conductive, or mixed. Vestibular symptoms, such as vertigo and imbalance, occur in adult patients 45% of the time.

Pathology

The vestibular aqueduct acts as a canal between the inner ear and the cranial cavity. Running through it is a tube called the endolymphatic duct, which normally carries a fluid called endolymph from the inner ear to the endolymphatic sac in the cranial cavity. When the endolymphatic duct and sac are larger than normal, as is the case in large vestibular aqueduct syndrome, endolymph is allowed to travel back from the endolymphatic sac into the inner ear. This often results in fluctuations in hearing levels. Enlarged vestibular aqueducts are caused by mutations in gene SLC26A4, which is also associated with Pendred syndrome and non-syndromic recessive deafness. Enlarged vestibular aqueducts often occur with other inner ear development problems, such as cochlear deformities. Enlarged vestibular aqueducts are part of the classic Mondini deformity. Enlarged vestibular aqueducts with enlarged endolymphatic sacs occur in Pendred syndrome, which is caused by a defect on chromosome 7q31. Enlarged vestibular aqueducts can also occur in branchio-oto-renal syndrome, CHARGE syndrome and renal tubular acidosis.

Enlarged vestibular aqueducts can be bilateral or unilateral.

Hearing loss caused by large vestibular aqueduct syndrome is not inevitable, although people with the syndrome are at a much higher risk of developing hearing loss than the general population. Hearing loss is very likely.

Diagnosis

Enlarged vestibular aqueducts are commonly picked up after newborn hearing screen when a child is identified as having a hearing loss. The hearing loss is commonly mixed and can be of any degree when first identified. The conductive component is due to a third window effect caused by the widened vestibular aqueduct. During an audiologic assessment, an air-bone gap in the low frequencies can occur due to the enlarged vestibular aqueduct acting as a third mobile window. Hearing loss in the contralateral ear to the enlarged vestibular aqueduct can also occur due to the chemical composition on both sides. Torticollis has also been found to be an indicator of an enlarged vestibular aqueduct in children. Identification of the enlarged vestibular aqueduct in a child is usually by MRI scan which identifies the fluid within the endolymphatic duct and sac. CT scan may be needed to see the vestibular aqueduct clearly. In adults, CT scan may be the first investigation. In order to diagnose the cause of the enlarged vestibular aqueduct, the physician will need a detailed family history, full examination to include vestibular examination and, if a bilateral finding, molecular genetic testing as appropriate. With unilateral enlarged vestibular aqueducts, molecular genetic testing is currently not recommended.

Management

References

1. (1999). "Non-syndromic hearing loss associated with enlarged vestibular aqueduct is caused by PDS mutations". Human Genetics.
2. (2016). "Vestibular Pathology in Children with enlarged vestibular aqueduct". The Laryngoscope.
3. (July 2003). "Enlarged Vestibular Aqueduct Syndrome in the Pediatric Population". Otology & Neurotology.
4. (2007). "Vestibular symptoms in children with enlarged vestibular aqueduct anomaly". International Journal of Pediatric Otorhinolaryngology.
5. (2013). "Significance of unilateral enlarged vestibular aqueduct". The Laryngoscope.
6. (2020). "Torticollis in children with enlarged vestibular aqueducts". International Journal of Pediatric Otorhinolaryngology.
7. Gasperin. "Enlarged vestibular aqueduct with bilateral sensorineural hearing loss following cranial trauma: a case report". Brazilian Journal of Otorhinolaryngology.