Teaching Case

45-year-old male patient presented to ENT surgeons with longstanding, severe bilateral sensorineural hearing loss, right side greater than left. No associated symptoms such as dizziness or vertigo. No relevant past medical history.

T2W imaging of the brain demonstrates dilatation of both endolymphatic ducts and sacs, confirmed on a heavily T2W volume sequence. Both ducts measure more than 1.5mm transversely at their midpoints in keeping with Large Vestibular Aqueduct Syndrome (LVAS). Bilateral vestibulocochlear anatomy was otherwise unremarkable.

Large vestibular aqueduct syndrome (LVAS) is a congenital anomaly resulting in progressive hearing loss and disequilibrium [1]. It is due to enlargement of the bony vestibular aqueduct which contains the endolymphatic duct and sac. The age at diagnosis ranges from infancy to adulthood, as in this case. It is thought that dilatation of these structures leads to problems in the circulation and ionic composition of endolymph, with often stepwise hearing loss following episodes of trauma such as a minor bang on the head, changes in atmospheric pressure (e.g. when flying or diving) and even playing musical instruments that require sustained Valsalva manoeuvres such as the trumpet. Sudden fluctuations in CSF pressure on impact may force hyperosmolar proteins into the cochlear duct which connects the CSF and endolymphatic spaces leading to hair cell/neural damage.

LVAS may be syndromic or sporadic in nature, uni- or bi-lateral. It is thought to be the cause of between 5 and 15% of cases of childhood deafness. It is linked to such conditions as Pendred’s syndrome and genetic testing may reveal the SLC26A4 gene (also called the PDS gene). Such patients have a combination of hearing loss and thyroid disease. It is also often associated with cochlear anomalies such as varying degrees of incomplete partition.

The female to male ratio is 3:2. Hearing loss may be sensorineural, conductive or mixed. Most children with LVAS hear normally for the first year of life and become progressively impaired. Vestibular symptoms may result in clumsiness and intermittent gait disturbance.
The condition is diagnosed on imaging, either high-resolution temporal bone CT or 3D volume T2W MRI which demonstrate dilatation of the bony vestibular aqueduct or endolymphatic duct and sac, respectively [2]. A transverse diameter at the midpoint of the duct of >1.5mm is considered abnormal.

Treatment is preventative, as the condition cannot be cured. Children may wear a helmet to prevent head trauma, avoid flying and contact sports. Hearing aids and vestibular rehabilitation can be offered. The degree of hearing loss is variable between patients and cannot be accurately predicted.

Take-Home Points:
Consider LVAS in all patients with progressive hearing loss since childhood, particularly if not born deaf.
Imaging is the key to diagnosis: CT or MRI can be used.
A dilated vestibular aqueduct or endolymphatic sac of >1.5mm at its midpoint transversely is diagnostic.
Look for associated cochlear malformations and consider syndromic associations, particularly Pendred’s syndrome.