Timothy C. Hain, MD of Chicago Dizziness and Hearing.Page last modified: September 22, 2012
In the "Large Vestibular Aqueduct syndrome" there is enlargement of the endolymphatic duct (ED on figure above) that connects the endolymphatic compartment (blue above) to the endolymphatic sac (which lies just under the dura of the posterior fossa, ES above). Persons with LVAS may develop hearing loss as well as be unusually vulnerable to inner ear disease associated with head injury. Not all patients with LVAS have it as a hereditory condition.
Many persons with LVAS also have Pendred syndrome (see below) (Berrettini et al, 2005). Presumably this vulnerability occurs because there is increased compliance (easier access) of pressure waves in the brain to the inner ear. Oddly though, this condition is basically the opposite of the situation in Meniere's disease, where it is classically hypothesized that the vestibular aqueduct (endolymphatic portion) is abnormally narrowed, but manifesting with similar hearing symptoms. It would seem likely that one of these mechanisms must be wrong. LVAS is also associated with renal tubular acidosis. (again, likely a genetic association).
Vestibular aqueduct diameter and hearing loss is highly correlated, according to Spencer (2012). This suggests that the pressure fluctuations experienced by the inner ear as a result of a larger vestibular aqueduct may cause hearing loss through wear and tear. It also suggests that surgical procedures aimed at increasing flow in the endolymphatic duct, such as for Meniere's disease, may be poorly concieved.
SLC26A4 is considered to be the major involved disease in inner ear malformations associated with bilateral nonsyndromic hearing loss (Chen et al, 2012). In Chinese patients, SLC26A4 mutaitons were found in almost 75% of individuals with inner ear malformations such as EVA or Mondini.
Audiometry: It may cause a fluctuating sensorineural hearing loss as well as a conductive component. Persons with LVAS may have a large air-bone gap (suggestive of conductive hearing loss) (Merchant et al, 2007). This is proposed to be due to an enhancement of the bone component, following logic similar to that applied in superior canal dehiscence syndrome.
VEMP: Similar to SCD, persons with LVAS-EVA may have VEMPs in spite of conductive hearing loss (Zhou, 2010).
Radiology: LVAS is defined on the CT scan as a diameter greater to or equal to 1.5 mm measured midway between the operculum and the common crus. According to Murray et al (2000), coronal CT scan is the best view for evaluating it in children. Enlarged vestibular aqueducts can also be seen on high-resolution MRI.
Conservative management, including avoidance of head trauma and contact sports, has been the mainstay of treatment. Surgery to close the enlarged structure frequently results in significant hearing loss (Welling et al, 1999).
See also: raisingdeafkids.org
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