Answer of September 2009

Clinical History:

27 year old male, referred from ENT surgeon for bilateral progressive sensorineural hearing loss since childhood, now profound deafness. CT temporal bone was performed.

Diagnosis:

Large Vestibular Aqueduct Syndrome

Discussion:

Large vestibular aqueduct syndrome (LVAS) is also known as large endolymphatic sac anomaly (LESA). It is the commonest imaging abnormality detected in children with sensorineural hearing loss. (1,2)
This condition is associated with autosomal recessive inheritance. (2)
There is also association with Pendred syndrome. (2,3)
LVAS is bilateral in up to 90% of patients. (2) Clinically, patients with LVAS usually present with progressive hearing loss since childhood. Majority of patients eventually develop profound sensorineural deafness. About 50% of patients also experience tinnitus and vertigo. (1) 
LVAS is readily diagnosed by CT scan of temporal bone. The imaging hallmark is dilated vestibular aqueduct measuring more than 1.4mm at mid point between the posterior petrous bone and the common crus at the level of vestibule. A more convenient way of assessment is to compare with the posterior semi-circular canal, which should be the same size or larger than the vestibular aqueduct in normal subjects.
LVAS is associated with dysplasia of the cochlea, vestibule and semi-circular canals. (1-3) Common findings include modiolar deficiency and bulbous cochlear apical turn. (2) They may be subtle on CT scan. High resolution T2W MRI allows better delineation of these small structures. More refined assessment of cochlear abnormality is important because cochlea implant is an option of treatment when there is bilateral profound sensorineural deafness. (2) Surgeons prefer to implant on the side of most normal cochlea. (2)