8The Enlarged Vestibular Aqueduct
The vestibular aqueduct is a slender bony channel carrying the endolymphatic duct from the vestibule toward the posterior fossa. When it is too wide it becomes the most common radiological inner-ear anomaly in children with sensorineural loss — and a clinical story of hearing that slips down a staircase, sometimes after a knock to the head. It rarely changes whether you implant, but it changes how you measure, what you tell the family, and what you expect when you open the cochlea.
FMeasuring it: the two thresholds
The enlarged vestibular aqueduct (EVA), also called large vestibular aqueduct syndrome (LVAS), is the single most frequently identified radiological inner-ear malformation in children evaluated for sensorineural hearing loss. The classic Valvassori criterion calls the aqueduct enlarged when its midpoint diameter exceeds 1.5 mm on axial CT. The more sensitive Cincinnati criteria add an opercular measurement: enlarged if the midpoint exceeds 1.0 mm and/or the operculum exceeds 2.0 mm, catching milder cases the single midpoint rule misses. Many clinicians use a practical shorthand of >1.5 mm at the midpoint and >2 mm at the operculum; the key discipline is to state which point you measured, because midpoint and operculum give different numbers on the same ear.[2007][2005]
TThe genetics: Pendred, SLC26A4 and IP-II
EVA is strongly linked to mutations in SLC26A4, which encodes pendrin; biallelic mutations underlie Pendred syndrome (EVA plus an iodine-organification defect and goitre), while EVA can also occur with one or no detectable SLC26A4 mutation. EVA commonly accompanies IP-II (the Mondini pattern), so an enlarged aqueduct on a scan should prompt a deliberate look at the modiolus and apical turns. The genetic background helps explain the bilaterality and the progressive course often seen, and identifying SLC26A4 status supports family counselling and thyroid surveillance. Because EVA may be isolated or syndromic, audiogenetic referral and, where Pendred is suspected, thyroid evaluation are reasonable parts of the work-up.[2005][2005][2017]
TThe clinical signature: a staircase down
The hallmark is sensorineural or mixed hearing loss that fluctuates and descends in steps, often progressing over years rather than declining smoothly. Sudden drops are classically triggered by minor head trauma, barotrauma, or Valsalva-type strain, which is why these children are counselled to avoid contact sports and head impacts. A low-frequency air-bone gap with normal middle-ear function reflects a third-window effect: the abnormally patent aqueduct shunts acoustic energy, mimicking conductive loss without any ossicular problem. The mixed pattern is frequently mistaken for otosclerosis; recognising the third window prevents a futile and risky stapes operation.[2005][2007]
CAt surgery, and the prognosis
Once loss has progressed to candidacy, EVA ears generally give excellent cochlear-implant outcomes because the cochlea is otherwise well-formed and nerve-bearing. Counsel the family for a perilymph pulsation or gentle oozing at cochleostomy — the wide aqueduct raises endolymphatic-sac connectivity and intracochlear pressure — which is controlled by a snug seal rather than feared as a true gusher. The third-window leak is usually a manageable pulsatile flow, distinct from the high-volume IP-I/IP-III gusher; a soft-surgery cochleostomy or round-window approach with a tissue seal handles it. Many families arrive having watched hearing slip for years on aids; the implant offer is best framed as the stable end of a fluctuating, progressive course, with realistic but generally favourable expectations.[2005][2020][2009]
What is the most likely explanation for her apparent conductive component, and what is the cochlear-implant outlook?
Under the Cincinnati criteria, which measurement defines an enlarged vestibular aqueduct?
Which gene is most strongly associated with EVA and Pendred syndrome?
What fluid finding should the surgeon expect and counsel for in a typical EVA cochleostomy?