Head and Neck ImagingLarge vestibular aqueduct syndrome
congenital anomaly of the
temporal bone with an apparently isolated large vestibular aqueduct, predisposing the patients to an acquired, progressive, fluctuating
sensorineural hearing loss. It is suggested that the progression of hearing loss is often triggered by head
trauma and activities that cause sudden fluctuation in cerebrospinal fluid pressure. The large vestibular aqueduct would allow back pressure to the
inner ear, resulting in damage to the membranous labyrinth.
The normal diameter of the vestibular aqueduct should not exceed the diameter of the posterior semicircular canal. More exactly, a vestibular aqueduct is considered large when it measures more than 1.5 mm at the midpoint between its external aperture and the common crus (Fig.1). On MRI, the content of the large vestibular aqueduct becomes visible: dilatation of the endolymphatic duct and sac is seen (Fig.2), although their size is not always proportional to the dilatation of the bony vestibular aqueduct.
Large vestibular aqueduct syndrome is seen in Pendreds syndrome.
A strong association between a large vestibular aqueduct and deficits in the cochlear modiolus has been shown recently (see modiolus anomalies). An isolated 'large vestibular aqueduct syndrome' may therefore be rare or nonexistent.
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Axial CT image through left temporal bone, showing clear dilatation of the vestibular aqueduct (arrow). There is also deficiency of the cochlear modiolus (arrowhead) (courtesy by Marc Lemmerling, MD, PhD, Gent, Belgium).
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Large vestibular aqueduct syndrome, Fig.1 | | Large vestibular aqueduct syndrome, Fig.2 (a) | | Large vestibular aqueduct syndrome, Fig.2 (b) |