The vestibular aqueduct extends from the posteroinferior surface of the temporal petrous to the medial wall of the vestibule and contains the endolymphatic duct that connects the endolymphatic sac to the utricle and saccule.

Enlarged vestibular aqueduct syndrome (EVAS):

• neurosensorial hearing loss in the context of vestibular duct enlargement more than the posterior semicircular canal which runs parallel and anterior to it

• the most common cause of congenital sensorineural hearing loss in children and young adults with a female-to-male ratio of 3:2 and being bilateral in 50-60% of patients

• coexisting with semicircular canal abnormalities but highly associated with cochlear anomalies including Mondini malformations. Vestibular aqueduct formation and the portioning of the cochlea are at the last stages of development of the inner ear in which both structures might be affected by a teratogenic insult

• high-resolution temporal bones CT demonstrates the bony outline of the vestibular aqueduct; but MRI (T2WI for vestibular aqueduct) further identifies the integrity of the cochlea, the cochlear nerve, and the fluid-filled spaces of the inner ear as well as associated parenchymal or vascular abnormalities

• precise assessment and description of cochlear anomalies are necessary as they might change the management including surgical intervene or cochlear implantation

Case contributed by Dr. Lorne Rosenbloom, neuroradiology assistant professor of McGill University.