Enlarged Vestibular Aqueduct

The vestibular aqueduct (one on each side of the head) is a narrow bony canal extending from the middle compartment—vestibule—of the inner ear toward the brain. It houses the endolymphatic duct and sac (see Label 15 on VEDA’s Web Ear Diagram) along with a vein and artery.

If a vestibular aqueduct is greater than 1½ millimeters in size (approximately the size of the head of a pin), it is considered to be an enlarged vestibular aqueduct (EVA). An enlarged endolymphatic duct and sac usually accompany EVA. The fluid-filled duct and sac are thought to help regulate the concentration of ions in the inner ear, which are important for initiating the transmission of sound and balance signals from the ear to the brain.

Causes
EVA seems to run in some families but not in others. It occurs more often in females than males. Genetic and as yet unknown environmental factors are thought to result in this disorder. EVA can be a symptom of Pendred syndrome (a genetic disorder causing childhood hearing loss), Mondini’s deformity (when the cochlea has only one or 1½ turns rather than the normal 2½), or branchio-otorenal syndrome (a genetic condition affecting the ears and the kidneys).

Symptoms
Hearing loss is commonly associated with enlarged vestibular aqueduct and is progressive with Pendred syndrome, sometimes resulting in total deafness. The hearing loss is generally sensorineural—involving the cochlea and the nerves serving it.

EVA can also produce problems with balance, although vestibular symptoms can be difficult for a child to describe and thus may not always be reported. Symptoms described in the medical literature include episodic spinning vertigo, mild unsteadiness, trouble watching revolving objects, and decreased visual acuity, among others. In a young child, signs and symptoms may also include grabbing of the head and walking in circles.

Testing
An EVA diagnosis is made using standard hearing tests and high-resolution, thin-section computerized tomography of the temporal bone. Vestibular tests may also be useful in assessing the impact on balance.

Treatment
Currently, no treatments can reverse or stop the progression of hearing and/or vestibular losses from EVA. People with EVAS are advised to avoid head blows and contact sports. Hearing aids or cochlear implantation may help. Vestibular rehabilitation therapy might also be helpful for managing imbalance and dizziness resulting from an enlarged vestibular aqueduct.

From VEDA publication F-28, Enlarged Vestibular Aqueduct