A common malformation: Enlarged vestibular aqueduct syndrome (EVAS)

Since the inner ear is a pressure sensor, it is important to keep the pressures steady in the ear.  This is a challenge because the ear bridges the space in the skull between the outside-the ear canal—and the inside, housing the brain.  When you sneeze or strain, the pressure in the fluid around the brain rises.  When your ears pop, it means the pressure of the air outside the skull has changed. Somehow the inner ear has to deal with these changes and keep functioning smoothly.

The eardrum and the Eustachian tube help to keep sudden unequal pressure changes from affecting the inner ear. It is the opening of the Eustachian tube, which runs from the back of the nose to behind the eardrum, that results in the pop you feel when you descend in an airplane.  But what about the pressure changes inside the skull?  The inner ear has two fluid compartments, the perilymph and endolymph compartments, each of which are connected by  very thin tubes to the inside of the skull.  It is important that these vent tubes are very narrow, so that any sudden pressure changes tend to die away as a wave travels down the tube. 

One or both can be too large.  The problem is usually the vestibular aqueduct, the one that passes from the innermost, endolymph-filled compartment and that ends in a sac under the brain. This allows changes in brain pressure to penetrate to the inner ear.  Pulsations due to blood pressure, coughing, sneezing and straining can be transmitted.  Sometimes during ear surgery a sudden gush of fluid can come from the inner ear when this is present.

Hearing problems are a sign of this condition.  Hearing can go up and down, or can gradually decline.  Balance can also be affected, with a decline in vestibular function over time.  Even minor head trauma can result in sudden losses of hearing or balance. 

The problem is visible on MRI and is one reason an MRI is important in progressive hearing loss.  Treatment is difficult because of the miniature anatomy of the inner ear.  Wearing a helmet or avoiding contact sports is a sensible way to slow the progression.

We have a new article coming out on one form of BPPV soon, and I’ll be discussing this in our next few posts.

Published by Vertigone

I translate the medical world of dizziness for non-medical people

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: