Large Vestibular Aqueduct Syndrome (LVAS)
Question: My child has been diagnosed with large vestibular aqueduct syndrome (LVAS). Exactly what is LVAS; what causes it; and more importantly, what can I do about it?A. M.
Answer: Large vestibular aqueduct syndrome (LVAS) is a fairly recently-diagnosed condition. Im not surprised you havent heard of it before.
Vestibular Aqueduct? What Is That?
The vestibular aqueduct is a narrow bony canal (aqueduct) that runs through the skull, connecting the inner ear (vestibule) to the cranial cavityhence its name.
Running through this bony canal is a membranous tube called the endolymphatic duct. Like other parts of the inner ear, the endolymphatic duct is filled with a fluid, appropriately called endolymph. This duct courses through the bony vestibular aqueduct and dumps into the endolymphatic sac, which lies between the inside of the skull and the membranes that cover the brain.
Back in 1978, this syndrome was dubbed the Large Vestibular Aqueduct Syndrome (LVAS) because only the large vestibular aqueduct part of this syndrome showed up on the CT (computed tomography) scans.
There are a number of names that refer to this condition. The most commonly used one so far has been Large Vestibular Aqueduct Syndrome (LVAS). Less commonly, it has been referred to as Enlarged Vestibular Aqueduct Syndrome (EVAS). Sometimes it is just called Vestibular Aqueduct Syndrome (VAS).
Researchers using high-high-resolution magnetic resonance imaging (MRI) techniques can now actually see the endolymphatic duct and sac. They have discovered that when the vestibular aqueduct is enlarged, so too is the endolymphatic duct and sac. It is the enlarged endolymphatic duct and sac that cause the hearing problems, not the large vestibular aqueduct itself. Therefore, some researchers have changed the name of this syndrome to better reflect this reality. They are now calling it Large Endolymphatic Duct and Sac Syndrome (LEDS). In addition, other researchers think that LVAS is really just a mild case of Pendred syndrome (PDS), a syndrome characterized by sensorineural hearing loss, goiter and an abnormal perchlorate discharge test. Therefore, whether you call it LVAS or LEDS or EVAS or just VAS or even PDS, you are talking about exactly the same condition.
You might be surprised at just how small the normal vestibular aqueduct isan average of 0.8 mm. LVAS is defined as a vestibular aqueduct with a diameter greater than 1.5 mm at the midpoint. In some cases of LVAS, the vestibular aqueducts are as large as 8 mm although the average for large vestibular aqueducts is around 3.7 mm.
Inner Ear Deformities and LVAS
Vestibular aqueducts are not fully formed at birth but continue to develop and change in shape until a child is about 3 or 4 years old. Because the vestibular aqueduct is one of the last parts of the inner ear to reach maturity, it is most vulnerable to developmental damage as a baby grows.
Large Vestibular Aqueduct Syndrome (LVAS) is one of a group of deformities that results from this abnormal or delayed development of the inner ear. LVAS is not congenital, but occurs sometime after birth and is the result of abnormal postnatal or early childhood development. Recent reports indicate that people who have LVAS are merely predisposed to the development of a hearing loss.
There are many deformities of the cochlear and vestibular systems. LVAS is often associated with many of them. In one study, various cochlear deformities were present in 76% of the ears that had LVAS. In this same study, there were also vestibular (balance) abnormalities in 40% of the ears with LVAS. This makes LVAS one of the most common inner ear deformities seen in people with sensorineural hearing loss from soon after birth.
Originally, LVAS was thought to be a variant of the Mondini type of inner ear deformity where the cochlea only develops 1 turn instead of the normal 2 turns. Now researchers recognize LVAS as a completely separate clinical condition. LVAS may be associated with Mondinis syndrome or it may occur by itself. This proves that the resulting hearing loss is caused by the large vestibular aqueduct and not by any other abnormalities.
Large Vestibular Aqueduct Syndrome may result in sudden, fluctuating, or progressive sensorineural hearing loss. It is defined as the combination of the clinical presence of sensorineural hearing loss in a child and the identification of the large vestibular aqueduct on a CT scan or the MRI identification of the large endolymphatic duct and sac.
The gross appearance of the CT scan of the inner ear often appears normal. Therefore, doctors need to precisely measure the diameter of the vestibular aqueduct in order to correctly diagnose the presence of LVAS.
In the past, LVAS was felt to be one of the most commonly overlooked causes of hearing loss in children. Even today, many audiologists are unaware of LVAS or do not suspect it, in part due to the presence of a conductive component in the resulting hearing loss. In fact, a fluctuating hearing loss and a conductive component often accompany LVAS and are important audiologic findings when diagnosing this syndrome.
If a drastic change in hearing has occurred in a child following a minor head injury, change in barometric pressure, or physical exertion, the cause may very well be LVAS.
CT scans are the preferred diagnostic tools of doctors. Credible CT and MRI scans now give the doctors an objective way to test for LVAS.
How Common Is LVAS?
Doctors estimate that LVAS occurs in at least 1% to 1.5% of people with sensorineural hearing loss or balance problems. More specifically, some studies have found that somewhere between 5% and 7% of the people with sensorineural hearing loss of unknown causes really have LVAS.
Just because you have a large vestibular aqueduct, doesnt mean that you will also automatically have a sudden hearing loss. In one study, the incidence of sudden hearing loss among people with LVAS ranged between 11.8 and 19.1%. In another study, the incidence figures were much higher, occurring in up to 60.9% of the people with LVAS. This means that there are still a lot of people that have a large vestibular aqueduct, but do not have the associated sudden hearing loss.
It's in the Genes
Researchers are now discovering that abnormal or delayed development of the inner ear is often caused by genetic defects. In one study, 39% of the cases of LVAS occurred within families indicating that sensorineural hearing loss associated with LVAS is an inherited recessive trait. They have now traced the gene thought to be responsible for LVAS to a location on chromosome 7q.
Characteristics of LVAS
Large Vestibular Aqueduct Syndrome has a number of characteristicssome of them rather unusual.
How Does LVAS Cause Hearing Loss?
The exact role that the endolymphatic duct and sac plays is still uncertain at present. However, some researchers feel they are somehow responsible for regulating endolymphatic pressure within the inner ear. They think the endolymphatic sac could serve as a reservoir for endolymph and, due to its capacity for water absorption, may have a pressure-regulating role. Other doctors think it could be the site for active ionic exchange of endolymph with the cerebrospinal fluid.
Doctors do not yet know exactly how LVAS results in hearing loss. They have proposed several theories and one or more of them may ultimately prove to be true.
One theory is that a sudden increase in cerebrospinal fluid pressure from a minor head injury or other activity could have compressed the dural envelope surrounding the endolymphatic sac thereby forcibly pushing the hyper-concentrated fluid in the endolymphatic sac back through the dilated duct in the large vestibular aqueduct and into endolymphatic circulation. This hyper-concentrated endolymphatic fluid then damages the hair cells of the cochlea, resulting in sudden hearing loss.
The reason this does not normally happen is because the inner ear is buffered from any rapid intracranial pressure changes by the narrow vestibular and cochlear aqueducts. When the vestibular aqueduct is larger than normal while the cochlear aqueduct remains normal in size, any rapid fluctuation in cerebrospinal fluid pressure from minor head trauma causes temporary force imbalances across the cochlear partition. This shearing action could cause damage to the delicate inner ear hearing and balance structures.
Another theory suggests that inner ear fluid movements or pressure changes caused by a relatively minor head injury cause a tear or rupture in an area of congenital weakness in the delicate membranes in the inner ear, thus causing permanent damage to the hearing structures.
In support of this theory, the results from one study suggest that hearing loss and vertigo attacks in people with LVAS may be caused by a rupture in the membrane separating the endolymph and perilymph. This is the same mechanism that is thought to occur in Menieres disease and in perilymphatic fistulas.
What Can You Do?
Since LVAS is caused by a genetic defect, you cant just make it go away. However, there are things that you can do to help your child cope with LVAS.
If your child has LVAS, one of the most important things you can do in managing this syndrome is to take the necessary steps to prevent additional hearing loss from occurring. This is especially important if your child has LVAS in both ears.
Doctors recommend avoiding head trauma as it causes the hearing loss to progress faster. Thus, it would be prudent to restrict your childs activities. Since minor head trauma can cause episodes of sudden (and irreversible) hearing loss, your child should avoid contact sports such as wrestling, football, rugby, soccer and hockey, for example. Baseball, basketball and cycling may be okay, although there still is risk. (In spite of LVAS, your child needs to have a life. Therefore in situations like these where there is the possibility of head trauma, your child should always wear head protection.)
Other activities that your child should avoid include things like bumper car rides, roller coasters, dirt bikes, skate board jumping, bungee jumping, radical/strenuous exercise, weightlifting and diving. In addition, you want your child to avoid activities that involve large changes in barometric pressure such as scuba diving. Even playing certain musical instruments is not without risk if they require high expiratory pressures. For example there is a report of a person with LVAS who had a hearing loss resulting from playing a trumpet.
If your child has a significant hearing loss, have him fitted with hearing aids as soon as possible. (Id suggest that you get considerably more powerful aids than your child needs at present as his hearing is likely to continue to get worse in the future.)
If the hearing loss progresses to profound where hearing aids are of little or no help, the good news is that Cochlear Implants generally work well in children with LVAS.
There are conflicting reports on surgical intervention in people with LVAS. Some doctors report that shunting the endolymphatic sac does not halt the progression of the hearing loss. Indeed, it is actually associated with the significant likelihood of profound deafness being the result. One study found an immediate decrease in hearing in four of seven ears after endolymphatic shunt surgery.
Other doctors have used surgical techniques that seem to work, at least in some cases. In one study, seven people with LVAS had surgery to obliterate their endolymphatic sacs to try to stop further hearing loss. Hearing remained stable in four of the seven, improved in two and continued to get worse in one.
Neil Bauman, Ph.D. was born with a severe hereditary hearing loss. He is a hearing loss coping skills specialist, researcher, author and speaker. He is not a medical doctor and does not prescribe/endorse treatment for medical problems. This educational article is for your information only. If you suspect that you have a medical problem related to your hearing, please seek competent medical help. Use the information here to help you make informed decisions, not as a substitute for any treatment that your doctor may prescribe. Send your questions to him at email@example.com or check his web site for more information at www.hearinglosshelp.com.
BACK to Table of Contents