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Causes/Kinds of Hearing Loss

Enlarged Vestibular Aqueducts (EVA), also known as Large Vestibular Aqueduct Syndrome (LVAS)

© June 2002 (last revised June 2014) by Neil Bauman, Ph.D.

Question: My child has been diagnosed with enlarged vestibular aqueducts (EVA). Exactly what is EVA; what causes it; and more importantly, what can I do about it?—A. M.

Answer: Enlarged Vestibular Aqueducts (EVA), also known as Large Vestibular Aqueduct Syndrome (LVAS), Enlarged Vestibular Aqueduct Syndrome (EVAS), and rarely "Dilated Vestibular Aqueducts" (5) or "Vestibular Aqueduct Syndrome" (VAS), is a fairly-recently diagnosed condition (since the late 1970s). I'm not surprised you haven't heard of it before. Back in 2002, not a lot was known about EVA, but since then, researchers have been busy finding out more and more about it.

Vestibular Aqueduct? What Is That?

The vestibular aqueduct is a narrow bony canal (aqueduct) that runs through the skull, connecting the vestibule of the inner ear to the cranial cavity (inside of the skull)—hence its name.

Running through this bony canal is a membranous "tube" called the endolymphatic duct. (5) Like other parts of the inner ear, the endolymphatic duct is filled with a fluid, appropriately called endolymph. This fluid flows through the endolymphatic duct and dumps into the balloon-like endolymphatic sac, which lies between the inside of the skull and the membranes that cover the brain.

Researchers still do not understand much about the functions of the endolymphatic duct and sac. Currently, they believe that the endolymphatic duct and sac help to ensure that the fluid in the inner ear contains the correct amount of certain ions that are used to send sound and balance information to the brain. (5)

Back in 1978, this syndrome was dubbed "Large Vestibular Aqueduct Syndrome" (LVAS) because only the large vestibular aqueduct part of this syndrome showed up on CT (computed tomography) scans.

Researchers using 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. (10)  At this point, they felt it was the enlarged endolymphatic duct and sac that cause the hearing problems, not the large vestibular aqueduct itself. Therefore, some researchers changed the name of this syndrome to "Large Endolymphatic Duct and Sac Syndrome" (LEDS). In addition, some researchers thought that LVAS was really just a mild case of Pendred Syndrome (PDS). Whether you call it  EVA or LVAS or LEDS or EVAS or VAS, you are talking about exactly the same condition.

You might be surprised at just how small the normal vestibular aqueduct is. At the half-way point, the diameter normally ranges somewhere between 0.5 mm and 1.4 mm and averages 0.8 mm. In 1978, researchers Valvassori and Clemis defined EVA as a vestibular aqueduct with a diameter greater than or equal to 1.5 mm at the midpoint. In some cases of EVA, the vestibular aqueducts can be as large as 8 mm, although the average is much smaller.

Then, in 2008, after further investigations into the size of the vestibular aqueducts in children with hearing loss, Dewan, Wippold and Lieu revised downward the size of vestibular aqueducts regarded as "enlarged". This new criteria is now called the Cincinnati criteria. The Cincinnati criteria defines EVA as either vestibular aqueducts that are 0.9 mm or greater at the midpoint of the aqueduct, or vestibular aqueducts that are greater than 1.9 mm at the operculum (opening at the larger end).

This, of course, meant that many more people have EVA than was formerly thought to the case. For example, in one study of 130 children with cochlear implants, the Valvassori criterion identified 16% of the vestibular aqueducts as "enlarged" whereas when using the Cincinnati criteria, 45% of the vestibular aqueducts were found to be "enlarged", a 281% increase.

Note: before 2003, CT scans were done using a 1.0 mm slice, while now they use a 0.6 mm slice. The 1.0 mm slice gave insufficient resolution to accurately measure the vestibular aqueduct to meet the Cincinnati criteria.

As a baby is developing in the womb, the vestibular aqueducts are short, straight and broad. After birth, they continue to develop and change their shape until they reach the normal adult form, usually when a child is about 3 or 4 years old. By that time, each vestibular aqueduct is about 10 mm long and shaped like an inverted "J".

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.

While an enlarged vestibular aqueduct is the hallmark of EVA, the exact role this malformation plays in the resulting hearing loss is still being actively investigated. (11)

How Does LVAS Cause Hearing Loss?

How does EVA cause hearing loss? The short answer is, "No one yet knows for sure", but the latest research is getting ever closer to answering this question. Over the years, researchers who study EVA have followed a number of  avenues of research based on various characteristics of EVA.

At first researchers thought that structural abnormalities in the cochlea that were associated with EVA were the cause of the resulting hearing loss. (11)

Large vestibular aqueducts (EVA) are one of a group of deformities that results from abnormal or delayed development of the inner ear. EVA is not congenital like doctors originally thought. They now know it occurs sometime after birth and is the result of abnormal postnatal or early childhood development. Recent reports indicate that people who have EVA are not born with a hearing loss, but merely are predisposed to the development of a hearing loss.

There are a number of deformities that can form in the cochlea and vestibular system. EVA is often associated with many of them. In one study, various cochlear deformities were present in 76% of the ears that had EVA. In this same study, there were also vestibular (balance) abnormalities in 40% of the ears with EVA. This makes EVA one of the most common inner ear deformities seen in people with sensorineural hearing loss that occurs in early childhood.

Originally, EVA was thought to be a variant of the Mondini type of inner ear deformity. Now, researchers recognize EVA as a completely separate clinical condition although it may be associated with Mondini dysplasia, or it may be associated with Pendred syndrome or it may occur by itself.

Mondini Dysplasia

Mondini dysplasia (also called the Mondini anomaly and Mondini malformation) is where the snail-shaped cochlea, instead of having the normal 2½ turns, only has 1½ turns. (In actual fact, the top and middle turns are fused together into one cavity.) Low-frequency hearing is processed in the apex of the cochlea. Thus, when the final turn is missing, people with this condition typically have low-frequency hearing loss, but normal high-frequency hearing.

Since up to 20% of the people with Mondini dysplasia have other malformations such as enlarged vestibular aqueducts, it initially seemed that EVA was associated with Mondini dysplasia. However, when researchers realized that the majority of people with EVA had normal cochlear development, they dropped this theory.

Enlarged Vestibular Aqueducts

After researchers dropped the Mondini dysplasia theory for hearing loss from EVA, they assumed the enlarged vestibular aqueduct itself caused the hearing loss. This seemed logical at the time since clinical studies showed that enlargement of the vestibular aqueduct was the most common structural abnormality associated with EVA, and in numbers of people, was the only structural abnormality. (11)

Their research suggested that enlargement of the aqueduct itself caused the hearing loss. One theory was that endolymph normally "flows" away from the organs of the inner ear and towards the endolymphatic sac.  However, since in EVA, the endolymphatic duct and sac are larger than normal, this enlarged duct could allow the endolymph to flow from the endolymphatic sac back into the hearing and balance organs. Researchers felt a sudden increase in cerebrospinal fluid pressure from a minor head injury or other activity compressed the dural envelope surrounding the endolymphatic sac. This squeezed the endolymphatic sac, and thereby forcibly pushed the hyper-concentrated fluid in the endolymphatic sac back through the dilated duct in the large vestibular aqueduct and into endolymphatic circulation. They thought this hyper-concentrated endolymphatic fluid then damaged the hair cells of the cochlea, resulting in sudden hearing loss.

Researchers felt the reason this did not normally happen was because the inner ear is buffered from any rapid intracranial-pressure changes by the narrow vestibular and cochlear aqueducts, much like a shock-absorber dampens up and down movement in a car when it hits a rough spot. 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 structures such as the organ of Corti or stria vascularis as well as damaging the vestibular (balance) structures.

Another theory was that the endolymphatic duct and sac were somehow responsible for regulating endolymphatic pressure within the inner ear. They thought the endolymphatic sac could serve as a reservoir for endolymph and, due to its capacity for water absorption, may have had a pressure-regulating role. This is because the endolymphatic sac has a surprisingly high protein content, giving it a markedly higher ionic content in relation to the ionic concentration of the endolymph contained in the remainder of the inner ear. Other researchers thought it could be the site for active ionic exchange of endolymph with the cerebrospinal fluid.

Yet another theory suggested that inner ear fluid movements or pressure changes caused by a relatively minor head injury caused a tear or rupture in an area of congenital weakness in the delicate basilar membrane or in Reissner's membrane in the inner ear, causing permanent damage to the hearing structures.

In support of this theory, the results from one study suggested that hearing loss and vertigo attacks in people with EVA 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 Meniere's disease and in perilymphatic fistulas.

Even today, the exact role that the endolymphatic duct and sac plays is still uncertain. However, since there isn't any correlation between the size of the enlarged vestibular aqueducts and the resulting hearing losses like there should be if the above theories are correct, current thinking is that having enlarged vestibular aqueducts, by itself does not cause the hearing loss, but that both the hearing loss and the enlarged vestibular aqueduct are caused by some, as yet unknown, defect. (5) In other words, the large vestibular aqueduct is a marker for some more basic process that is going on within the inner ear that causes hearing loss. (11)

Pendred Syndrome

Another theory was that EVA was a milder form of Pendred syndrome since about 25% of the children with EVA have the more serious Pendred syndrome disorder, which typically causes hearing loss from birth and progresses to profound hearing loss. (11)

Pendred syndrome has several characteristics often associated with it.

The first common characteristic of Pendred syndrome is a malformed cochlea where the cochlea only has 1½ turns, instead of the normal 2½ turns. This is called the Mondini malformation (mentioned above). However, you can have Pendred syndrome without having the Mondini malformation and numbers of people do.

The second common characteristic of Pendred syndrome is enlarged vestibular aqueducts (EVA). That is why researchers used to think that EVA was a milder version of Pendred Syndrome.

The third common characteristic of Pendred syndrome is thyroid problems. Pendred syndrome affects the thyroid (makes it grow larger than normal—this is called a goiter, although thyroid hormone levels typically remain normal). If a goiter is going to develop, it typically forms in adolescence or early adulthood. Goiter is a relatively-common feature of Pendred syndrome, but numbers of people with Pendred syndrome never develop a goiter. Conversely, many people who develop goiters don't have Pendred syndrome. (10)

The fourth common characteristic of Pendred syndrome is that it typically causes hearing loss in early childhood. Children who are born with Pendred syndrome may begin to lose their hearing between birth and age three. Typically, hearing will worsen over time with the hearing losses occurring suddenly. Some hearing may return in the days/weeks following each episode of sudden hearing loss. (10)

Almost all children with Pendred syndrome have hearing loss in both ears, although one ear may have greater hearing loss than the other. (10)

The fifth common characteristic of Pendred syndrome is that it is a genetic disorder caused by mutations of the Pendred syndrome gene SLC26A4, formerly known as the PDS gene. This mutation is recessive. Therefore, a child needs to inherit two mutated SLC26A4 genes—one from each parent—in order to have Pendred syndrome. (10)

Researchers estimate that mutations on the SLC26A4 gene, which causes Pendred syndrome, account for about 5% to 10% of all hereditary hearing losses. (10)

It appeared that EVA was associated with this genetic mutation, thus confirming that EVA was a form of Pendred syndrome. For example, "Enlargement of the vestibular aqueduct (EVA) is a radiologic finding known to be associated with mutations of the Pendred syndrome gene (SLC26A4)" (3) and, "EVA can be a sign of a genetic disorder called Pendred syndrome." (5)

However, current research reveals that this is not necessarily true. Only a subset of the people with enlarged vestibular aqueducts actually have the Pendred SLC26A4 genetic mutations. Some people with EVA have the Pendred mutation on both genes, some only have it on one gene, and others don't have this mutation at all. Thus, numbers of people with EVA do not have Pendred syndrome. This shows that EVA is caused by other genes, non-genetic factors or a combination of these. (3)

Current Theory

"The discovery of the first gene associate with Pendred syndrome moved research into Pendred syndrome in a new direction." The result was that researchers moved away from investigating the gross physical changes in people with Pendred syndrome into investigating, at the molecular level, mechanisms that underlie Pendred syndrome and EVA. (11)

Researchers now know that the SLC26A4 gene contains the instructions for making a protein, called pendrin. (Incidentally, pendrin not only is found in cells in the inner ears, but also in kidneys and thyroid glands.) (10) Pendrin is embedded in the membranes of inner ear cells, including cells of the vestibular aqueduct.

In mouse embryo studies, researchers have discovered that pendrin expression in the endolymphatic sac is chiefly responsible for the development of normal endolymph volume, and that loss of pendrin leads to an increase of endolymph (enlarged endolymphatic duct and sac), increased acidification of the endolymph and a failure to develop normal hearing and balance. (14) Thus, when pendrin is not present or is not functioning properly, one result is hearing loss.

Furthermore, the protein expression of pendrin in the endolymphatic sac is important for inner ear fluid homeostasis. (14) This keeps the ionic content of the endolymph at the correct electrical potential relative to the electrical potential of the perilymph (normal endocochlear potential).

Researchers have also discovered that "cells use a variety of transport mechanisms, such as pumps and exchangers, to maintain the proper ion composition on both side of the cell's outer membrane." Proper pendrin expression helps move negative ions across cell membranes. (11) Preserving the correct ionic levels is especially important for sensory cells like the hair cells in the inner ear because ions are key players in transmitting sound signals from the inner ear to the brain. (11)

One clue that helps us understand the role of pendrin in hearing loss is that the endolymph in the inner ears of people with EVA is unusually acidic. This suggests that this abnormality underlies hearing loss in people with EVA. Pendrin normally helps reduce the fluid's acidity by neutralizing it with negative ions. But when the pendrin protein is not fully functional, as apparently is the case in people with EVA, acidity rises and damages key hearing structures. (11)

One of these hearing structures is the stria vascularis. The stria vascularis forms the outer wall of the scala media, the middle of the three fluid-filled compartments in the cochlea. The scala media is filled with endolymph. In fact, the stria vascularis is responsible for making the endolymph and also for generating and maintaining the “cochlear battery’s” charge (technically called its endocochlear potential [EP]) by maintaining the proper ion balance. It achieves the proper ion balance in the endolymph by using a variety of pumps and exchangers, such as the potassium ion pump. (11) In fact, the stria vascularis is particularly rich in ion pumps. These pumps are critical for maintaining the correct ion composition of the endolymph—a high potassium concentration and a low sodium concentration.

In mouse ears that did not have the fully-functional pendrin protein, researchers noticed degeneration of the stria vascularis.  Damage to the stria vascularis disturbs these crucial ion levels and impairs sensory cell function, resulting in hearing loss." (11)

Furthermore, "immune cells called macrophages were also found to accumulate in the stria vascularis, suggesting that immune system malfunction could also contribute to the degeneration of this structure." (11)

Thus, researchers have moved away from the idea that enlarged vestibular aqueducts in themselves cause hearing loss. The new thinking is that lack of fully-functional pendrin in the inner ear from a genetic mutation results in damage to the stria vascularis, which, in turn, results in improper ion balance in the endolymph. This ion imbalance prevents the hair cells and associated structures from sending proper sound signals to the brain, and the result is hearing loss.

This explains why hearing loss does not correlate with the degree of enlargement of the vestibular aqueducts. In fact, you can have hearing loss and have normal-sized vestibular aqueducts. Numbers of people have more severe hearing loss in the ear with the smaller enlarged vestibular aqueduct or in the ear with a normal vestibular aqueduct than in the ear with the larger enlarged vestibular aqueduct. Thus the absence of EVA in one ear does not mean that that ear will have normal hearing. It may, or it may not.

The current model suggests that hearing loss in people with EVA stems from impaired function of the stria vascularis and that enlarged vestibular aqueducts are only "markers" at best. (11)

Diagnosing EVA

In the past, enlarged vestibular aqueducts (EVA) were felt to be one of the most commonly overlooked causes of hearing loss in children. Even today, many audiologists are unaware of EVA 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 EVA and are important audiologic findings when diagnosing this syndrome.

EVA 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.

Either a CT (computed tomography) scan or an MRI (magnetic resonance imaging) are used to evaluate whether a person has enlarged vestibular aqueducts. Credible CT and MRI scans now give the doctors an objective way to test for EVA. As a result, parents can be informed ahead of time that their child's hearing could suddenly deteriorate. This gives them a chance to make realistic educational and therapeutic decisions. Most importantly, they can take precautions to try to avoid further hearing loss.

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 EVA.

These scans are particularly recommended when a person's hearing loss occurs suddenly, is greater in one ear than the other, or varies or gets worse over time. (5) Therefore, 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 EVA.

How Common Is EVA?

Doctors estimate that EVA 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 EVA.

In children, researchers are currently finding that 5% to 15% of children with sensorineural hearing loss have EVA. (5)

Just because you have a large vestibular aqueduct, doesn't mean that you will also automatically have an episode(s) of sudden hearing loss. In one study, the incidence of sudden hearing loss among people with EVA 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 EVA. This means that there are a lot of people that have a large vestibular aqueduct, but do not have episodes of sudden hearing loss.

Its in the Genes

 Enlarged vestibular aqueducts (EVA) are an inherited genetic mutation. Thus a basic knowledge of how genes combine will help you understand how you pass on EVA to your children.

Humans have 23 pairs of chromosomes. One chromosome from each pair is inherited from the father and one from the mother. Along the length of these chromosomes are arranged 20,000 to 25,000 pairs of genes. Genes are the means by which we inherit various traits (and disorders too, such as inherited hearing loss) from our parents. We have a pair of genes for every trait we inherit. We inherit one set of genes from each parent. (6) (Note: so far, researchers have identified more than 100 different genes that have mutations causing hearing loss.) (6)

Most genetic disorders (and hearing loss is no exception) are inherited in an autosomal manner. Autosomal is a fancy word that simply means both men and women are equally likely to have a given disorder such as hearing loss and pass it on to their children of either sex.

Here is how genetic inheritance works. You inherit a pair of genes for each trait you have from your parents. Genes may be dominant or recessive. Lets call the dominant gene "D" and the recessive gene "r" of any gene pair. Also, lets assume the first gene in the pair is from the father and the second gene in the pair is always from the mother. These genes can combine in one of 3 ways—you can receive a dominant gene from each parent (DD), one dominant and one recessive gene (Dr [father] or rD [mother]), or two recessive genes (rr).

Dominant genes give you the trait they carry so if you have either one or both dominant genes (DD, Dr or rD), you display the dominant trait. You only show the recessive trait if you have both recessive genes (rr).

 Mutations are changes in your genes. It is only mutated genes that cause conditions such as EVA or hearing loss, for example, not normal genes. If the mutation occurs in a dominant gene, then the resulting inherited trait will be dominant. If the mutation occurs in a recessive gene, then the resulting inherited trait will only be inherited recessively.

Note: hearing loss can be inherited in a dominant or recessive manner, depending on the specific gene that is causing the hearing loss. (6) For example, in my family, the mutated genes causing reverse slope hearing loss (RSHL) are inherited in a dominant manner. On the other hand, the mutated genes responsible for EVA are inherited in a recessive manner.

To make things very simple, lets assume that EVA is caused by a single gene (which it's not—here are a number of genes involved). If both parents give you a dominant gene for this trait (DD) you will have normal vestibular aqueducts. If one parent gives you a dominant gene (DD, Dr or rD) and your other parent gives you a recessive gene (Dr, rD or rr), the dominant gene will prevail—so you will have normal vestibular aqueducts but you will also carry the recessive gene for enlarged aqueducts and can pass it on to your children. If both parents give you a recessive gene (rr) then you will have enlarged aqueducts.

Thus, if you and your spouse each carry a recessive gene (Dr, rD) but do not have EVA, then on the average, if you had four children, one would have normal aqueducts (DD), 2 would have normal aqueducts but be carriers of EVA (Dr or rD) and one would have EVA (rr).

Note very carefully that this is on the average. Its just like flipping a coin. On the average, if you flipped a coin a good number of times, it would come up heads 50% of the time and tails 50% of the time (assuming it was perfectly balanced). But it is entirely possible for this same coin to come up heads 4 times in a row or tails 4 times in a row. It is the same in genetics. Thus if you had 4 children, you could conceivably have 4 children with EVA or 4 without EVA or any combination in between.

This is why, if your first child has EVA, it doesn't predict whether your next child will have EVA or not. It a new "flip of the coin" each time.

However, if your spouse only carried dominant genes (DD) and you carried a recessive gene but did not have EVA yourself (Dr, rD) then none of your children could ever have EVA, but on the average, 2 would be carriers of EVA (rD, Dr). Thus in real life in your family, all your children could be carriers for EVA,  none of your children could be carriers for EVA, or any combination in between.

If you have EVA (rr) and your spouse only carried the dominant genes (DD), then all of your children would be carriers of EVA (Dr or rD) but none of them would exhibit EVA themselves.

The result is that EVA can appear to skip generations or several generations and suddenly appear again. It will only appear again if both parents carry the recessive gene and each parent passes the recessive gene to the child.

Now that you know how genetic traits are passed from parents to children, lets look at some complicating factors. There is no one gene that causes EVA. In a study by National Institute of Deafness and Communication Disorders (NIDCD) researchers, approximately 25% of the participants with both EVA and hearing loss had Pendred syndrome. (Pendred syndrome is inherited in the traditional autosomal recessive manner as described above.) It is the result of two mutations (rr) of the SLC26A4 gene. (6)

Now here's the kicker. About 25% of the participants only had one mutation (Dr, rD) of the SLC26A4 gene and yet their families had a similar inheritance pattern to those families that carried both mutations. This suggests that there are other genes involved that have not yet been identified. (6)

The remaining 50% of the people in this study did not have either mutation of the SLC26A4 gene—yet they still had both EVA and hearing loss. (6

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 EVA occurred within families indicating that sensorineural hearing loss associated with EVA is an inherited recessive trait. They have now traced the gene thought to be responsible for LVAS to a location on chromosome 7q31.

More specifically, researchers now know that the EVA gene lies in the 1.7cM interval between the flanking markers D7S501 and D7S2425. Interestingly, this region overlaps the region containing the SLC26A4 gene responsible for Pendred syndrome (PDS), which was identified recently.

This suggests that different mutations in the SLC26A4 gene can cause a variety of related conditions ranging from nonsyndromic recessive hearing loss (NSRHL) with enlarged vestibular aqueducts (basically EVA) to the severe Mondini deformity and Pendred Syndrome. Some people with Pendred Syndrome have fluctuating hearing loss similar to that observed in people with EVA.

Another theory is that a separate gene responsible for EVA may exist close to the Pendred gene, and that mutations in both are required for full Pendred syndrome, whereas a mutation in only one of these genes may result in hearing loss associated with a variety of cochlear abnormalities.

It appears that there are a number of genes, as yet unidentified, that may be associated with EVA. In one study of children with profound hearing loss, 12 were found to have mutations of either the connexin 26 or connexin 30 genes. Using the Cincinnati criteria, 8 of the 12 were identified as having EVA while 4 had normal vestibular aqueducts.

Even so, the most common cause of EVA and hearing loss is mutations in the SLC26A4 gene. However, not all cases of EVA are caused by this genetic mutation. (5) EVA may be associated with Pendred syndrome or the Connexin 26 or Connexin 30 genes (and who knows how many other syndromes), or it may occur independently from such syndromes.  Other, currently unknown, genetic or environmental factors may also cause EVA. (5) Thus, much of what constitutes EVA remains a mystery at this time.

Characteristics of EVA

People with enlarged vestibular aqueducts have a number of characteristics—some of them rather unusual.

1. In routine CT scans, EVA is found to be a relatively frequent inner ear anomaly among people with sensorineural hearing loss of unknown cause.

2. Hearing loss associated with EVA is acquired in the years following birth. It is not congenital as was previously thought.

3.  Often one ear is affected more than the other. (11)

4. Hearing loss is commonly associated with EVA. For example, in one study of 33 ears with EVA and no other inner ear deformities, 31 of the 33 ears had sensorineural hearing loss. Eight of these also had a conductive loss. However, the sensorineural hearing loss was the most predominant component. Over time, 65% of the ears had progressive hearing loss.

5. On the average, hearing loss is greater if you have EVA and do not have any other cochlear deformity.

6. In people with EVA and no other cochlear deformities, hearing loss is generally much greater in the higher frequencies than in the lower frequencies.

7. If you have EVA without any other cochlear deformities, your ears are subject to sudden drops in hearing. This does not appear to be the case if your ears have associated deformities such as Mondini dysplasia. In these cases, you may have a progressive hearing loss instead. Therefore, it is important to differentiate between cases where the large vestibular aqueduct is the only inner ear malformation seen on CT scans and those with associated cochlear and/or semicircular canal abnormalities.

8. The hearing loss caused by EVA is primarily a sensorineural hearing loss. However, because other abnormalities are often present, there may also be a conductive component as well. One study indicated that 90% of the time hearing loss was comprised of both sensorineural and conductive losses although the sensorineural hearing loss was the most predominant. As a result, an air-bone gap exists to some degree in almost all people with EVA. Incidentally, the conductive component can easily be misinterpreted as a middle ear ventilation problem or a type of otosclerosis.

9. EVA in both ears (bilateral) is much more common (80 to 91%) than EVA in only one ear (unilateral).

10. If you have EVA and also injure your head or neck, you may develop Post-traumatic Meniere's Syndrome.

11. Sudden hearing loss has been observed frequently among children with EVA. This is one of the important points differentiating EVA from Meniere's disease. With Meniere's disease, the majority of people are middle aged; with EVA, they are young children. Incidentally, the vestibular aqueducts of people with Meniere's disease are often rather small. In people with EVA, they are larger than normal.

12. The fluctuating sensorineural hearing loss of people with EVA does not resemble the low frequency loss characteristic of Meniere's disease. Unfortunately, most health care professionals still associate fluctuating hearing loss with just Meniere's disease. The hearing losses in EVA are basically flat or down-sloping high frequency losses.

13. EVA generally follows a characteristic pattern. People with EVA hear normally during the first year or few years of life. Progressive sensorineural hearing loss may not develop until the teenage years. Hearing loss usually occurs in early childhood, less commonly in adolescence, and occasionally in adulthood. In one study all but 2 people had hearing loss in early childhood (< 5 years old). One developed hearing loss at 17 and another at 45. In both of these latter cases, the hearing loss was precipitated by head trauma.

14. Another important characteristic is that most people with EVA experience sudden hearing loss following a minor head injury or other activity which causes increased intra-cranial pressure (increased cerebrospinal fluid pressure). In one study the figure was 85.7% while another study reported 61%. A mild bump on the head, tripping or falling down or even jumping can jar the head enough to result in more hearing loss. Also, sudden hearing loss can follow a minor illness such as a common cold, strenuous exercise or a sudden change in barometric pressure.

In one study of 12 children with EVA, five had sudden hearing losses. Three of the episodes followed relatively minor head injuries. The fourth occurred while forcefully playing a trumpet, and the fifth occurred immediately after an airplane flight.

In another case, a six-year-old child ran into a goal post while playing soccer and hit his head on the left side. This resulted in sudden hearing loss in the left ear. Three years later, after mild head injury while on the school playground, the child again reported an immediate hearing loss, this time in the right ear. An audiogram done that same day revealed severe to profound hearing loss in the right ear and profound hearing loss in the left. A CT scan revealed bilateral large vestibular aqueducts with no other inner ear abnormalities. Over the next month, hearing fluctuated between moderate and severe.

After episodes of sudden hearing loss, hearing may recover to the previous level, or much more commonly, it may recover partially to a new "normal." One girl with EVA had characteristic attacks of sudden hearing loss following minor head trauma, common colds or exercise. Her high frequency hearing is now almost non-existent but her low-frequency hearing tends to recover shortly after each episode.

15. Most children with EVA travel an unpredictable path. They often pass newborn hearing tests, but begin to lose their hearing within the first few months or years of their lives. From this point on, their hearing resembles a roller coaster rides, dropping into abrupt episodes of hearing loss, followed by recoveries over the following days or weeks.(11) Hearing loss in EVA generally follows a step-wise pattern. Each incident causes the hearing to drop another step. The hearing loss will follow one of two patterns. One is a gradual progressive stepwise hearing loss, but with fluctuations. The other is sudden bouts of hearing loss of at least 15 dB that may fluctuate to profound levels following minor head injuries or fluctuations in the pressure of cerebrospinal fluid (CSF). Usually these acute drops in hearing do not recover to previous levels. The end of this downward progression typically is profound hearing loss.

The truth is that it is impossible to predict what the future holds for a person with EVA although hearing generally worsens with time and some become profoundly hard of hearing and eventually require cochlear implants in order to hear. In others, for whatever reason, hearing remains fairly stable, at least in one ear and they can manage their hearing losses with hearing aids. (11)

16. If you have EVA, not only can you experience episodes of sudden hearing loss, but these episodes can also result in damage to the vestibular (balance) system in your inner ears. That is why you may also commonly experience vertigo, balance problems or other symptoms of disequilibrium in addition to sudden hearing loss. In people with EVA, tests of inner ear balance function are usually abnormal. Approximately one third of the people with EVA have a history of vertigo. In one study, complaints of dizziness were present in 29% of the cases.

What Can You Do?

Since EVA is caused by a genetic defect, you can't just make it go away. You have to live with it. However, there are things that you can do to help your child cope with EVA.

Prevent Further Hearing Loss

If your child has EVA, one of the most important things you can do in managing this condition is to take the necessary steps to prevent additional hearing loss from occurring. This is especially important if your child has EVA in both ears.

Doctors recommend avoiding head trauma as it can cause hearing loss to progress faster. There are two exceptions to this rule. One situation is if your child has EVA in both ears and your child's hearing has already progressed to a profound loss so that there is little hearing left to lose. The other situation is if your child only has EVA in one ear and the hearing loss has already reached profound in that ear. In these two situations, since there is nothing left to lose, there is no need to further restrict your child's activities.

Apart from the above, if your child has EVA, it may be prudent to restrict your child's activities. Since minor head trauma can cause episodes of sudden (and sometimes 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 EVA, 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 EVA who had a hearing loss resulting from playing a trumpet.

At the same time it is important not to unduly restrict the activities of children with EVA. They need to be allowed to take part in as many activities as possible having regard for their EVA. Based on the experiences of hundreds of children with EVA, here is a good way to tell whether your child can participate in any given activity. All you need to do is look at your child's past history. Activities that have caused hearing loss in the past will likely cause hearing loss in the future if the child participates in them. It's that simple.

Some children are so sensitive to EVA that minor head bumps result in hearing loss. Other children with EVA can run full tilt into the goal post and not have any resulting hearing loss, even though the episode resulted in concussion! Therefore, the only reliable indicator for your child is his/her past history.

Fortunately, most children are not unduly sensitive to head trauma and changes in air pressure. For example, only a handful out of hundreds polled had hearing loss after flying in commercial planes. Therefore, you can most likely let your child fly—unless he/she has a history of hearing problems from flying. If you have EVA and have a cold or flu resulting in sinus or nasal congestion, it may be wise to either refrain from flying at such times, or take a nasal decongestant to help minimize any risk of further hearing loss caused by the changing air pressure in the plane. (5)

One doctor wrote a letter to the school on behalf of one child with EVA. I thought it fairly presented the risks of EVA and a plea not to unduly restrict childhood activities (see yellow box below). However, ultimately it is the parents who decide those activities in which their child will and will not participate.

To whom it may concern:

X____ has enlarged vestibular aqueducts (EVA). This is a congenital anomaly of the inner ear which predisposes him to hearing loss from what can be fairly minor head trauma.

In theory, any degree of head trauma can do this and thus to completely protect him would require parents to preclude all physical activity. This is an unreasonable demand for any child.

Thus my recommendations to parents are to avoid contact sports, but allow all other athletic activities with the understanding that this involvement does entail risks, but risks that are appropriate given the benefits of such activity. X____'s parents are well aware of these risks and concur that he should be able to take part in all non-contact sports.

Avoiding purposeful contact between soccer balls and his head is obviously a wise choice. It is equally obvious that such contact could occur accidentally, but that would only be preventable by avoiding all sports. I would not choose this extreme measure for my own children and X____'s parents are in agreement on this.

If I can provide any further information, please let me know.

                                Dr. _______
 

 

Amplification

If your child has a significant hearing loss, have him fitted with hearing aids as soon as possible. (I'd 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 EVA.

Medical Treatment

"No treatment has proven effective in reducing the hearing loss associated with EVA, or in slowing its progression." (5)

Although some ear specialists recommend steroids (such as Prednisone) to treat sudden sensorineural hearing loss, there are no scientific studies to show that this is an effective treatment for EVA. (5)

Surgery to drain endolymph out of the endolymphatic duct and sac, or to remove the endolymphatic duct and sac has been found not to be effective in treating EVA. In fact, either of these surgeries can be harmful and can destroy hearing. (5)

There are conflicting reports on surgical intervention in people with EVA. 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 EVA 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.

However, it seems that surgical intervention has fallen out of favor now and is seldom undertaken as the benefit/risk ratio is not all that favorable. 

Therapy

Hearing loss from EVA is no different than hearing loss from other causes. If your child is still young, it is important to obtain speech/language therapy during the language learning years so that your child can develop good oral speech and language skills.

In addition, children (and adults) with deteriorating or fluctuating hearing loss may experience emotional problems such as depression, frustration and anger. You should promptly seek appropriate help for you child if this occurs.

_______________________________

There is a wonderful information and support E-mail list for people (and parents of children) with EVA. Hundreds and hundreds of parents have received help and support from other parents farther down the EVA road.


Here is what one of the mothers on this wonderful, supportive list recently said: "Neil, I must say what a wonderful help you are. Your knowledge and input are a blessing to this group. Because of you and this group I go to the doctors appointments well prepared, and sometime more knowledgeable than the doctors. I know just the right questions to ask. I can never say thank you enough for what you and this group do."
—A. R.


If you would like to join this EVA support group, type your E-mail address in the box below, and then click on the Yahoo Groups button. You can unsubscribe at any time.)
 

Subscribe to the LVAS list


Some selected references:

(1) Abe, Satoko, et. al. 1999. Fluctuating Sensorineural Hearing Loss Associated with Enlarged Vestibular Aqueduct Maps to 7q31, the Region Containing the Pendred Gene. American Journal of Medical Genetics 82:322-328 (1999).

(2) Callison, Diana, et. al. 1998. Large Vestibular Aqueduct Syndrome: An Overlooked Etiology for Progressive Childhood Hearing Loss. Journal of the American Academy of Audiology. Volume 9, Number 4. pp. 285-291. August 1998.

(3) Clinical and Genetic Analysis of Enlarged Vestibular Aqueducts. 2013. http://clinicaltrials.gov/ct2/show/NCT00023036?recr=Open&state3=NA%3AUS%3AMD&lup_s=12%2F28%2F2013&lup_d=30.

(4) Dewan, Karuna, et. al. 2008. Enlarged Vestibular Aqueduct in Pediatric SNHL. Otolaryngol Head Neck Surg. 2009 April; 140(4): 552-558.

(5) Enlarged Vestibular Aqueducts and Childhood Hearing Loss. 2012. http://www.nidcd.nih.gov/health/hearing/Pages/eva.aspx .

(6) Genetics of Enlarged Vestibular Aqueducts (EVA). 2012. http://www.nidcd.nih.gov/health/hearing/pages/genetics.aspx .

(7) Hain, Timothy. 2001. Post-Traumatic Vertigo. http://www.tchain.com/otoneurology/disorders/post/posttrau.html .

(8) Joachims, Zoha, et. al. 2000. Heredity in Large Vestibular Aqueduct Syndrome. The Journal of Otolaryngology. Volume 29, Number 4, pp. 244-246. 2000.

(9) Okumura, Tomoko, et. al. 1995. Sensorineural Hearing Loss in Patients with Large Vestibular Aqueduct. Laryngoscope 105: March 1995.

(10) Pendred Syndrome. 2012. http://www.nidcd.nih.gov/health/hearing/pages/pendred.aspx .

(11) Saltsman, Kirstie. 2014. Genetic Studies Lead the Way to Understanding EVA, a Childhood Hearing Disorder. http://www.nidcd.nih.gov/health/inside/spr2014/Pages/pg1.aspx .

(12) Tan, T. Y. 1999. Large Endolymphatic Duct and Sac Syndrome—A Case Report. Singapore Medical Journal. Vol. 40(05).

(13) Tong, Karen, et. al. 1997. Large Vestibular Aqueduct Syndrome: A Genetic Disease? AJR:168, April 1997.

(14) Xiangming, Li, et. al. 2013. SLC26A4 Targeted to the Endolymphatic Sac Rescues Hearing and Balance in Slc26a4 Mutant Mice. PLOS Genetics. Vol. 9, Issue 7, e1003641. www.ncbi.nlm.nih.gov/pmc/articles/PMC3708829/ .